Cam degreeing... Here is an idea...will it work??

I have been searching around for the proper way to degree an LT1 and have been coming up with mixed reviews, so and so says "the only reason to degree the cam is to verify the grind." Well so and so says "that isn't true and it must be degreed (by degreeing I actually mean setting the cam to specs with cam spacers or offset key ways)" With this being said, so and so said "if you actually degree it, it will throw off the ignition timing and injector timing."

I was thinking (just an idea), what if you set up your engine and find top dead center, install a pointer, and a timing tape (like you can get from jegs) on the crank pully set to zero.
-Verify how much off your cam is and then use a timing light to see how much off your ignition is.
-If I am right, if the cam is zero degrees off like it should be you should read 4* BTDC because that is the way the engine is manufactured.
-Now if the cam when installed and checked and it is say 3* advanced and you put a timing light on it, according to one arguement, you should still get the 4* BTDC, which in turn verifies that degreeing the cam has no effect on the ignition timing and if you do degree it you will have to make other changes to sync everything back up.
-But if you get 7* BTDC then the arguement that stands that if you properly degree it, it will effect ignition timing and that properly degreeing the cam is the right thing to do and that degreeing the cam to manufacture specs is actually sync'ing up timing and you don't need to adjust the computer when you properly degree your cam.

- I think I got that right ?? advance = BTDC/ retard = ATDC

I am looking for input on weather this idea will hold water or not.

Well I don't know who told you those things, but you just need to pack your bags and hit the road, because they're not people you want to be getting advice from anymore...


First off, just for the record, it is no different degreeing the cam in an LT1 than any other motor in the world...

Secondly, cam timing, and igntion timing, are 2 completely different things, do not get them confused with eachother.

Degreeing you cam will verify's that everything was ground in place, and that you achieve the cam timing you were looking for. Remember, by just sticking a cam in "straight up", you are assuming that the person that ground the key on your crank was dead on, the person that ground the keyway in your timing chain was dead on, and the person that ground your cam was dead on. Do you really want to take those chances?

Contrary to what you have been told, degreeing your cam in will not effect ignition timing. Ignition timing is controlled by the position of the crank position sensor. The cam position sensor is for the sequential fuel injectors... and it is basically just a reference point for the ecu.

Typically on a normal sbc, you will make best power around 4 degree's advanced. You were throwing around numbers like 7, etc, and I don't have time to read into what you were trying to say... but shoot for around 4 and you should be good, and right were GM wanted it.

Also, advance and retard is figured by the relation of intake centerline vs. the lobe seperation of the cam. If you have a cam that has a 112 lsa, and you want 4 degree's advance, you will install the cam at 108 degree's intake centerline. If you have a 112 lsa cam and want to install it 4 degree's retarded, you will install the cam at 116 degree's intake centerline.

Hopefully this helps all those who have been confused about what degreeing cams is all about.

Later
Chuck

Originally posted by chucks97ss

Contrary to what you have been told, degreeing your cam in will not effect ignition timing. Ignition timing is controlled by the position of the crank position sensor. The cam position sensor is for the sequential fuel injectors... and it is basically just a reference point for the ecu.

Degreeing the cam will change the position of the optispark, which will change the timing. You will have to compensate in the pcm program for how ever many degrees it changed. Otherwise, any cam changes need to be ground into the cam.

If you change the position of the opti on the cam, the pcm doesnt know that this change occured and will continue to fire the coil as normal, which will end up advanced/retarding your timing depending on what your cam is at

And how can the timing be controlled with the CPS when over half of the model years of LT1s dont have them? The CPS has nothing to do with timing. I believe the CPS is an obd2 thing to see misfires right?

Unless your having to really move the cam timing alot I would not think the ign. timing would be off enough to really make a big difference?

See thats the debate I am trying to solve, Chuck says that degreeing an LT1 is like any other motor and Serene says it will effect the opti and programing is required. Now giving both of you know what you are talking about someone still has to be wrong.

From what I am getting from Chuck is that follow the instructions on degreeing your cam, say you have a cam ground for a 112 centerline and when you install it and check it, it comes to 107*. By the directions of Comp Cams, you need to set it to 112* by using cam spacers or offset keyways.

Now from what I am getting from Serene is that if I do that then I will be throwing off the opti and the ignition will be off hence needing programing to fix this problem.

and now my original question is, If I was to install a degree tape and pointer to the crank pully and use a timing light wouldn't that solve these debates.

Am I being clear or am I looking at things the wrong way?? I just want to get the cam installed properly and get the most out of it,

Originally posted by john-e-boy
See thats the debate I am trying to solve, Chuck says that degreeing an LT1 is like any other motor and Serene says it will effect the opti and programing is required. Now giving both of you know what you are talking about someone still has to be wrong.

From what I am getting from Chuck is that follow the instructions on degreeing your cam, say you have a cam ground for a 112 centerline and when you install it and check it, it comes to 107*. By the directions of Comp Cams, you need to set it to 112* by using cam spacers or offset keyways.

Now from what I am getting from Serene is that if I do that then I will be throwing off the opti and the ignition will be off hence needing programing to fix this problem.

and now my original question is, If I was to install a degree tape and pointer to the crank pully and use a timing light wouldn't that solve these debates.

Am I being clear or am I looking at things the wrong way?? I just want to get the cam installed properly and get the most out of it,

*IF* Serene is right, and the LT1 ignition timing is controlled by the optispark reference signal (which I personally will not believe to be true until it is proven certain... since MOST if not all aftermarket fuel injection ecu's control timing based off the crank ps, not the cam), the effect degreeing your cam in correctly will have little to no effect at all on your timing. We're talking 1 or 2 degree's here. Something easily fixed with reprogramming which you would only ASSUME someone installing a cam is going to do anyways. So the debate of whether or not this is actually true, seems of little or no use to me for someone doing it right.

Look up GM's spec for what they want the cams in LT1's installed at from the factory. It's going to be in the 4 degree's advanced range, with maybe 1 or 2 degree's variance allowed. So why all the sudden is it bad to degree in a cam, when all you're trying to do is get it in at 4 degree's anyways? All you're doing is verifying it is in tolerance. You really think you can install a cam straight up, and it's going to be on the nose from what the cam card says is ground into it? Personally I don't believe you understand degreeing cams, if you've ever even done it, because if you really did I don't think you would be saying what you are about this... You're making it sound as if when you degree in a cam you are dramatically changing the advance or retard it was originally intended to have.... which in most normal applications like this, is not true at all. It is simply something all GOOD engine builders do just to verify their work is 100% exactly the way they want it... A simple analogy is comparing 2 ways of building engines. 1 person buys all their parts from a catolog made to fit their particular application. They have the block machined by a local machine shop and brought to within tolerance. They then bring it home and assemble the engine without a dial bore gauge, calipers, mic's, bridge, or even plastigauge anywhere in site. They are purely depending on luck that the motor will run right... Then compare that to an engine builder who fully blueprints everything. They measure every single clearance, and KNOW that everything is within their tolerance, and this motor is going to run forever and a day. So all being said, by all means, do whatever you want, I'm just giving you my opinion to ponder. I am not wrong, and I will not waver. What I've said is fact. So if you want to disagree with me fine, but I really don't care to keep debating on this issue.

Chuck

Originally posted by john-e-boy
From what I am getting from Chuck is that follow the instructions on degreeing your cam, say you have a cam ground for a 112 centerline and when you install it and check it, it comes to 107*. By the directions of Comp Cams, you need to set it to 112* by using cam spacers or offset keyways.


Are you sure you're not confusing lobe seperation with intake centerline? What you just described is the cam has 5 degree's more advance ground into it than the cam card states (which would be a prime example of why cams should be degree'd to verify everything is correct, and not way out of wack like this)...


Chuck

I have done alot of searches on this sublect and have heard of cases where the cam was off as much as 9* so thats talking about more than 1* - 2* off, I am not trying to waiver you, I am doing what I think every GOOD engine builder does before building, "research"! If i go ahead and put my cam in and I am faced with this problem of being off more than 1* or 2* then i would like to know what to do. After all I thought that is what this board was intended to do, help get a job done right.

Since I don't understand degreeing cams, from my research advance vs. retard effects top end vs. bottom end and to get the most out of a cam would involve being dead on (yes I know technically). I am not the type of person that would disreguard what an expert would say and go based on what someone else might say.

So with what has been said, do you according to Chuck, degree the cam and program the computer for the changes or do you program the computer for how far off the cam is.

I'm not confusing the two, I threw 112 out there because it was in my head. Looking at my card, it says to install the cam at 108 intake centerline, now on sbc's, not LT1's, normally you would set the intake centerline to 108 using spacers or offset keyway and set the timing using the rotation of the distributer. With LT1's you can't do that.

So whats the proper way of setting up a cam, find out how far off of centerline you are and make up for it through programing, degree your cam to centerline and program the computer so it knows what you have done, or degree your cam to centerline and the ignition should follow.

another question, is the cam says to install the cam at 108 centerline, giving that GM says 4* advanced, do you install it 4* advanced from 108 centerline.

Originally posted by john-e-boy
I am doing what I think every GOOD engine builder does before building, "research"!

Hmm, I've never seen Warren Johnson doing research on the internet? ;) Good engine builders know this stuff, but beginners definitely need to do research, which I am happy to see you doing. Too many people assume they know it all, and get themselves into trouble. So doing research is highly comendable. :thumb:

Originally posted by john-e-boy
I have done alot of searches on this sublect and have heard of cases where the cam was off as much as 9* so thats talking about more than 1* - 2* off


My 1 or 2 off numbers were not set in stone. Obviuosly there are cases, like yours here that are exceptions... Here's something to think about regarding this example you gave... How do we know for sure it's 9 degree's off? What probably happened in this case was user related. The cam this person used had 4 degree's advance built into the cam. Then when they installed the timing chain crank sprocket, they used the advanced keyway, which advanced it another 4 degree's... That would be 8 degree's advanced simply by the person not knowing what they were doing... the other 1 degree was probably from the parts used not being exactly perfect... Not that this has anything to do with your question, but if this was a car I was working on, that would be the first thing I'd check...

Originally posted by john-e-boy
Since I don't understand degreeing cams, from my research advance vs. retard effects top end vs. bottom end and to get the most out of a cam would involve being dead on

Well, in basic terms yes... but most adjust their timing according to what makes the best power. Typically for a sbc spinning less than 7500 rpm, around 4 degree's advance is where the best curve is. You haven't givin any details about what size motor this is, how much the heads flow, and how big the cam is, so I can't tell you if this will work for your combination. But for most, that is what you'd want to shoot for.

Originally posted by john-e-boy
So with what has been said, do you according to Chuck, degree the cam and program the computer for the changes or do you program the computer for how far off the cam is.

You do both. And my question to you is, why can't you do both. What is your reason for only being able to do one or the other? If you can't do it right, I don't recomend doing it at all. And I really feel this whole discussion is highly overrated. But it's cool that you are asking these questions, because most on here probably wouldn't.

Originally posted by john-e-boy
another question, is the cam says to install the cam at 108 centerline, giving that GM says 4* advanced, do you install it 4* advanced from 108 centerline.

If the lobe seperation of this particular cam is 112 degree's, and you degree it in to 108 degree's intake centerline, the cam is in 4 degree's advance. Loctite the bolts, torque them down, and go get some dyno tuning done.

Chuck

Originally posted by john-e-boy
Since I don't understand degreeing cams, from my research advance vs. retard effects top end vs. bottom end and to get the most out of a cam would involve being dead on

No no no, I did not see this the first time I replied... Being dead on would not be good for whatever you are trying to do, unless you are building a very high end 8k+ rpm racing engine.

Chuck

when I degreed my cam it was 110 centerline but I needed 108

I just advanced the crank gear 2 degrees. So I should change timing -2 degrees ? Thats what I did.

Here are a few "facts" that I have personally experienced.

If you alter the phasing of an LT1 cam with offset keys or cam bushings, you will definitely alter the injector & ignition timing. This may not hurt anything, but in some cases where the cam was moved 4 or more degrees, it can have an effect on part throttle drivability (hesitation/knock). This is due to the injector timing change. Changing the ignition timing (with programming) did not cure the problem. I have seen this problem 1 time & also discussed it with Mike from (Modern Musclecar / Ramchargers) who also acknowledged seeing the problem with altered cam timing. Now to prevent self abuse, I will not try this anymore.

To correct, you can also elongate the optispark bolt holes & rotate the unit. If you are really getting picky I suggest you check this as well.

The typical cam will be ground close to perfect so this may be nothing to worry about. Personally, if it is off by 4 or more, I would question the quality of the cam/timing set anyway. Also a stretched timing chain will retard the cam phasing slightly as well, so it will automatically retard itself as the chain streches. Keep this in mind.

Hope this helps.

Originally posted by chucks97ss
*IF* Serene is right, and the LT1 ignition timing is controlled by the optispark reference signal (which I personally will not believe to be true until it is proven certain... since MOST if not all aftermarket fuel injection ecu's control timing based off the crank ps, not the cam), ...........Chuck
Just to clarify.... In the LT1, spark and injector timing is based on the high and low res signals produced from the cam-driven optical sensor in the OptiSpark distributor. The 92-95 LT1's so not even have a crank position sensor, so they are in effect, relying on a "pseudo" crank postion derived from cam position sensor.

The 96/97 LT1's added a crank position sensor, but it is used only for misfire detection. The PCM still takes info from the OptiSpark sensor for ignition and injector timing.

I run a MoTeC M48Pro ECU, and it too uses the high and low res pulses from the Opti to set injector and ignition timing. It does not rely on a crank position sensor, since I do not have one.

Alright, thanks for the clarification Lonnie and Fred...


Chuck

Originally posted by SILVERZZ28
Unless your having to really move the cam timing alot I would not think the ign. timing would be off enough to really make a big difference?

Well...i suppose not if you are n/a but if you are using a power adder, it could be the end of your motor depending how far its off.

Originally posted by chucks97ss
*IF* Serene is right, and the LT1 ignition timing is controlled by the optispark reference signal (which I personally will not believe to be true until it is proven certain... since MOST if not all aftermarket fuel injection ecu's control timing based off the crank ps, not the cam), the effect degreeing your cam in correctly will have little to no effect at all on your timing. We're talking 1 or 2 degree's here. Something easily fixed with reprogramming which you would only ASSUME someone installing a cam is going to do anyways. So the debate of whether or not this is actually true, seems of little or no use to me for someone doing it right.

It is true as verified by Fred. I don't even see how its debatable that the CPS controls ignition when half the cars don't even have them.

Assuming programming is not what I'm talking about. I'm not talking about a normal tune, I'm talking about adjusting the timing by however many degrees it was off. Oh, also, we are not only talking 1 or 2 degrees here. I bought a ****ed up LT1 extreme duty timing chain, that gave me a bunch of problems, and ended up being the culprit of my problem, being 9 degrees off.

[QUOTE]Originally posted by chucks97ss

You're making it sound as if when you degree in a cam you are dramatically changing the advance or retard it was originally intended to have.... which in most normal applications like this, is not true at all.

I don't know if this is directed at me, but oh well. In certain situations it can be alot of degrees. We are talking minute measurements here. One degree is extremely small, one slight imperfection can mean many degrees. IMO, you are not really degreeing, but checking to verify the tolerances on the crank keyway, timing set, and cam. Sure if its 1 or 2 degrees off, unlike mine, you'll be fine, but otherwise I would be taking the stuff apart and finding the culprit.

Originally posted by Lonnie Pavtis
If you alter the phasing of an LT1 cam with offset keys or cam bushings, you will definitely alter the injector & ignition timing. This may not hurt anything, but in some cases where the cam was moved 4 or more degrees, it can have an effect on part throttle drivability (hesitation/knock). This is due to the injector timing change. Changing the ignition timing (with programming) did not cure the problem. I have seen this problem 1 time & also discussed it with Mike from (Modern Musclecar / Ramchargers) who also acknowledged seeing the problem with altered cam timing. Now to prevent self abuse, I will not try this anymore.


Interesting...however, when i was reading about Fred's past SDI experiences, he said the system only had the capabilities to batch fire. Would this same concept not apply here as well? Or maybe it just doesnt effect the car at WOT since the injectors are almost open all the time.


The typical cam will be ground close to perfect so this may be nothing to worry about. Personally, if it is off by 4 or more, I would question the quality of the cam/timing set anyway. Also a stretched timing chain will retard the cam phasing slightly as well, so it will automatically retard itself as the chain streches. Keep this in mind.

Exactly.

OK I just went out and checked the tolerances on my cam, after checking and rechecking it, I came up with a 112 centerline on a comp cam 306 which says to install at 108 centerline.

What is my next step now??

First try moving the crank sprocket to the advanced position... Then if you're still not right, you'll need to install a bushing in the cam gear and mess with it until you get it to where you want it...

Later
Chuck

???

Lonnie just said that doing that could effect part throttle drivability. Moving the position of timing components with other keyways, bushings, etc is IMO not a good choice on the LT1.

I would take the timing set off and see if you can exchange it for another one, something isnt right. You should be within a degree or two. My motor was within 1 degree of spec.

most all LT1 cams are ground with 4 degrees added in already. nowadays cams are pretty well close to perfect 99% of the time. the grinding machine wont mess up, but whoever puts the info into the machine can.
and i agree with the guy who said elongate the bolt holes in the opti to allow you to rotate it if you move your cam around.
jeremy

Originally posted by Serene
???Lonnie just said that doing that could effect part throttle drivability. Moving the position of timing components with other keyways, bushings, etc is IMO not a good choice on the LT1.

Right... if you're going to be physically moving it a lot. I've heard they start having problems if you move them around 4 degree's or more...

Originally posted by Serene
You should be within a degree or two. My motor was within 1 degree of spec.

Exactly... that's why I said to move the crank gear to a different keyway... I don't know how many motor's you've built... but most timing sets come with a crank gear that has 3 slots in it that you can use. "technically" they are supposed to be, 1 slot 4 degree's retarded, 1 slot straight up, and 1 spot 4 degree's advanced... That means the timing set has all those built in, that it will add to whatever is ground into the cam from the manufacture. For a cam that has 4 degree's ground in, you would use the straight up position. I have a feeling that john-e-boy installed his crank gear in the 4 degree's retarded position, which is why his cam is in at 0 degree's. But I could be wrong, it might be just a really bad timing chain, but before he takes it back I would at least check that out first... because it could be a simple fix. And if this is the case, it will have absolutely no effect on the previously discussed problems regarding the ecu. The gear was simply installed incorrectly by the user.

Chuck

BTW. John-e-boy... are you positive you have TDC set correctly? That is absolutely vital if you expect your numbers to be correct. It can not be even a hair off.

Originally posted by chucks97ss
Exactly... that's why I said to move the crank gear to a different keyway... I don't know how many motor's you've built... but most timing sets come with a crank gear that has 3 slots in it that you can use. "technically" they are supposed to be, 1 slot 4 degree's retarded, 1 slot straight up, and 1 spot 4 degree's advanced... That means the timing set has all those built in, that it will add to whatever is ground into the cam from the manufacture. For a cam that has 4 degree's ground in, you would use the straight up position. I have a feeling that john-e-boy installed his crank gear in the 4 degree's retarded position, which is why his cam is in at 0 degree's. But I could be wrong, it might be just a really bad timing chain, but before he takes it back I would at least check that out first... because it could be a simple fix. And if this is the case, it will have absolutely no effect on the previously discussed problems regarding the ecu. The gear was simply installed incorrectly by the user.

Chuck

BTW. John-e-boy... are you positive you have TDC set correctly? That is absolutely vital if you expect your numbers to be correct. It can not be even a hair off.

Most timing sets come with the 3 keyways sure, not the ones for the lt1 with the stock WP. HOWEVER, using those keyways is effectively moving the opti as well as the crank sprocket position is changed, just because its not on the cam doesnt mean its not going to change the timing.

I would for sure check to make sure you are checking it right and make sure you have the dots lined up and are using the right keyway.

Originally posted by Serene
HOWEVER, using those keyways is effectively moving the opti as well as the crank sprocket position is changed, just because its not on the cam doesnt mean its not going to change the timing.

I don't think you really understand what I'm trying to say... And I'm kind of getting tired of explaining it. No offense, I just don't have a lot of time to waste on the computer right now. Hope you all get things figured out.

Later
Chuck

imo if you have to move the cam around that much the cam isnt right anyway. get the correct advance/retard ground into the cam, that way you wont have to mess with cam timing.
the opti just isnt adjustable like a sbc distributor.... why put up with the hassle and headache when you could just have it ground into the cam?
also, if specs are within 1 degree, i wouldnt even mess with it. timing chain slop will account for that much if not more.
jeremy

Originally posted by Jerm93z28
imo if you have to move the cam around that much the cam isnt right anyway.

Guys, what I've been trying to say all this time is that the cam is probably not the culpret, I think he's got his crank gear in the wrong position. But whatever.

Later
Chuck

uh....thats what I've been saying as well. Cams are ground on CNC machines I think, so theres a low chance of error on those.

Originally posted by Serene
uh....thats what I've been saying as well. Cams are ground on CNC machines I think, so theres a low chance of error on those.

Thank you... then we also agree that if the cam is accurate, and he corrects his timing chain error, gets it set at 108 intake centerline, he will be home free... Because at that point his timing chain is in what we call "straight up" position (what the ecu is looking for), and therefore he has nothing to worry about regarding his optispark. This is what i've been trying to say all along.

Later
Chuck

Ok as far as retarding/advancing timing on the cam, I was thinking although you can do things like compensate with opti bolt holes being elongated, lets think here for a second, does it really matter if your injetors aren't pulsing a few degrees on the mark? I mean 93 LT1's had batch fire injection & they would pulse at the wrong time on almost every valve :D but the excess fuel on the back of the valve while it was closed worked great in cooling the valve. Point is, is it really that important? Especially if you are retarding the valve timing by 4*, think about it, the PCM doesn't know so it'll spray fuel 4* ahead of time when it was acctually supposed to spray right? or do I have it backwards? no seems right, Now piston will be 4*closer to TDC before it fires the injector which if worst comes to worst it'll put the fuel on the valve & it'll end up going into the chamber regardless, so you will loose a bit of emulsification as the result but I'm sure the shorter LSA (112 instead of 117 stock) will end up opening the valve a bit earlier anyways so all should cancell out right? What you guys think, am I crazy? or am I right?

Matt.

Originally posted by bunker
Ok as far as retarding/advancing timing on the cam, I was thinking although you can do things like compensate with opti bolt holes being elongated, lets think here for a second, does it really matter if your injetors aren't pulsing a few degrees on the mark? I mean 93 LT1's had batch fire injection & they would pulse at the wrong time on almost every valve :D but the excess fuel on the back of the valve while it was closed worked great in cooling the valve. Point is, is it really that important? Especially if you are retarding the valve timing by 4*, think about it, the PCM doesn't know so it'll spray fuel 4* ahead of time when it was acctually supposed to spray right? or do I have it backwards? no seems right, Now piston will be 4*closer to TDC before it fires the injector which if worst comes to worst it'll put the fuel on the valve & it'll end up going into the chamber regardless, so you will loose a bit of emulsification as the result but I'm sure the shorter LSA (112 instead of 117 stock) will end up opening the valve a bit earlier anyways so all should cancell out right? What you guys think, am I crazy? or am I right?
Matt.

Nope, I agree with you 100%... All sequential systems are different too. Some pulse before the valve opens, others pulse after the valve shuts... So injector timing being slightly off is nothing to even remotely worry about. And at this point I go back to what I originally said regarding this whole problem... If you're going to do this right (dyno tune it after installing the cam), then there is no reason to worry about this problem. Because you're going to adjust timing according to what makes power on the dyno. So long as you can still adjust timing, it doesn't matter what the reference angle is. Whatever makes best power is what you set it at.

Later
Chuck

Hehe cool, yeah I'm definetly going to degree my cam, I'm acctually thinking of getting max 4* advance so 108 ICL or maybe even no advance which I think should help take advantage of the lower & higher lift numbers on the heads better, I've heard of this resulting in TQ loss but I've talked to a good friend of mine who said back in the day when they used to build race engines he noticed a huge increase in power by retarding timing & no loss in TQ, but then again every engine is different, but I personally see it as an advantage. Since I asked GREASE on this board running my cam & when he degreed his he found his was at 102 ICL which would mean its 6* out of wack, he retarded it 4* & dynoed 405RWHP @ 365RWTQ SAE with mild but nice set of heads max flow 255cfm, mid flow was good like 196 @.200 lift & 241 @.300 . I think its very important to check that stuff IMHO.

I will compensate with timing ofcoarse, but my understanding is also that if I retard 4* that would mean I have to advance 4* on ignition timing since the piston will be again 4* closer to TDC before the opti would reference to fire, right? I guess.

Matt.

Originally posted by bunker
Hehe cool, yeah I'm definetly going to degree my cam, I'm acctually thinking of getting max 4* advance so 108 ICL or maybe even no advance which I think should help take advantage of the lower & higher lift numbers on the heads better, I've heard of this resulting in TQ loss but I've talked to a good friend of mine who said back in the day when they used to build race engines he noticed a huge increase in power by retarding timing & no loss in TQ, but then again every engine is different, but I personally see it as an advantage. Since I asked GREASE on this board running my cam & when he degreed his he found his was at 102 ICL which would mean its 6* out of wack, he retarded it 4* & dynoed 405RWHP @ 365RWTQ SAE with mild but nice set of heads max flow 255cfm, mid flow was good like 196 @.200 lift & 241 @.300 . I think its very important to check that stuff IMHO.

I will compensate with timing ofcoarse, but my understanding is also that if I retard 4* that would mean I have to advance 4* on ignition timing since the piston will be again 4* closer to TDC before the opti would reference to fire, right? I guess.

Matt.

I think you're out in left field regarding your retarding the cam theory.. but more power to ya ;) Some motors will want less timing. But most of the time they are high horsepower/high rpm style motors... not street motors.

Tune the motor according to what makes power, not a number. So just get it on the dyno and adjust to the point it is making the most power. Then maybe back it off a couple degree's to be safe.

Later
Chuck

My experience mirrors what Lonnie Pavitis posted way back in the beginning - once you start getting to 5+ degrees of "adjustment" (using an offset drilled cam dowel bushing) there were hp losses (on the order of 10rwhp on a 420rwhp car) that couldn't be "worked" out with timing changes - but were resolved with a cam with the exact same lsa/advance, but with the advance ground in. (this was on a heads+cam LT1).

Really the main thing you are going to want to do with your advance/retard is adjust where your overlap is relative to TDC, as the other valve events are better altered through the lobe itself.

And in the greater scheme of things cams are cheap - you are better off just getting it ground the way you want it - get it spec'd out correctly, and degree it to verify the install went fine, but other than that I wouldn't use the adjustable keyway or an offset bushing.

Whether retarding/advancing helps depends greatly on the rest of the combo as it is all relative, but again, you should be looking at this from a valve events perspective - the icl, lsa, etc. are all going to be a byproduct of those and lobe choice.

As far as being out in the left field, you mean for advancing ingnition timing relatinve to valve timing correct? Yeah I mean I"m just trying to say that when you retard timing, you will most likely have to advance it to compensate. You are right though, changing valve timing can affect cylinder pressure & make/loose power, so thats why if you need to advance ignition timing to compensate for valve timing (ONLY BECAUSE OF OPTISPARK, THAT IS WHY) then yeah like you say, stay where you are & go from there. You might need less ignition timing with the changes for ultimate results.

Matt.

OK i found out I was having problems with my piston stop and trying to move my degree wheel. Here is what I did...

I installed the degree wheel and then the piston stop and set up the dial indicator. From there I found out where it first hit the stop and set the degree wheel to 0* and then went backwards and got a reading of 41*, now from here instead of moving the degree wheel (which was a PITA and throwing things off) I figured I would just subtract 20.5* off the two numbers.

first reading, after setting the dial indicator to zero at the point of highest lift,I got from going back and then slightly forward to .50 was 87* - 20.5* = 66.5*

The second reading I got from going forward to .50 was 169.5* - 20.5* = 149*

So the result is 66.5* + 149* = 215.5* divided by 2 = 107.7* ICL

So i am pretty much right on key, Right??

My main problems were the set up, I had a hard time tightening the degree wheel on to the crank and then making sure that when I moved it the crank didn't move, so I figured why move it? just subtract the 20.5 from your #'s and your doing the same thing. Comp Cam doesn't give any kind of degree wheel lock with that makes it easy to move the wheel with ease.

The second problem I had was I used the spark plug hole piston stop, while trying to adjust the degree wheel I ended up bending the piston stop. It is soft brass so I doubt it hurt anything.

Thanks for all the help.

John

Yes that would work perfectly well, more accuretly then trying to utighten the wheel since the crank will move a tad, sometimes what works is putting the car in 6th gear so it won't move, but subtracting works very well. As far as doing damage with spark plug piston stop don't worry, it probably just touched a valve & didn't do much when it bent since the valve is much stronger & probably had a bunch of carbon build up so it never even got to the steel :)

Matt.

Im not going to argue anything here as cam timing is still a little out of my league. But how do you adjust the timing on an LT1 without doing it in the computer, and are we talking vented or nonvented optis here?

The way I understand it on a vented is the cam dowel pin drives the opti directly, and the wheel that the cam spins in the opti is plastic with a hole just for the pin.

Lets say you are running an aftermarket cloyes true roller on a vented opti with elec waterpump (obvously)...if you have it at #1 TDC and the gears lined up how they are supposed to be (not familiar with AM gearsets yet), since the opti isnt adjustable, like an old style dist. is, how do you adjust the cam timing mechanically?

Oh, and does anyone have a more indepth tutorial or something on timing and all that good stuff, I have seen the one on CCs website, but looking for something different.

Valve timing & ignition timing are two different things bud, also you can do a bit of compensating for timing on the opti mechanically by elongating the bolt holes, but you can definetly adjust it in the PCM, we are talking about advancing/retarding valve timing at the timing chain & how it affects injector offset/ignition timing as the result since the opti won't know what you did unless you had the degrees ground into the cam, etc... but we're all clear about it by now I'm sure.

Matt.

Geez, you boys really get technical!

I tried reading all the thread, but I got lazy and skipped a few lines -
hopefully this hasn't already been discussed:

Where are you taking the dial reading? From the lifter, or primary
side of the rocker arm?

I was taught to take the reading from the rocker arm to
account for any tolerances in the valve train. This will accurately
show the valve timing while accounting for lifter and pushrod
play (using a solid lifter in place of the hydraulic).

Set the valve for zero lash and do a secondary measurement
for cam degree as a 'double check'.

The intent here is to ensure proper valve train geometry (lengths,
tolerance, positioning, etc).

Regarding the LT1 Crank Position Sensor. What year motor are
we talking about? I have the GM SHop manuals for the 1996 model
year.

I can look up the reference signals for you all.

I apear to be a little late here but will relay what a few PRO tuners have metioned many times.

First off, degreeing the cam by moving the pin position in relation to the Crank most definately changes injector and ignition timing and if it is a OBD-II car pisses the CPS off.

Second, once moved changes made in the PCM never realy seem to cover the loss. HP losses of 5-10RWHP were recorded time and time again. Same cams speced out and checked once delivered were used to verify testing.

The consensus in the end was make sure it was ground right the first time ;)

ALWAYS check against the spec card by Degreeing the cam in but if it is off get it cut correctly :D

Remeber you only have ONE chance to do it right the first time ;)

seems great but I'm sure you'll see a loss in power if you don't compensate with ignition timing, for 4* of retard of valve timing you need around 4* advance in ignition timing depending ofcoarse you may only need 2* because of the DCR etc... changes.


Matt.

Matt ...

The cams in Question WERE tuned to the proper specs to account for the change. The cams were ordered identical save for the 4 degree change. then they were checked on a Cam mapping machine to make sure all was well. then they were stuffed in the engines and tested and tuned.

The cams that did not need the change in the program always came out on top.

For some reason(Like say no one has the source code) there is more to it then you are able to account for in the program.

Will drilling the cam gear and degreeing it in work? Yes.

Will it work PROPERLY? No.

Good luck all ;)

See keep talking this is what I like to hear acctually, the other side of the story, I was thinking why would the 4* make a difference? See if we are discussing a matter of fuel mapping, isn't retarding by 4* acctually help bring things back more a less to spec by using the timing chain? Think about it, the stock cam is on a 117LSA, we are using a 112lsa or 110lsa cams, this alone makes the cam open the intake event soon by ohh what a few degrees? now when you retard the timing you are making this even open say a few degrees later, all in all bringing things back to somewhat normal as far as fuel mapping is concerned, & this is what we don't take into consideration. Then bring in 93 LT1s that operated on a batch fire injection system where all injectors would fire at once, now don't you think that threw the fuel mapping out the window if you compared it to sequential injection? I mean think about it, obviously the difference is neglidgeble. Did you know that although drawbacks follow at times, excess fuell on the intake coolst the valve preventing detonation. So many thing we don't take into consideration when you think about it, I mean, am I wrong?

Matt.

Alot of confused people here. Some more so now, after reading this thread. BTW, a search for posts by 'arnie' here, and in LT1 Tech will find numerous cam degreeing posts. Some feel I am an expert on confusing people. :) Must admit, occasionally I agree. :(

Some points to note:

Great majority of cams are ground correctly, both in comparo of the intake/exhaust relationship, and in relation to the opti drive pin.

With above note digested and accepted, the primary point/purpose of degreeing a cam, is to check and correct (if necessary) for any crank/cam attachment hardware errors. IOW, tolerances in the crank gear keyway, crank keyway, cam gear, and cam dowel hole location in cam gear. 'Lining up the dots', will not assure anything other than the engine will run. 'Blueprinting' an engine, is not necessary for the engine to run. OK, let's move on.

The correction cam be made with offset crank gear keys, or with an offset bushing surrounding the opti drive pin, which also locates/positions cam on cam gear. This applies for ANY sbc, opti in front, or distributor in back.

If the cam to crank timing relationship needs to be corrected, IOW, if the cam is out of sync with the crank, (valve timing events not occuring when supposed to) remember, the cam itself is ground correctly, the cam is out of time, the opti is out of time, and the injectors are out of time. Understood? When the cam is off, it means the opti drive dowel is off. If the opti is off, the injector timing is off. Understood? The ignition and fuel timing will NOT be screwed up by correcting the cam timing. Quite the contrary. You are correcting them. Why? Cuz they are timed correctly, when they are driven off a correctly timed cam.

It has been stated, deviating too much from recommended cam specs, will reduce power. I agree, cuz you are adversely affecting your injector timing, and if not adjusted in pcm, your ignition timing as well. However, as stated, this is deviating from recommended, on the cam card, cam mfr. timing specs. We are talking 4*-5* here.

This is NOT the same as deviating from what you will find, when checking an installed cam installation. THIS deviation is done to achieve the cam mfr. (oem or aftermarket) timing specs the cam was designed for. IOW, here we are deviating TO, not FROM mfr. specs.

Some other points to make:

When setting up degree wheel, set it up so you are rotating the crank, not the degree wheel. This is achieved by bolting the degree wheel to the crank snoot correctly, using bolt and nuts to your advantage.

Take your indicator readings off dummy lifters, not the valve, retainer, or rocker arm. The idea is to remove as many variables, in the checking procedure as possible. If there is a valve train issue, that should be delt with separately, not during the degreeing procedure.

Crank gears with more than one keyway for timing adjustment purposes, are intended for 'tuning' adjustments, not for degreeing corrections. IOW, degree the cam, using means noted above, and later, if desired, to change the engine characterisics, cam timing can be altered from mfr. recommended specs 'in the field', using one of these alternate keyway locations. This is the cam timing deviation noted above, that can adversely affect ignition and injector timing, if done to extreme or gone the wrong way.

With the above stated, IF in/during your degreeing process, you determine the cam/crank phasing is off (out of mfr. specs) that far, (unlikely) say 4*, and there is a 4* alternate keyway in crank gear, :shrug: go for it.

Arnie.. you forgot one thing ;) With a Distributer car you can change the the postion of the senser (Distributer or Cam Positon senser as the Vortec calls them) to correct this. This puts the Sensor in alignment with the 'Crank'.

The flaw is your assesment is that you are assuming by lining the cam up correctly with the crank the opti will be lined up correctly as well. The Opti (installed with a timing chain at 0*) is correctly positioned to begin with no matter where the cam comes out.

That in and of it self is the nut of the problem here. The Opti is NON-adjustable. all the other systems on a SBC are adjustable. The Vortec provides a testing sequence to adjust the Cam position senser back to proper alignment.

Now having said that IF there was a way to adjust and CHECK opti-spark alignment there would be no issue. There is not. Making it adjustable would not be hard but there are no provisions to correct the alignment once the cam adjustment is made.

Matt brought up some very good points. My cam thinking is slow this morning but if I remember it is not the LSA we need to look at but the intake center line. I know they change as well. In either event the Opti is supposed to run in time with the Crank shaft because all events are arranged around the Crank position and assume a basic cam position. Even when the LT4 was installed in 97 the program was not changed. Only program that came out was for the Vette. The F-Body used a standard 97 F-Body tune.

In the end the biggest key is the one we do not have. A complete break down of the source code the see what other tables there are being controlled by Opti Position in relation to the crank.

I hope the has cleared the mud a little ;)

Originally posted by OneFlyn95z28
Arnie.. you forgot one thing ;) With a Distributer car you can change the the postion of the senser (Distributer or Cam Positon senser as the Vortec calls them) to correct this. This puts the Sensor in alignment with the 'Crank'.

To correct what? Maybe I didn't make myself clear. At the top, I mentioned, in more cases than not, (great majority of cases) dowel is correctly (when it is not, that is a separate and different issue, in itself, of which I won't go into here) indexed on cam, in relation to lobes. I do not consider this assumption! :) Anyway, with the cam degreed, the dowel is positioned where it was intended. This means opti/injectors are correctly timed. That is the reason for the ?, to correct what? Nothing to correct.

The flaw is your assessment is that you are assuming, by lining the cam up correctly with the crank the opti will be lined up correctly as well. The Opti (installed with a timing chain at 0*) is correctly positioned to begin with no matter where the cam comes out.

When the dowel is correctly indexed, the opti WILL be correctly positioned. Don't ASSUME, by installing the cam, dot to dot, if that is what you are referring to with "installed with chain at 0*", it is correctly positioned. What is important, is where the dowel 'comes out'. I explained that above.

That in and of it self is the nut of the problem here. The Opti is NON-adjustable. all the other systems on a SBC are adjustable. The Vortec provides a testing sequence to adjust the Cam position senser back to proper alignment.

No need to have the opti adjustable, unless, as noted and explained above, the cam is timed (tuned) to other than mfr's. intended specs. Then as I noted, pcm adjustment would accommodate. As for the Vortec adjustment procedure of which I am not famiiar, but ? whether that adjustment has much to do with cam/crank indexing. However, if it did, is it easier, for GM, to have their mechanics do the adjustment procedure you noted, or perform the degreeing procedure?

Now having said that IF there was a way to adjust and CHECK opti-spark alignment there would be no issue. There is not. Making it adjustable would not be hard but there are no provisions to correct the alignment once the cam adjustment is made.

Again, see above comments.

In either event the Opti is supposed to run in time with the Crank shaft because all events are arranged around the Crank position and assume a basic cam position.

Sure it is SUPPOSED to run in time, but don't ASSUME the basic cam position. Done correctly, with cam degreed to crank, GM procedure would appear to be redundant, if indeed it was relevant. GM understands their cam/crank relationship can be less than optimum. As noted though, which is easier for their mechanics to perform?

In the end the biggest key is the one we do not have. A complete break down of the source code the see what other tables there are being controlled by Opti Position in relation to the crank.

Software, I see this as irrelevant to this discussion on timing hardware. Happy new year. :)

Arnie:

Understood about the 'removal' of variables.

As stated in my reply previously, the cam is degreed
by itself first, then double checked with the pushrod
and rocker arm set to zero lash (dummy mech lifter).

As my "mentor" once said, "the cam may be in phase,
but it's the valve reaction that matters"

He just enforced the idea to double check with all the
component to make sure the valve movement is timed
properly.

Might seem a little anal, but it made sense to me.

Originally posted by Zero_to_69
As my "mentor" once said, "the cam may be in phase,
but it's the valve reaction that matters"

He just enforced the idea to double check with all the
component to make sure the valve movement is timed
properly.

Might seem a little anal, but it made sense to me.

Explained that way, understood. Took care of the cam, and then turned your attention to the valve train. Sounds like a mentor that 'covers the necessary bases'.

Originally posted by OneFlyn95z28
The flaw is your assesment is that you are assuming by lining the cam up correctly with the crank the opti will be lined up correctly as well. The Opti (installed with a timing chain at 0*) is correctly positioned to begin with no matter where the cam comes out.

That in and of it self is the nut of the problem here. The Opti is NON-adjustable. all the other systems on a SBC are adjustable. The Vortec provides a testing sequence to adjust the Cam position senser back to proper alignment.

One needs to have in mind, that GM engineered the opti/injectors to be in correct/accurate time when the cam dowel is indexed accurately, period! Either it is in time (indexed correctly), or it isn't. If it isn't, to a degree of inaccurate index, based on the degree of indexing error between crank and the dowel itself. *Establishing above, the scenario that the cam dowel is indexed accurately with the lobes on the cam, the cam degreeing procedure WILL also insure that the injector/opti drive dowel is positioned accurately/correctly. I'm confident GM engineers are also aware of the stackup of tolerances on the associated components of the crank to cam linkage hardware. This obviously, is the focus of the cam degreeing operation, in my posts.

*I established this scenario to keep my discussion devoid of the incorrectly ground cam variable, and resulting, more confusing, knee jerk counter measures necessary, intentionally.

BTW, I personally, have not ever witnessed a cam setup and ground. However, common sense would lead me to believe the drive dowel hole is drilled in beforehand, and thus used to index cam, for the lobe grinding operation. Barring an operator error, it is thus highly unlikely the cam lobe would be indexed incorrectly with (opti) drive dowel.

Ok as clear as can make it with out going to far off the path.;)

The Opti has NOTHING to do with the cam other then it is driven off of it by the pin. :D

That is what I keep trying to say but you keep relating it to the cam .

The opti NEEDS to be indexed to the crank not the cam. This is where the problem is.

WHEN you degree the cam in you are Moving the Opti from the correct position it needs to be. That position is in relation to the crank not the cam.

Technicly the Opti is driven, and indexed, off the timing set(two sprockets and a chain)not the cam. The ONLY thing the cam provides is a pin that indexes the opti to the top sprocket and hence the crank shaft.

IF you move this pin position to line the cam to the crank correctly you just moved the opti and the correct Opti to crank position has been lost.

SO this correct way to dail in a cam would be to use custom made offset cam dowel pins. That way you could position the cam correctly and NOT move the opti from its correct position ;)

The problem here is when you move the cam to correct one problem you move the opti the oppisit direction and cause another.

BTW if you are degreeing a cam it is because the Pin is not where you would like it in relation the the lobes on the cam and you are moving them to a position you would to match the crank position. Basic math;)

Does this clear it up any?

Ok this is what im am going to do....Slot the Dist. bolts and make a pointer set at TDC off of the balancer. use a timing light to set the timing... That should take care of it. I will post results.

Originally posted by OneFlyn95z28
IF you move this pin position to line the cam to the crank correctly you just moved the opti and the correct Opti to crank position has been lost.

I have no clue, as to how you figure the dowel, hence the opti, is located/indexed correctly to begin with. Ellis, we need to agree that we disagree, and are about 180* apart. :) Neither of us is making any headway with the other. In the end, one of us has to be incorrect. Take care.

I guess we can agree on that. To me it is some thing that is always so. Then again I am just a mechanic ;)

I think the only way I could show you was to be in the same room and go over each part and the manufacturing process of each one to explain.

HEY It is snowing out side...Kool!

The way I understand it I don't see anything to argue about, retard vale timing with timing chain & advance your ignition to compensate a few degrees, fuel sync to crank isn't important IMHO.