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.

[QUOTE]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.

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.

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

 

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...

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.

 

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

 

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.

 

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 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.