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

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, 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

 

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.