Alright, I have searched with no 100% answer yet. Lets say I have a cam. I degree it to verify the specs. It comes out say 6* off, like Grease's was 7 I believe. Can I adjust that, or does it throw off the opti timing? If it does, can that be compensated for in the ecu? One second I read it can, the next thing says not a chance. Whats the deal? I don't want to leave a bunch of power on the table with a cam thats not right, so is there a solution to it? Also, if I am able to run it advanced or retarded, and I use a Cloyes timing set, I then have to upgrade to a 95 opti right? Too much variation and esoteric stuff with these cars. sigh....oh well. Thanks!

 

IMO, if you alter the relationship between the dowel pin and the crank from stock, you will advance or retard the initial timing. It might be possible to change the timing in the pcm to compensate. You would have to be sure that you changed it in ALL tables, though. Even then, I am not sure that would cover every contingency. There was a thread on another board that a guy had done some degree changing and it did not rev well (probably initial timing retard). We wondered as well, if programming could remedy the situation.

 

so you are saying that an adjustable timing set does no good on an LT1 then, say you advance the timing a few degrees, the computer will compensate? Or will it just not run right since it is meant to be where the pin is with the dots lined up?

 

The pcm is not going to compensate by itself. Because the opti is installed in a fixed position (unlike an old SBC distributor that you could turn to adjust initial timing) it relies on the cam to be precisely in the same position as stock for baseline timing. If you move the cam, the timing will be advanced or retarded along with the cam.

 

I guess the next question is, how did people like Grease compensate when the cam is off by 7 degrees or so? Do you just deal with it and have a car that runs like poo with a cam? I'd be suspicious that maybe some of these 320 and lower cam dynos are due to a badly ground cam. I've heard with the cam too far advanced it only costs a few hp, but a few retarded can kill 20 or more. Any other ideas?

 

Dunno. I guess you will have ask them. I am just describing it the way I see it. If wrong, someone needs to debunk me. If I got a cam that was ground wrong, I'd get another.

 

Rob, isn't that the idea here. IF the cam is ground correctly, which it may very well be, that means the problem is in the connecting hardware, IOW, one or any combination of the following possibilities, keyway location in crank, crank gear, and/or dowel pin location in either the cam gear or cam itself. If the connection between the crank and cam is causing the cam timing to be off, the ignition timing will be off as well.

OR, if the cam timing is off to begin with...

IIRC, I attempted to explain what needed to be corrected, in that thread as well. I remember getting an adolecent smart *ssed reply from someone in Cleveland for my time/trouble. Took care in attempting to explain the correction process when degreeing in a cam. I must have done a poor job. Try a search. Anyway, in that case, I believe (I think) the cam was ground off.

 

What I'm talking about is spark timing. Because the initial spark timing is dependent on the position of the cam (because the opti is tied to the front of the cam), if you have to alter the base position of the cam (when degreeing it), you also alter the spark timing. Sure, you can degree the cam to make up for any manufacturing error, but when you move it, you throw the spark timing off.

 

I agree Rob. What I was attempting to note above, is if the cam timing is off, the ignition timing can be off as well. If the error is in the keyway in the crank gear or in crank snoot, the opti is affected as well. If the dowel hole in the cam gear is off, the opti is also affected. If the dowel hole in the cam is off, cam timing is off, however, the opti is unaffected. A correction for any error, other than a cam dowel hole location error, will also correct the ignition timing as well.

To put things in perspective, and view from another angle, the actual location of the dowel needs to be off for an ignition timing error.

 

The opti is driven by the slot in the cam gear, right? Changing cam timing moves the cam in relation to the cam gear and should not effect the ign timing.

 

Yeah, if the dowel moves, the initial timing moves. And why I first posted "if you alter the relationship between the dowel pin and the crank from stock, you will advance or retard the initial timing."

I have been going over this so much that I was beginning to doubt I knew what I was talking about. Sometimes saying the same thing in too many ways makes it more confusing.

 

Rob, the spark timing is not dependant on the position of the cam, but the cam dowel itself. So, you will not alter the opti timing by changing the location of the cam itself.

What I was attempting to note above, is if the cam timing is off, the ignition timing CAN be off as well. If the error is in the keyway in the crank gear or in crank snoot, the opti is affected as well. If the dowel hole in the cam gear is off, the opti is also affected. If the dowel hole in the cam is off, cam timing is off, however, the opti is unaffected. A correction for any error, other than a cam dowel hole location error, will also correct the ignition timing as well, which is/should be the goal .

To put things in perspective, and view from another angle, visualize the cam dowel on the engine. If the actual location of the dowel is off location, there will be an ignition timing error.

Was gonna delete the post immediately above this one, (after posting this one) but you had already responded, so I left it.

 

Arnie, you can't move the cam without the dowel moving with it, right?

 

This would require relocating the hole in cam. IOW, a replacement cam. This would imply the cam timing error would be the result of the hole in the wrong position. This exception was noted above.

 

I have the answer now...a variable dowel pin hole.