cam timing question
 

Bckground - SC cam used in a 3.4L 930.

What would be the effect of timing it more retarded, say around 1.35mm vs advanced, say around 1.6mm?

Would it affect how "freely" the engine likes to rev? How fast the turbo might create boost?

thanks.

I hate to refer you to your own thread:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/288664-camshaft-timing-question.html
As I posted before, I was told by Neil Harvey of Performance Devlopments that when he performed the dry assembly mach-up of my engine to check for piston to valve clearance, etc., he indicated that 1.7MM was the optimal cam timing for *MY* particular engine on the street. I ended up using 1.65MM.

Well... I did recall & re-read that thread.

Reason for another post is: I intentionally retard my CAM after that post and what I'm seeing is NOT what its supposed to be.

The engine seems out of breath and my boost comes on waaaaayyyyy later. Hence want to re-ask the question.

I know each engine is different, but I think someone (DonE?) had tried different settings on same CAM - hoping to hear from someone.

Sandman, how did you know 1.65mm/1.7mm is optimal for your engine?
What does optimal mean in this case?

thanks.

Even though I did the final assembly on my engine, I had shipped the entire thing off to Performance Developments for all the machine work. They literally measured EVERYTHING. All tolerances were checked and/or fixed. I had SC cams purchased from Imagine Auto along with the 3.4L Ps&Cs (JE pistons with Supertec cylinders). According to Neil, he thought the cams should be timed at 1.7. I did 1.65 just in case and the car has been like a missle! Granted it does feel like it stops making big HP at around 5,500 RPMs...but it does pull like a train.

How did Neil know to advise about 1.7MM? I guess years of building and designing serious race engines gives a person that sort of "feel".

Hobie, I'm not sure if you're on Rennlist under a different user name, but here are some recent threads about re-timing cams with the engine in the car:
http://forums.rennlist.com/rennforums/showthread.php?t=296000
http://forums.rennlist.com/rennforums/showthread.php?t=294289&page=4

Thanks for the reference to Rennlist... I was thinking about re-checking the cam timing as well; though I also learnt from my last rebuild that to get the same # again, you need to clamp the chain (for the left side) just like when it was first installed. This is the part that can't be done easily with the engine in the car :(

As for 1.7mm vs others, I was just curious if anyone can describe the results of deviating from "optimal". I think I understand what should happen, but what about reality?