944vaguy

OK, so we all know about thecam offset key. And there are a lot of questions and comments concerning theperformance that is gained by advancing the cam by 4 deg. Rogue_Ant did a great write up onthe performance that he gained at the dyno (https://rennlist.com/forums/924-931-944-951-968-forum/634732-n-tune-19.html#post9898601) but there is something missingin all the articles and all the other write ups..
What if the camis advanced by one tooth (9 deg.)and then the key is put in retarded by 4deg.??? You end up with timing advance by nine deg. and the cam advanced by 5deg. !!! Why has nobody tried this? Would this not be a better performance gainthan any other set up. By advancing the ignition it would give an increase inperformance as shown by the tune that is popular in the programming of the chipupgrade, and than you would have the additional performance of the cam advancement.I do not think that the extra 1 deg. of cam timing is that dramatic I think itwould come from both the cam and the ignition. I am going to do mine like thisas soon as the weather breaks but just want to throw it around a little withyou motor guru guy’s.

odonnell

The DME actually controls the timing, not the rotor position. If the DME calls for X degrees of timing advance, the coil fires at a certain time based on crank position and speed. The rotor contact is wide enough to allow this over a wide range of spark angles. So, there would be no impact on spark timing by adjusting the cam timing.

I had the same thought until someone reminded me of this.

944vaguy

Now that you say that I have to agree... It always takes someone to rattle the old grey matter into gear.

V2Rocket

That said, there is a decent bit of power to be found in the US NA engine if you have a means of advancing the ignition timing and running premium gas.

The offset key is so cheap and easy to do that it's a no-brainer...and even with fully stock DME/AFM the advanced camshaft is still GOOD.

FRporscheman

I love my car since I advanced the cam timing, I wish I did it 10 years ago. And I was timid and only did 2.5 degrees! What about an offset flywheel setscrew, to trick the DME's TDC signal? Or even easier (cuz I'd rather install standalone than remove the flywheel, LOL), offset the ref sensor by 4 degrees or whatever.

odonnell

Easiest solution would be to install a separate programmable spark system like Megajolt. It's pretty inexpensive and works great. You leave the rest of the EFI system alone.

jhowell371

I miss real distributors you could adjust. Eons ago my 1963 Corvair Turbo Spyder's distributor had a vacuum advance and pressure retard mechanism for Turbo boost. To paraphrase from the movie "The Treasure of the Sierra Madre", "We didn't need no stinking electronics back then"

Van

You can change the ignition timing by drilling and tapping a new hole for the TDC reference set screw in a new spot.

FRporscheman

Yeah, but the real question is if you can do this with the bellhousing still on!

944vaguy

So the question is what would be the best valve timing and ignition timing for drivability and performance using premium gas. Lets say you had the engine out and prepared to relocate the timing pin on the flywheel and had the offset key for the cam. The cam can be set at 2,4,5,7,9..... advanced and the ignition anywhere, what would be the best settings? Now that is the question!!! One should be able to gain a considerable amount of HP & TQ while maintaining or improving drivability if the numbers were right......

V2Rocket

4 degrees makes a BIG difference.
don't know if anybody has gone beyond that aside from just putting the belt 1 tooth ahead.
i was going to do that sort of experiment but lost interest in tweaking the 8v engine.

GPA951s

Remember cam timing and ignition timing are different.. The computer CANNOT change cam timing.. That is valve opening relative to where the piston is in it stroke. Advancing that will get you more out of the hole but give you less at top end. and Vice Versa..

924srr27l

But an adjustable pulley could change it?





R

V2Rocket

^^no, even putting the belt a full tooth off would not change the ignition timing. remember how wide the conductive surface of the ignition rotor is, it is very tolerant of off-position camshaft. spark timing is all referenced to crankshaft so cam position doesn't matter on 944.

FRporscheman

fixed it