What is correct timing for this engine at idle(distributor vacuum hose disconnected? )now it's 8 degrees before TDC

best setting for good performance of course

 

Its not only the base timing, but the total advance and the rate of advance that makes the best performance. Send an email to Lars v8fastcars@msn.com and request a copy of his timing paper.

Just me, I'd look for a total of 36* at 3000 RPM and let the initial fall where it wants to. But that's also with a curve kit and maybe a little modification to the stop bushings.

 

i know but still want know this basic setup

 

Look on the tune up sticker under the hood

Look in the GM shop manual

 

36* all in without vac advance, 52* with vac advance at cruise. This is maybe 16* initial timing or so. Mechanical advance and vac advance amounts vary so you'll have to experiment a little.
Have the 36* come in by 3000 rpm.

 

In your first post you asked where to set timing for best performance. What do you mean by "this basic setup"?

Scott

 

Sorry just what u guys think is good timing for good performance but still in safe "area"

 

Advanced until you get the best performance, right up until you get the pre-detonation ping from whatever fuel you're running, then back it off... At least that's what I used to do as a teenager... Dunno what kind of damage I may have been doing in the long run, but I was young and dumb and abused my old hot rod... so nothing lasted very long anyways... Fortunately I haven't had to mess with mine in my new vette... Kinda figured the next time I would mess with it , would be when I'm at the dyno with the experts ... ;-P

 

I agree. Also, use full manifold vacuum from below the throttles, not ported, which comes from above the throttle blades.

 

http://gmheritagecenter.com/docs/gm-...t-Corvette.pdf

Page 137.

According to this document, your car came equipped with distributor part number 1111490. This distributor was designed to provide 26 degrees of mechanical advance, if I am understanding the chart correctly (4 degrees initial, 30 degrees all in at 5100 rpm) The vacuum advance provides 19 degrees of advance. These numbers are all hypothetical you'll need to measure to make sure of them, the parameters on your car could be different due to production tolerances, and who knows, somebody may have replaced the distributor. You never know.

So, doing some quick math indicates that if you set your initial at 10, you should get an all in timing of 36 degrees. Re-curve the distributor so it comes in by 2500-3000 rpm, instead of the stock 5100 rpm. Problem: The stock vacuum advance canister, at 19 degrees of advance, will give you 55 degrees at cruise, which may be a bit much (52 is generally accepted as about the most you want to go) replace the vacuum advance with a unit that provides about 16 degrees of advance, and you should be just about optimized. Send an e-mail to Lars and ask for his paper on vacuum advance units to find out the part number of the one you need. Use manifold vacuum for the vacuum advance, and your timing at idle should be about 26 degrees, which is about right, too.

So, to summarize: re-curve distributor, replace vacuum advance unit, use manifold vacuum for vacuum advance, and set initial at 10 degrees. This is all theory, you'll have to measure with a timing light to verify, and make changes accordingly if need be.

Scott

 

Hey Scotty, sweet site! didn't know all that info was available in PDF on line.

 

okay so 10degree at idle? or?? (sorry i'm not mechanic and actually dont speak english so i dont always undestand all things )

 

I can't take the credit for finding it, someone here in the forum turned me on to it. You can find all kinds of crazy specs and arcane information there!

Scott

 

10 degrees if you get a new vacuum advance canister. If not, it's just fine where it is right now.

Scott