I recently bought a 77. The engine has been rebuilt. Original 350 with all original, stock heads, etc I am having difficulty getting the timing/performance cvorrect. Instructions say that timing should be 8degrees. However I have been told that it should be advanced to as much as 12 - 18 degreews for optimum performance. Can anhyone offer advice

thtanks Al

 

Try this link. Lot's of good info . . . http://forums.corvetteforum.com/c3-t...long-post.html

 

For normal operation, set per GM specs. If you wish to set up the engine for best performance, then you need to recurve the distributor. Do a 'Search' for the write-up on how to set distributor up for performance....written by Lars Grimsrud. It has all the info you will need. It's basic concept is that you set timing for maximum advance allowable and that timing at idle is just a result. With a stock engine, this usually gives you something in the 12-18 deg. range at idle. (But, the process is not as simple as just resetting the timing at idle.)

 

Follow these instructions to the letter, including making sure you have your dwell set, that your advance is functioning as it should, and that you have the correct idle mixture. You will be happy.

I set mine to factory specs after I got it and it always ran hot. After I set the timing according to this post the engine ran better and much cooler. One of the things I found was that my vac advance was failing

 

thanks for the responses. a great help

 

Al, I have a 77 L-82 vette with automatic trans. I read the posts cited above before working on my car. As others have indicated they are great sources of information. Here is what I learned working on my car last year.

My car's specs calls for 12 degrees of initial timing (all numbers are with the vac can disconnected and plugged). Trouble is, if you do that your all in timing will only be about 28 degrees. You will see from reading the material cited above that you want to get to around 36 degrees. What I found is that my distributor only provides 16 degrees of mechanical advance (12 initial plus 16 = 28) and it comes in really fast (all in by 2000 rpm or so). I am not sure if your engine is the same, but my guess is that it is.

Anyway, I played around with the Mr. gasket kit and couldn't get more than 16 degrees of advance with any combination of springs and weights. (I think it has to do with the shape of the center plate which would be tough to change).

What I did was set my initial at 18 degrees, which gives me 34 all in. I didn't try going all the way to 20 initial. The car seems to run fine. It seems to pull stronger in the upper rev ranges and I don't have any problems with pinging, etc. The idle is better too (you will need to adjust the idle speed down after you advance the timing).

I hope my experience saves you some time and effort. I think my solution gave me most of the benefit without having to rework the distrubutor. Good luck!

Dan

 

Dan - thanks much! I will be pursuing that this week end.

Al

 

The amount of mechanical advace movement is determined by the little brass bushing that is pressed onto the advance limiter (stop) pin. If you do not have enough mechanical advance movement, either the bushing is too big or the advance mechanism is bound up/restricted for some reason.

 

7T1Vette, I am pretty sure that is not the case on our (1977) cars with the HEI distributors. I looked and looked for such a limiter and there is none that I can find. The center plate (I hope that is what it is called) on our cars is completely flat, rather than curve. When the weights are fully extended, the littlle ears lie flat against the center plate. There is no way for them to extend any further. My distributor is well lubbed and free so I know that is not the problem. When I encountered this situation last year and posted on the forum about it, someone told me that 16 degrees is all these old HEI distributors provide. Not sure who is right, but if someone has worked on an HEI distributor of this vintage and can show Al and I how to increase the mechanical advance, I'd like to know how (pics would be nice).

Anyway, although I was concerned that going to 18 degrees of initial would cause problems with starting/pinging, it did not, so I am happy.

Dan

 

Al, did you work on your timing last weekend? Was your experience consistent with mine? Did you find a way to get more than 16 degrees of mechanical advance out of your distributor?

Dan

 

DanielA

You can try flipping the plate in the center over and seeing if that changes the advance amount.

Or try a junkyard and look for a plate #369 (22°) or #416 (24°).

This will allow you to keep the initial timing down around 12 or 14 (lower) which is easier for carb idle adjustment.

Or you can get a couple extra junkyard centers and grind on them to open the weight opening a little more.

The speed of advance will be by the springs, don't use the springs to limit advance amount.

If I remember correctly, GM had hundreds of different advance combinations.