I've got a '71 455 engine that was previously installed in my '69 GS400. I have a sniper EFI installed and a Summitracing blueprinted HEI distributor. Looking for some help on getting the timing set correctly.
Start by reading this thread, it has all the info you need. If you still need help with specific questions, ask away... http://www.v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/
Thanks Philip that is very informative. Where is a good start for initial timing ? Larry. The Sniper does not control timing. Dual sync distributors are hard to find for a 455
Not sure if you realize this or not, but I am the author of that thread Phillip linked for you. The reason I wrote that thread is because your question is a very common one that I saw all the time so I figured I would address it in a thread. Guys ask where to set their initial timing like they actually have a choice. Unless you have an aftermarket distributor that has an adjustable mechanical advance, you don't. You can choose what total advance you want to run, but the initial advance will be based on that. https://www.summitracing.com/parts/sum-850039/overview/make/buick I don't see them specify how much mechanical advance is built into that distributor. You need to know that. Say there is 25* of mechanical advance in that distributor. If you want to run 34* of WOT timing, then you are limited to 9* initial. It's simple math, 34-25 = 9. I'm just using that as an example, your distributor may have more or less mechanical advance. The linked thread explains how to set up the total timing. That way, your initial ends up where it has to. Notice I haven't mentioned the vacuum advance. That is because they need to be tuned individually, and you will need a way to adjust the amount of degrees the vacuum advance adds. All this is addressed in that thread. BTW, everything I have read about the Holley Sniper EFI says it has the option of controlling timing. You just need to lock out the mechanical and vacuum advance and get an adjustable rotor. Not impossible with the HEI.
Larry, thank you for tge info. I am a novice mechanic learning as I go. This site is a valuable resource. I grabbed tge instructions that came with the distributor. It states: "The distributors mechanical advance provides 10* of advance. Mechanical advance provides 20 degrees total beginning with 6 degrees off idle then progessing to full advance at approximately 1800 RPM. Don't want to sound dumb but I just want to do this right !
Can you post a picture of those instructions? The distributor turns at half the crank speed, so 10* of distributor rotation equals 20* at the crank. That is what they seem to be saying. If that is accurate, then your distributor has 20* of mechanical advance. Buick v8's run best with 30-34* of WOT timing. I would start with 32*. That means your initial timing will be 32-20 =12*. Here's the problem. To set the initial timing accurately, there should be NO mechanical advance. Looks like the distributor has very light springs in it to speed the mechanical advance rate (all in at 1800 RPM). You can approach this in one of three ways. You can warm the engine up fully, and then idle it down as low as it will go without stalling, then set the initial timing to 12*. The lower the engine RPM, the less chance that there is some mechanical advance at idle. The second way is to temporarily install some heavier stock type springs, set the initial timing and swap the original springs back in after. The third way is to set the total timing. There is a word attachment in the 1st post of that linked thread. It explains how to use your timing light to set total timing. Very important, THE VACUUM ADVANCE SHOULD BE DISCONNECTED AND PLUGGED WHEN YOU DO THIS.
OK, I read that as 20* of mechanical advance. Follow what I advised you to do. LEAVE the vacuum advance plugged and disconnected. After you set the timing, drive the car including some WOT blasts, and listen for ping. If you don't hear any, hook up the vacuum advance and follow their instructions.
