Gumby's V8 Timing Notes

[Gumby]

Gumby's V8 Timing Notes



I repost this allot, if it had its own thread, maybe less often

Here are my personal timing notes Ive gotten from pro's and have served me well.

Also note if your using a MSD, you need to use a conventional induction timing light, not a fancy digital one. The multi sparks will mess with them as noted all over the MSD tech help board.


"Most V8's run best at WOT, with a total timing of 30-36*, all in at 2500 RPM, or less. The easiest way to determine your total advance is to use a dialback timing light. You simply connect the light, plug your vacuum advance, and have a second person slowly rev the engine. With the dial back feature, you adjust the light to keep the timing mark in sight as it rises. When the timing mark stops moving, you hold the RPM's steady, adjust the dial until the balancer mark lines up with the 0 on the timing tab, and read your total advance off the dial.

To do this with a conventional timing light, you need to make a 30* mark on your balancer. With a balancers of 6 3/4" in diameter. Circumference (360*) of a circle is pi(3.14) X diameter. 6.75 X 3.14 = 21.195"/12 = 1.76" (30*). Looking at the engine from the front, measure exactly 1 3/4" clockwise around the balancer, and make a second mark. This is your 30* mark. Connect up your timing light, and watch your 30* mark as you increase the RPM's. At some point, your 30* mark will stop rising, and move no higher. This is the RPM, where all of your mechanical advance is in.

SUBTRACI INITIAL DUMMY OF 10-12* [personal note as I always forget]

At this same RPM, with the distributor loose, adjust it so that your 30* mark lines up with the 0 on the timing tab. You now have 30* of total timing. Line it up with the 2, 32* total, ect.

Keep in mind that a stock distributor usually has stiff springs in it, that don't allow full advance in until 4000 RPM or more. For best performance, you want your advance in at 2500 RPM, or before. The easiest way to do this is to purchase a Crane adjustable vacuum advance kit. It comes with 3 sets of springs to allow your advance in as early as 1600 RPM, or as late as 3200 RPM, or anything in between. For points distributors (Jegs part # 270-99601-1,) (GM HEI, 270-99600-1). What I did was purchase the kit, and install the lightest springs(2 yellow). I used these springs to adjust my total timing, that way, I didn't have to rev the motor very high to see my total. Afterward, I installed the springs that brought my advance in at 2200 (2 silver)

One important note is to make sure the timing is returning to the initial setting, when the engine is idling. So when setting your timing, pay attention to when the advance starts, as well as when it is fully in. Having the distributor in the advance curve, at idle speeds, can cause excessive rpm drop with an automatic trans, with some camshaft/converter combinations. Generally, the more agressive a camshaft you use, the more important this will be. Advance curves should generally start at around 1000- 1200 rpm, when your idle speed is around 800 in Park."


"The crane adjustable is the only way to go, but it need to be modfyied to work right. Sounds dumb but yes it does. Ill see if I can find the info, not a 100% secret but it was a discovery done by Dave Ray the GM engineere who designed the IGN system for our cars. And he does that mod to all the Dizzy's he sells. [I got lucky since I know him, he did my large cap.]

davessmallbodyheis.com

quick google found the mod pic's
http://rides.webshots.com/album/563501537slUJqh

"