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

"

[crazy longhorn]

I like to shoot for around 3000 total, & figure 34 degrees on pump fuel. On an all out race deal, you wont need the vac advance, & the curve will probabley be much quicker with around a 38 degree total. I am not to concerned about the initial....if the total is right on. This all figures on a heavy(4000 lb truck)....IMHO, this is right. A lite car, with low gears can really take advantage of the faster curve. crazyL

[HEI451]

Hi, Gumby, Dave Ray here.

[crazy longhorn]

Gumby...explain to this old man , How you cut the curve @2200, & got the vac advance to work with that? Or did you forget about the vac advance? crazyl

[SkeksisNV]

Looking at that crane mod, looks like its not for a HEI dizzy? Would the only thing that needs to be done to the large cap dizzy is just drill out a screw hole in the vacuum can to put the stop on the other side? Sorry, not great at fabing things, good at turning wrenches and screwdrivers lol.

[Gumby]

Originally Posted by crazy longhorn

Gumby...explain to this old man , How you cut the curve @2200, & got the vac advance to work with that? Or did you forget about the vac advance? crazyl

Those are just the notes I use, bits and pieces writen by different folks who know more then me that I keep around as I often forget.

But Im sure Dave could help you with that.

Originally Posted by SkeksisNV

Looking at that crane mod, looks like its not for a HEI dizzy? Would the only thing that needs to be done to the large cap dizzy is just drill out a screw hole in the vacuum can to put the stop on the other side? Sorry, not great at fabing things, good at turning wrenches and screwdrivers lol.

Ask Dave 3 post up.

[crazy longhorn]

Originally Posted by Gumby

Those are just the notes I use, bits and pieces writen by different folks who know more then me that I keep around as I often forget.

But Im sure Dave could help you with that.




Ask Dave 3 post up.

Gumby, give us specs on your combo( comp ratio,camshaft ,carb ...ect .) Also, I need to know if you are running a vac advance? On the crane kit, yellow/yellow is the light (fast curve). On my street toys, I tend to run a yellow/blue, or yellow/silver combo. That tends to give me all in around 2800-3000 rpms Now I do run a stick shift, so it may tune a little differently than your auto trans truck After 25yrs or so tuning on a sb Chev, Dave may yet show me a trick or 2.....but my chit runs like stink! crazyL

[HEI451]

Anyone that wants a pictures set for either the points OR HEI distributors on how to CORRECTLY modify the stock GM vacuum advance, with the CORRECT design stop, or, mount the Crane 99619-1 adjuster to it, send me a real e/mail and request them. I also have pictures of the Crane stop on BOTH points and HEI distributors, easy to mount and use.

Request pictures from this e/mail address - info@davessmallbodyheis.com

[Gumby]

bump for Lugnutt

[crazy longhorn]

Lugguntt....do not set the curve that loose, on a DD ! We run 38 total @ the track on my bro's S-dime (383, but no vac advance). The curve is set @ 2600....on the street, my old longhorn was set up totally differntly. Understand,that on the track, that old truck runs differently ....even with the small cam (XE-268), she is running 12.6/106 mph. On your driver, you might skip on a couple of gumby's notes! Just my thoughts....If you have not figured it, I have no damn use for Dave Ray? I have learned every thing that I have "old school"? Time to get off the soap box...longhorn

[Marv D]

Originally Posted by crazy longhorn

I have no damn use for Dave Ray

Ya know whats funny is Dave is not an idiot,,, He actually makes a decent product... but he is like Jay Allen , Barry Grant, and a host of others that should have never been introduced to the internet,, and never have been allowed to communicate (in any way) with the public (customers).... they just ain't very good at it!! LOL For every client they acquire with any expertise they 'may' have,, they run off 20 with their arrogance and unwillingness to even consider that they may not be the all knowing master they think they are.

more to the point
The shape of the chamber and the fuel has a TON to do with the timing requirements. Fast-burn / Vortec / old iron performance castings/ smogger era castings / aluminum heads / tiny chamber with a BIG dished piston...... IMO You really can't put a blanket "this curve is best" on any particular pile of parts until you have the fuel curve correct, and then a means to measure the results of changes in timing curve.

Not to dispute any thing posted here,, just saying the ONLY way to find the IDEAL timing curve for your particular motor and driving (street or track) is to FIRST get the fuel curve RIGHT,,, then you need DATA!!! Be it MPG, EGT, ET, 1/4mile MPH,,, the 'buttometer' is a very unreliable data collection unit. It is dramatically swayed by the effects of how light your wallet became in the latest dose of 'bolt-on" parts.

[crazy longhorn]

Originally Posted by Marv D

Ya know whats funny is Dave is not an idiot,,, He actually makes a decent product... but he is like Jay Allen , Barry Grant, and a host of others that should have never been introduced to the internet,, and never have been allowed to communicate (in any way) with the public (customers).... they just ain't very good at it!! LOL For every client they acquire with any expertise they 'may' have,, they run off 20 with their arrogance and unwillingness to even consider that they may not be the all knowing master they think they are.

more to the point
The shape of the chamber and the fuel has a TON to do with the timing requirements. Fast-burn / Vortec / old iron performance castings/ smogger era castings / aluminum heads / tiny chamber with a BIG dished piston...... IMO You really can't put a blanket "this curve is best" on any particular pile of parts until you have the fuel curve correct, and then a means to measure the results of changes in timing curve.

Not to dispute any thing posted here,, just saying the ONLY way to find the IDEAL timing curve for your particular motor and driving (street or track) is to FIRST get the fuel curve RIGHT,,, then you need DATA!!! Be it MPG, EGT, ET, 1/4mile MPH,,, the 'buttometer' is a very unreliable data collection unit. It is dramatically swayed by the effects of how light your wallet became in the latest dose of 'bolt-on" parts.

I will never call Dave an idiot....I see that he is really damn sharp? What I have seen, is that he is too set to 'his rules', & will not accept anything else? Enough said ....let us build some trucks....longhorn

[Gumby]

He is a "grumpy old man" in all the best ways, and has tons of great stories. Always one of those in every garage, just listen and be polite and you will learn ALLOT and also get a chuckle at times. Just soak it up.

That’s just part of that generation. Like the duck show, Phil is a great guy with lots of knowledge, but you see how things often turn when the younger folks talk up, razing his own grand kids even. Oh your a college boy, oh your a straight A man. Im a C+ guy. Not 100% their fault, just that era was at the time in-between have and have nots where ya might have to work to survive then go to school and they don't take no one trying to tell them different on anything or make them feel less then.

If you were face to face with him, 90% of folks would just listen, not that he is scary, but that kind of guy that you best just show respect or move along. But he is also a tough guy, got shot 3 times and still beat the guy down and held him for police when he tired to rob a store in his presence. [ if I saw a gun, id be hiding behind the chip display ]