Any of you guys have any time to read through this and try and help me out. I'm stumped beyone belief here.

http://www.chevytalk.org/threads/sho...5&o=93&fpart=1

 

First off, on the truck, if you didn't do whatever has to be done to make it go to the static timing (disconnect the EST wire, put in diag mode, whatever it is) then its normal timing will something comlpetely other than the static setting. So that test doesn't really tell anything.

I'd suggest taking a look at the timing mark vs TDC situation, first of all. Make sure the balancer hasn't slipped or something.

Then, if you have access to a dyno for tuning, adjust the timing for best power; and forget what the light says. The engine will tell you in no uncertain terms what timing is best for it. If the light doesn't give you the "number" you expect to see, well, then the problem is your expectations or your measurement equipment or technique, not the engine. Rule #1: Give the engine what it wants. Rule #2: if the engine wants something different from what you think it should, see Rule #1. That is the entire book of "rules" for tuning an engine.

I agree with the guy that said he never sees a SBC that needs more than 40° at WOT. Usually they want 35-38° at WOT, and if the compression is too aggressive, they'll ping at that setting. Even if they don't ping, advancing it further rarely gives more power.

Being fixated on the "number" that the "light" gives you is not real productive. Concentrate on giving the engine what it wants; then write down the "numbers" that the "light" gives you, and that way you can put it back to optimum, whatever that "number" is, if you have to disturb it later.

 

I'm not really 100% sure about taking your advice and just forgetting about what the light says and give the motor "what it wants". If it's showing 42 degrees at idle, then something is wrong, and I wanna know what it is. I didn't spend countless hours and dollars just to not set it up properly and be guessing at the timing all the time. And as far as the truck goes, even without unplugging anything, there has to be a factory number that I should be able to look for when the light is on the balancer since I'm sure that GM doesn't just "give it what is wants" on the assembly line.


Tom

 

What RB is saying is that every engine is different. One size carb doesnt fit all, neither does one timing setting.

 

The factory adjusts them on the production line by disconnecting the EST wire, or by some such procedure. They don't adjust them while in "normal" operation. When operating "normally", the timing will never be at the static setting, and isn't predictable unless you can see all of the variables that the ECM is seeing. If you want to duplicate the factory procedure for the truck, then you should find out what the procedure is for it; then you should be able to see it with your light at the factory spec of 0° or 6° or whatever it is, which is going to be different from whatever the ECM jacks it around to under whatever conditions it happens to be under at the moment.

The engine can't see the number on a dial-back light. All it knows, is that the air/fuel gets lit off at some time in the relation of the piston to TDC; if it gets lit too late, then the max amount of heat energy doesn't get extracted from the hot gas and turned into mechanical energy, and instead goes out the exhaust; if it gets lit too soon, it explodes, and parts get destroyed. That's it. If you imagine what's going on inside the cyl as the engine runs, and imagine adjusting the timing from too far retarded to too far advanced, the power output will be way too low when you start out; then it will increase smoothly as you advance it, then level off and stay there for a range of a few degrees, then drop rapidly. Optimum is the point at which it levels off.

That point is different for every engine. There's no magic number. Although, for most typical normal SBCs, it is usually around 36°, for optimum power. Yours looks like a pretty typical motor in that regard... its requirements are going to fall somewhere close to there. I'd bet, if you did what is normal on a dyno and adjust the timing for max output, you'd find it ending up somewhere real close to there.

I'd suggest though, if the absolute value of that "number" is important to you for some reason, first verify the timing mark accuracy. Otherwise you could end up chasing ghosts for quite a while without really accomplishing much of anything.

Incidentally, 42° at idle might be what the engine wants. Or, you might find that your mech advance is active at idle speed and your vacuum advance is hooked to constant vacuum, in which case it would be totally normal and correct. In no case would it automatically indicate, all by itself, that something is wrong.

And don't forget also.... you're building a unique engine, not one of a million low-perf grocery-cart motors on an assembly line; you're not concerned with emissions, or altitude variations, or random fuel variations, or climate changes, or any of those things that the factory takes into account when developing a timing "spec". Factory "specs" don't apply to your situation. You can't open some book somewhere and find "Tom91Bird's new engine", and it show you a "spec" for your combo.

Make sense?

 

I don't want to hi-jack this post but RB seems to know a LOT.

How the heck do those dial back timing lights know what the heck is going on anyway?

Seems RPM, distributor cap terminal spacing and whatever would enter into the picture unless it knows the RPM and estimates from there.

As far as on topic, I idle at 20-25° with my setup with a max of 34.5°. Base is set at 6°

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SMaster

SBC 383 w/TFS 23° aluminum heads, full roller, 11:1 SRP's.
CC306 camshaft .544/.576 w/1.6 RR
730SD w/30# injectors, 58mm Holley, Holley Stealth Ram Intake
700r4, 3200 Vigilante converter, 3.73 gears w/BFG drag radials.
4040# Step Side Chevy pickup truck
8.34/83.80mph w/1.88 60' w/stock suspension