What is the best rpm to have all your timing in:
I have read 2000 to 3000 rpm's?
What determine where all the timing need to be in by rpm?

There are a lot of factors that influence which timing curve you should use (carb type manual vs. vacuum sec, street vs. strip, compression, risk of detonation, N/A vs. spray, launch RPM, etc...). I'll assume that for the sake of this discussion we're talking all out performance N/A street/strip ride with manual secondary carb. IMO, the sooner all the timing is in the better. An engine will make the best power with full advance. Many racers run with their timing "locked out", or fully advanced, with no mechnical advance. This allows them to leave the line with full timing and therefore maximum power. To the extent that the tires/suspension will hold full power at launch you're almost certainly better off with all the timing right away. On my own car I've experimented with different timing curves. At present I'm running an MSD pro billet distributor. I have 20* initial timing and I run the black bushing which gives me 18* of mechanical advance. I'm currently using the most agressive timing curve with two light silver springs. I've found that this provides the best ET for my car, but on a marginal track I will get tire spin. Many people use the timing curve to delay full power on launch. This is particularly helpful with cars that run on a small tire or launch on spray. If you have some different weights/springs/bushings (depending on whos distributor you're using) then you're probably best off to start with a moderate timing curve (say all in by 3,000) and tweak it from there.

HTH.

I'm also just beginning to mess with my timing curve. I just mapped it for the first time and its all in by 3000RPM.

What i want to know is, what actually dictates the amount of mechanical advance? Right now i have 20 degrees mechanical so I'd like to keep it there. Is it the weights or the springs that dictate the amount?

I would like to play with the RPM where my full advance is "all in" but would like to keep my 20 degrees of mech advance.

The weights and springs determine how fast the advance comes in. The slot built into the mechanism determines how far the advance will go or how much mechanical is available. On oem distributors the slot can be welded or brazed to reduce the amount of travel (advance), or you can lengthen the slot with a file to increase the amount of advance. If your the amount of advance is correct just dial in the rate of advance with springs and weights. The heavier the weights and lighter springs the faster the advance will come in. You can mix spring wieghts, example: one light spring and one medium. The weights need to be the same for balance and proper cam action.

Thanks.

Are there any guidelines on what type of rate works for what type of car.

i.e., what would a lightweight, small tire, small (4.xx) gear, stick shift, hi rpm car like?

as a opposed to what a heavy, big tire, big (2.xx) gear, 3 speed auto, low rmp car like?

Here is all the data that I verified today:
TIMING TUNING SPECS:
RPM Degrees RPM Degrees
1000 18* 2250 30*
1250 22* 2500 30*
1500 26* 2750 32*
1750 28* 3000 36*
2000 28*

Initial 18* @ 900 RPMs
Advance 28* @ 900 RPMs
Total 36* @ 3000 RPMs

CARB SPECS
Pri Jets 72
Sec. Jets plate 134-21
PWR Valve 6.5 Hg
Idle 900 RPM's
Mix Screws 2 turns out @13Hg
Auto in Drive 750 RPM's @ 8Hg
Needs a 4.5 pwr valve
I did hook the vacuum up to a full manifold Vacuum and she had better response than the ported/carb base plate. I will have to buy a tee since I have the PCV hook to manifold.
She did get hot running her in the garage without the dialback light, so I had to manually adjust rpm and check timing (what a pain in the Wass).
I check the plugs after a little driving and they were fine.

After changing the PV tomorrow, I will check the Sec spring and see what changes they like.

What I don't understand is that if total timing= base + mechanical (say base is 18 and mech is 21, you get 39 total)

What would happen if you had 14 base and 25 mech, that still gives you 39 total.

Is it quicker launch,better top end , smoother idle, what???


Sorry for the stupid question, I just like learning as much as possiable,( maybe I should learn how to spell first) LOL

Thanks guys

Different engine combos like different amounts of advance both total and rate. It all depends on burn efficiency within the combustion chamber, amount of load on the engine dictated by vehicle weight and gearing. Many variables. A light bodied car will take a more aggresive advance curve than a heavy one because it has less load. Lower octane fuels need a slower curve than higher octane because of the diff in burn rates. A lean or rich mixture will like more advance then a perfect fuel mix. Closed chamber heads with a good quench will need less timing than open chambers with poor quench, burn rates. Experimentation is the only way I know of finding what a combo likes, sure would be nice to have a chassis dyno.

I've heard that you want as much initial timing as you can get with still being able to start the car.


JP

Not true, With a good battery and starter you might be able to start the engine with say 25 degrees initial, try launching a heavy car with a tight converter or highway gears with that much initial and I bet you'll just fart through the carb.

Slowpoke, you are thinking about this the same way the local distriobutor man does. FOr a low ( 4.0+) geared clutch car, high compression mill, he set it up to be in by 3250, a bit late do to compression adn gears. For a shallow geared car, lower compression, I'd say 1000 rpm less would be a better fit.