So which springs are you running with that timing setup?

It has been my experience that the vacuum goes away SO fast the timing returns to whatever it was at that rpm. If it is to low at that rpm when I "nail the throttle" I do get a slight hesitation. Advancing the base timing a little more makes the hesitation go away. Therefore, I must conclude in my case the vacuum advance add's little to address the hesitation problem. Don suggested, and I concur, that instead of running so much BASE advance, which causes starter problems, that I increase the advance curve of the weights and springs. Go for more advance at a lower rpm by changing springs and a more aggressive curve as the rpm builds. BUT, if you end up using springs that are too light, the weights don't return properly everytime, so the timing tends to bounce around at lower rpm. In that case, you would lighten up the weights themselves.

I'd like to run 22 base and a 14 bushing with a more aggressive curve and a max in at 24-2500 rpm. I will probably need a timing retard electronic to get the starter to agree to that. The starter is "she who must be obeyed" you see. :)

Why do I run vacuum advance?

Two reasons:
1. More advance at light throttle under cruise rpm conditions will generally optimize mpg. Which in turn increases your total range in miles before having to stop for gas.

2. My engine HAS to idle about 900-1000 rpm. When I finish adjusting the carb for best idle rpm, the throttle plates are open enough to cause "run on" or "dieseling" when the motor is hot and shut down. With vacuum advance (ported to DIRECT intake manifold vacuum) I can get my 1,000 rpm idle speed without having to open the carb plates as much. So the motor dies smoothly when shut down because the throttle plates close more completely and disallow that little bit of extra air/fuel to be drawn and cause the "run on" condition, when hot.

Ernie, you clearly know what you want and how to get there. Remind me, how much compression with your latest engine build?

Old motor:
12.5 to 1, with iron heads no less! When it knocked from low octane it sounded like Thor and his mighty hammer at work. :)

I'd run the timing retarded, a bunch, to get by with pump gas and NEVER let the rpm fall to low and load the engine to much. Running race gas and advancing the timing really woke it up.

New motor:
At 9.6 to 1 now, still iron heads, with the proper timing I can pull nicely from about 17-1800 rpm. I can take off in third gear with no problems. 3rd gear is good for about 110-115 mph, by the way, it's TALL.

I do believe the "quench" built into this motor allows me to run a little more advanced timing than might other wise be recommended. Forged pistons, 7,000 miles later and so far, so good.

... and your timing curve starts off with 20 degrees with roughly 16 more coming in before 2000rpm, correct?

Currently I'm running one heavy silver spring and one light silver spring with the black (18) bushing. That brings it all in around 3000 rpm. At 20 base with another 18 it's 38 total at 3000 rpm.

Elm has a pretty good setup, I'm a hair to high.

Ernie, I think Pat was referencing Bobcat's setup, not mine. I am running 16-17 degrees initial plus the 18*black bushing, for a total of 34-35. I am running two silver light springs. I had been at 18-20 initial plus the 18 black and that was when I was running hot so we retarded it a bit, which seemed to help. I have not experimented with the timing since then, but I am planning on that in Oct.

Ah, hard to keep up, still working on my first cup of coffee this am.

Two light springs, I was worried that setup might lead to "hunting" at lower or idle rpm's because the springs might not be strong enough to pull the weights back in. But that's something I want to try, to get the advance in a little quicker.

Correct. For some reason, I just didn't want to jump on Ernie.:p We've talked about the "20 degree initial timing" line of thinking before and, granted, some swear by it. Even over on the FE Forum there are a couple of people who run it and like it. If you have all your timing in by 3000, and your cam really doesn't kick in until 3000, then there's an argument to made that it doesn't really matter one way or another. But I do enjoy reading posts by guys that have fixed their problems by running 20 degrees initial.;)

This may not be the right thread, but that is what I want to better understand. If a cam is optimized to "come in" above a certain range, say 3k rpm, how does that correlate to how the base and advance is set...

Don says that I should be running 20-22 base + 14 advance with it all in at 2800-3000 rpms. That's a long way from where I am now.

How much advance you run, or NEED to run is dependant on a couple of variables. One would be the cam profile and it doesn't have to be "that radical" to warrant 20 degrees. My cam profile is somewhat modest, 2000 to 6200 rpm. Cylinder filling is the issue. With more overlap at low rpm the spark needs to get a head start to get full ignition. A single plane non heated intake is another potential problem, compounded by running twin carbs. That all combines to make for a "wet" fuel mixture at lower rpm, the fuel droplets aren't atomized as well and remain liquid to some degree. So you need more time to fire the "rich" mixture.

Smaller intake ports or runners, maybe a single carb, give you better throttle response at lower rpm, you won't need as much advance, even with a healthy cam. There is no "one" setting that works for all engines.

I think Don's advice is pretty close when you consider most of us are running a healthy cam and big intake. Tuning of the carb itself will also have an impact. Accellerator pump squirt, spring rate for the vacuum secondary, power valve setting. But timing is FIRST, carb is second.

I agree with all of what you posted, and that there is no one rule of thumb. Don Gould, however, contends that where FE engines with moderate cams aer concerned, a big initial of 20+, with a total of around 34 and maybe 36 max is the target setting.

What is a moderate cam anyway? :) Reminds of my high school days when cam's were rated like "3/4 race" and "full race". My old motor was truly a "full race" cam, didn't come on until 3000 and was good to 7000, a real beast to tame on the street. My current cam has that great "lumpy idle" and works best slightly over 2000, I guess it's "3/4" race, maybe "moderate"?

Oh, and compression is another factor! At only 9.6 to 1 my cam would prefer higher compression to make up for the lack of cylinder filling at lower rpm.

Which cam are you running?

I submit that if you have 36 degrees total timing, all in by 2800rpm, your engine will run the same at 2800 and above regardless of whether your initial timing is 10 degrees or 20 degrees.

Thats an accurate statement patrickt. But the issue is: How well does it do from low rpm when you nail the throttle?

This discussion of cam profile and timing is relevant to the thread because timing issues are what led to the ring gear failure in the first place!

Not only, "Is their a hesitation at low rpm and going to WOT?" Also, I have found more advance makes a big difference on how well the car recovers from fuel slosh following hard braking or cornering. Now how many threads have we seen where people ask about that? Hesitation, motor dies at stop signs, bogging during cornering, etc. While carb adjustment and modifications help, TIMING should be at the top of the list to get a handle on it.

Having the WRONG ring gear didn't help, but still, hard cranking with the advanced base timing remains the central component.

Oh yeah, my cam is Comp Cams 292S, flat tappet, as recommended by George at Gessford. I don't think they make that profile for FE's today. IF I was going with a new cam I'd give serious consideration to dual pattern cam. Different profiles for the exhaust and the intake. Because of my high gear ratio's I needed a cam that would pull well from a lower rpm than I was running, which was a 3000 to 7000 profile. Real bad bog at low rpm I never could overcome, it just hated ANYTHING below 3000.

Very interesting your comments about the dual pattern cam. I am running the 294S advanced 5* on install. I am beginning to understand why maybe a dual pattern would have been worth considering. My car runs VERY well, but I can "feel" that there is a LOT more power in this engine that I haven't released yet due to timing and carburetion. I have been preoccupied sorting out the overheating issue and just common problems associated with putting a new car on the road. At present state, if I am in 5th gear at 65 mph its almost bucking and I am running about 1800 rpms. If I floor it, with my sidewinder and 750 Mighty Demon it pulls immediately and relentlessly like a freight rain and Gawd knows where the top is, somewhere way the hell north of 140 mph.

I'm still researching the whole dual pattern cam thing, but it sounds promising. I'll still go with flat tappet if I ever decide to make a change though. :)

Ditto on that. Not because my block requires it (it does) but because I love the sound, I like the nostalgic perspective and mostly I loved chewing all my nails off during the 20-minute torture test.:eek:

Now Don't Get Me Wrong...
 

... I'm not poo-pooing a hefty initial advance on an FE. It is a bit outside the traditional norm, but I don't think any of us really have a truly traditional FE anymore. If you can crank & start with 20+ initial, with no detonation, heat, or other issues, then I'm all for it. But I do wonder whether or not that might have contributed to your flywheel's toothless grin.:p