Total timing?
 

I just did some reading over at Fordmuscle.com and I think I now know why my car's been a bit of a disappointment. I've been running 32* total timing on my car and my CR is only about 9.0:1 . According to them I should have my total timing between 38-42*! One of their project cars picked up 30rwhp and a boatload of torque by going from 30* total to 42*!
Anyways, my initial timing is 14* and it only seems to advance 18* (even though it's on a 10L weight) so I think I need new weights and probably a spring with less tension.
Anyways, what does everyone else run for advance? What should I use as my starting point?

42 sounds a little high to me, but hell, there are dozens of factors that play into it. That is also the reason that you shouldn't set your timing to a specific setting based on something you read in a magazine, or online.

You are going to have to experiment. Buy a recurving kit for your distributor, change the weights, and try one think spring and one thin spring, and see how that feels. If it's better, try two thin springs, etc. The recurve kits usually come with 3 different sets of springs, and by mixing and matching them, you can alter your curve. Don't forget about vacuum advance, too. The factory units have differ in the amount of advance they permit. Some only allow 8 degrees, while others go as high as 16.

Experiment. That's the only way to find what will work best for your combination of parts and geographic limitations.

Take care,
~Chris

I agree that 42 sounds pretty high. Maybe the gas up here isnt as good but i probably wouldnt run it past 36 otherwise a bad batch of gas could wreak havoc. But PKRWUD is dead on. Do some trial and error and find what works best on your engine. And just work your way up. Dont just crank it to 42 and risk damaging things. Try it in 2 degree intervals and see how it goes.

I also thought 42 seemed a little high. I'm going to start at 36 and go from there. I'll worry about the vacuum advance once I get the mechanical curve I want. My car has the adjustable vacuum advance so I can change it, I'll adjust it by driving it up a steep hill and see how it behaves.
I think my car does need a fair bit more timing because it seems to be out of where the powerband for this motor should be at the track. I get my best times and MPH by running it up to 6300+ rpms and it bogs out of the hole bad (2.0 60' times on sportsman pros) even with a 4000rpm launch, saying to me there's no torque down low.

If you ignore your vacuum advance now, your curve will be way off. When you're at WOT, your vacuum advance is at it's maximum, but when you're cruising, it's hardly used at all. You need to include it in your calculations for racing, and can ignore it if you want to figure a curve for highway cruising.

Take care,
~Chris

I thought that at WOT there was virtually no vacuum at the spark port? When I crack the throttle open from idle with the vacuum guage hooked to it it stays at 0, if I hold the engine at say, 2000 rpm, it settles to about 20" and back at zero at idle. Also everything I've read says the same thing, I think you've just mixed yourself up today PKRWUD, everthing else you've said makes sense to me except this.

I'm running 33* with my 331. Still need to experient though.

Also, vacuum under WOT should be zero and at idle I'm at ~11 or 12 in. hg.

E

At a full vacuum port my car pulls 14" at idle, it's only zero at the timed port, sorry I didn't clarify that.

Vacuum advance operates on PORTED vacuum, not MANIFOLD vacuum. You seem to have them backwards.

Check your ports yourself. Oh wait, you mention that in your last post. So you understand you were mistaken, and how important it is to calculate in your vacuum advance. Good.

You had me worried for a minute there.

Sh*t, I'm sorry Chris. Isn't there no vaccumm at WOT? Maybe 1?
Maybe your just testing us?:D Right Jim?

Actually, as I read that, I don't think you have a clue about PORTED vacuum (the vacuum source for your vacuum advance).

Manifold vacuum is what exists underneath your throttle plates. When they are closed, manifold vacuum increases. If your vacuum advance was hooked up to this source of vaccum, you would be fully advanced at idle, and the timing would retard as you accelerated. This won't work. So, the engineers needed to figure out a way of having the opposite effect, but that meant creating vacuum as the throttle opened, and lessening it as the throttle closed. Quite a paradox. Until someone realized that the transfer slots, the grooves that are cut into the venturi above and below the throttle plate, worked on a similar principal. Rather than depending on the vacuum created when the throttle plates are closed, they used the vacuum created by the air rushing by a small port at the narrowest part of the venturi. The faster the air would rush by, the more vacuum would be created. So, at closed throttle, there would be no PORTED vacuum, whereas the farther the throttle was opened, the more PORTED vacuum there would be. It's just like a minature fuel feed, except it goes to the ported vacuum port instead of the bowl.

Get it?

Take care,
~Chris

gofast-
That wasn't aimed at you, but the explaination is still accurate.

:)

Take care,
~Chris

I dont know if Im reading this correctly, but I dont think there is any vacuum advance at WOT.

You know, I never knew that. That seems to make alot of sense. explained well too.......

In a nutshell, ported vacuum and manifold vacuum react opposite to the throttle opening.

Think about it. If the vac advance was hooked to mani. vac., you'd be phucked!

Thanks gofast, I try.

:)

Take care,
~Chris

Yes, there is. In an engine with vacuum advance, the TOTAL advance is made up from three sources:

max vacuum advance
max mechanical advance
base timing

C'mon guys, carburetors weren't that long ago! you guys are making me feel old.

Ive been wrong before, and I may be now but I was sure vac adv was 0 at WOT. Only mech and at WOT. Ive had a few and still own a carbed. As far as how it all works and the way you explained it is correct and it makes since to think there would be vac adv at WOT but I beleive there was a reason that there wasnt any. I used to run my truck 73 F100 at the track with no line hooked to vac advance. Later down the road I started driving it daily and put a line on it. Got better gas milage but no improvement in times at all with the same base timing. I believe it only works at part throttle.

I'm confused? Howcome my car hasn't detonated itself to death then? With the vacuum advance hooked up my car goes to about 50* advance @2500 and it doesn't ping but if I crack the throttle wide open with the light on it, the timing falls to my original 32* mark? Vacuum advance is mostly for fuel mileage, otherwise why would a lot of performance distributors not have it? This is the website I've been reading... http://www.fordmuscle.com/archives/2...ng/index.shtml

Ahhhhh! I now see why you are confused. That article is incorrect. If you read the sidebar right next to it, where it says "Tuning Vacuum Advance", you will see that they contradict themselves. The sidebar is correct, the article is mistaken.

The reason that you setg the base timing with the vacuum disconnected is so thet you can accurately set it. If the vac was hooked up, you wouldn't know how much of your advance was mechanical, and how much was vac. BUT, you MUST include the vacuum advance in your calculations.

Hope this helps.

Take care,
~Chris

I missed this part, sorry.

When it comes to racing, you are rarely at speeds of less than 2500 rpms, and since that is where the timing is usually fully advanced, there is no point in having a vacuum advance.

This may be slightly different in some Ford applications, because for a few years, they had vacuum advance units that had two ports on them, and had two different vacuum sources to help control the advance, to reduce emissions. Those are useless, when it comes to performance.