Thread: Vacuum Advance

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Discussing theory here - not arguing.

That's what I've been trying to say

Me too.

So, if I put it like you say, I can use that big old 300 overlap cam, and my emissions will be good?

a. I didn't say it. The guy I quoted did.
b. Emissions may not be good, but they will be better.

Simple, you use a delay valve, spring loaded. Acts as a regulator, smooths vac out

Why bother with the extra parts? Connect the vacuum to ported, set the initial timing correctly, and you don't have to mess with it.

If I run a cam with overlap, I want my idle higher, or it will die

Granted. But why get the idle with vacuum? Turn up the idle adjustment - that is, unless you have to crank the idle up so far it uncovers the idle transfer slots.

The idle circuit is a seperate circuit. The slots you talk about is the part throttle slots.The accellerator makes up by giving a shot of fuel

True. However, the common terminology for those slots is the "idle transfer circuit." That's because it effects a transfer from the idle to the main metering circuit. As the slots are uncovered additional fuel is introduced into the airstream. That prevents the stumble. You shouldn't have to depend on the squirter to do the job of the idle transfer circiut.

I'm not saying your process won't work. I'm just saying mine will.

Originally posted by DennyW
Discussing theory here - not arguing

Me also:

Why bother with the extra parts? Connect the vacuum to ported, set the initial timing correctly, and you don't have to mess with it.

I didn't know you wanted to eliminate the idle circuit. Just go with a Predator then, no idle circuit

But why get the idle with vacuum? Turn up the idle adjustment - that is, unless you have to crank the idle up so far it uncovers the idle transfer slots.

Anything off of base idle, is no longer on the idle circuit. It's on the off idle circuit, idle transfer circuit, part throttle circuit. Kinda like the pole piece, reluctor, or pickup. Any three means the same thing.

That's because it effects a transfer from the idle to the main metering circuit.

Actually, it goes to the power valve circuit next, then main metering.

As the slots are uncovered additional fuel is introduced into the airstream. That prevents the stumble. You shouldn't have to depend on the squirter to do the job of the idle transfer circiut.


The accelerator has three functions:
1. To make up for the fuel that condenses onto the manifold surfaces when the throttle is opened suddenly.
2. To make up for the lag in fuel delivery when the throttle is opened suddenly, allowing more air to rush in without sufficient nozzle fuel.
3. To act as a mechanical injection system to supply fuel before main system starts.
Also: As the throttle is opened quickly, the intake manifold vacuum instantly drops, moving the pressure towards atmospheric. A high manifold vacuum tends to keep the mixture well vaporized. As the pressure rises toward atmospheric, fuel drops out of the vapor, condensing into puddles and wet spots of liquid on the walls and floor of the intake manifold. Thus, the mixture which is available for the cylinders is instantly leaned out and the engine will hesitate or stumble UNLESS more fuel is imediately added to replace that which has been lost to the manifold surfaces. This is especially important with big-port manifolds or manifolds with large plenum areas because these have more surface area onto which fuel can condense.
If anything, we are getting our brains to work, hahaha

I'm not saying your process won't work. I'm just saying mine will for sure.

You did good Danny, most people have no idea how complicated a carb. is, or how it really works. a vac. adv. is the same way. It does a lot of dif. tasks from the time you start the motor until you cut it off after a few miles.

Denny,

I disagree with several of your comments, but I concede that your process will work if properly implemented. Where you and I differ is in the simplicity of getting the process to work.

Anyhow, you and lt1 have your process and I have mine. Apparently both work. No sense beating this horse to death.

However, you know what my answer is going to be the next time the question is asked.

Im gonna try to throw in a few facts here.

fact 1- where did the book come up with the instructions to unplug the vac. adv. and plug the line before setting the time?
answer- because most cars came from the factory with manifold vac. at the dist. you had to unplug it so you could set the timing

fact 2- the guy asked would he have better response time with ported vac?
answer- no, dist. vac. adv. with manifold vac. is part of low end power, same as if you adv. your cam timing. cam timing adv.= better response off of the line. manifold vac. at the vac. adv. = better response time from stop light to stop light

fact 3- pre 1972, 90% of the cars came from the factory with manifold vac. at the dist.

fact 4- 1972 to 1985 when they stop putting mechanical vac. advs. on cars 90% of them ran with no vac or ported vac. when the motor was cold or idling. after the motor wormed up and you started to move then it switched over to manifold vac. which was 99% of driving time.

fact 5- most people today run manifold vac. on their hot rods, not because its the best thing to do, but because its what they was raised with. you can run either, so you should run what fells best to you and the hell with what everybody else think.

fact 6- most of my information comes from shop manuals, or OJT, not hot rod or car craft. Everything you read in the hot rod books is somebody's opinion, with no hard facts or trying to sell you something.

fact 7- me and Danny has close to 75 yrs. Certified, ojt, factory trained, in the shop every day experience and Henry you're quoting somebody from another forum who may or may not ever seen the inside of a shop. if ported vac. was the way to go then most people would be doing it. the ported vac. people are in the minority here. over the yrs i built up a pretty good following tuning cars up my way, just think what I could have done if I had did it the right way.

Hey guys, good informative thread! Now this is how you have a good debate with differing opinions being supported by technical and practical information... and no juvenile name calling

Thanks for the discourse!

Dan J

Originally posted by Dan J
Hey guys, good informative thread! Now this is how you have a good debate with differing opinions being supported by technical and practical information... and no juvenile name calling

Thanks for the discourse!

Dan J

I agree dan j , but for some reason nobody in this debate has been able the convince the other one that they are right.

Originally posted by lt1s10
I agree dan j , but for some reason nobody in this debate has been able the convince the other one that they are right.

Yep, and like Denny said...

Originally posted by DennyW
....we are just discusing, right?
Remember, that's how racing gets started, hahaha

This just reminded me that some of us used to resolve our debates over who REALLY knew what they were talking about by running a little heads up race down an old farm road

Regardless of who'd win, we'd usually find time to test the other guys "theory" out anyway... you know, just to "prove" the other guy was wrong!

Good stuff guys.

Dan J

lt1,

I was trying to keep it civil, I don't agree with your method, and I'm not the only one, but I didn't denigrate your sources of information. (at least I had some other than my resume.)

Hot Rod and Car Craft, indeed.

That's twice . . .

Danny quote...It's not our process, it's the manufacturer's process, they designed the thing,

lt1 quote....most of my information comes from shop manuals, or OJT.

that is my point Henry, me and Danny are not giving our opinion, we're telling you what the GM shop manual says. anything other than that is an opinion. you say your trying to keep it civil and you're telling me and Danny we dont know how to do our job. you are right, my resume is all ive got and just because it don't have engineer in it don't mean that i dot know how to do my job. as far as im concerned you just crossed the line. end of discussion.

Hey Guys I will be At the dyno and I promise I am going to try it both ways. I'll post on the 19th of december.

Denny,

Thanks for the discussion. I know you believe in your method, and not mine (and I totally convinced that you can make manifold vacuum work), but I certainly enjoyed the back-and-forth . . . and I learned some things about manifold vacuum.

lt1,

Whatever . . .

dude go to fordmuscle.com youll find a step by step ignition tuning and distributor curving guide

Dude, that thread was 4 months old . . .

The Winner is Timed Vacuum ADVance. Listen guys I dynoed to max Hp 289 Max tq297 on a dyno jet dyno. I switched from constant vacuum to timed No Difference in HP. Lost one 1 lbs/ft of torque with time vaccum. Car responded an had a better idle with timed vacuum. the Dyno rules. When I drove the car home I could not believe the car. My mod are 302 roller motor, cross wind(air gap clone), BG 650 dp, AFR 165 heads, Crane 2030 cam, 4 hole spacer, K@N extreme air assmbly. The air fuel ratio (wide band) is the way to tune. I appreciate everones responses. The reasson why I did'nt dyno the car soon is that it is a kit car and I don't have a top.

Later Dennis E. Kelley

I find that extremely interesting. . . .