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Is your vac advance connected to timed vacuum port or constant manifold port? The reason I ask is because I have a mild cam in my 302 and it pulls crazy vacuum at Idle (15inch) and my initial timing is extemely low 4 degrees. I was thinking that if I switch to timed vacuum I can increase initial and have better response. Any opinions appreciated. If it wasn't so cold out I get the car out but no heater or top no test drive until warmer weather
Now, there's a subject that generates both heat and light. Do a search on "timing" or "distributor timing" and you'll find a lot of comment.
I contend that most applications work best on ported vacuum. Others will tell you different, but I'm right :LOL:
Quote:
Originally posted by dennis kelley
Is your vac advance connected to timed vacuum port or constant manifold port? The reason I ask is because I have a mild cam in my 302 and it pulls crazy vacuum at Idle (15inch) and my initial timing is extemely low 4 degrees. I was thinking that if I switch to timed vacuum I can increase initial and have better response. Any opinions appreciated. If it wasn't so cold out I get the car out but no heater or top no test drive until warmer weather
i use manifold vac. most of the time so i can run lower base timing for hot starting purposes. then the vac, adv. will adv. the timing when you start the motor for good response. sometimes it can cause some heating problems in hot weather. try it both ways and see what way you like best. **)
ps- and dont believe nothing that Henry tells you :LOL: :LOL: :LOL:
yeah what he said:LOL: :LOL: :LOL: :LOL:Quote:
Originally posted by lt1s10
i use manifold vac. most of the time so i can run lower base timing for hot starting purposes. then the vac, adv. will adv. the timing when you start the motor for good response. sometimes it can cause some heating problems in hot weather. try it both ways and see what way you like best. **)
ps- and dont believe nothing that Henry tells you :LOL: :LOL: :LOL:
Dennis if im reading this right you are looking to increase your response time. you have 4 degrees base timing and when you crank the motor you are idling with about 15 degrees total timing (i don't know what that is, im just using 15 degrees) so you have about 15 degrees timing when you accelerate, then the timing falls off. so you go to ported vac. and increase your timing to 10 degree base timing and when you start the motor, then you still have 10 degrees of timing, as far as im concern you just lost 5 degrees of timing which will hurt your response time. if response is what you're looking for.:confused: :DQuote:
Originally posted by dennis kelley
Is your vac advance connected to timed vacuum port or constant manifold port? The reason I ask is because I have a mild cam in my 302 and it pulls crazy vacuum at Idle (15inch) and my initial timing is extemely low 4 degrees. I was thinking that if I switch to timed vacuum I can increase initial and have better response. Any opinions appreciated. If it wasn't so cold out I get the car out but no heater or top no test drive until warmer weather
I will agree with that S-10Quote:
Originally posted by lt1s10
Dennis if im reading this right you are looking to increase your response time. you have 4 degrees base timing and when you crank the motor you are idling with about 15 degrees total timing (i don't know what that is, im just using 15 degrees) so you have about 15 degrees timing when you accelerate, then the timing falls off. so you go to ported vac. and increase your timing to 10 degree base timing and when you start the motor, then you still have 10 degrees of timing, as far as im concern you just lost 5 degrees of timing which will hurt your response time. if response is what you're looking for.:confused: :D
I'm glad we cleared that all up. :whacked:
Quote:
Originally posted by dennis kelley
Is your vac advance connected to timed vacuum port or constant manifold port? The reason I ask is because I have a mild cam in my 302 and it pulls crazy vacuum at Idle (15inch) and my initial timing is extemely low 4 degrees. I was thinking that if I switch to timed vacuum I can increase initial and have better response. Any opinions appreciated. If it wasn't so cold out I get the car out but no heater or top no test drive until warmer weather
Anytime you go from manifold vac. to ported vac. you gonna hurt your response time. you will gain it back some place else, but your response time will slow down. try it both ways and see. :D
Quote:
Originally posted by Henry Rifle
I'm glad we cleared that all up. :whacked:
quote....I was thinking that if I switch to timed vacuum I can increase initial and have better response.
henry, this was the ?, and i dont belive that you agree with what.
:HMMM:
lt1,
This is all I'm saying:
-That having full vacuum advance at idle with a lower initial is not necessarily a good thing.
-That every technical article I've read tells me the same thing.
- That every performance car I've owned - granted, no Ford engines, just Pontiac and Chevy - worked best when connected to ported vacuum.
I don't disagree with you, it's just this has always worked for me. One thing we totally agree on is . . . "try it and see which works best."
Hey guys I'm going to the dyno next friday and I'll try it both ways. The problem is that the vac advance at idle with the consaant vacuum forces me to run extremely low initial timing. I appreciate everyones input. I'll let you know how it turns out. the engine is a 302ford with AFR 165 heads, demon 650dp, 1 3/4 headers, MSD ready to run unit with 6AL. I've never used the timed port and I thought because it has no vacuum pull at idle I could increase timing. Last Trip to the dyno 273 RWHP and 298RWT. I'm shotting for 300 hp an 300tq at the wheels. The motor seems to law down above 5000 rpm.
Thanks S10 and everyone for your input
Ok dennis let us know, but the truth is each motor combination needs dif. things, but if your problem is above 5000 your vac. adv. wont help you no way. youll be working with the mechanical adv. then. this thing with Henry got started a long time ago and now if anybody ask about adv timing he says ported and i say manifold, which is the way i ran it for 30 yrs. and didnt like it the other way, but he says hes always run ported. most Hi prof. motors dont run any vac adv. so work with it a little and see what you come up with.:DQuote:
Originally posted by dennis kelley
Hey guys I'm going to the dyno next friday and I'll try it both ways. The problem is that the vac advance at idle with the consaant vacuum forces me to run extremely low initial timing. I appreciate everyones input. I'll let you know how it turns out. the engine is a 302ford with AFR 165 heads, demon 650dp, 1 3/4 headers, MSD ready to run unit with 6AL. I've never used the timed port and I thought because it has no vacuum pull at idle I could increase timing. Last Trip to the dyno 273 RWHP and 298RWT. I'm shotting for 300 hp an 300tq at the wheels. The motor seems to law down above 5000 rpm.
Thanks S10 and everyone for your input
hes setting it up on a dyno next week so its no telling what he will end up with. if youer looking for max top end hp ,its no telling what your idle is gonna be. :HMMM: :DQuote:
Originally posted by DennyW
:) Move your timing to 10BTDC. Install heavy weight springs in the distributor.:)
that new dyno loads the motor. :DQuote:
Originally posted by DennyW
He needs to set it up like the old days with a load on it, then set the timing for max pull.
Here's my point. In this case, Dennis says he has to run very low initial timing because of the high manifold vacuum. When he drops the hammer, ported and manifold vacuum are essentially equal, and he's left with that low initial. If he uses ported, he sets a higher initial, and the immediate drop-off isn't as severe.
The following article was written by Kenneth Steinbach on another forum, and I find it quite logical.But again, the dyno will tell.Quote:
Centifugal advance is strictly related to engine speed. Vacuum advance is related to engine load. Under light load, ie. low throttle angle conditions, cylinder pressure is relatively low and the less dense air/fuel mixture tends to burn slowly. Therefore additional ignition timing is necessary to burn all the mixture, hence vacuum advance. On the other hand, at wide throttle openings engine load is high, manifold vacuum is near zero because the engine is no longer sucking past partially closed butterflies, cylinder filling and pressure are greater, and the denser mixture burns faster. The vacuum seen by the vacuum advance diaphragm is not enough to overcome the spring which opposes the vacuum signal, so no vacuum advance occurs. The issue of ported vs. manifold vacuum is very simple, and 99% of what was said in the stangnet forum is wrong. The main reason for using ported vacuum rather than manifold vacuum is to reduce hydrocarbon emissions at idle. If you have an extra 10-15 degrees of advance at idle you'll gain nothing in performance but will double or triple your HC emissions. Another issue is idle quality. If you have a lumpy cam, vacuum at idle tends to be unstable, resulting in a constantly fluctuating vacuum signal which would cause erratic vacuum advance activity. A third reason to use ported vacuum is idle speed. If you increase timing at idle by 15 degrees, idle speed is going to increase by several hundred rpm. If you try to compensate by turning down the idle speed screw on the carb you may close the throttle blades too much and disturb the relationship between the blades and the idle transfer slot which will result in an off idle stumble. As far as ported vs. manifold at WOT, there's no difference. Neither produces enough vacuum to actuate vacuum advance.
OK, Dennis, it's your responsibility to tell us the results. Don't make us hunt you down.
. . . then, there's daylight saving time . . . :LOL: :LOL: :LOL:
Discussing theory here - not arguing.
Me too.Quote:
That's what I've been trying to say
a. I didn't say it. The guy I quoted did.Quote:
So, if I put it like you say, I can use that big old 300 overlap cam, and my emissions will be good?
b. Emissions may not be good, but they will be better.
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.Quote:
Simple, you use a delay valve, spring loaded. Acts as a regulator, smooths vac out
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.Quote:
If I run a cam with overlap, I want my idle higher, or it will die
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.Quote:
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
I'm not saying your process won't work. I'm just saying mine will.
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.Quote:
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. :)
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. :LOL:
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.:HMMM: :D
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 :D
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. :confused: :LOL: :LOL:Quote:
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 :D
Thanks for the discourse!
Dan J
Yep, and like Denny said...Quote:
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. :confused: :LOL: :LOL:
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 :DQuote:
Originally posted by DennyW
....we are just discusing, right?
Remember, that's how racing gets started, hahaha
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.
:mad:
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. . . .