alsant
Well-Known Member
Thanks for the info Mattax , well appreciated. Learning curve on my part.
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Ported Vac or Manifold Vac
- Thread starter alsant
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Just stirring the pot: I'm technically running manifold vacuum to my spark control, but I'm faking a ported vacuum advance curve electronically.
Although on a more serious note, an advance curve is an advance curve, an air/fuel ratio is an air/fuel ratio, and the engine doesn't care how you set them. Too much advance gives an unstable idle whether it's from a computer or an advance can. Some full on race cams may benefit from 24 degrees of idle timing, but it's rare for this to be ideal on a milder engine.
Although on a more serious note, an advance curve is an advance curve, an air/fuel ratio is an air/fuel ratio, and the engine doesn't care how you set them. Too much advance gives an unstable idle whether it's from a computer or an advance can. Some full on race cams may benefit from 24 degrees of idle timing, but it's rare for this to be ideal on a milder engine.
Mattax
Just the facts, ma'am
Here, these posts and the links will save you from doing a ton of searching.
Timing Terms and Purpose of Timing
Distributor curve help needed
I just checked the curve of my stock distributor (ported vacuum blocked) and need some help to optimize. Car is a 70 Duster with a stock 360, stock converter, 3.23 gears, 28" tires. Distributor currently has FBO black & gold springs with no limiter plate. 500-24* 1000-24* 1500-25* 2000-27*...
www.forabodiesonly.com
slantsixdan
=..=
Buncha info on ported vs. manifold advance (on Mopars, not Fords) here.
The cam in my slant 6 has 250 degrees duration @.050" and it's ground on a 108 LSA. I have it sitting on about 22 degrees initial timing with 10 degrees mechanical and it runs really well. It's also a measured 10.6:1. It also runs better on manifold vacuum to the vacuum advance. But a mild engine will likely not benefit from that.
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Ok, that cam has 250 degrees at 0.050 instead of 220 degrees? Ok, now I understand why it was so rowdy.
Yeah. She's a rowdy girl. lol
It goes full circle. I’ll say it again. IF you use too much cam for your compression you’ll likely need more initial timing than you can get and still get a curve.
Then you can use MVA.
I’m on the other end. At 12:1 (actual, measured not a guess) with 255 @ .050 and I’m betting I’ll need 20-22 initial. That can be easily done without MVA.
I will be testing with ported VA on the dyno and if it looks like I can use VA (ported) in the car I will.
The claim that every engine needs some absolutely insane amount of initial to get the idle correct is 100% bullshit and it needs to be called that.
Chrysler didn’t miss the boat on that.
Sadly, the OP has not done a search on here because this horse and 4,976,213 other horses along with it has been beat to death just on this forum.
Next up the “all in” or “lock it out” crowd will come along and exclaim that’s the only way to do it, when in fact its wrong 99.9% of the time.
I just wanted to head that off at the pass before it even starts.
Chrys DID miss the boat on MVA. And the nonsense about EFI not needing a lot of initial timing.....is just that nonsense. The same parameters that make a carbed engine require a certain amount of idle timing....are there with EFI. My Toyota Cressida, an inline 6 EFI engine, idled at 22*. The GM LS engines, high compression [ relatively ], & short duration factory cams, idled with 22* also. As for EFI....
A friend has aftermarket EFI on his 400 cube V8 engine [ I think it is Megasquirt, not 100% sure ], found best idle was with 30* of timing.
As I stated earlier, GM used MVA. My GTO idled at 26* with 10.75 CR & a cam that had 200* @ 050. [ That is 12-14* less duration than the 340/440 Hi -po cams ] .But, but, but...you thought high compression & short duration cams were good with 12* initial idle timing...
Below is the section from the Pontiac workshop manual. Also included are quotes from an English & Australian tuner. See, MVA works worldwide....
A friend has aftermarket EFI on his 400 cube V8 engine [ I think it is Megasquirt, not 100% sure ], found best idle was with 30* of timing.
As I stated earlier, GM used MVA. My GTO idled at 26* with 10.75 CR & a cam that had 200* @ 050. [ That is 12-14* less duration than the 340/440 Hi -po cams ] .But, but, but...you thought high compression & short duration cams were good with 12* initial idle timing...
Below is the section from the Pontiac workshop manual. Also included are quotes from an English & Australian tuner. See, MVA works worldwide....
22 degrees? That’s what I’d consider normal for a performance engine.
Of course, you move the goal posts AGAIN and add EFI to the mix.
I don’t give a steamy flat **** what your Toyota does.
It has nothing to do with what the OP is doing.
Maybe at sea level. lol
Those are the guys that tune their automatic transmission cars in neutral or park. lol The same guys using MVA.
So in the Turk world, Turk, EFI doesn't use or need timing at idle? It uses a different 'air' than carbed engines? Perhaps it doesn't even need something like a spark plug to ignite the mixture? You haven't got a clue....
Lord hammercy, Bewy. "THIS" thread by "THIS" poster is talking about "THIS" particular build, which has a CARBURETOR and a DISTRIBUTOR. It is not EFI, so your EFI argument is a moot point HERE. Please take it elsewhere, so as not to gum up the OP's thread anymore.
RRR,
It is completely relevant & I am sorry that you cannot see that. The same principles are at stake whether carb or EFI. And I take offence that I am ' gumming up' the thread. Before the thread disappeared, I had provided info & the OP asked where the thread had gone because it contained useful info, some of which came from me. I have also provided many links from a wide range of sources on MVA benefits, in a thread that is about man v ported VA. That is not gumming up a thread, that is providing real time useful info. If you do not understand that idle requirements with EFI are similar to a carbed engine, then you know a lot less than you think you do. The link in post #37 came from an article where MVA was added to a carbed engine. The purpose of finding out the idle on an LS engine, & including it in the article was: to show that it doesn't matter whether carb or EFI, the engine could use that amount of idle timing, because the same parameters are at work in both systems. Below is the original article that compared MVA to PVA [ which is what this thread is about ] & the LS clip was included with it.
It is completely relevant & I am sorry that you cannot see that. The same principles are at stake whether carb or EFI. And I take offence that I am ' gumming up' the thread. Before the thread disappeared, I had provided info & the OP asked where the thread had gone because it contained useful info, some of which came from me. I have also provided many links from a wide range of sources on MVA benefits, in a thread that is about man v ported VA. That is not gumming up a thread, that is providing real time useful info. If you do not understand that idle requirements with EFI are similar to a carbed engine, then you know a lot less than you think you do. The link in post #37 came from an article where MVA was added to a carbed engine. The purpose of finding out the idle on an LS engine, & including it in the article was: to show that it doesn't matter whether carb or EFI, the engine could use that amount of idle timing, because the same parameters are at work in both systems. Below is the original article that compared MVA to PVA [ which is what this thread is about ] & the LS clip was included with it.
the thread never disappeared, and you'd know that if your lust for manifold vacuum and articles about pontiac motors along with highlighter and annotations didn't leave you blind to that fact.
Dave999
Well-Known Member
Goodness, this snowballed
I use manifold vacuum
my cam below
my CR 12.5:1
super unleaded not regular
port on port induction i.e 1 carb per cylinder 1 runner per cylinder 1 vacuum take off on 1 runner. standard OEM set up for mine was ported from 1 carb,
My carbs have no ported vacuum just a pipe tail for a vacuum gauge so vacuum is taken from that fitting on the manifold side of the throttle on 1 carb
initial 15 total mechanical 28. i took out half of the advance in the distributor
maybe i could have achieved the same with more initial and no vacuum and a lot more distributor fiddling (awkward on a bosch mopar electronic hybrid)
who knows i like it as it is, i can slog it on the freeway at 70+ for 100s of miles and go to the track.
more than one way to skin this cat...
Dave
I use manifold vacuum
my cam below
my CR 12.5:1
super unleaded not regular
port on port induction i.e 1 carb per cylinder 1 runner per cylinder 1 vacuum take off on 1 runner. standard OEM set up for mine was ported from 1 carb,
My carbs have no ported vacuum just a pipe tail for a vacuum gauge so vacuum is taken from that fitting on the manifold side of the throttle on 1 carb
initial 15 total mechanical 28. i took out half of the advance in the distributor
maybe i could have achieved the same with more initial and no vacuum and a lot more distributor fiddling (awkward on a bosch mopar electronic hybrid)
who knows i like it as it is, i can slog it on the freeway at 70+ for 100s of miles and go to the track.
more than one way to skin this cat...
Dave
Mattax
Just the facts, ma'am
@alsant ant My advice is to ignore the nonsense and/or ask them to take it to their own thread. Worst case start a new thread. You can also put members on your ignore list and you won't see their posts.
How do you determine what is useful and relevant and what is not?
Well one way is to learn the fundamentals. That will help you seperate what is possible, what is plausible, and what is uh lets be nice and call it a misunderstanding. Whether to use manifold vacuum source or a ported vacuum source depends on the distributor design as well as the engine. When the spark should be fired at idle speed is effected by the timing of when the intake valve closes, the piston dwell time at the top, how much compression is generated at idle, how much heat is in the cylinder, etc. The fact is that Ford used venturi vacuum around 1949. Chrysler used ported vacuum in 1959. Kaiser used manifold vacuum on their Jeep engines in 1963. Chevy used ported vacuum on their high performance engines in in 1965. AMC used a mix of both in the 1980s on their v-8s through a non-linear valve. What does this have to do with anything? Not much other than the following. Some people just refuse to let facts get in the way of their beliefs. The facts discredit the claims made that ported vacuum is a product of poor engineering, are an emissisions reduction method, blah blah blah. The facts can be verified independently and you should do so.
Another way to decide what is relevant is observe whether the person has any real first hand knowledge or experience, or is just repeating things he or she has been told and beleives. For me, once someone has been exposed as a BS artist, they are forever discredited as a reliable source of guidance. Sometimes these are well meaning people, but as I wrote over at Speed-talk, they don't recognize the limitations of their knowledge. Knowing enough to be dangerous as we say. LOL. It doesn't matter if you were an engineer or a magazine writer.
How do you determine what is useful and relevant and what is not?
Well one way is to learn the fundamentals. That will help you seperate what is possible, what is plausible, and what is uh lets be nice and call it a misunderstanding. Whether to use manifold vacuum source or a ported vacuum source depends on the distributor design as well as the engine. When the spark should be fired at idle speed is effected by the timing of when the intake valve closes, the piston dwell time at the top, how much compression is generated at idle, how much heat is in the cylinder, etc. The fact is that Ford used venturi vacuum around 1949. Chrysler used ported vacuum in 1959. Kaiser used manifold vacuum on their Jeep engines in 1963. Chevy used ported vacuum on their high performance engines in in 1965. AMC used a mix of both in the 1980s on their v-8s through a non-linear valve. What does this have to do with anything? Not much other than the following. Some people just refuse to let facts get in the way of their beliefs. The facts discredit the claims made that ported vacuum is a product of poor engineering, are an emissisions reduction method, blah blah blah. The facts can be verified independently and you should do so.
Another way to decide what is relevant is observe whether the person has any real first hand knowledge or experience, or is just repeating things he or she has been told and beleives. For me, once someone has been exposed as a BS artist, they are forever discredited as a reliable source of guidance. Sometimes these are well meaning people, but as I wrote over at Speed-talk, they don't recognize the limitations of their knowledge. Knowing enough to be dangerous as we say. LOL. It doesn't matter if you were an engineer or a magazine writer.
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I tried. I even asked nicely, but he refuses. So I'm done.
Mattax
Just the facts, ma'am
Maybe that's best.
Post a new thread when you have all the specific info for your engine, including the curent timing from idle to as high as you care to measure.
Let this thread drift off into oblivion....
Post a new thread when you have all the specific info for your engine, including the curent timing from idle to as high as you care to measure.
Let this thread drift off into oblivion....
LS&S
Well-Known Member
Hi Mattax.
Tried to write you about an alternator issue, but your inbox is full. Just FYI
Mattax
Just the facts, ma'am
Some day I'll get around to fighting with paypal and renewing my membership.
Easiest thing is go to my website and e-mail me.
Website is listed in my FABO profile under "about"
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