Manifold Vacuum Advance what am I not getting?

[340inabbody]

That doesn't answer a thing. I asked if it ran good without the higher advance. This tells me nothing. The point YOU'RE missing is that I am an advocate of MVA. Lemmie tell you something. I've been working on and tuning on cars since 1974, I promise you "I" am not missing the point.

I don’t know what you mean by “run good”. That’s a hard question to quantify. When I tuned it, I didn’t look at my timing light at all. I timed it based on what sounded good and smooth and what gave me the highest vacuum. Will it run at 24° yes. Does it seem to run better at 42° I believe so. I believe an engine is more efficient when you have higher vacuum. So I think I answered this question correctly or is best I could.
I can also say that I repeated this tune 3 times and all three times it came out to 42° so it was consistent.

 

[RustyRatRod]

I don’t know what you mean by “run good”. I don’t know what you mean by run good that’s a hard question to quantify. When I tuned it, I didn’t look at my timing light at all. I timed it based on what sounded good and smooth and what gave me the highest vacuum. Will it run at 24° yes. Does it seem to run better at 42° I believe so. I believe an engine is more efficient when you have higher vacuum. So I think I answered this question correctly or is best I could.

Do you know when an engine runs good versus when one runs like crap? If you don't, we have no business trying to help you. That's like saying you don't know what a woman is.

 

[340inabbody]

This is my timing like is it working? It seems to be functioning correctly is a calibrated and accurate and not being affected by noise of the distributor box. I don’t have a clue.

 

[92b]

I just mean that you would tune the car differently for MVA versus ported that’s all. Different curve, a different total advance, a different, initial advance, etc. etc..

The difference will be at idle. For the most part once the ported signal is activated for all practical purposes manifold and ported will be pretty simular. When you say tune I assume you are refering to timing only and not air fuel ratio.

 

[340inabbody]

Do you know when an engine runs good versus when one runs like crap? If you don't, we have no business trying to help you. That's like saying you don't know what a woman is.

Rusty, I’ve provided a clip of how this engine is running. It’s not all that different from 24° to 42°. But I would say it’s better at 42° because the vacuum is higher and it runs smoother when you have a higher advance at idle. I thought that was typical for most engines.

 

[340inabbody]

Here’s another video

 

[Newbomb Turk]

This is my timing like is it working? It seems to be functioning correctly is a calibrated and accurate and not being affected by noise of the distributor box. I don’t have a clue.

View attachment 1716283821

Is that 1980 rpm? Is that where it idles?

I wish we would have discussed what an actual “good” idle is.

Good doesn’t always mean smooth.

Just cranking timing in at idle until the engine idles smooth is a fools errand. You will go down the wrong hole every time.

I know it’s subjective but if you can get the engine to idle consistently UNDER curb idle that’s ALL the initial you need.

Bet your *** the book readers will come in and call bullshit but rise above their ignorance and don’t jam a bunch of timing in it to get some fantasy idle.

I have said and I still say a performance engine with even reasonable .904 lobes the idle speed should be no lower than 900 rpm. In gear if you use a converter. I like 950-1000 just to keep oil on the cam lobes at idle.

That’s not to say what I tune won’t idle lower than that, because they will. It’s hard on parts with low idle speeds.

The cams you can buy today have lobes faster than anything just a couple of decades ago.

At any rate, a smooth idle isn’t the best idle.

If that timing light is correct and the damper hasn’t moved GET IT BACK TO 20-22 initial NOW. And tune it from there.

You’ll kill it like that.

 

[340inabbody]

Is that 1980 rpm? Is that where it idles?

I wish we would have discussed what an actual “good” idle is.

Good doesn’t always mean smooth.

Just cranking timing in at idle until the engine idles smooth is a fools errand. You will go down the wrong hole every time.

I know it’s subjective but if you can get the engine to idle consistently UNDER curb idle that’s ALL the initial you need.

Bet your *** the book readers will come in and call bullshit but rise above their ignorance and don’t jam a bunch of timing in it to get some fantasy idle.

I have said and I still say a performance engine with even reasonable .904 lobes the idle speed should be no lower than 900 rpm. In gear if you use a converter. I like 950-1000 just to keep oil on the cam lobes at idle.

That’s not to say what I tune won’t idle lower than that, because they will. It’s hard on parts with low idle speeds.

The cams you can buy today have lobes faster than anything just a couple of decades ago.

At any rate, a smooth idle isn’t the best idle.

If that timing light is correct and the damper hasn’t moved GET IT BACK TO 20-22 initial NOW. And tune it from there.

You’ll kill it like that.

You’re saying do not tune for Max vacuum? I can certainly take the initial down to 24° but my vacuum will be at 10Hg. The problem with the idle speed is that there’s a significant drop when it goes into gear.

 

[Newbomb Turk]

I don’t know what you mean by “run good”. That’s a hard question to quantify. When I tuned it, I didn’t look at my timing light at all. I timed it based on what sounded good and smooth and what gave me the highest vacuum. Will it run at 24° yes. Does it seem to run better at 42° I believe so. I believe an engine is more efficient when you have higher vacuum. So I think I answered this question correctly or is best I could.
I can also say that I repeated this tune 3 times and all three times it came out to 42° so it was consistent.

Jacking timing to an engine with cranking compression that high is a power killer.

Manifold vacuum is a bad way to select your initial timing?

Why, because long duration, high overlap cams cause EGR. This does require more timing BUT you can never get the idle efficient enough no matter how much more than optimal initial timing requires.

Set the vacuum gauge aside, set the initial at 24 and start there without MV hooked up.

I just went through this last Sunday. I had to unfuck something I did correctly because some jack *** read that you need as much initial as the engine will take.

It was garbage. Did it idle “smoother” with 30 initial? Yes, but the time was off. It was smoother but it ran like ****.

I put it back to where it was supposed to be and even the owner was smart enough to see it was screwed up.

What spark plug do you have?

 

[Newbomb Turk]

You’re saying do not tune for Max vacuum? I can certainly take the initial down to 24° but my vacuum will be at 10Hg. The problem with the idle speed is that there’s a significant drop when it goes into gear.

Right, but jamming another 18 or 20 degrees of initial isn’t the fix.

You can’t fix a fucked converter with a timing light.

All you will do is kill more parts.

I wish you were closer and I wasn’t so busy.

I’d put your engine on my dyno and sort it out.

What you are doing is trying to fix a hard part issue with tuning.

That’s not a good plan.

 

[92b]

When comparing vac readings at idle are you adjusting idle speed so it is at the same rpm in each instance?

 

[340inabbody]

Jacking timing to an engine with cranking compression that high is a power killer.

Manifold vacuum is a bad way to select your initial timing?

Why, because long duration, high overlap cams cause EGR. This does require more timing BUT you can never get the idle efficient enough no matter how much more than optimal initial timing requires.

Set the vacuum gauge aside, set the initial at 24 and start there without MV hooked up.

I just went through this last Sunday. I had to unfuck something I did correctly because some jack *** read that you need as much initial as the engine will take.

It was garbage. Did it idle “smoother” with 30 initial? Yes, but the time was off. It was smoother but it ran like ****.

I put it back to where it was supposed to be and even the owner was smart enough to see it was screwed up.

What spark plug do you have?

Thanks I guess I don’t know how to tune for best idle. That’s why I’m here to learn. I am currently using Autolite 63 I came down from the 65’s as part of the recipe for helping with detonation (along with a slower curve).

 

[340inabbody]

When comparing vac readings at idle are you adjusting idle speed so it is at the same rpm in each instance?

Trying as best as I can.

 

[340inabbody]

Right, but jamming another 18 or 20 degrees of initial isn’t the fix.

You can’t fix a fucked converter with a timing light.

All you will do is kill more parts.

I wish you were closer and I wasn’t so busy.

I’d put your engine on my dyno and sort it out.

What you are doing is trying to fix a hard part issue with tuning.

That’s not a good plan.

I get it. 42° is way out of wack from what you guys consider normal or acceptable. I have no feel for this. But I hear you loud and clear and it is probably where Rusty was coming from as well.

 

[Newbomb Turk]

Thanks I guess I don’t know how to tune for best idle. That’s why I’m here to learn. I am currently using Autolite 63 I came down from the 65’s as part of the recipe for helping with detonation (along with a slower curve).

Because Autolite thinks it’s plugs are super plugs and one range fits 3 ranges in other plugs I can’t tell exactly what that plug is.

It’s either a 9 or a 12 in Champion.

A 12 is at least 2 ranges too hot for that cranking compression.

I also don’t use plugs with a black shell. You need to see color changes on the shell and black plugs don’t do that very well.

 

[4spdragtop]

She's beautiful! Sounds great too!

Rusty, I’ve provided a clip of how this engine is running. It’s not all that different from 24° to 42°. But I would say it’s better at 42° because the vacuum is higher and it runs smoother when you have a higher advance at idle. I thought that was typical for most engines.

 

[340inabbody]

Because Autolite thinks it’s plugs are super plugs and one range fits 3 ranges in other plugs I can’t tell exactly what that plug is.

It’s either a 9 or a 12 in Champion.

A 12 is at least 2 ranges too hot for that cranking compression.

I also don’t use plugs with a black shell. You need to see color changes on the shell and black plugs don’t do that very well.

What do you recommend? Hope this doesn’t high jack this thread lol thats all I need is to turn a Ported VA vs MVA thread into what the best spark plug to use thread LMAO

 

[Newbomb Turk]

Thanks I guess I don’t know how to tune for best idle. That’s why I’m here to learn. I am currently using Autolite 63 I came down from the 65’s as part of the recipe for helping with detonation (along with a slower curve).

I also should say 10 inches of vacuum is pretty standard for what I’m assuming is a fairly large cam.

Again, hooking up the vacuum hose to try and fix a converter issue will only aggravate the rest of the tune up.

 

[Newbomb Turk]

What do you recommend? Hope this doesn’t high jack this thread lol thats all I need is to turn a Ported VA vs MVA thread into what the best spark plug to use thread LMAO

I’m only guessing because we don’t know your actual compression ratio or
what your cam timing looks like.

But I’d say a 9 Champion is as hot as I’d start with.

Can you post a picture of a couple of your plugs?

Let’s see what they look like.

 

[CFD244]

The hand drawn curve is not meant to be precise but more of a concept or an example or close approximation for discussion purposes.

The total curve will be different (at idle anway) and thats my point.

The centrifugal advance portion of the curve is dictated by the springs of the distributor. B But they will and should have different curves and again thats the point.

With Manifold vacuum advance at idle I am able to achieve a higher idle advance without having too much at WOT or under acceleration causing detonation. And in my case can lower to a more retarded state if needed.

Also at t=0 seconds ie start of cranking there is little to no vacuum to speak of until just before ignition. So the cranking advance should be low aiding starting and idle capability which is another advantage of MVA. Right?

Again this is my concept and I am throwing it against the wall here. This is what I am thinking.

Does this make sense? Does anyone believe what I am saying is incorrect?

This makes sense to me. That's why I am trying it.

 

[340inabbody]

I’m only guessing because we don’t know your actual compression ratio or
what your cam timing looks like.

But I’d say a 9 Champion is as hot as I’d start with.

Can you post a picture of a couple of your plugs?

Let’s see what they look like.

I pulled my number one plug to look at it but honestly, I have almost no time on this motor as it is this may be 20 minutes of tuning and driving around about 7 miles. I don’t trust you yet for high uses. I’m having some brake issues and I’m working through.

 

[340inabbody]

I’ve didn’t see any speckles or anything like that under high mag

 

[Newbomb Turk]

I pulled my number one plug to look at it but honestly, I have almost no time on this motor as it is this may be 20 minutes of tuning and driving around about 7 miles. I don’t trust you yet for high uses. I’m having some brake issues and I’m working through.

View attachment 1716283849

View attachment 1716283850

Too much timing and the plug looks pretty hot.

You can use that type of plug. It doesn’t have that dark black coating on it.

Those are better to read.

 

[Newbomb Turk]

I’ve didn’t see any speckles or anything like that under high mag

View attachment 1716283851

You should have a fuel ring around the bottom of the porcelain. It should be a light gray and .100-.125 wide.

I’m jealous of your microscope.

 

[340inabbody]

You should have a fuel ring around the bottom of the porcelain. It should be a light gray and .100-.125 wide.

I’m jealous of your microscope.

So should I enrichen the idle mixture a bit? I don’t have my Wide band sensor hooked I need to weld in a bung…