[LukeNukem]

Explain using a vacume gauge to set optimum timing at idle. I heard someone mention this a few days ago.

 

[waltman]

Talk to sixlitre, he's the man

 

[Schrof]

Vacuume+Timing(Base, Spout. Diss.) = ZIP,(Timing set to MECH BASE. Spec., Vac. not involved) as applied to "Optimal Idle Timing"
Vac, in inHG,@ Idle(Per MFG.) =Eng. "Health", used to "Troubleshoot" other problems, ie., burnt valves, Vac leak, etc...Use "Search Function", it's all in there.
Schrof

 

[Sixlitre]

Explain using a vacume gauge to set optimum timing at idle. I heard someone mention this a few days ago.

Are you carbed or EFI ?

If you're carbed, start with this;



It's like having your cake and eating it too. A tiger off the light and incredible cruising economy.

All you really need is a mityvac/mitymac, which is both a vacuum gauge and a vacuum pump (very important for testing and adjusting the vacuum cannister on the side of your dist). You can also use the pump to bleed your brakes all by yourself. Obviously you have a timing light, so you're good there.

Read it and get back to us with questions

Sixlitre

 

[OnceWasChuck]

Sixlitre, what are their total timing numbers (32* and 52* with vacuum advance) based on? Ideal total timing numbers tend to vary greatly between different engines, and different combustion chamber shapes will have a huge effect. Base timing of 6* is also pretty dang low ...

Anyways, any idea where they're getting their numbers, and what engine that's on?

 

[Sixlitre]

Sixlitre, what are their total timing numbers (32* and 52* with vacuum advance) based on? Ideal total timing numbers tend to vary greatly between different engines, and different combustion chamber shapes will have a huge effect. Base timing of 6* is also pretty dang low ...

Anyways, any idea where they're getting their numbers, and what engine that's on?

Chuck

If you get a Crane adjustable vacuum cannister(@$15) it'll pay back faster than anything you've ever bought in your life ! With it you can custom tailor your vacuum advance to suit your truck's weight, gearing tire load, everything !

For my particular Mopar it needed to have 32 degrees mechanical in before 2600 rpms, that's a sort of given on low compression 360s. My older 340s used to like 34 or even as much as 38 degrees.

Where the base or initial timing is, after you get 32 degrees by 2600 rpms, is inconsequential. Yes I did note it for later reference, but it doesn't matter at all. All that matters is getting the dist mechanical weights to give you the 32 before 2600. Yes, it does start at -30 as well.

After you've got that then comes that unique way of test driving for the optimum vacuum advance. In my case, my car pulled 6 lbs vacuum at cruise(2000 rpms in drive).

Knowing this I used the mitymac vacuum pump to duplicate the vacuum on the cannister while the mechanical weights were swung out all the way at 2600 rpms.

Checking with the timing light each time I would stick an alan key into the cannister and adjust it until I got it to read 52 degrees.

On one Mopar it liked 57 degrees at cruise. This has absolutely no negative effect on performance, but adds up to 6 free mpg to your cruise economy.

I've done this on two Fords and a Chevy or three and it works equally as well (better on the Ford truck). Yes the numbers were a little different, but you're vacuum gauge and those tests will tell you which numbers your vehicle likes.

Clear as mud ?

Sixlitre

p.s./
I don't remember the mechanical timing the Ford liked, but the sweet spot for his vacuum cannister was 47 degrees IIRC. Woke that gas sucking pig up to the point where his mileage almost doubled and he walked all over his neighbour's truck (made his weekend).

 

[OnceWasChuck]

Nice, thick gumbo mud. :thumbup

I'm already pretty familiar with the benefits of getting the timing set as close to ideal as possible, and I definitely agree it makes a bigger difference than just about anything else you can do. I was just curious where those numbers were coming from and what you recommended for testing and setting cruise timing. Curving the mechanical advance for full throttle is pretty easy if you're willing to spend a little dyno time, but finding the best vacuum advance curve under part throttle cruise for economy takes more than a little more work, so whenever I find someone with good info on the subject, I always hit 'em up for whatever I can find out. :rockon

How are you measuring for best cruise advance? Are you looking for the total advance that yields highest vacuum at cruise conditions, and then setting the vacuum advance canister to yield that advance at that vacuum? (Sounds circular, but I'm sure you know what I mean -- sort of an iterative process to find a setting that will give you highest possible cruise vacuum.) In other words, when you say one Mopar liked 57 degrees total timing at cruise, what are you watching to determine that it's running better on 57 than 55?

Right now I'm running TFI, so no vacuum canister for me, but I'm hoping to switch the truck over to Megasquirt sometime over the next year -- which would give me full control of all timing parameters. :thumbup

 

[Sixlitre]

Nice, thick gumbo mud. :thumbup

I'm already pretty familiar with the benefits of getting the timing set as close to ideal as possible, and I definitely agree it makes a bigger difference than just about anything else you can do. I was just curious where those numbers were coming from and what you recommended for testing and setting cruise timing. Curving the mechanical advance for full throttle is pretty easy if you're willing to spend a little dyno time, but finding the best vacuum advance curve under part throttle cruise for economy takes more than a little more work, so whenever I find someone with good info on the subject, I always hit 'em up for whatever I can find out. :rockon

How are you measuring for best cruise advance? Are you looking for the total advance that yields highest vacuum at cruise conditions, and then setting the vacuum advance canister to yield that advance at that vacuum? (Sounds circular, but I'm sure you know what I mean -- sort of an iterative process to find a setting that will give you highest possible cruise vacuum.) In other words, when you say one Mopar liked 57 degrees total timing at cruise, what are you watching to determine that it's running better on 57 than 55?

Right now I'm running TFI, so no vacuum canister for me, but I'm hoping to switch the truck over to Megasquirt sometime over the next year -- which would give me full control of all timing parameters. :thumbup

Chuck

Like you say figuring out mechanical full advance is fairly easy. Yes a dyno is the best, but most vehicles have people who've done it already and can get you in the ballpark.

A starting point for vacuum at cruise readings might well be the stock system. I know zero about megasquirt to I'll stick to the method for vacuum advanced carbs and you can extrapolate it into/onto your set up.

We were told 45-48 was a starting point for Mopars for full timing all in, including the added vacuum advance. This was borne out by taking the engine up to 2600 and reading the timing when the mitymac was supplying the same vacuum to the cannister that my car would at cruise (in my case 4 or 6 lbs{can't remember which})

Then I could take the 47 degrees (that it had) and subtract the mechanical advance (32 in my case) and that left me 15 degrees that the cannister was adding in.

Luckily Mopar used dozens of different vacuum cannisters through the 70s to allow for the different weights and gearing of so many different cars. Every one of them had a number stamped on the vacuum arm that goes into the dist. If it said 7.5 it was really 15 degrees that it would add in.

Using the excellent 70s Mopar service manuals and the Echlin and Standard catalogs I found a cannister that would get me above 52 degrees. Think it cost under $15 new.

Remember that it's going to give you 52 degrees at cruise regardless. What you need to set is what amount of lbs of vacuum your actual vehicle needs at cruise so it won't detonate.

What you're doing by driving your car/truck on the test drive at a cruising speed and rpm, in final high gear with a vacuum gauge, is determining how many lbs of vacuum it will exert on the cannister to activate the vacuum advance at the right time/lbs. In this low-tech way your particular engine, in your exact vehicle is actually stating exactly when it needs the vacuum all in.

Too much or too little lbs of vacuum and that's when you ain't gonna get away with 52 or 57 degrees total timing, and you throw up your hands like some Chevy ape and say "it doesn't work I'm-a-gonna tear off the vacuum cannister !" , kissing your mileage good-bye.

Honestly it took me several tries to understand the procedure, but if you follow it to the letter until you've got it straight in your head, it works everytime with every vehicle.

In answer to your question, what am I watching, you're listening and watching for detonation. I had zero rattle at 47 total timing, meaning I wasn't getting my money's worth out of the gasoline I was using. I jacked her to 52, changed cannisters and then 55 and finally 57 on one vehicle, as I'd backed her down from 60 which was rattling.

I guess what I'm saying is the alan key adjustment is adjusting "when" and at what vacuum {actual engine demand} the diaphram inside the canister is delivering the full amount of degrees. That's what determines if it's gonna rattle or give you mind blowing mileage.

Adjusting the alan key will not change the amount of degrees that cannister gives you, just tailor it to suit your vehicle's weight, gearing, gas grade, torque and power. Whoever thought it up was a genius in my books.

That said, I don't miss any of this with the computer in my early EFI'd 86 5.0 litre doing a much better job of all that and more IMO.

In future years I would like to MAF the truck and my 90 Lincoln in preparation for 351s and/or 393s or 408s.


Sixlitre

 

[OnceWasChuck]

Okay, that's what I actually thought you were probably doing, tune for knock and then back off a few degrees. Cool. :thumbup

Actually, the reason your factory EFI 5.0L does so well is the knock sensor. I believe they used one in 86 too, my reference doesn't go back past about 88. :cry Anyways, it does exactly the same thing -- the computer's timing table is set just far enough up to cause knock, and it uses the sensor to retard the timing and hold it just below the threshold.

To heck with MAF conversion, go Megasquirt! If you're used to doing your own tuning, you'll do much better with a fully tunable system, and it's cheaper than a MAF swap as near as I can see. Don't get me wrong, I love the MAF system on my Stang, but when you swap you'll also lose your knock sensor. I know the MS guys are working on incorporating knock sensing now, and they may have it already, I don't remember. Besides, a properly tuned MAP based controller is honestly better than MAF in most cases ... and it'll certainly be better later when you get tired of your plain jane 393 and want to go turbo/supercharger. :histerica As far as I know, the only reason the factories went over to MAF was the fact that it would automatically compensate for incompetent maintenance, or the complete lack of any maintenance. There are no power advantages, and MAF actually costs you top end power because of the extra intake restriction.

Megasquirt can be found here. It's essentially an open source system, and is about 1/10 to 1/5 the cost of most aftermarket systems with the same capabilities. I also strongly recommend their forum, tons and tons of information there, the link is on the left. I've been watching the forum for a year or two to learn and I haven't even set up MS on anything yet. :toothless

 

[Sixlitre]

Okay, that's what I actually thought you were probably doing, tune for knock and then back off a few degrees. Cool. :thumbup

Actually, the reason your factory EFI 5.0L does so well is the knock sensor. I believe they used one in 86 too, my reference doesn't go back past about 88. :cry Anyways, it does exactly the same thing -- the computer's timing table is set just far enough up to cause knock, and it uses the sensor to retard the timing and hold it just below the threshold.

To heck with MAF conversion, go Megasquirt! If you're used to doing your own tuning, you'll do much better with a fully tunable system, and it's cheaper than a MAF swap as near as I can see. Don't get me wrong, I love the MAF system on my Stang, but when you swap you'll also lose your knock sensor. I know the MS guys are working on incorporating knock sensing now, and they may have it already, I don't remember. Besides, a properly tuned MAP based controller is honestly better than MAF in most cases ... and it'll certainly be better later when you get tired of your plain jane 393 and want to go turbo/supercharger. :histerica As far as I know, the only reason the factories went over to MAF was the fact that it would automatically compensate for incompetent maintenance, or the complete lack of any maintenance. There are no power advantages, and MAF actually costs you top end power because of the extra intake restriction.

Megasquirt can be found here. It's essentially an open source system, and is about 1/10 to 1/5 the cost of most aftermarket systems with the same capabilities. I also strongly recommend their forum, tons and tons of information there, the link is on the left. I've been watching the forum for a year or two to learn and I haven't even set up MS on anything yet. :toothless

Wow !

Megasquirter, on the surface, looks like a viable alternative to Tweecer or MAF, like you say !

My favourite EFI reference is this;



I figured I'd better grab the 80-87 book before the later book superceded it and it became extinct.

Thanks for the tip, and remember that vacuum arm will always deliver ALL it's advertised degrees. All we're doing by adjusting it is to slow down or speed up when it delivers the degrees. If you need less degrees you need a lessor cannister.

Thanks for the tip on megasquirt, does Fireguy know about these guys ?

Sixlitre

 

[OnceWasChuck]

Wow !

Megasquirter, on the surface, looks like a viable alternative to Tweecer or MAF, like you say !

My favourite EFI reference is this;



I figured I'd better grab the 80-87 book before the later book superceded it and it became extinct.

I was actually going by the 88+ Probst book, which was why I didn't have the info on your 86. Lots of good, quality info in Probst's stuff. Eventually I'll have to pick up the edition you have, but the only pre-91 stuff I have around right now is carbureted (for now, at least). :toothless

Thanks for the tip, and remember that vacuum arm will always deliver ALL it's advertised degrees. All we're doing by adjusting it is to slow down or speed up when it delivers the degrees. If you need less degrees you need a lessor cannister.

Thanks for the tip on megasquirt, does Fireguy know about these guys ?

Sixlitre

I would assume he does, but I don't know offhand. There are a number of vendors running side (or in some cases primary) businesses assembling MS boards for people -- might be something he'd want to look into, since he's got plenty of electronics experience. Actually, there are probably a few things regarding MS that he might find a market in, and I'm all for Bronco guys who help the community so much being able to make a good living. :twotu: