Technical Vacuum Advance Poll

So vac advance and I get 25 MPG from my 355? Cool beans man.

A mechanical advance distributer properly set up will work fine. I have run them for years. I generally depending on my gearing and the body that it is in get 20-22 from my 355 with a full mechanical advance Mallory.

If I am running vac advance where I draw my vacuum depends on my intake carb setup and the distributer in question. Some distributers want ported vacuum and some want more than that. Some of the old Ford stuff is really touchy about that.

 

This is a case of where the term 'YMMV' really applies... LOLOL

Now, I did see that large of an improvement on a car I owned. A built FE, my highway mileage went from about 8 mpg to nearly 13, a big difference even in the days of cheap gas. Even picked up a few mpg around town. I'll note that this forever cured me of wanting a 'race-type' distributor on a street car.

There are a ton of variables involved that will affect your results, but after my initial experience above I subsequently installed vacuum advance on any motors I acquired that didn't have it and always picked up fuel economy. Besides the mileage, vacuum advance also reduces the tendency for 'loading up' at low speeds.

 

The setup I have on my '63 has '64 part numbers on the carbs. It was a swap meet buy many years ago at back to the '50s. When I put it all together It was on a fresh rebuild of the original 390 from my car. Anyway, I decided to use an original 390 4 barrel dist. with vacuum advance and the port on the metering block was manifold vacuum. The correct carbs for Ford 3X2 are different than a lot of other Holley 2 bbl carbs in ways I'm sure I haven't found yet.

I saw your other thread and was going to get you some carb numbers and metering block numbers but accessing the car right now is difficult with winter storage and all. The center carb you choose to use may well have a ported vacuum tap on it.

 

Wrong post

 

Technically correct, but that is only true at factory RPM specification. Just about everyone gooses the idle RPM up a bit, because ... it idles smoother ... and cooler.

One guess as to why.

 

LOL in 1973 I installed an iron Vette dual point in a L79 I had in a '57 wagon. I did not notice an improvement in mileage but I did notice an improvement in performance. The points and condenser were shot, bad enough that the car would not start with the starter. I preferred a mechanical distributer ever since.

I do not buy the vac advance deal, perhaps on a stock engine. I guess that in reality my L79 was stock until I changed the distributer but the distributer was stock. LOL No matter what you own stock or souped the distributer needs to be curved properly. Even a vac advance original distributer can use a little help. No one can expect one distributor to be properly curved for every engine that a manufacturer produces, 2 bbl, 4 bbl, high compression, low compression they all come of the ***embly line with the same distributer, well mostly all.

 

- how would you set timing on this set up on a 350 Chevy? - think that it kinda goes with Crazy Steve's thread " do we outsmart ourselves"

 

Time it till it spark knocks
and back off one or two

 

Bones while Steve is correct that 390 6V Galaxie solid lifter engines use a centrifugal advance dual point distributor with no vacuum advance,the 390 6V T-bird hydraulic cam engines used a single point distributor with vacuum advance,the ford tripower manifolds also came in 2 configurations the Galaxie version had stepped height carb mounting pads while on the T-bird version they were almost flat due to the more level engine mounting in the T-bird.If your putting this in a 65 Galaxie the T-bird manifold may work better I think they also have a more level engine mounting than the earlier Galaxies,but you should be able to look at your car and tell the difference will be noticeable.I prefer to run manifold vacuum to my vacuum advance but thats just my preference.

 

Oh I get that part. My car that we can’t talk about here with the 271/289 HiPo came from the factory with no vacuum advance. I was saying the center Holley should have a fitting for port timing. I though. I will go out and check my set of three ducks, that I haven’t got on my car yet!








Bones

 

Too, late for me! I already have the Galaxie version! I bought the intake in Tulsa, ten years ago, picked up some carbs three years ago in Pennsylvania, had a Hamber sell me the rest of the carbs I need from Alaska. My friend gave me an air cleaner lid and I bought the air cleaner bottom from a guy on an FE forum. Still missing one fuel inlet! But, I have to get the 462 built first! Been working on the C-6 problem lately!








Bones

 

Yep, there it is. A 1/8 inch pipe plug for timed port vacuum on a center Holley from a 3X2 set!

Edit: I just read Center of the Galaxie’s post! I too gathered all my stuff, from many points! Lol not sure what year my carbs are, but now I have 2 1/2 sets of carbs! Lol. I will get and list my numbers . Maybe tomorrow! Old out there right now! Lol












Bones

 

Numbers- the 352 listing seems odd but the 260 and 289 listings would be for the over the counter Ford offerings.
CFM numbers next to the HolleyList numbers

 

My understanding is Ford didn't install the '61 390 6V carbs/intake at the factory but threw them in the trunk for the dealer to install. The '62-63 'Birds were done at the factory as Ford used 406 heads on what was still a basic hydraulic cam 390 as Ford didn't want to pay the dealer for a full top-end change. This limited power which was desirable due to the limits of the Cruisomatic. To my knowledge, this was the highest HP motor ever hooked to a Cruisomatic.

 

I could never understand going to manifold vacuum. At idle the spark is advanced due to high vacuum signal. You crack the throttle, the manifold vacuum signal drops, the spark retards. I ***ume doing that could eliminate a spark knock problem under initial acceleration but if that is the case the advance curve is incorrect to start with. I realize it is a never ending debate but I can't remember how many times when I had my shop in the old days that a car would come in with an off-idle bog due to the vacuum advance being connected to manifold vacuum. Dang I'm old.

 

Two reasons for using manifold vacuum; one, it will help reduce engine temps at idle. Two, it makes the motor more efficient at idle.

 

Ford usually run better with ported vacuum, while Chevys run better with manifold vacuum.
And then..we have the 289 and 302 Fords that ran both.

 

Explain please!

The engine should be timed at idle with enough advance for maximum flame propagation [not too much to cause detonation]
This should be set statically , so the engine will idle at that setting.

Why would you want vacuum advance at idle, to have it suddenly retard as soon as you open the throttle.[due to a drop in vacuum]

Ported Vacuum gives the engine all the same manners as a full centrifugal distributor, and with good part throttle cruising manners.

 

You are correct in that the engine should be timed 'statically' (without vacuum advance connected) no matter whether you're using vacuum advance or not. Now if you're not running vacuum advance or are using ported vacuum, you would then adjust idle mixture and idle speed and be done. But after that, what happens when you connect manifold vacuum? The motor now speeds up....

The 'why' it speeds up is the key. You haven't touched the carb in any way; no one has pressed the throttle, the mixture is still the same, but you have advanced the timing with the vacuum advance. More timing starts the fuel mixture burning sooner. With it starting sooner, it has time to fully burn before the power stroke is done, putting more pressure on the piston, producing more power. As there's no load on the motor, the additional power turns into more rpm. This increases efficiency.

The other effect, cooler running, is a byproduct of the same thing. Because the mixture is getting fully burned on the power stroke, you're no longer sending still-burning mixture out the exhaust, heating the exhaust ports as it leaves. You'll also usually find that you can lean the mixture out further with no ill effects. You can also close the throttle more to reduce the idle speed which will help with preventing run-on when shutting the motor down.

I'll grant that's there's a lot of variables between motors that may prevent one from responding to this, but if it works this is the best way IMO. I'll always at least try this method when tuning.

 

The manifold vacuum is more in tune with the “ load” of the engine. Mechanical advance only knows one thing” rpm”. The “ ported” vacuum is somewhat of a combo of the two. Manifold vacuum has little to do with engine speed, kind of. You can have the engine running 3000 rpm with no load and have high manifold vacuum. You can be running 1500 rpm pulling a trailer up a hill, with your foot on the floor and you will have very low vacuum.
But to answer which is the best, totally depends on the engine, how the disturber is set up.
I have ran both, before. Usually with a Holley carb , I use ported.








Bones

 

“Why would you want vacuum advance at idle, to have it suddenly retard as soon as you open the throttle.[due to a drop in vacuum]”

Happens every time a car part throttles up to a stoplight, before car stops, light changes and driver nails it.

Ported or full, same sudden change.

 

We had a Ford 1 ton truck with an inline six in our shop when I was in the Air Force that was a real dog. We sent it to the motor pool because it ran so bad; we got it back a week later with a new paint job and it STILL ran bad. One of the guys I worked with played with the timing and moved the vacuum advance to a manifold source, and it ran much better after that. Then it went to the motor pool for something, and it came back running like **** again because they put everything back to the way it was.

 

cfmvw,
.LOL Slow learners ?

 

Vacuum advance pol.- election speculation that ****s?

Sent from my SM-T350 using The H.A.M.B. mobile app

 

I have 3 vehicles that still have distributors (and one that doesn't). 64 Chevy truck - ported, 57 T-Bird - ported, 28 Model A with Buick nailhead - manifold. The reason I'm running manifold vacuum on the Buick is that it has a mild cam that was used in a 425 2x4 engine. It has an automatic transmission and I get a smoother idle with the extra advance at idle.

 

Another benefit of manifold vacuum....

 

I prefer manifold vacuum simply due to it being more reliable and consistent than ported vacuum.Larger than stock cams, deposits and slight air leaks in the carb can greatly affect the ported vacuum signal,I prefer to setup the distributor with the desired total and then limit the vacuum advance so that total + vacuum will be 50 or less at cruise,I don't care that vacuum increases advance at idle,as Steve points out it will be more efficient and run cooler,it will retard again as soon as you load it to prevent ping,and by limiting at cruise to 50 or less will prevent tip in ping.The early styleFord vacuum cans with removable ****** are easy to adjust the limit of amount of vacuum advance a little harder to adjust the setpoint,The later Ford vacuum advance cans that are adjustable with the little allen wrench are easier to adjust setpoint but require some fabrication to limit amount.The total + vacuum amount will vary a little depending on your combination but 50 is a pretty good ballpark for the combos I have run.As far as cams I can't remember the last time I put together a rig with a stock one.

 

No it doesn't.

With ported vacuum, there is no vacuum advance at idle.
And as soon as the throttle opens ,guess what?.........no vacuum,so it is still the same[ there is no retarding because there wasn't any vacuum advance to retard]
The only advancing is done by centrifugal until the throttle is lifted at cruising speeds.

As for the engine "picking up RPM" when connecting the vacuum! The very same can be achieved by statically advancing the Dist a bit more [on ported vacuum]

If the timing is set at maximum advance for flame propagation, any further advancing [by vacuum] will be in the "knocking zone"

On a poorly set up engine.........Full vacuum could easily be misinterpreted as a "Gee Whizz Tuning Miracle" at idle.

My preference is full centrifugal advance. But I can see the advantages in vacuum advance for cruising/economy. Ported vacuum is the best of both worlds.

 

I like ported vacuum as makes engine idle rough. I impress everyone at Cars And Coffee w/my “Lunati Pro Stock” cam story. Using headers as a secondary combustion chamber keeps
all that nasty ceramic coating burnt off !

Hahaha

 

Ported Heads are better