Distributor Vacuum line

[chap52]

I am putting two 94's on my flatty and don't want to run the vacuum line off a carb. Where else can I plug it in?

[51 MERC-CT]

All depends on what you're running for distributor.

[chap52]

running the stock one with a Petronics system in it.

[ken ct]

Talk to Charlie,ny on here im not sure it will work right with a loadamatic stock dist. I mean running 2 carbs. Usually requires a Chevy conversion.

[chap52]

DUH! just noticed the threaded hole in the new manifold...Thanks for walking me through this senior moment...

[Walt Dupont--Me.]

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The threaded hole in the manifold is not the correct place for the vacuum line to the loadamatic dist. That dist is made to use ported vacuum from a fitting in the back float bowl of the stock carb. Those dist work good on a bone stock engine. when you start putting dual carbs and other performance parts on the engine it screws up the vacuum to that dist. If you use that manifold vacuum you will have full advance all the time even at idle. That is why you should use a converted Chevy dist or a Mallory ect. Walt

[ken ct]

Originally Posted by chap52

DUH! just noticed the threaded hole in the new manifold...Thanks for walking me through this senior moment...

Like Walt said you CANNOT use Manifold vacume. Call Charlie,ny,he converts the Cheby's to the flathead. ken ct.

[richard rink]

chap52,
My set-up with dual 94's and Pertronix ignition on my 8cm is very much a "shade tree" approach, but here goes. Since the vacuum signal coming from the dual carbs is reduced by half, I decided that less restriction on the advance of the breaker plate during acceleration would approximate normal operation, i.e., as from a single carb. To that end, I removed both the small springs from the breaker plate and replaced one of the springs (only one) with a slightly weaker spring. A small amount of vacuum applied to the vacuum line causes rotation (advance) of the plate, as would occur with a single carb. This installation presumes that your distributor is in excellent condition and that the plate rotates easily, etc. Engine performance with this set-up is excellent; with heavy acceleration, the engine will "ping." Meets my needs. Richard

[V8 Bob]

Originally Posted by richard rink

chap52,
......Since the vacuum signal coming from the dual carbs is reduced by half......

Curious, but did you actually measure the vacuum signal? When I switched to dual 94s on my stock '51 239", I saw no loss of manifold, or distributor signal vacuum from either 94.

[BUBBAS IGNITION]

Interesting discussion on the Ford Load A Matic distributors. ( Ford pressure type).
These units use no centrifiugal advance and use a vacuum signal only to provide advance.
The problem is that this signal is carb venturi vacuum ( not manifold vacuum) and is a very small signal.

Looking up the Ford specs shows...

A signal range from 0 to 3.7 Vac In..

200 rpm= 0 degrees
500 rpm= 1 degree @ 0.3 Vac in
1000 rpm= 5 1/4-6 1/2 @ 1.32 Vac in
1500 rpm = 8-10 degrees @ 2.85 Vac in
2000 rpm = 10-11 degrees @ 3.7 Vac in

Theres the problem, when mods are made to the engine such as camshaft, carbs etc. It isnt that the signal isnt there its the fact that i cant duplicate a 2.85 Vac in signal etc.
So therefore anything that we do to the engine will change the advance curve etc..

[chap52]

Wow, thanks guys for the info. I will check out that dist. change. Much appreciated...

[rick r]

if you are running 12volt, an early 80's 318 chrysler dist. can also be converted to work in a flathead. this gives you electronic ign.

[richard rink]

Originally Posted by V8 Bob

Curious, but did you actually measure the vacuum signal? When I switched to dual 94s on my stock '51 239", I saw no loss of manifold, or distributor signal vacuum from either 94.

V8 Bob,

I measured the vacuum signal off the venturi port on one carb of the dual set-up and with rpm's of approximately 2000 or so, saw a vacuum of between 1-2 on my gauge. I have not measured the vacuum on a single carb set-up. The claim that a dual carb configuration reduces venturi vacuum by half is what I have read in the opinions of rodders such as Barney Navarro et al.

[chap52]

Thanks

[Ol' Ron]

This doesn't mean anything unless you can put a load on the engine. The centrifugal advance doesn't recognize load either and that's where the vacuum canister modifies the advance curve to match the engines needs in both cruise and power. You just can't make a silk purse out of a sows ear. The converted SBC is the way to go.

[chap52]

Now I am just shaking the cookie jar for the nickles for a distributor. Thanks for the great sage advice.

[chap52]

Tracked down a ready to go converted Chevy distributor from [email protected] for less than $200.
I will update in a few weeks when I get it all back together.
Thanks again...

[Walt Dupont--Me.]

Originally Posted by BUBBAS IGNITION

Interesting discussion on the Ford Load A Matic distributors. ( Ford pressure type).
These units use no centrifiugal advance and use a vacuum signal only to provide advance.
The problem is that this signal is carb venturi vacuum ( not manifold vacuum) and is a very small signal.

Looking up the Ford specs shows...

A signal range from 0 to 3.7 Vac In..

200 rpm= 0 degrees
500 rpm= 1 degree @ 0.3 Vac in
1000 rpm= 5 1/4-6 1/2 @ 1.32 Vac in
1500 rpm = 8-10 degrees @ 2.85 Vac in
2000 rpm = 10-11 degrees @ 3.7 Vac in

Theres the problem, when mods are made to the engine such as camshaft, carbs etc. It isnt that the signal isnt there its the fact that i cant duplicate a 2.85 Vac in signal etc.
So therefore anything that we do to the engine will change the advance curve etc..

Babba, I've never checked one of these stock 8BA dist for total advance in a stock engine. 2000 rpm= 10-11 degrees. Doed that mean 20-22 degrees engine degrees? Thanks Walt

[BUBBAS IGNITION]

Originally Posted by Walt Dupont--Me.

Babba, I've never checked one of these stock 8BA dist for total advance in a stock engine. 2000 rpm= 10-11 degrees. Doed that mean 20-22 degrees engine degrees? Thanks Walt

That's 22 engine degrees. Interesting that all the engines starting from 1942 upward used 11 degrees distributor or 22 degrees engine.
I now ship all our distributors set at 16 degrees Engine after shipping and discussing issues with many customers etc.
And it appears the engines also have another 2-4 engine degrees added in design of the slot for starting as well.
Have you found that the notch to pin location to be at tdc or slightly advanced?