running dual carbs

[36tbird]

I'm bettin' Joe means no vacuum. Joe, what kind of gas mileage do you get? I'm running just a single 48 on my 8BA with the Pertronix Chevy centrifugal advance. It runs great but my mpg seems lacking. Haven't made a precise measurement but I think it might be around 10 mpg.

[Mike51Merc]

Originally Posted by flatjack9

If you are talking about an 8BA carb, it not ported vacuum, it is a combination of venturi and manifold vacuum and is less than manifold vacuum. On a modern engine, ported vacuum means it is closed off at idle, other than that it's the same as manifold vacuum.

Jack, isn't it true that venturi vacuum increases when throttles open, while mainfold vacuum drops?

Isn't that why the load-a-matic distributor will retard timing instead of advance it when connected to manifold vacuum?

[flatjack9]

Yes that is true. However this is only during acceleration. It kind of operates like the vacuum retard on the earlier distributor. Once you have reached your desired speed, you back off on the accel pedal and manifold vacuum will shoot back up giving full advance. I don't remeber the specs for the advance curve on the 8BA, but I don't think it takes a lot of vacuum to achieve full advance.

[Fox Valley Hot Rods]

Originally Posted by 36tbird

What if manifold vacuum is all you got, e.g. strombergs? I'm assuming that manifold vacuum is slightly less than ported. Can the reduced vacuum be mitigated with an adjustable vacuum advance set to the lowest setting?

Some after market Strombergs had a vacuum port. If you need one let me know. Also, when you run dual carbs you shouldn't run just vacuum advance from the stock dist. You need to upgrade to an aftermarket dist. with mechanical advance or it will never run properly.

[36tbird]

I confused you with my post. I meant that as far as vacuum I have only manifold vacuum available. I currently have a Chevy distributor with only mechanical advance and I'm trying to build one that will have both, mechanical and vacuum.

Is there a boss on existing Strombergs that can be drilled and tapped for the vacuum port yours have? Thanks.

[Ol' Ron]

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Not6 knowing the difference between running good and running great. depends on what's exceptqble to the driver. We had a 4x4 mu son uses 9n h9s business (Forester). Been running this for 5 or 6 years seemed to run fine. Had trouble with it last month and put it in the shop. The increase in power is hard to discribe. Like putting a blown hemi in your Henry J. If you know what that is.

[Fox Valley Hot Rods]

Originally Posted by 36tbird

I confused you with my post. I meant that as far as vacuum I have only manifold vacuum available. I currently have a Chevy distributor with only mechanical advance and I'm trying to build one that will have both, mechanical and vacuum.

Is there a boss on existing Strombergs that can be drilled and tapped for the vacuum port yours have? Thanks.

The base already has the hole drilled and tapped for the late distributor. No extra work required. It's venturi vacuum. I'm leaving in the morning for the Iola car show and won't be back until Sunday. I'll try to take a picture then for you. But the after market Strombergs (some, not all of them) had a vacuum port in the base to use as replacements for the Holley if you wanted that option.

[Chris]

Originally Posted by Fox Valley Hot Rods

Some after market Strombergs had a vacuum port. If you need one let me know. Also, when you run dual carbs you shouldn't run just vacuum advance from the stock dist. You need to upgrade to an aftermarket dist. with mechanical advance or it will never run properly.

Why is that? It does not make enough vacuum to advance?

On top of that, who makes a decent and affordable mechanical advance distributor for the 48-earlier flatheads (2 bolt style) other then Mallory or MSD?

[Human Fly]

Originally Posted by Chris

Why is that? It does not make enough vacuum to advance?

On top of that, who makes a decent and affordable mechanical advance distributor for the 48-earlier flatheads (2 bolt style) other then Mallory or MSD?

Or is there a unit to put in the pre 48 to make it mechanical? Rather than having to buy some ugly new dizzy?

[36tbird]

Chris, I am not aware of any like that. Wish some enterprising, smart type would make and offer such a thing.

In lieu of that, I just bought one of the 8BA style front covers and bolt on cam gear drive to put on a 59a in order to run a converted Chevy distributor. I found that using early water pumps, there ain't much clearance between the housing shaft back of the fan belt. So, I am messing with a non aluminum Chevy distributor to turn down the housing shaft for some clearance. Also, I am going to have the distributor sit up more for belt clearance under the housing base. This will require making a longer distributor drive shaft rod. I figured the steel distributor housing will have more meat and strength for the extension than an aluminum housing. Pictures later when I try to get all of this together.

If I cannot get adequate clearance on the shaft for the belt from turning it down, I may have to engineer a double pulley for the water pumps. My buddy Kahuna sent me one and it has given me an idea on how to make some double pulleys.

Apologies to the purists for this project.

[Fox Valley Hot Rods]

Originally Posted by Chris

Why is that? It does not make enough vacuum to advance?

It's venturi vacuum which it what the late dist. uses for advance. They are a replacement for the Holley which was stock on a 49-53 engine. Works just like the Holley except it's a Stromberg.

[36tbird]

Chris, are you sure that there is not enough vacuum or just a crummy vacuum advance module on the distributor? I understand the the stock Ford advance mechanism is not so good.

[flatjack9]

Originally Posted by Human Fly

Or is there a unit to put in the pre 48 to make it mechanical? Rather than having to buy some ugly new dizzy?

The pre 48 distributor is a centrifugal advance unit with a vacuum brake which was initially used to prevent ping on acceleration. But with todays higher octane fuel is generally not needed.

[Ol' Ron]

Originally Posted by 36tbird

Chris, I am not aware of any like that. Wish some enterprising, smart type would make and offer such a thing.

In lieu of that, I just bought one of the 8BA style front covers and bolt on cam gear drive to put on a 59a in order to run a converted Chevy distributor. I found that using early water pumps, there ain't much clearance between the housing shaft back of the fan belt. So, I am messing with a non aluminum Chevy distributor to turn down the housing shaft for some clearance. Also, I am going to have the distributor sit up more for belt clearance under the housing base. This will require making a longer distributor drive shaft rod. I figured the steel distributor housing will have more meat and strength for the extension than an aluminum housing. Pictures later when I try to get all of this together.

If I cannot get adequate clearance on the shaft for the belt from turning it down, I may have to engineer a double pulley for the water pumps. My buddy Kahuna sent me one and it has given me an idea on how to make some double pulleys.

Apologies to the purists for this project.

I



I've used the SBC dist on the early 59 block with the original water pumps and no modifications to the dizzy. Just space the generator aou about a 1/4" had over 70K on the insallatiion before the engine blew.

[Human Fly]

Originally Posted by flatjack9

The pre 48 distributor is a centrifugal advance unit with a vacuum brake which was initially used to prevent ping on acceleration. But with todays higher octane fuel is generally not needed.

Really......so do you just block the vacuum hole in the dizzy/timing cover?

[flatjack9]

I remove the piston from the distributor and block the vacuum hole at the manifold.