Multiple Carb Conversion

[Jim Shepard]

I thought I’d start a new thread for this, although I’ve mentioned it in other topic threads. I’m fabricating a triple carb intake manifold for my B2B. I’m currently running the factory two barrel Stromberg that came on the 230 cars in the mid to late ‘50’s. It runs better than the one throat Carter B&B but suffers from the same design flaw as the factory Carter and intake manifold - the six cylinders do not all get the appropriate amount of fuel at the appropriate time. Hence, my adventure down the “design and build your own manifold” road. As you know, the MOPAR flathead six has three siamese’d intake ports - two cylinders sharing the same intake port. Now for many years this completely satisfied MOPAR engineers and customers. However, it is not the most efficient design in terms of speed, power and fuel consumption/distribution.

 

The ideal setup would be for each cylinder to receive fuel through a dedicated intake port. Now you’re spending real money for an F head setup. Efficient but not very cost effective for most of us. The next best setup is to have each Siamese’s port have a dedicated intake runner/carburetor.

 

I’ve seen several threads on this subject and I have borrowed shamelessly from them. My design will be a simply log plenum with three intake runners and three carburetor intake flanges. I’ve talked with George Asche several times and I think I’ve got the B&B sizes and jetting dialed in. If not, I shouldn’t be too far off.

 

At any rate, I got my flanges back from the CNC shop today so the actual welding/fabricating is not long off.

 

More to follow…

Edited August 30 by Jim Shepard

[lostviking]

Good luck Jim. I'm pretty sure you will get something going that is better than the stock setups. I'm only using two carbs (not installed yet), but even that will give better fuel distribution. A carb for each intake port is IMHO, and many others, the best bet.

 

I look forward to seeing you work on this.

[ggdad1951]

Next year at the Q

[48Dodger]

"...in terms of speed..."

Very interesting, very interesting indeed.

 

48D

[Jim Shepard]

11 hours ago, ggdad1951 said:

Next year at the Q

Yea, it might be worth coming back out next year (in case you were thinking of staying home…).

[Jim Shepard]

Got three carbs all ready to be installed. George Asche is assembling a linkage setup. Should get it in the next several days.

[Jim Shepard]

Well I thought I should start documenting this little adventure. Here’s a photo of the first mockup. Those are the three carburetor mounting flanges. They’re sitting on top of the “log,” which serves as a plenum chamber. Each carburetor sits slightly forward of lining up directly with its intake runner so as to clear the firewall.

[Sniper]

Looks good so far. How did you determine plenum volume? I have a vague recollection that it should equal 1 cylinders displacement but I can't remember if that was for port injection or in general.

[Jim Shepard]

I found an article that discussed old school logs made back in the day. Although most of these were crafted without much scientific basis, the article did quote the work of some engineer who came up with a formula for determining log diameter and length. Among other things, factors such as engine displacement, number of cylinders, distance between outside intake ports, etc., were part of the calculation. 

[Jim Shepard]

Latest mock up photo. Almost ready to start welding

[Jim Shepard]

I’ve made my first jig. This will ensure the carb intake flanges and runners are welded to the log in the correct orientation and position.

[ggdad1951]

Maybe go thicker on that plate...heat deflection might get ya otherwise.

[Jim Shepard]

I’ll probably just tack weld and then take the plate steel off. I decided to have the machine shop drill my holes. I needed an exact size that I couldn’t find bits for. Won’t be long now before the welding starts.

[Sniper]

On 9/29/2024 at 9:59 PM, Jim Shepard said:

I found an article that discussed old school logs made back in the day. Although most of these were crafted without much scientific basis, the article did quote the work of some engineer who came up with a formula for determining log diameter and length. Among other things, factors such as engine displacement, number of cylinders, distance between outside intake ports, etc., were part of the calculation. 

Sometimes research can take you down a rabbit hole lol. I've run into that quite a bit. When I made my air cleaners for my dual throttle body fuel injection setup I just pretty much decided to squeeze in the biggest air filters I could and that turned out to be 7 inch diameter for each throttle body. Since then I've rethought it and I've decided to go with a 14 inch air cleaner and just punched two holes in the base plate to mount on the throttle bodies and have them share a common element. Will that work better? I don't know did I do the math to see which had more area for filtration? Nope. I just kind of winged it LOL

[Jim Shepard]

Well I got some welding done on the manifold. Welded the three carb intake runners to the log. Next is the intake runners between the log and the block. Having the carb runners welded allows me to dial in George’s linkage.

[Jim Shepard]

Got some more welding done. Also mounted George Asche’s linkage and finally found after market air cleaners that fit. As it turns out, I’ll have to modify the linkage some, but the main parts (rod, levers, flange bases…) should work. Gettin’ close to removing the stock intake and carb. Gotta be done by April 5 so I can show it off at Tim’s BBQ…

[48Dodger]

After seeing it in person, I can't wait to see it in action with the new white walls on my race track!

 

Tailgate BBQ #18, just around da corner!

 

48D

Edited November 21 by 48Dodger

[Jim Shepard]

I got the stock intake manifold off today. Held up the log and it looks like it’ll match up pretty good. The only clearance issue was the hand brake cable, which I removed. I’ll have to figure out another way to activate the park brake…

[Jim Shepard]

Didn’t really like the pushrods that came with the Asche linkage - much too modern looking. So I’m making my own and trying for a more original look/design.