NA carburated bridgeport
 

After much discussion on a different post i have decided that the S5 ecu will not keep up to a bridgeport configuration. Therefore i have decided on a custom manifold holding a carburator.
Now i was curious what cfm you guys would recommend for a large bridgeport on s5 Na irons. i was thinking about using rx8 rotors for this and using a single 4 bbl but i may use 2 smaller carbs so i can at least have some low end.
Also for the manifold i was going to bore out the S5 LIM and make a custom UIM. should i bother to keep the looped shape for the upper or just ignore that also what runner length would you recommend.
i was tossing making sliding tubes like the 26b uses so if i do this what would the max and min runner length be? and should that be vacuum or rpm dependent for the slides i was thinking about using the spark advance circuit to controll it. i might source out a GXL-SE setup to controll the ignition but im not familiar with this at all is this electronic spark advance or vaccum?
thanks for any input.

To calculate your max and min runner length you'll need to know the actual CFM needs of your engine, and without knowing exactly how you modified ports I can't really guess off the top of my head. Also, It would be RPM dependent, not vac dependent .

Why would two smaller carbs net you more low end then a properly set up 4bbl? It's all in your design, RB makes a 4bbl manifold already for the 13B, AFAIK (I might be wrong, might only have been for the 12A, too lazy to check)

Why would you ever want to run a carburetor?

Most of the "bad press" that big ports get comes from the time of carburetors where fuel control was poor and ignition curves were approximated by a distributor.

To run a bridgeport properly, you need a programmable EMS.

If it's a cost issue, then there are many used Haltechs/Microtechs often for sale.

Get a RB lower intake manifold and an inexpensive set of ITBs then fabricate an airbox.

im putting a carb on an NA not a V8 in it. If you guys all want to drive with the same stuff then why dont you just get a honda?

but if you guys need a reason to give me advice theres 2 reasons im doing this

1.) this is a car i gave to a buddy and he doesnt know shit about cars but hes one of those guys that thinks he knows to much so you cant teach him anything. Carbs are pretty well fool proof so i figure its a good starting point for him. And ive never done anything with a carb for years now figure it will kill some time and get some old crap off my shelves.

2.) Why not you trip over NA engines in the wreckers.

where in Alberta are you?

all hes saying is programmable efi is light years better than a carb. yeah you can do what you want but to fully utilize the power a bridge port is capable of, it is so much easier with data logging and the ease of tuning with a stand alone. good luck but you should watch who you are a smartass to, he is one of the more helpful people that can give real answers learned from experience, not internet hear say.

I'm not sure what this means. I'm quite happy with my Honda. It's a reliable an interesting car that gets 90 MPG...

This is exactly the reason not to use a carburetor. I don't know if you have ever experienced a carbureted bridgeport, but I have and it's aweful. It will buck and sputter in traffic, only be happy running at wide open throttle, get disgusting fuel mileage in the city and be hard to start in poor weather. The jetting will never be quite right because of the ambiguous vacuum.

I'm not quite sure what this means.

WTF are you talking about? :confused: Nobody said anything about the type of engine or car, only that carbs suck. Have you ever driven a carb'd bridgeport on the street?

You effort you want to put into that variable-length intake would be much better put into a proper EMS. The result will be far superior.

Wow, 12 posts and already making friends with AC and NZ


If you can, start playing with EFI. A carb isn't fool proof on a bridgey, especially on a street car. A 600 CFM might be able to keep up around town. I've sen guys run 750 on them so I'm sure others have used 800's. There seems to be plenty of 600's around, if you have one use it.

Unless I an forced by class rules to use one I usually prefer to go down to the river and give a carb the old "floatation test"

If you are going to carburate it, then use a DCOE style Weber and a manifold that merges the primary and secondary ports like this:

http://www.britishv8.org/MG/BrianKraus/BrianKraus-F.jpg

That will smooth out the vacuum signal as much as can be done, which will make tuning far easier.

The Holley style carbs with separate primary and secondary butterflies are a real pain as the vacuum signal between the two is wildly different.

IMO the newer Holleys are very simple to tune and the manifolds are simple to find. I'd run a 650 dp and take it from there. Oh and dont believe what you read. Carbs dont suck! With a bridge ported motor one can only assume that this isnt going to be your daily driver. So logic tells me your looking for simplicty and raw power. If thats the case than the Holley gets my vote. :icon_tup:

See, that's exactly my point. :) With electronic fuel injection, bridge ported cars make great daily drivers and even get reasonable mileage (on the highway, that is).