I know there are probably a bunch of possibilites as for carb choices but which would be a compatible and sufficient carb to run on a half-bridged 12A? I was looking at OER carbs but I heard that having Sterling modify my Nikki carb would work if it was modified to run with the half-bridge? Keep in mind like everybody else i'm trying to keep my budget low. Thanks

 

PM Sterling or Carl and ask, that's probably the least expensive option. From there you could go 48-51 mm Weber. I'm not familiar with the OER carbs, Isn't Robert selling those? He would would be the one to talk to for those. Then there's the Holleys. I have both a 600 and 650, with intakes, if you're interested. They are non-RB carbs and will take some tuning and linkage work, but you can have either for 300 shipped. Carbs are in good condition, I don't like messing with them.

 

Sterling carb on a half -bridge? I dont think that set up would be the best because the stock intake isnt going to flow air like a RB intake or the side draft/down draft intakes. Weber would be my 1st choice in carbs but I'm still working on a Demon carb set up.

 

Something like a holley would prolly be the best overall choice for 1/2BP engine. Remember, the purpose of only BP on the secondaries is to retain lower RPM drivability. Weber, Delorto, Mikuni, and other large 2BBL side/down draft carbs have the engine running on all ports, all the time. If you are gonna go that route, just do a full BP.
A 1/2 BP engine, using a 2 stage 4BBL carb will give you the low end of the SP primary ports, and the upper end of the BP, more effectively.
I'm sure a sterling carb would work on a 1/2BP, but the CFM rating would be a little low, thereby hurting the potential output.
Granted, holley carbs are not the greatest on a rotary, but there are very few other choices for a 2 stage carb, without getting mega-pricey.

 

Well said!

 

I have a weber IDA 48 on my 12a half bridge, the carb is excellent on the mid and top end but it does lack a bit below 3000rpm, but this could also be because I am still tryingh to get the tuning down perfect.

 

You asked me about this in a PM, and shame on me, I never replied. While the idea is good, the intakes don't work that way. On the RB intakes, if you go for a Holley, other than the 465, RB mills out the top of the intake so all 4 ports are open. I have both intakes in the shop if someone needs pics. I think one reason for the milling is for butterfly clearance on the 600+ cfm carbs.

If they were kept seperate, like the 465s, performance would be better, in theory, but increased overlap may play a part as a reason for the milling.

 

You will never be able to get the low end torque back on a 1/2 bp. Hook up a vacuum gauge to 1 rotor only and you will see what overlap does. At about 3k, the overlap starts to work in favor of drawing in more air, (vacuum gauge will smooth out), at 4k, they will take off. It's the nature of the beast, so to speak.

When I first had my 1/2 bp running, I had RE headers and presilencers, the rest of the exhaust was stock except for some odd brand muffler. The vacuum gauge needle vibrated so fast it was a red blur. By 4k it was steady. When I went full 3" exhaust, it vibrated less and began to steady earlier. Even with 120 psi+ on all rotor faces, I'm lucky to pull 10hg on the gauge.

 

I never said RB intakes were the best designed. In fact, I never anything RB sells was the best. They're just one of the few *still* in the game.
I did say holley carbs are not the greatest on a rotary, but they are one of the few that build a 2-stage carb. There are several others, but they all fit pretty much the same intakes.
If it were me building a 1/2BP, I'd hunt down a twin webber carb/intake setup that uses the twin 2-stage 2BBL carbs (dunno what they are called), or go EFI with primary/secondary throttle plates. This would allow for better idle/low rpm drivability, along with the "hold on to yer ***, fred" kick in the upper range.
That's just my opinion, I *could* be wrong.

 

I'm not a big fan of the Holleys on a rotary either. That's why I have 2 complete setups sitting in the cabinet and a Mikuni on the 1/2 bp, even though it's not 'supposed' to be big enough for my porting.

Not picking on you Rogue, and I apologize for not answering your PM a long time ago.

I'm hoping to get my hands on one of RE's old 36 DCDs and see if it runs better with that setup.

 

NP Scott. I understand, besides, you did once state that you was still thinking of an answer in another thread. I'm sure that had a few people wondering.
36 DCD? Is that the codename given to those twin 2 stage 2BBL carbs? I know a single webber sure perked up the old school 4 bangers, I can only imagine what a pair would do for a rotary, 1/2BP or otherwise.......

 

36 DCD is the model of the carb from the old RE catalogue. There is a pic of it in this link. https://www.rx7club.com/1st-generation-specific-1979-1985-18/dual-carb-setup-582277/ I don't know if it is a 2-stage carb or not, but 2-stage may improve low end torque quite a bit. It's all in the amount of overlap.

 

Yep, the 36 DCD is the setup I am reffering to. The ad lists it as twin, progressive 2 BBL carbs. That would be the bomb on a 1/2 BP or even a good SP street setup.

 

I was the 1 that started that dual carb tread and this was 1 of the reasons why. I think this setup may be the best in a 1/2 bridge ported motor. Just my .02

 

Remember, with 1/2 bridgeports, even if the throttle plates feeding the bridged ports are closed, there is still exhaust overlap. Exhaust goes up the bathtub (dip) in the rotor face and into the next intake cycle regardless if the throttle plate feeding the bridged port is open or closed..............

As for the Mikuni 44 pph, the biggest chokes that can be installed in that carb are 40mm.

 

Run it without venturies ala the orig killer-bee 13-B mikuni carb.

 

My brother in law has the dual carb set up on his 13B streetport and loves it I on the other hand have a 48IDA on my 1/2 bridge 12A and think its just fine. I only race my car so i'm not worried about the below 4k driving but after 4K it pull like a freight train and keeps pulling all the way to 9500 rpm and the funny thing is it is still making power just starts to detonate because i still have stock ignition

 

I'm looking at this setup. Can you let me know if you think it will run alright and maybe give me your input on some changes I should make? I know its kind of a difficult question to answer but how much power could this setup make?
- 1/2 bridge 12A
- RB header to 3" exhaust
- Sterling Nikki carb (adequate enough?) or Weber 45 DCOE?
- DLIDFIS
- E-fan

 

can u run w/o chokes

 

Nope

 

48ida period there is nothing better. It doesn't matter what carb you run the engine is still going to see the bridge and you're stil going to get lumpy. And Trochoid when you were refering to a vaccume gauge on 1 rotor. It does that no matter what the port. Stock ports do the same thing. You could run a 45dcoe on a full bridge. It's been done w/o chokes, but it won't drive too well at anything but WOT.

 

Agreed 481 IDA or even 51 IDA Weber are unbeatable, and no BP NA rotary will make power under 3K as stated by Trochoid, my 4 port 13B BP with 48 IDA came on like a turbo at 3500 rpm.

 

48 ida on my half bridge 13b i do have a dellorto i need to get rid of if you want to go that route

 

Why not try a spreadbore carb? Something with small primaries and large secondaries.