wankelTII

Ok, i am still totally in the planning stages of everything, but i am getting more and more sure of what i want to do.

I have a 4 port s5 engine that i want to tear down, do a half bridge port, and rebuild with high compression rotars. Ok, now lets assume this is done.

I want the engine to be carbureted just for simplicity, and fairly low cost.

I would like to run the 2 large ports off the carb's secondaries and the 2 small ones with the primaries (makes sense right)

I want to use a 500cfm Edelbrock Thunder Series carb, because from what i hear they are simpler to tune and i dont have to really do anything except plug a little passage and the carb will be good for 1g+ acceleration in any direction with no fuel spilling or starvation of any kind (at least thats what the tech guy at Edelbrock said).



My questions are, why is it that most of the carb set ups i read about include open spacers? Is there some reason for this? Doesnt this hurt low end power? Strong vacuum signal for carb but low air velocity in intake... ?



Also, are my 2 larger ports going to want to out flow my carb? Ok, lets call the bridged ports B ports and the others will be stock or street ported so they will be S ports. What i am trying to say is: With a 500 cfm carb will my S ports make enough vacuum signal for decient low end power and gas mileage (below ~4000rpms) and is there any chance the B ports will out flow the secondary side of the carb at high rpms?



Also the secondaries on the Edelbrock are adjusted with a screw to change spring tension, but i have read about people having trouble with vacuum secondaries on rotaries, is this true?



Any light you guys can shed here is very much appreciated!

wankelTII

ok, sorry

I was trying to edit my post and somehow this happened



please delete!

Rx7carl

I wouldnt run an open plenum. I use a dual plenum on my manifolds ( Sterlingcarbs and ported stock manifold). Ive tested IR, dual plane and open plenum. The open plenum gives up too much on the low- mid rpm range.

wankelTII

Yeah, i didnt think an open plenum would be very streetable. I could see how a dual plenum would work well though. The guys on another forum have said that a bridge port will not work with a carb because there is too much overlap and this causes pulsations in the intake manifold. Has anyone ever had a carbed bridge or half bridge?

RONIN FC

I ran open plenum so the secondaries would operate. The open plenum also dampens the pulses your talking about. They dont go through the carb as much.



Just speculation, but I would look into using a 650 cfm, mech secondary carb with the bridgeport.

It may run mostly on accell pumps on take off. I dont think a bridgeport will pull enough air through the venturi boosters to be drivable with a carb that isnt a double pumper.

BeaterRX7

If you're running a half-bridge keep your primary and secondary airflows separate. Otherwise you don't get the benefits of different porting, you just get an average of all four ports.

iceblue

A EFI system is more efficient and far simpler to tune.



If you insist on a carb a choice without first flow testing your ports would be ignorant. So port the motor then grab a carb based on this. I prefer down draft setups.

BeaterRX7

RONIN FC

Flow testing your PORTS, another good one. What about the rest of the setup?



Your not exactly wielding an orb of uncommon knowledge when you say carbs arent eficient as EFI.

I know, I know, we should all be installing r-tek's with S-AFC's onto an old, rigged ECU...

But unfortunately, this is a thread about carbs



BeaterRX7: How are you doing this? Are you cutting a four hole spacer?

BeaterRX7

Weber 36DCDs on a Rotary Engineering intake with separate runners. I initially had a PB&J reworked Nikki on a stock, but mildly ported intake.