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 B ports off the carb's secondaries and the S ports (stock or maybe streetported) off of the carb's primaries (makes sense right)
I think 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).

First, why is it that most of the carb set ups i read about for rx7s 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... ?

With a 500 cfm carb will my S ports make enough vacuum signal for decient low end power and gas mileage, and is there any chance the B ports will out flow the secondary side of the carb at high rpms? Obviously gasmileage isnt a huge concern, but i dont think it will be THAT bad on the highway if i get this set up correctly and as long as i keep my foot light.

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? why?

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

 

Just for the record, I know nothing about carb'ing rotaries but for some reason (I'll do some research) I thought the stock tb flowed about 750 cfm. I'm not a genious but the amount of air that a bridge will need to run correctly would be sevierly limited by using the 500 cmf carb. I'm probably wrong though. Sounds like an interesting project.

 

thanks for the info.
I am thinking a 600 might be a bit better, but i dont know, and i think a 750 sounds alittle too big, but again i dont know. I am trying to keep the car as daily driveable as possible. I have another car, but i would like to sell it and drive the 7 for a while before i get something else.

 

OK.

Hmmm...You are aware of how much of a pain in the butt a bridgeport is with a carb, right?

OK. Not all carbs like a huge difference in airflow between the primaries and secondaries. Best to check that yours will work.

I don't know anything specific about that carb. But the same steps apply to all carb conversions. You need to go to a low pressure fuel system. You need a new intake manifold. The stock ignition has to be dumped for a distributer system and all the appropriate wiring changes made.

Spacers move the power band up, but most importantly provide a place to stick vacuum nipples and isolate the carb from the heat of the engine.

With a carbureted bridgeport, you will never have decent low end and good gas mileage. Actually for the most part this applies to all NA bridgeports. The tunability of fuel injection is key to making a bridgeport behave.

High overlap between intake and exhuast. Especially with a bridgeport.

 

If i am NOT running an open spacer then shouldnt a HALF bridge have a decient amount of low end power? Before the secondary plates open it would be like driving a stock ported engine running off of 2 ports with a 250cfm carb. Then when the secondaries open the bridge ports will start getting air and fuel. The difference in air flow between primaries and secondaries would be a concern, but thats why i am asking these questions.
Ok, so should i just stick to a street port all around?

 

Even with the secondaries closed, you still have massive overlap between intake and exhuast. This causes a major pulsing vacuum signal (half bridges can pulse anywhere between 5 or 10 inches of vacuum) that likes to mess with carb metering.

Bridgeports and EFI is a great combination.

 

Well i am going to go efi later, but i am just kinda interested in carburetors right now, i may hate them after working with them but i am just curious. I may just use a stock 6 port engine and play with a carb set up and then build my 4 port engine for a microtech and boost.