Just want to make sure I have this right. On a stock 12A RX-7 the first point of restriction is the exhaust, then the carburetor, then the intake manifold and then the engine ports. Is this right?

Assuming that you have a free flowing exhaust, at what cfm of carburetor does the stock intake manifold become a restriction. I know the stock carb is 325cfm and a modded nikki can get up to 415cfm. Does the modded nikki flow more then the stock manifold can utilize. Plus I know the 79 and 81+ manifolds are different. And Paul Yaw says on his page that contrary to popular belief that the 79 carb doesn't flow any better then the 81+. So is one of the manifolds better up to a high airflow rate?

Thanks

 

You are correct about the points of restriction in airflow. The biggest bottleneck is the exhaust by far, and should be your starting point for gaining horsepower. As for the carburetor and intake manifold, I would have to believe that for the stock Nikki to achieve 415 cfm, porting of manifold would be absolutely necessary.

Unfortunately, I'm only speculating. I never ran the stock carb on my engine, right now I have a Dellorto carb on my engine. Supposed to be pretty ideal for a stock engine, however mine is street ported.

 

I drive in a Spec RX-7 road racing series. One of my fellow racers did some extensive dyno testing and flowbench testing of parts for his car.

1. We are allowed to remove cats and use any exhaust, but must use stock exhaust manifold.
2. Out intake is stock (stock carb, stock jets, stock air filter housing with K&N).
3. Engine internals and ports are stock
4. Emmissions is intact (except cat is removed)

He found the stock intake (filter housing, carb, and manifold) was actually MORE restrictive than the stock exhaust manifold.

There are significant gains to be made by repalcing or modifying the stock filter housing. Replacing either the carb or exhaust manifold by itself doesn't do a whole lot - but doing both together is huge.

The above comments are in terms of pure cfm. Obviously, tuning any of the stock parts can also give gains (Grosse jets in carb, port matching, etc).

 

Thanks Guys.
Does anyone know which manifold, 79 or 83, flow better?