Too much?
 

I have been planning on running a TWM 50mm (IDA type) throttle body on a downdraft intake on a large street ported 13B. I would prefer to not do a bridge port, since I would like some bottom end. For the most part, I generally just autocross the car.

The challange is that most folks use 42 or 44 mm chokes in the IDA. This really drops the actual size of the port. a 50 mm throttle body will flow a good deal more than a 48 IDA (even a 51 IDA).
That is why I ask if it is too much...

It would probably depend a lot on the intake manifold design. An IDA on a manifold makes for an intake tract that is about a foot long. With a flat TB on that same manifold it would be great for top end intake tuning but your bottom end will suffer.
The IDA's need to be choked down to create a venturi to draw fuel. Without some kind of limit in choke size I doubt the velocity will be high enough to give you good low end.
Why not use a factory intake system? If you are looking for low end grunt that might be something to look into since they aren't that great for high RPM's.

might be a little large for a street port. short manifold will give good top end power and torque. longer manifold will give better low end power and torque but this is not the rotaries strong point. for perspective I tried a 50mm TWM IDA throttle body on a 13b peripheral port motor and had tuning issues. the throttle body manifold combo suffered from some reversion problems and a smaller TB would have worked better. with some intake experiments and lots of tuning work it could work fine.

Hey Tims,
what are you using for engine management?

that engine had a Haltech E6K at the time. car owner has since switched to a Gene Berg carb that basicly puts the opening to a 48mm TB and it runs fine. 48mm would have been a better TB for our setup. It wasn't the ECU's problem it was the fact we didn't have the right intake manifold and the car owner didn't want to experiment. so he switched to the carb. I have seen guys in Australia use the 50mm so it can be done just gotta work out the kinks. good luck

I don't know if you have your heart set on that carb, but I highly recommend the Sterling. I've been autoxing all year, and so far no other 1st or 2nd gen has come close to my power that I am putting down. This car is also a daily driver and there are no issues with driveability. Just a thought...