I am looking into building an N/A 3-rotor setup for my FD. For a bit of a background , Ive owned 5 FCs over the past ~6 years (4 N/A), and now my FD which is pretty much full bolt-on. Since my 1st T2 I was hooked on turbos and havent really looked back , and have concentrated alot more on turbo sizing and specs more than porting. I now would like to go back and build a nice N/A engine for my FD, because Ive realized that even though my turbo cars were faster, I think I had the most fun driving my old S5 N/A. I just really liked the resposiveness of the engine and not having to constantly worry and moniter boost and water/oil temps in fear of blowing it. ANYWAY, what Im getting at is that in N/A applications, Im not very experienced with porting. While I realize without FI the HP output isnt going to be astounding, I would still like to shoot for ~375-400RWHP. I have done a bit of research on the subject of N/A 3-rotors. It seems the norm power for stock port/stock 9.0 rotor and stock IM 20Bs is right around 230WHP (N/A). Also Ive found a few all-out race applications (PP) making closer to 450WHP. I would like to build something in the middle, Intake will be ITBs and exhaust header will be custom made, and using S5 N/A rotors. I dont have any experience building or tuning P-port or bridgeport engines, and Im not even sure if I would like something like that due to reliability/streetability. Main reason for me going N/A from my perfectly running 13B-REW is that i would like the piece of mind that the engine will last 100k with me beating on it, so I dont want to make it fragile. Do you guys think a large SP engine will meet my HP goals, or will something more aggressive be needed? Sorry for the long post, and thanks for any help I can get.

yup i think with a good intake and exhaust 375hp is doable, be a really fun car too!

Thanks, when doing a large SP for N/A vs FI engines, is there any different techniques to the porting?

A street port 9.7 and ITB's will get somewhere near 350rwhp. If you want higher, you can go half bridged or semi PP. GTO-Rx7 will have his semi PP 20b up and running in the near future over at the Rx7club forum. Pay close attention to that forum for his progress.





http://www.rx7club.com/showthread.php?t=454580

Depends on you hp goals. Most engines don't need porting with FI because the air is being forced through the intake. In a NA set-up, porting is more important because you are worrying about intake velocity and flow issues. NA engines are basically suction air pumps. You have to port the engine so that the engine is able to draw in more air efficiently. To do that, you really have to understand the internal flow dynamics of these engines to understand how to correctly port them to meet your specific hp goals. Also intake design and runner length is important in a NA set. This is something you simply just can learn over night. It may take you months of reading and understanding for all the info to make since and sink in. Here is a thread that will help you get started in understanding NA intake terminology. RotaryGod does a good job of explaining things some here.



http://www.rx8club.com/showthread.php?t=20148

There is little to learn from 2 rotor N/A's manifold design that you can use on a 20b.



I would go p-port and ITB.