Hey folks, had some questions and through searching I’m seeing over a decade of knowledge but wanted to get the up to date answers for things.

I’ve got a GSL-SE with the series 3 13B pulled right now. I had an o ring in the front cover let go and oil pressure was low so I pulled it to diagnose and see what was wrong. While I had the engine out I saw no reason not to put the car back together with stock power, so I started collecting series 4 13B parts to make some additional power.

Right now I’ve got 6 port series 4 irons with the secondary and aux ports with a bridge, and the primaries seem to have a street port. Housings have the inner piece removed as well. I’ve got one good series 4 NA rotor and am searching for a second, but I’ll be using my GSL-SE front cover and oil pan to mount all this into my car, and powering it with a Haltech PS1000.

My question relates to intake and exhaust. This will be a street driven car that I will be using for fun and autocross/track days. On the exhaust side I’ve seen lots of talk about header length being something that unlocked the NA potential for these motors, but I wasn’t sure if there was a go to off the shelf solution, or if folks are fabbing their own.

Regarding intake, my end goal is ITBs mainly for sound and throttle response, currently looking at JAFA Engineering’s setup that uses the S4 LIM. Not sure if that makes more sense than a DCOE style setup, but I’m assuming an IDA style will be too peaky for my purposes, although I could be wrong. But for the time being, and to not run my budget to the moon, I was thinking to use the stock series 4 intake. I think it was peejay that had a post talking about how it’s actually a very nicely designed setup and was unfairly maligned, but I could be misremembering.

long story short, I want to see what the current recommendations are for a 6 port half bridge. I’m shooting for 200whp and I think that should be attainable, but I’m more concerned with ensuring I have a nice usable power band than hitting the number.

 

here are my thoughts. firstly i would make the exhaust such that you can change the length pretty easily, you will want to try at least the common lengths and see what the engine likes best. my idea was this; Racing Beat sells 3 foot lengths of pipe, you'd buy 3 of these and a bunch of exhaust clamps. if you cut one of the pipes in half (and started with a ~32" RB header), if you have all the pipes in there, 3 foot pipe + 1.5 foot pipe + header + collector, is about ~90" which is what Mazda did in 1979-80. you can then remove sections and see what it does. once you figure out what the engine wants, then you can make it more permanent.

for the intake if you're EFI, then IDA vs DCOE is not the important thing. you're looking at intake length. in the past people would just pick something, and tune around it. the intake does matter, if you're ITB, you're primarily interested in intake length. if it was up to me (its not BTW) i'd pick the one that give you the most flexibility, or the straightest. the other way would be something like the S4 intake, which would just do what it does, and you can move on and spend your time working on some other part of the car.