xotic_crx

Skip to bottom if you don't wanna read my back story.

Hello, finally got my motor finished and broken in and took it to the track to start nailing down the tune. First off, I noticed that my speedometer is off and that I have an LS trans (which is why it felt slow in 3rd *facepalm*). Secondly, I think that my stock 60mm TB is holding my car back some. But, here's a quick rundown of the build then we'll discuss

B18C1 stock bottom end w/ ARP fasteners all around, PR3 pistons (11.5:1 CR)
B18C1 head with multi-angle valve job and a little cleaning up casting marks, Supertech springs & OEM retains, .005" shaved
Edlebrock 4730 cams on stock gears.
Blox V1 (oooold) intake manifold with 60mm TB and 3" SRI (soon to be fixed to a true CAI)
Toda style PLM header and 2.5" mandrel exhaust with just a magnaflow.

So, while it wasn't as noticeable on the datalogs from the track since it was around 50*F, but when it's been in the 70's and 80's I'm noticing slight vacuum at WOT above 6K rpm. I've seen it come down to 940mBar from 1BAR around 5K. I looked back at my logs from my SOHC with the same TB, and it had a consistent mBar across the rpm range

TL:DR

What I'm long winded about is what size should I go with. This isn't a drag car, primarily an autocross car so I don't want to kill mid-range. If I have to open up the inlet of the mani, I will. Should I just get mine done by Maxbore to 64mm, or go to a 66 or 68mm Omni or something?

93egSLEEPER

Get maxbore to put his treatment on it. My last GSR had the maxbore 66-64 taper and my torque and mids were awesome. I also ran the P30 IM which helped as well.
Also IMO DO NOT get a true CAI. I would play around with a tuned length SRI w/ BPI v-stack on your setup. Plus since you do your own tuning you can do it for basically free.
Start with 24" of pipe and tune from there.

AaronEJ

i would recommend you a 68mm throttlebody, its a perfect combination with a midly built
B18.
Just port match it to your intake manifold and you will be fine, and you will definitly not kill midrange with it.
get a Omnipower one and you wont have any issues with it.
And for the intake a length tuned 3" with a velocity stack and filter will get you some nice midrange bump, just start somewhere in between, i you case it should be somewhere round 800mm long.

xotic_crx

Well, i wanted to run the CAI because I've noticed my IAT's have been notably higher since I put this motor in and went to the short ram (all I had laying around) over my SOHC with my AEM CAI. If memory serves right, they were about 30-35* above ambient before, and 50*+ above ambient temps now at cruising.

Speaking of length, I was going to just order a 3" piping kit and build one myself.