iwanagofast

Been wondering about doing a mod and wanted some other peoples input i was gonna buy a set of itbs for my all motor ls vtec 82mm 13.2 comp. i was gonna get a plenum built onto the itbs and haveing the horns welded into it from the itbs. also have it a little larger then what a normal na honda would need and sticking a 75mm throttle body on the end of the plenum. my thoughts were i could still have my throttle response, low end, and mid range power as well still getting the top end being fed through the 75mm tb and have the capabilities to keep all my sensors map, iac, iat, and vacuum for brake booster and fpr.

iwanagofast

basically like this but with the plenum a little bigger and with a 75mm tb on the end

http://www.google.com/imgres?q=honda...siJmEAg&zoom=1

redhatch8u-up

you dont need a throttle body on top of ITBs

ej1995

the only real benefit i could see from this is if you boosted it with ITB's...then you'd need the plenum. other than that its just not practical, however not that difficult if you just feel like you need to go down that road.

just say you build this manifold with ITB's. if you do build it then you've got to figure out the sensors and vaccuum, if you don't build it and do regular ITB's then you've still got to figure out what you are going to do with the sensors and where to draw vaccuum from, etc.

from my understanding some of the BMW V8 cars had ITBs with a flange on top and the plenum bolted down on it with a gasket in between. so its been done by other manufacturers.

redhatch8u-up

!!

Fabrik8

You only need one set of throttles, and the other would just become a flow restriction. The plenum you listed has a large tube to attach a low restriction duct that feeds cold air from somewhere else and allows easy attachment of a filter somewhere else. You need the local plenum volume to get decent throttle response if you're ducting air from somewhere else.

The reason that ITBs are mostly used for top-end power is because the length is usually tuned to a top-end power range (short!) and there are some other flow considerations. You can tune the runner length of an ITB setup for low- or mid-end power, but then you'll lose power in the other ranges because the length will be wrong and therefore the tuning will be compromised. So making an ITB setup with a secondary throttle at the opening of the plenum doesn't actually make you gain anything, because the low/mid/top end power tuning is not getting changed at all. If you use the big throttle body and open the ITBs all the way, now you have a regular plenum setup with more local volume after the throttle plate. If you open the big throttle body all the way and use the ITBs, now you have the same plenum runner length but less throttle response. So you're only shifting minor things around, like small amounts of throttle response or local flow restriction. You're not changing the length of anything, so you're not gaining a broader range of runner tuning, etc.

I'm still a little confused about what you're saying.

redhatch8u-up

you are not confused, he has no idea what he is talking about.

ej1995

i think he knows what he wants, but i think he has no idea about how to achieve it. definitely coming at it from the wrong direction