Plenum
Turbo Mini Forums

Had a question about plenums. Are people fabricating there own, or are they finding some second hand ones? If fabricating, what are the main things to keep in mind? Also, on an 850cc motor, would I really want to go to a HIF44 Turbo carb? I think a hif38 would be plenty of fuel for the size motor, even with the turbo. I may be wrong though. Any info is appreciated!

-James

The main thing to keep in mind if fabrication your own plenum is the restrictor ring:

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=513

How do the restrictor rings work, in exactness. The provided link is good for some of the stuff I needed. But, how would I get my hands on a restrictor ring to duplicate/use? What are the pressure holes for, obviously pressure, but they don't vent to air do they?

-James

The restrictor ring is there to keep the pressure through the mouth of the carb lower than the actual plenum pressure.

The vent hole (at least the main one) goes to the float chamber, and as it is in the unrestricted part of the plenum, it carries a higher pressure into the float bowl than what is going through the mouth of the carb. Around 3psi more pressure.

The extra pressure is needed in the float bowl so as that when the carb is under boost, there is still a pressure difference between the two so as that the fuel can be sucked through the jet.

If the extra pressure wasnt there then the float bowl would become pressurized via the jet instead and if the pressure is running that way then the fuel obviously cant.

There was a theory talked about on here by, i think, Wil_H and someone else (sorry if thats wrong) that every 90deg bend in charge piping equates to a 1psi pressure loss.

So if you took a sensing pipe from the begging of the pipe work and had 3 or more 90deg bends in there (not including possible pressure loss over an intercooler) then fed the float bowl with that it could possibly work.

Also one of the members with an a-series turbo in another car sucessfully used a pilot tube to feed the float bowl.

Hope that helps.....More importantly hope that was all right...i've been drunk alot recently!

Edited by James_H on 8th Jul, 2009.

Okay, let's see if I get some of this then, sorry about the ignorance, I'm just starting on the mini turbo scene.

- The restrictor ring controls the float pressure. The main hole(the largest one) is a roughly 37mm hole that goes into the carb where the aircleaner/ used to be. The two lowest holes on the restrictor would be for this purpose(the fixing bolts) I imagine. The two upper holes vent into the float chamber to pressurize it, so that the needle is not doing the pressurization. Hope that's correct and understandable.

-James