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My Son did this to his R31 about 12 months ago.

Apparently thare is a pipe at the back of the plenum and another at the front that he bypassed with a length of pipe and let the plenum etc drain.

It has lasted 12 months as I say, but don't know if it will last forever (who knows?).

He then went on to install a thermo fan and that seems to be functioning OK as well.

ps I am not confident enough to do these to the R33.

All the best.

El Bee

i did this to my 3lt when i had it...i never really noticed much difference but i can imagine its there for a reason, whether it be to heat the cold air in the mornings quicker so it runs better OR whether its to stop excessive heat soak into the large, thick aluminium inlet manifold and plenum which could actually get hotter than the coolant given half the chance. I spose after market custom plenums dont run any coolant through them.

i think there's something similar on the SR20DETs, AFAIK, from what i think i remember reading - it's there to heat up the manifold etc in the freezing conditions in japan and help the car start/keep running.

i'm pretty sure that's the reason anyway. someone correct me if i'm wrong???

  • 2 years later...

To stop the throttle body freezing shut. They serve no other purpose.

i removed everything on my 25/30 and ran some 10mm fuel hose underneath the plenum to connect all the coolant galleries up. the flow through the throttle body is only necessary if you're seeing icy conditions - even then it's not really needed.

remember to run a vertical hose up to above the radiator cap level, then plug it. you can use it to fill the coolant up to the very top so there's no air bubbles.

the coolant running through the inlet manfiold helps the fuel atomise when the motor is not at operating temperature. As cold fuel has more tendancy to form as a droplet this providing a dodgy fuel burn and poor running.

isnt a problem much now days cause temp isnt that cold anymore

Edited by nick81xd
  • 1 month later...
  • 1 year later...
Anyone else bypassed the TB? I did it the other day but not sure if there is any difference.....cant see it doing any harm as it till gets pretty hot!

Im SURE there was a thread about the TB bypass like 2 days ago.

Ive done it to my R33. Its not needed for AUS, NZ conditions as it doesnt get cold enough really.

Have done it on all my Hondas too. All G!

Actually, the freezing shut thing is correct, but not the main reason.

If your on the open road in low temps, at a consistent throttle, the icy cold air will form ice crystals around the TB therefore it sticks OPEN. Not the nicest feeling coming into a corner :D

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