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Throttle Coolant Bypass. Rb25 - Rb20 - Rb30

psi

By psi,
in Tutorials / DIY / FAQ

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psi Experienced

psi

Posted
Posted

This is a great little mod to lower the intake manifold air temp from around 77 degrees to somewhere near 45 degrees in summer, even colder in winter, great for making more throttle responce and horsepower! It bypasses the coolant in the throttle body.

You will need to find the throttle heater hose, which is mounted on the bottom of the throttle as part of the throttle. It is added by factory for 2 main reasons.

1: Because the throttle is heated to the same temp all the time, the air going through it is also raised which makes tuning the factory computer so much less complicated, the air is always about the same temp.

2: Due to the raised temp, the situation of thottle 'iceing' is removed. Throttle 'iceing' is where you drive though some moist cold air and the throttle actually gets little ice crystals on it and freezes it in place. When you go to lift off for a corner the throttle wont come back.. VERY SCARY! This sometimes happens in air temps below about 5deg. If this happens and the throttle wont come back, just push the throttle harder to brake the ice seal and then lift off, or turn the engine off..

The mod: built into the bottom of the throttle aspart of the casting is a little tube. you need to bypass this tube... simple! 2 easy ways to do this,

1: remove the 2 hoses from the bottom of the throttle, 1 from the 'do not open' bleed screw on the front of the intake manifold and then the other that goes back down the back of the engine to the firewall.. u will need to use 2 new hose clamps and about 45cm of hose. run the new hose from the bleed screw UNDER the throttle and onto the the back join on the fire wall.. or

2: just cut a peice of metal tube (copper, steel or alloy) a smidge longer than the throttle bodies hose barbs and use the standard hoses. just insert the new metal tube under the throttle and join it all up.

NOT FINISHED YET, now u have to get the air out of the system, that is what the 'do not open' screw is for. This screw is the highest point in the engine that the air will get to, so any time u disconnect ANY part of the cooling or heating system, you MUST bleed the air out. you will need a 10mm spanner. Start the cold engine and let it idle.

as it warms up, undo the 'do not open' screw a few turns(but not all the way out!). as the engine gets hotter u should see some bubbling come up though the thread, this is good.. u will loose a very small amout of coolant. when the bubbling has stopped, thighten the screw back up. Repeat these steps 2 or 3 more times when u start the cold engine(generally over a week of driving to work or whatever).

It is vital ALL the air is removed from the system!

This little mod is way less than 1 hour to do even if you take your time and tripple check everything!

The end result is an intake manifold that you can actually touch after a long cruise.. this means it goes harder. It looks totally factory, does a great job and gives more thottle feel.

Happy cruising!

  • 2 weeks later...
turbo_brian Community Regular

turbo_brian

Posted
Posted
has anyone tried this yet?

I have a Dyno day coming with another club, I am going to do before and after Dyno runs on the same car to see what sort of differences are made, I am also going to measure Throttle body temps for the duration of both runs as well.

B.

gl0ck. Explorer

gl0ck.

Posted
Posted
I have a Dyno day coming with another club, I am going to do before and after Dyno runs on the same car to see what sort of differences are made, I am also going to measure Throttle body temps for the duration of both runs as well.

B.

choice, any chance of loading pix after doing this little mod? also dyno pics?

turbo_brian Community Regular

turbo_brian

Posted
Posted
choice, any chance of loading pix after doing this little mod? also dyno pics?

I can load pics, but it will be of a non-Nissan, so not sure how helpful they will be...

Will definately get before and after dyno results.

B.

gl0ck. Explorer

gl0ck.

Posted
Posted
I can load pics, but it will be of a non-Nissan, so not sure how helpful they will be...

Will definately get before and after dyno results.

B.

yeah load it dude, shouldnt be any problem tryna figure it out.

- Mat

  • 3 weeks later...
psi Experienced

psi

Posted
  • Author
Posted

ok, sorry guys, I dont have pics cos i moved the throtle ages ago..

I will see if i can get to and mod one of the million skylines around and take foto's for you.

As for the AF ratio, I didn't notice stuff all change! The engine still consumes air in the same way, just that the intake temp is a bit lower, which in thery should have a more dense air charge.

If somebody has done a dyno run, that would be interesting.. I noticed that the throttle was more scrisp from cruise onto power.

This trick will work on any factory engine that uses coolant to 'warm' the throttle. In the old days of carby's, guys used to add a non-heat transferring device or spacer between the carby and the intake manifold to do the same trick. Yep, factories have been doing this to us for decades.

that help?

_x_FiReStOrM_x_ Community Regular

_x_FiReStOrM_x_

Posted
Posted

Good writeup!!... only downside i can see is the car will 'idle up' for longer as the coolant is no longer there to melt the waxpellet. It now has to rely on conduction of engine heat instead. But imo, its a worthwhile mod if you can put up with this.

  • 7 months later...
J3TR33 Community Regular

J3TR33

Posted
Posted

iv always wondered why my rb25 has those two nipples with nothing connected. But it seems like when they did the de+t conversion for my car, they got the water feed and return from these two hoses,

is this all good? is there enough water flow for the turbo?

thanks

gotRICE? Veteran

gotRICE?

Posted
Posted
in the 1st post it says, the coolant passing through the tb makes tuning the factory ecu alot easier, so is this mod stock ecu friendly?

Hasnt caused me any problems and its been done for months.

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