Throttle body coolant bypass to turbo?

[vanilla gorilla]

I'm going to be installing a Mitsubishi turbo on my car, and as far as i know it has to be watercooled. So I was thinking about running the turbo coolant lines from the throttle body coolant return to the turbo. I was telling my LS1 buddy about it, and he said that I should just bypass the throttle body completely, and just cap off the coolant fittings on the throttle body. He's got it done on his car and he says it will probably make mine run better and give possibly more power. So my question is is this a good idea or should I continue to run coolant to the throttle body and run the turbo off of the throttle body return? Will bypassing the TB hurt performance or drivability? And the million dollar question.....will it hurt the gas mileage?

Thanks for any help in advance.
vanilla gorilla

[crunchymilk55]

Do you live in a cold (freezing) area?

[NateS]

I read a write up about this. Basically, if you live in an area where it is normally hot or warm all the time like Florida or something smiliar then this mod should not hurt you at all. If you live somewhere were you get pretty hard winters and it gets pretty cold outside then I probably wouldn't do it. Having the coolant run through the TB helps so the TB does not freeze when it is very cold out. I have heard of a minimal power gain if any from it because the TB would not be warm from the coolant running through it but, the gain is not really noticeable.

[kjewer1]

There are a lot of misconceptions out there regarding what the coolant lines to the TB do (not necessarily in this thread), at least on DSMs. I'd like to take a moment to try to clear some of them up. I would expect all Mitsu cars to work like this as well. I've run without the FIAV and the ISC, using the closed throttle switch to adjust idle speed, carbuerator stylee, so I have some personal experience in this area.

The coolant passes through the Fast Idle Air Valve (FIAV). The FIAV is a waxed based valve (not unlike your thermostat) that reacts to temperature changes, bypassing air around the throttle plate in varying amounts. It is a "Normally Open" valve, meaning at atmospheric temperatures it is open, at least partially. On a cold winter's day, it's wide open. On a hot summer day, it may only be slightly open.

Having that valve open rasises idle speed, since it is bypassing air around the throttle plate, just like the BISS, and just like the ISC. Once coolant temp comes up, meaning the car is warmed up, the wax FIAV closes, and idle drops to what it is supposed to be as determined by the ISC, since that is now the only thing bypassing air around the throttle plate.

You can probably already see the problem with simply removing the coolant lines from the TB. You'll always have the high warmup idle. This is a real pain in the ass for obvious reasons, like trying to negotiate tight parking lots and such at 2000 rpm, and other reasons, like idle surge from Coasting Fuel Cut, etc. In order to complete this mod, you need to also block off those air passages related to the FIAV. I've done this mod before, and it's not rocket science, but you have to put down the computer and go do some disassembly and investigation to see exactly what it is you need to do. In my case I removed the FIAV and ISC subassembly, and made a block off plate to disable both of them.

Once the FIAV is blocked off, you now lose your higher cold idle/warmup idle speed, since no air can bypass the throttle plate. For poeple in warm climates, this probably won't be a problem. In cold weather it can be a pain in the ass. I found that in reasonable weather (cold but still above freezing IIRC) the choke function in the ECU adding more fuel brought idle speed up just enough to let it run on its own until it was warmed up.

I highly doubt this is worth any real power gains however. I don't think the TB being at coolant temperature is going to put enough heat into the incoming charge air to make a difference. The throttle body is not meant to be a good heat exchanger There is very little surface area invloved, and the air is moving pretty quickly through it. These qualities are the exact opposite of what you try to design into a heat exchanger like a radiator or intercooler. Not to mention that on a turbo car the charge air is not exactly cool either.

Now, using these lines to feed a turbo is an interesting idea and I definitely give you guys credit for it. There is a supply and a return, and they are even the right size. They also appear to be in the same location as the turbo feed lines, at least on the turbo cars, meaning one comes from the head side of the tstat, and the other comes from the front water pipe. So that gives me some confidence that they will still get the job done (cooling the turbo).

Are the driveability trade-offs and extra labor involved in blocking the FIAV off the right way worth it? I don't know, I'm not sure what your other options are in turboing an NT. But hopefully I've provided enough information here for you to make that call based on your local climate.

[Talon69]

You have got to be the most amazing person on this damn forum by far Kevin!!!!

[blk_srt]

how did you change your name?

[crunchymilk55]

that's his sn on the dsmlink forums. I would think he would have no problem getting anything administrative taken care of real quick on this forum

[kjewer1]

Yes, this is the last forum that still had my 6 year old screen name. All others have long ago been updated. I wanted to make this one match, but have been reluctant to bother the admins with it. Admining a site takes a ton of time, and they don't get paid for it, which I know first hand Thankfully they graciously took care of it for me today when I finally asked.

[NateS]

Wow kevin, you made my explaination look like a little kit pissing on an ant compared to you steamrolling the sob. Hahaha.

[MexRocket]

yah, If you were a girl, thor would try to make out with you, maybe that is why my car idles so high =O

[kjewer1]

LMAO, you guys are killin me.

[vanilla gorilla]

Thanks for the info. You guys always help me out. Based on everything you guys have told me I think I will leave the TB like it is...but still feed the turbo from it somehow. I'll tell my LS1 buddy about what I learned.