The stock throttle body setup has coolant recirculation lines that must serve some type of purpose. This is what I would like to know.

On my old DSM I omitted these lines and did not have any problems. The throttle body between a DSM and an EVO are different although I am sure the engineering behind the coolant lines remains the same. Something about running 180 degree coolant through my throttle body which is supposed to be cool air does not seem like the best idea.

Any ideas?

 

Its to keep the TB from icing up in severe cold weather. If you let your car warm up (like you should) it wouldn't be a problem anyway.

 

it can be deleted, you might suffer in some cold weather cold driving till the motor heats up.
mine is off but Seattle weather is not that cold, and I don't notice any dramatic problem

 

Did anyone notice a difference with that on a dyno with the evo

 

The DSM and EVO throttle bodies have two mechanical and one electric control of idle speed.

The electric control is the stepper motor controled by the ECU that opens up a bit to raise idle, and closes to lower idle.

The first mechanical idle control is the Base Idle Set Screw (BISS) The BISS is a screw that blocks off a passage that allows airflow to bypass the throttle plate. You turn the screw out and more air bypasses the throttle plate raising your idle, turn the screw in and less air is bypassing the throttle plate and your idle goes down.

The second mechanical idle control is the Fast Idle Air Valve (FIAV) The FIAV is a plastic/wax plug that blocks off a passage that allows airflow to bypass the throttle plate. when this plug is cold is shrinks and blocks less of the air passage and more air bypasses the throttle plate raising your idle, as the coolant heats up, the plug gets warm and grows blocking more of the air passage so less air is bypassing the throttle plate and your idle goes down.

If you get ride of the coolant lines to the throttle body, the car will remain in "high idle mode" for a lot longer because the entire engine bay has to warm up before the FIAV will expand. The electric control can somewhat compensate for this, but if you live in a cold climate the compensation required will be out of it's range of adjustment and you will need to adjust the BISS on a seasonal basis to compensate.

Keith

 

Keith,
That is the type of info I was looking for. I was almost certain that the FIAV had a wax piece of some type and required this coolant to work properly. I also know that even some Honda's for instance run coolant through the TB and IM to speed warmup of the car. Although the Mitsu designs actually needs the coolant circulation to work as designed.

The difference on a dyno would probably be null difference. I am looking at this in bit more of a logical way. Hot air = hotter intake temps. Do you think that omitting these lines during summer months or when the weather is say 40 degrees or warmer that this would be a good idea?

 

Too me it would not be worth the trouble to take them off for summer, and put them back on in winter.

I doubt if the having a 170 deg throttle body rather than a 100 deg throttle body has ANY affect on intake air temperature. At anything other than idle, the air is moving through the throttle body really fast, and there is very little heat transfer area in the throttle body, so I doubt if it heats up air temperature much if any.

They are not hurting power, and perform a useful function.... so I just leave them alone

Keith

PS: Just was thinking about it.... under heavy load the coolant may actually be REMOVING heat from the throttle body. Your intake manifold gets pretty dang hot since it is bolted up directly to the head, and the throttle body is bolted up to the intake manifold getting heat from that direction.... anyone know how hot our intake manifold gets under heavy load?

 

Good tech info above. I'd say a Cometic spacer between the intake manifold and head would yield better results anyway.

 

Its been tested many times in (mostly in GM cars to my knowledge) to gain a 1-3hp at most. I run it as a "free mod" on nearly every car I have owned in the last 10 years. I have never noticed high idle speeds but I am usually pretty good at letting my cars warm up before driving them anyway.

 

I am running an Ebay Phenolic spacer which is similar to the Hondata unit. these alone have said to add 5-10whp although I think of it as a supporting mod. I wanted to try something different. The gasket is not leaking as far as I can tell that is!

 

that's very interesting information

 

FWIW : I removed the recircs on my Z for the same reasons mentioned above. Dual 60mm throttle bodies - no known issues ..

just let the car warm up. Should be universal to any car with coolant recircs installed. It is a preventive measure so that the throttle bodies dont stick open for people who just jump in the car and go.

 

Sometimes I jump in my car and just go. Life can't always wait for the EVO. Maybe I should keep mine circulating as is.

 

I completely blocked off the stepper motor and FIAV so the only adjustment I have is the BISS. I have a standalone and I have never had trouble. I wouldnt recommend this on a stock ECU. I do make changes to the BISS every once in a while as the weather changes. It only takes like 30 seconds to adjust.

 

I got rid of the FIAV coolant lines on my 2g, and blocked off the air pasages with a home made block off plate. I eventually got rid of the ISC too and went just off the BISS. I found on my car that the BISS did very little to adjust idle speed when that was all I had, though that doesn't seem to be the typical result. I had a 1g throttle body installed, which has the seperate throttle closed switch, which I used to set idle speed much like you do on a carb. With the FIAV blocked off but the ISC still functioning, the ECU could still idle as fast as 1500-1700 rpm in cold weather, which worked fine for me.

I fully intend to get rid of the FIAV on the EVO, since I'm running AEM and the fewer things interfering with idle speed the better, IMO. I would not bother with this "mod" for power production reasons, I doubt it matters much. Getting rid of two more coolant lines that will eventually fail and leave you screwed is a better excuse that that.