T/B coolant bypass??
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T/B coolant bypass??
So back in the day when PDM-USA (aka pdmturbos) still had their shop in (near) Denver, they suggested a cool idea that bypasses the engine coolant to the throttle body. Not too sure about OBD II and later cars, but on my '93 there's an in and out for the coolant that goes through the t/b, which helps keep emisions down with cold starts but hurts you later by heating up the whole t/b to close to the temp of the engine (at least of the coolant) making it breathe hot air. I tried this mod and it worked well (5hp, easily, noticed on the butt dyno). Only prob was sometimes I would idle at 1500-2000 so I quickly put it back to normal and it good as always. If any one else has tried this and succeeded, please let me know what you did.
BTW- after bypassing (just a simple male to male piece of piping in place of the t/b) I couldn't find anything to re-plug the now open nipple ends at the t/b but when I asked PDM they said I could just leave it open- could this have screwed up my idle?
Sorry for the long post but this was an easy yet highly functional mod for me and I imagine with a real CAI, you would really notice the drop in air temp/gain in power. A good gimmick for N/A tuning...Thanks
BTW- after bypassing (just a simple male to male piece of piping in place of the t/b) I couldn't find anything to re-plug the now open nipple ends at the t/b but when I asked PDM they said I could just leave it open- could this have screwed up my idle?
Sorry for the long post but this was an easy yet highly functional mod for me and I imagine with a real CAI, you would really notice the drop in air temp/gain in power. A good gimmick for N/A tuning...Thanks
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From: Glen Rock, PA
Car Info: 95 Impreza coup, green, 5speed 1.8l awd
i have heard of this but in winter the TB with freeze and stop moving but in summer this is a good idea and yes there are some plp on this board that have tried this but dont knot if they had the same problem
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Ya I never had freezing probs with mine but I didn't want to run it long when it was idling like that.
AJ- did you plug up the ends of the t/b when you did the bypass? If so, what did you use?- b/c I couldn't find anything to fit over it (but the guys at the ACE hardware I was at weren't the brightest bulbs in the box) so I was sorta SOL. Thanks!
AJ- did you plug up the ends of the t/b when you did the bypass? If so, what did you use?- b/c I couldn't find anything to fit over it (but the guys at the ACE hardware I was at weren't the brightest bulbs in the box) so I was sorta SOL. Thanks!
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Rather than bypassing I was considering just installing a small ball valve to shut off the flow. I have this diagram and it seems that will work fine. This way you can turn it on and off at will:
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Thanks, Peaty. That is a very good idea.
I just don't know how to go about doing it. Can I get a valve like you said that just has a 3/8" hose coming off it or will I need to make my own??
I still think doing this as a permanent mod would not hurt anything (freeze) unless you were in extreme cold temps, below 0 degrees for a long time. Even then, there's enough heat in that engine compartment, just from the exhaust alone, to keep everything in there from freezing. You also need something to get wet before it will actually freeze/seize. Thanks.
I just don't know how to go about doing it. Can I get a valve like you said that just has a 3/8" hose coming off it or will I need to make my own??
I still think doing this as a permanent mod would not hurt anything (freeze) unless you were in extreme cold temps, below 0 degrees for a long time. Even then, there's enough heat in that engine compartment, just from the exhaust alone, to keep everything in there from freezing. You also need something to get wet before it will actually freeze/seize. Thanks.
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Car Info: 19' Impreza Sport Manual / 99 Miata / 13' OB
I think in cold weather it will help warm up the car quicker but you are right chances are it won't hurt to keep it bypassed. I'm sure they make small ball valves though out of metal. I'm going to look into it this week. I'm a little concerned about the bypass being less restrictive and causing less flow to the other areas since it won't have the TB to slow it down anymore.
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From: Papillion, NE
Car Info: '02 OBS '03 Baja
Oh yeah, plenty of small, brass ball valves out there. Female threads in/out. Nibco, Apollo, many brand names. Go to the local hardware store and get one (3/8th Inch ?) and the associated threaded pipe, then just hose clamp the collant hose onto the pipe. You can even get barbed/ribbed pipe with threads on one end I believe. Brian
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Car Info: 19' Impreza Sport Manual / 99 Miata / 13' OB
My dad having been a master plumber I'm very familar with Apollo brand. I want to look in the McMaster catalog though for an all SS version. I may be able to "find" one at work too in the shop 
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Just curious- why/how would less restriction is the overall coolant system cause less flow or cooling abilities to other areas? I would think it would be better for the rest of the system in the long run since it would circulate faster (more full fluid cycles)...
Would Subaru try to use the flowing air in the t/b to create some sort of 'cooling' effect for the rest of the system? If so, this is where I see it causing problems down the road. Just a different thought.
I really don't know anything about the entire cooling system, etc. of these cars but in my head, that is the answer that seems most logical. Or am I just going :banana:'s
Thanks for all the help on this fellas!
-Andy
Would Subaru try to use the flowing air in the t/b to create some sort of 'cooling' effect for the rest of the system? If so, this is where I see it causing problems down the road. Just a different thought.
I really don't know anything about the entire cooling system, etc. of these cars but in my head, that is the answer that seems most logical. Or am I just going :banana:'s
Thanks for all the help on this fellas!
-Andy
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The coolant will take the path of least resistance. If TB affords some resistance to flow relative to a straight pipe, which I'm guessing it does, you may not have as much going to say #5 (heater core) or the radiator by looks of the diagram, as more than normal coolant goes through the bypass and back to the pump. But blocking it off would send more to those.
Last edited by Peaty; Feb 28, 2004 at 04:38 PM.
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Origami posted by Rallysportz
Just curious- why/how would less restriction is the overall coolant system cause less flow or cooling abilities to other areas? I would think it would be better for the rest of the system in the long run since it would circulate faster (more full fluid cycles)...
Just curious- why/how would less restriction is the overall coolant system cause less flow or cooling abilities to other areas? I would think it would be better for the rest of the system in the long run since it would circulate faster (more full fluid cycles)...
Coolant must remain in the radiator long enough to dissipate the heat to the air drawn through the radiator core by the fans or vehicle motion. If some sort of high-flow, high-volume water pump were used, the engine would actually run at a higher operating temperature if the coolant could not shed engine heat to the ambient air.
Small changes to flow such as a throttle body bypass probably wouldn't have any detrimental effects.
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Car Info: 19' Impreza Sport Manual / 99 Miata / 13' OB
I've got stuff apart today because I'm cleaning my Green Filter, I like to take the whole airbox out and clean it. I need to take a closer look at where exactly the coolant enters the TB, I took a quick peek yesterday and didn't see it. I hope it's not too hidden.