My manager at work brought this up...why wouldn't you put your BOV BEFORE your intercooler (ie. between the compressor and the IC) instead of inbetween the IC and throttlebody? The intercooler is a slight flow restriction, so wouldn't you keep the turbo spooled up ever-so-slightly more with the BOV in this alternate position?
I believe this is the set-up he has on his turbo car...but, I'll ask tomorrow...
I don't think this would have any downfall, except placement issues...anyone?

 

daym, that is an interesting thought. maybe it has something to do with the heat of the charged air before the IC tho? i dunno.. i am curious as to the answer to this one too

 

The BOV is there to vent "air" that bounces off your throttle-plate so it doesn't hit the compressor. You wouldn't want to make that "air" go back through your I/C first before venting it...

 

makes sense, dont know why i didnt even comprehend that at first

 

 

My BOV is before the intercooler. The first IC piping piece from the compressor has the BOV on it.

 

Some of the Supra guys put their BOV's on their i/c piping...

 

that isnt a good idea to do unless you have a filter on the bov. At idle you will have a vaccum and the valve is open. Im sure when he is driving it is closed but it does collect on the rim of the valve so when he is idling crap will get in there.

 

I understand the purpose of the BOV...so, if it's right near the turbo the air in the charge pipe will have to bounce off the throttle plate and make its way back to the BOV on the other side of the intercooler, which would be bad...but, conversely there will be less air to hit the throttle plate on this set-up, when the BOV is open, because there is less charge pipe/less charge air between the turbo and BOV?

 

I don't get it. How come? As long as the BOV is somewhere between the compressor and the throttle body, it should produce the same results. Isn't that right? Why would the air going back thru the IC be any worse? Just curious.

 

I don't think it would nessecarily be harmful, but what's the point of putting it before the I/C anyway? Seems to me the shorter the path that "air" has to travel before being vented the safer...why wait 'til the last minute to vent it. Then again, maybe it doesn't matter, after all it is pressure...

 

they guy is right! the air would first be travling to the TB and as you shift and the TB closes. now where is it going to go. now it hits the TB hard then has to travel back to the bov. by the time that happens you are finished shifting and the new compressed air hits the air comming to the BOV. It makes more sence to put it near the TB. it is a lot less distance to travel.

 

Hate to break it to you guys but the air does not travel back... its not a train. When you close the tb, the pressure builds up through the entire system. The BOV senses the higher pressure and blows off the excess. Does not matter where it is in the system, the pressure through out will be the same, that is what causes it to blow off...

 

xThat's what I started to think...

 

yes the turbine is still spinnig when the butterfly closses adn creates pressure in the charge pipe and thats what makes the blow off!! but if bov is messed up or you dont have one the air can go back to the turbo and f#ck it up!

 

yes i agree with boostinb18, the fact that its pressurized makes no difference its the fact of a pressure wave, surgin from the TB back to the turbo which shocks the turbo, basically think of you drivein your car at 65 in fifth gear and the putting it in reverse, thats what happens when the pressure wave hits the turbo it trys to stop it from spining, very bad for the turbo.

and if im correct what the blowoff valves does it equalizes the pressure in the charge pipe when not boosting.

we had an eclipse here that have a broken blowoff vavle flange, and it was not blowing off at all, but the weird thing was it would sound like it was blowing off, but it would flutter, and the car felt reallly fast,

so we tested a theory, reved it and put our hand in front of the blowoff, no air was coming out when the throttle plate closed, we listened really carefully it was actully going back into the intake piping, you could hear it from the intake filter, and fluttering back and for against the turbo....

the reason it was fast was because it was keeping all the charge air, but it was beating the turbo up


[Modified by pornstarSR, 11:47 PM 6/13/2002]

 

IC to TB and IC to turbo correct? So what would happen if I take out the IC to TB and just put an intake on there (and plug the hole on the IC). This would eliminate the blow off valve. What would be the consequences? Reason for this hypothetical question is me trying to find a way around my turbo issue right now.

Is there a way of running turbo without a blow off valve?

 

btw, how bad is compressor surge? i think i have it.

 

I agree, because if you think about it the closed throttle plate would probably cause a lot of turbulence between the TB and IC piping before actually getting to the BOV on the other side of the IC.

 

there are 2 forms of compressor surge, IIRC both of them will lead to premature wear of the thrust (?) bearings which leads to turbo failure.

 

it builds up in the system...

having the BOV near the TB allows the air flow to maintain the max. speed all the way thru the IC and IC piping.

The BOV is connected to the motor side of the TB and once that area is in vaccum (off gas) the BOV opens to allow the pressure to 'blow off'

 

Chris Rado has his before the intercooler also

 

Its hard to put a BOV before the intercooler on a honda...as the piping from the turbo to the intercooler is pretty short...low to the ground...and would be hard to find a good place to mount it [the bov].

liam

 

but you have to remember that chris rado is also running some crazy fuel and a race car, so he can pay for new turbos and what not....

but depending on application,different parts are needed, if you all read sport compact car magazine you will remember a hyundia tiburon Twin motor both turbo charged running something like 20lbs on each, no intercooler, he was running methanol, so each aplication has different setups, weither or not you put the blowoff before or after the intercooler, havinga blowoff is better than not in my opinion

 

This is a great discussion about a good question. But, many of you are fogetting the basic physics involved. before I proceed, I need to prepare:

[hip waders]

It is VERY important to understand that there is a major difference between "BlowOff Valves" and "Compressor Bypass Valves". This discussion is relavent to BOV applications. More specifically, this discussion is related to the use of a BOV positioned before the throttle plate. (It is common practice in many racing venues to implement a BOV after the throttle plate to prevent overboosting. These are commonly refered to pressure relief valves.)

Think for a moment what a blowoff valve (very rare on production vehicles) is designed to do... It prevents compressor surge and maintains turbine shaft speed during [lifted throttle] shifts, reducing transient spool time and potential damage to the turbocharger. This is accomplished by venting excessive airflow when the engine demand is lower than the compressor supply volume (closed TB).

Now, if the BOV is capable of doing its job (preventing compressor surge and mantaining shaft speed) before the intercooler, it would make sense to place it there. Why? Because the air temperature before the intercooler can exceed 300 degrees F, and all of this heat is removed from the intake charge air by the intercooler. If we choose to vent the excessive airflow BEFORE the intercooler, it is simply hot air released to the atmosphere. If we choose to vent the excessive airflow AFTER the intercooler, we have effectively heatsoaked our intercooler and wasted xx% of cooling efficiency for no good reason at all. That's not a good practice in racing...

[/hip waders]


[Modified by B20C5 Turbo, 12:58 AM 6/14/2002]