Something to read although very old.

If you have no BOV, would you go and install one? If you do so, does it need retune?



"The classic blow-off valve.

"The blow-off valve is designed as an emissions control device for OE manufacturers. It came about when smaller engines made more and more power using larger turbochargers and bigger intercoolers. As you close the throttle, the build up of pressure and the larger volume inside the intake has to go somewhere; it can't go into the engine because the throttle is shut. Instead, it has to do a U-turn and it comes screaming out the airflow meter. That creates the 'gobble-goggle' sound.

"The gobble-gobble sound is something the public has grown to love.

"The airflow meter is not all that smart and does not realise the air is going in the wrong direction; it therefore measures the air twice (once going into the engine and again going out in the wrong direction). The computer now tips in twice as much fuel as what's required, making it run rich - making it not pass emissions.

"Therefore, manufacturers fit a blow-off valve - or a recirculation valve as they are actually called. A recirculation valve opens when it senses manifold vacuum, returning the air trapped at the throttle body to between the airflow meter and the turbocharger. As such, the airflow meter does not take a double reading - the car now passes emissions.

"Unfortunately, we've had people ringing up and wanting the "audible gear change alarm".

""What audible gear change alarm?" we ask. "You know, when the Sierras were running around and just when they went to change gear it used to go whoda-whoda-whoda" they tell us.

""No pal, that is the dump valve..."

"Some people do think that at the absolute upper extremes of boost levels - about 30-plus pounds - the blow-off valve does, somewhat, save the compressor wheel and shaft from trying to rotate backwards. It doesn't actually rotate backwards at all - all you're hearing is cavitation. What happens is, you've shut the throttle, the turbocharger is doing 100,000 rpm and now has a boost spike of 50 psi. Because it's working in a higher region than what it's designed for, it slips; it basically does a skid like a car tyre does when you dump the clutch. That's the noise you hear - the whoof-whoof-whoof is the air doing a skid."

Is there any performance gain to a blow-off valve?
"We've tested one on a manual gearbox performance car run at Winton Raceway. I think it was running 1 minute 40s back then, but it would lose 2 seconds a lap putting the gobble-gobble valve on. When you look at data acquisition, what you find is - as you change gear - the blow-off valve dumps all the pressure built up through the intercooler and pipes. It then goes back to zero manifold vacuum when you get back on the throttle, you have to build all that boost back up.

"The fact that people think that they keep the turbo spinning is a problem. The people that suggest this have never had an engine on the dyno and never had a turbo tacho in their hands. What people don't realise is, when you shut off the throttle, you shut off the air supply to the engine - this shuts off the exhaust gasses coming out of the engine. When there is no exhaust flow, there is no energy to keep the turbine spinning - the turbo slows down at an alarming rate.

"If you change gears at quite a good speed, you can actually get a boost spike on changes; if you're trying to hold a constant 30 pounds, when you do a racing change you'll get 32-33 pounds when you crack the throttle open again. If everything's working well, you've got a full head of stream waiting to go into the throttle as soon as it's opened.

"I've done this on a rally car and it was quicker through every timed section without a dump valve. You'll never hear a World Rally Car going pssshhht because they don't use a dump valve - you get the woof-woof-woof noise instead."

http://www.autospeed.com/cms/article...estions&A=1457

 

There is no reason not to run a BOV on a non-race car. If it's MAP it doesn't matter and doesn't need a retune. If it's MAF, then the BOV needs to be pre-MAF. Otherwise you wind up going pig rich every time it opens because the ecu doesn't know there is less air. The other option for a MAF car is just run a recirc valve and dump the air back into the inlet of the turbo. It's the same thing as a BOV, but it just dumps to the turbo instead of atmosphere.

 

It is MAP tune.

If the car is bought with no BOV. Is it worth the hassle to install one.

I just read that many people run without BOV and there is mixed opinions about the effect of no BOV on turbo life and spool time specially that it is manual transmission car.

So, the question is, if you bought it without BOV is it necessary to modify the cold piping to install one?

Boost is already 22 psi by HKS WG spring.

 

they're simple to install, and with that much boost, yes, no questions asked.

 

I believe it needs welding on one of the cold pipes. Not sure which is best location to get the pipe out and weld connection for the BOV.

Any link for BOV install?

 

thats the cleanest way to do it, yes.

http://www.frozenboost.com/index.php...a4c6190289abcd

there are other options. you can mount it between couplers with one of these t pipes. you'll run a vacuum line from the port in the bov to the intake manifold, post throttle body. im guessing you're not running a MAF?

do you have pictures of your setup?

 

I'm no expert but that "boost spike" that you get when you shift gears without a BOV could be bad for a motor. According to the reference, you would get a 10% increase in your max boost as soon as the throttle blade reopened.

 

its actually harder on the comp. wheel than the motor.

 

As mentioned above, it's MAP tune. No MAF.

Those BOV are they rated by boost? Seen some of them says it can handle 20 psi. I am looking for more than 20". I don't want it to open under boost. I know BOV are actuated by vacuum when the throttle is closed.

Also, those couplers are max of 2.5" dia. I think my cold pipe is bigger, maybe 3".

 

http://www.frozenboost.com/product_i...a4c6190289abcd

thats exactly what you're looking for.


and then... http://www.jgsturbo.com/wgpg.html

thats a great BOV. have fun man. enjoy your cool new sounds and weird looks (and revs) from ricers...


*EDIT* nevermind that t is wrong, the BOV v-band needs to be 2.5". i'll find it, gimmie a sec.


WELL... what material is your pipe made of? steel or AL?

 

It's made of steel. I just measured the circumference of the pre and post IC pipe.

Pre IC pipe circum=9.5" equivalent to 3.5" dia
Post IC pipe circum=11" equivalent to 3.75" dia

The inlet and outlet pipes, each of them, were made in one piece using pipes and elbows welded together.

 

mmk. well if you goto racepartssolutions.com you can order the BOV there, and you can order it with either a steel or AL flange, obviously you want steel. then i'd just take it to a local competent exhaust shop and have em weld it up for you. you can place it where ever you want, though IMO it'd be best pre IC. if you dont plan on getting in/out of the throttle quickly very often it doesnt matter.

 

I feel split between these two:

RPS 50mm Blow Off Valve with Steel Flange
http://www.racepartssolutions.com/products.asp?cat=147

JGS Blow Off Valve with Steel Flange. Not sure if I should get 50mm or 60mm?
http://www.racepartssolutions.com/pr...od=JGS%2DTK300

Also, note sure what boost they will handle without popping open?