I can remember as a kid going to ATPA tractor pulls and hearing the pulling tractors blow off, but it was louder then normal released more than just once. What aftermarket blow off valves do I need to get for my DMax to sound like that? Any Help appreciated!

The only purpose of a blow off valve is to keep the turbo spooled, I have a 87 GN and putting a blow off valve on it is a waste of money? Some people say it saves the turbo because when your under boost and take your foot off the gas all that boost between the turbo and the throttle plate has to go somewhere and it blows back out the front of the turbo making a unique noise. I never put a blow off valve on my GN and my turbo lasted about 120,000 miles before the bearings gave way. If GM didn't put one there then I would save my money.

the LB7's have a wastegate, but the LLY's are now controlled electonically via the variable veins on the turbo.. no need for one.

The only purpose of a blow off valve is to keep the turbo spooled
Not necessarily... A BOV is there to prevent compressor surge when lifting off the throttle (looks like TDP refers to this as "turbo bark"). Another version of this valve is a compressor bypass valve which is used primarily in vehicles that use MAFS - a bypass valve recirculates the vented air pre-turbo (post MAF) so the vehicle won't go rich between shifts and idle - keeping the turbo spooled between shifts is more of a side effect. This is used widely in turbocharged apps (gas) today (Nissan, Toyota, Subaru, and DSM come to mind). I've often wondered why turbo diesels do not use a bypass valve (especially in manual trans vehicles)....

the LB7's have a wastegate, but the LLY's are now controlled electonically via the variable veins on the turbo.. no need for one.

Two different things... A wastegate controls boost on the exhaust side. A BOV (or bypass valve) vents charge air at closed throttle (on the cool side) - it's purpose is not to control boost (like a wastegate).

BTW - no offense intended to those I quoted - just wanted to clarify to avoid confusion. Hope I didn't come off as an ass - I apolgize if I did :D

Not necessarily... A BOV is there to prevent compressor surge when lifting off the throttle (looks like TDP refers to this as "turbo bark"). Another version of this valve is a compressor bypass valve which is used primarily in vehicles that use MAFS - a bypass valve recirculates the vented air pre-turbo (post MAF) so the vehicle won't go rich between shifts and idle - keeping the turbo spooled between shifts is more of a side effect. This is used widely in turbocharged apps (gas) today (Nissan, Toyota, Subaru, and DSM come to mind). I've often wondered why turbo diesels do not use a bypass valve (especially in manual trans vehicles)....

Compressor surge does not hurt the turbo most gas automatic trans turbos don't have BOV, but the manual versions of the same vehicle do have BOV. The reason for this is to keep the turbo spooled while the driver is shifting. On an automatic the transmission is shifting so fast the BOV would serve no purpose thus saving the car company 15 bucks a car. My GN uses a MAF and it as neither BOV or bypass valve and it doesn't go rich between shifts? ;) All the compressor surge or boost just comes back out the front of the turbo killing its spool, making that "turbo bark."

Two different things... A wastegate controls boost on the exhaust side. A BOV (or bypass valve) vents charge air at closed throttle (on the cool side) - it's purpose is not to control boost (like a wastegate).


ah..yes yes.. wastegate actually controls the amount of boost you can put into the engine on the exhaust side while the blowoff valve is on the intake side and releases the extra pressure built up in the discharge tube between shifts or what have you.. I get those mixed up all the dang time... I come from a supercharger background and then I have to learn all about turbo's.. lol.. thanks for the clarification

Compressor surge does not hurt the turbo most gas automatic trans turbos don't have BOV, but the manual versions of the same vehicle do have BOV. The reason for this is to keep the turbo spooled while the driver is shifting. On an automatic the transmission is shifting so fast the BOV would serve no purpose thus saving the car company 15 bucks a car. My GN uses a MAF and it as neither BOV or bypass valve and it doesn't go rich between shifts? ;) All the compressor surge or boost just comes back out the front of the turbo killing its spool, making that "turbo bark."
I should've explained a little better - a MAFS car would go rich at shift/idle when using a BOV (which is why a bypass valve would be used). This wouldn't apply to your car since your car does not have a BOV (or vented bypass valve for that matter). Compressor surge does, however, eventually lead to turbo damage. Quote directly from Garrett's site:

The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it. - http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html

I do agree, however, that surge is minimal on auto cars since you don't lift between shifts - this is probably why GM doesn't use a bypass valve on their vehicles (most are auto applications).

Again, no offense intended - just want to clarify...:D

ah..yes yes.. wastegate actually controls the amount of boost you can put into the engine on the exhaust side while the blowoff valve is on the intake side and releases the extra pressure built up in the discharge tube between shifts or what have you.. I get those mixed up all the dang time... I come from a supercharger background and then I have to learn all about turbo's.. lol.. thanks for the clarification

No problemo ):h

I should've explained a little better - a MAFS car would go rich at shift/idle when using a BOV (which is why a bypass valve would be used). This wouldn't apply to your car since your car does not have a BOV (or vented bypass valve for that matter). Compressor surge does, however, eventually lead to turbo damage. Quote directly from Garrett's site:

The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it. - http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html

I do agree, however, that surge is minimal on auto cars since you don't lift between shifts - this is probably why GM doesn't use a bypass valve on their vehicles (most are auto applications).

Again, no offense intended - just want to clarify...:D

ok, i know you are right about what a turbo does, but how do you make the flutter sound with the BOV/wastegate?

BOV. You'd put it after the intercooler, before the TB. You won't get a vent between shifts, however, if you have an auto...

A blow-off valve or bypass valve is of no use on a Diesel because they do not use a throttle plate like a gasoline engine. In fact, there would be no vacuum source for the BOV to function properly.

There ya go! Shows what I know about diesels (which is why I've been hanging around here)! lol! Thanks for clearing that up - I often wondered about this too....

Yes There is a BOV for the Duramax. It is made by BD-power.

http://www.dieselplace.com/forum/showthread.php?t=18085&highlight=bov

A blow-off valve or bypass valve is of no use on a Diesel because they do not use a throttle plate like a gasoline engine. In fact, there would be no vacuum source for the BOV to function properly.

Why does a BOV need a vacuum source?:confused: A BOV does not use a vacuum source it simply uses a spring that pops open when the boost spikes allowing the excess air to whissssssssshhhhhh out. A bypass valve needs vacuum.

That would be a pop off valve. BOVs and CBVs need vacuum to open to vent excess boost when the throttle plate closes. A pop off valve, however, opens at a preset level of boost (determined by spring stiffness) to prevent an over boost situation...

I should've explained a little better - a MAFS car would go rich at shift/idle when using a BOV (which is why a bypass valve would be used). This wouldn't apply to your car since your car does not have a BOV (or vented bypass valve for that matter). Compressor surge does, however, eventually lead to turbo damage. Quote directly from Garrett's site:

The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it. - http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html

I do agree, however, that surge is minimal on auto cars since you don't lift between shifts - this is probably why GM doesn't use a bypass valve on their vehicles (most are auto applications).

Again, no offense intended - just want to clarify...:D

My first question is why would my GN run rich at shift/idle when using a BOV? :confused: At idle the BOV is closed so how would that make my car run rich? At shifts it would still not open because you never take you foot off the gas when you are running down the track. There are some GN guys who are using BOV they say it protects the turbo from the surge (we all know it is for the noise);) . I got 120,000 miles of my turbo without a BOV that's no bad. My car came stock with a Garrett turbo and they didn't put one on to save GM the extra money (cost vs. benefits) each car. So if my car had a BOV the turbo would have lasted me till 125,000 miles WOW 5,000 more miles, for 700 bucks I'll just get a new bigger turbo. IM sure Garrett would say that, now they can sell you another item. The main purpose of a BOV is to keep the turbo spooled in-between shifts on a manual transmission when the driver takes his foot off the gas to shift gears:D . I am only talking about cars/trucks with wastgates on them.

Yes There is a BOV for the Duramax. It is made by BD-power.

http://www.dieselplace.com/forum/showthread.php?t=18085&highlight=bov

Well what do you know!

My first question is why would my GN run rich at shift/idle when using a BOV? :confused: At idle the BOV is closed so how would that make my car run rich? At shifts it would still not open because you never take you foot off the gas when you are running down the track. There are some GN guys who are using BOV they say it protects the turbo from the surge (we all know it is for the noise);) . I got 120,000 miles of my turbo without a BOV that's no bad. My car came stock with a Garrett turbo and they didn't put one on to save GM the extra money (cost vs. benefits) each car. So if my car had a BOV the turbo would have lasted me till 125,000 miles WOW 5,000 more miles, for 700 bucks I'll just get a new bigger turbo. IM sure Garrett would say that, now they can sell you another item. The main purpose of a BOV is to keep the turbo spooled in-between shifts on a manual transmission when the driver takes his foot off the gas to shift gears:D . I am only talking about cars/trucks with wastgates on them.

My Twin Turbo Z came stock with recirculation valves (and the car is an auto). I switched to BOV's because the stock re-circs are only good for 20 PSI in most instances. The only time I had a problem with my car running rich/stalling was when I lifted abruptly off the gas (say in a burn out situation or a quick burst of speed followed by lifting). The car would run rich and possibly stall due to the fact that the MAF had already metered the air that the turbo had compressed, so when I lifted off the gas and shut the throttle bodies all the air got blown off while the Maf had already told the injectors how much fuel to add for that metered air, thus a rich condition. The BOV aids in keeping the turbo spooled but it doesn't keep it totally spooled. Even on helicopters (I fly them for a living) we have what is called a bleed band to prevent compressor surge. Although your turbo lasted 120,000 miles without a BOV it is in an Auto, which means your turbo wouldn't experience a surge at every shift. They (BOVs) are definitely more important on Manual tranny vehicles.

There are some GN guys who are using BOV they say it protects the turbo from the surge (we all know it is for the noise);) . . . .The main purpose of a BOV is to keep the turbo spooled in-between shifts on a manual transmission when the driver takes his foot off the gas to shift gears:D . I am only talking about cars/trucks with wastgates on them.

I run two of the older HKS racing units on my gasoline setup. Partially to prevent compressor surge upon closing the throttle at the end of a 1/4-mile run, but mainly to prevent the possibility of damaging my water-to-air intercooler or blowing it competely off the carburetor. I also installed a burst panel off a fuel car "just in case".;)

http://www.hangar18fabrication.com/misc_images/DSC00902.JPG

Nice setup:cool2: ):h

This is the desired effect i'm going for! http://www.crankitupdiesel.com/Matt_LondonST.WMV

Thanks crank it up!

There are some GN guys who are using BOV they say it protects the turbo from the surge (we all know it is for the noise)*. I got 120,000 miles of (out of) my turbo without a BOV that's no (you mean not bad, right?) bad. My car came stock with a Garrett turbo and they didn't put one on to save GM the extra money (cost vs. benefits) each car. The main purpose of a BOV is to keep the turbo spooled in-between shifts on a manual transmission when the driver takes his foot off the gas to shift gears**.

*- no, imports use it for the noise, darn rice rockets, domestics use it for safety.

**- and the BOV just releases the pressure in the intake track for 1) to not destroy the TB, 2) not trap the built-up pressure from blowing out of the turbo's compressor side.

What you are hearing is turbo bark in thos vids. You DONT WANT THAT SOUND!!!! If you want it put some sorta fueling box on your truck get swinging som high boost and lift your foot off the throttle as quick as possible. That whoop whoop whoop sound is your compressor going from thousands of RPM to nothing in a spit second. Take something and spin it at 20k rpm and stop it instantly. Sound like something you want to do??? Not I. If you lift slowly or roll outa the gass you shouldnt get it. Burnouts and truck pulling is very hard not to though.

*- no, imports use it for the noise, darn rice rockets, domestics use it for safety.
Not for the noise here - all about performance baby! :D

http://members.cox.net/nsracingsr20/SE-R/IM000241.JPG

Looks good, for a sentra! LOL

200SX - get it right! j/k lol! It's not too shaby - 325 whp in a 2750 lbs daily beater can be fun ;)

Not for the noise here - all about performance baby! :D

http://members.cox.net/nsracingsr20/SE-R/IM000241.JPG

:offtopic:

Looks like you're missing 4 cylinders and another turbo ;) :

http://www.hangar18fabrication.com/images/DSC01500_640x480.jpg

What you are hearing is turbo bark in thos vids. You DONT WANT THAT SOUND!!!! If you want it put some sorta fueling box on your truck get swinging som high boost and lift your foot off the throttle as quick as possible. That whoop whoop whoop sound is your compressor going from thousands of RPM to nothing in a spit second. Take something and spin it at 20k rpm and stop it instantly. Sound like something you want to do??? Not I. If you lift slowly or roll outa the gass you shouldnt get it. Burnouts and truck pulling is very hard not to though.

20K is a lot on the low side don't ya think. I thought most spin around 100+K RPMs

20K is a lot on the low side don't ya think. I thought most spin around 100+K RPMs

:iamwithst Note the RPM on this TO4B H3 compressor map:

http://64.225.76.178/catalog/compmaps/Fig8.gif

:offtopic:

Looks like you're missing 4 cylinders and another turbo ;) :


lol! Well, yea, but I drive this car about 500 miles a week - I need something a bit more "tame" than a TTSBC :D I'm with ya, though...

Very nice setup, BTW....

Anyway, back on topic.... BOVs..............:grd:

http://www.fast-diesel.com/duramax/turboguard.html

...

This is the desired effect i'm going for! http://www.crankitupdiesel.com/Matt_LondonST.WMV

Thanks crank it up!

is it mostly the load that hes smoken like that... i know it aint stock but still