Does anyone run an aftermarket blow off valve. I was asking becasue with the 6637 mod and 4" exhaust it sounds like the turbo blows to the atmosphere as it is. Also sometimes when getting on it and it shifts it has a constant air blow off(No reduction in perforance or lag). Just wondering if an aftermarket BOV with a stiffer spring would help this.

If you do have one:

post pictures.
place you put it
Brand
Video of sound and function if you have one.

 

What you hear is the pressure from the turbo blowing back through the 6637. It has always done this, just you hear it with the open air filter. The boost has to go some where once the trans shifts and the RPMs go down. This is normal, and nothing you can put on the stock turbo will stop this. I had this all the time with my stock turbo, I don't hear this anymore.

If you are talking about your wast gate. I wouldn't think it is open all the time.

 

You only need a blow off valve if the engine has a throttle body.
Since a diesel doesn't have such a thing, you don't need a BOV.

 

Like the others have said, no BOV is necessary because our engines don't have throttle bodies. BOV's are designed to protect the turbo against pressure spikes when you let off the pedal and close the throttle body butterfly valve. Since we dont' have anything that closes off the intake, we don't get those pressure spikes that gas engines do. As an experiment, mash the pedal to the floor on your truck, get up to full boost and then let off the pedal. Your turbo will make a noise, but if you watch your boost gauge, you'll only get a very very tiny spike in boost before it falls. A BOV would be pretty much non-functional in that situation, and would have to be triggered electronically by the accelerator pedal. Even if you managed to wire it up that way, it's still not going to do any good.

Those noises that you are hearing now have always been there. The stock airbox muffles the noises that the turbo makes. Only if you know what to listen for and when to listen for it, you can faintly pick up some of those sounds even with a stock airbox. Now that you've opened up the intake, you don't have anything to muffle the noises that the turbo is making.

Those noises are specific to that turbo. If you bolt on a different brand/model turbo, the sounds that you hear during operation will be completely different. The noises produced is a long list of combined parts such as compressor housing size, turbine housing size, wheel trim (inducer and exducer size), type of bearings used (journal vs ball bearing), etc. All of these effect the turbo shaft speed, the choke line, give the turbo a specific compressor map, surge line, and more. This is why turbo's spool up differently, produce different amounts of airflow, and why they all sound different.

Last, the type of air intake you use will determine how much noise actually reaches the cab. With a closed off box intake such as the stock one, it's going to muffle nearly all the turbo noise. With something completely open such as the 6637, you're going to hear everything. With an intake that has a shield around it (such as the AFE Stage II), you'll get some turbo noise, but perhaps not all of it.

As an example, the other week I was data logging another truck running the same 38R turbo as mine, except I have an AFE Stage II and he was running a 6637. His turbo noises were much louder from his truck than what I hear on mine. Not only did he have the same high pitched whistle from the turbo, but there was also a secondary "vacuum cleaner" sound that I don't hear from my truck. So intake setups do play a role in how much sound reaches the cab. Personally, I like to only hear the whistle, and not the vacuum cleaner noise. Others have different preferences on the amount of noise they tolerate.

 

yea i know the sound is the pressure let off. I was just wondering if you could run a blow off valve. Since its atmospheric anyway. Just for the sound change. I see what your saying with the throttle body.

I am curious as to why a diesel does not need a throttle body cause even my other turbo cars had throttle bodies. I know the turbo is not the reason. So what is the reason that a diesel does not have a throttle body like gas engines.

 

The diesel engine design doesn't have to have a perfect fuel air ratio for it to run properly.
The amount of power generated is controlled by how much fuel is injected each time.

 

Because diesels do not constantly run at the stoichiometric 14.7:1 air/fuel ratio like a gas engine does. A diesel typically runs leaner than a gas engine, but can also run richer too. All of this depends on engine load, fueling, amount of air, RPM's, altitude, temperature, etc. You can even manage to get some diesels to run as lean as a 50:1 air/fuel ratio (although our Powerstrokes don't really reach that point).

Also remember that diesels are compression ignition, not spark ignition. These engines run much higher compression ratios than gas engines, and take in much larger quantities of air than gassers. So there is no need to regulate the airflow in a diesel like you have to do with a gas engine. Generally, if you add more air, you get more power and less smoke. Of course, that's just a generalization of diesels, however there's much more to it and it get's complicated when you start playing around with air, timing, fueling amounts, injection pressure, and RPM's.

 

yea i know about the compression and all but i didnt know it could fluctuate that much without a negative affect. Thats pretty cool.

 

Easy way to visualize it is that with just an open tube between the turbo & valves (essentially), the air will go through the valves as they open & close whether there's fuel in there to burn with it or not. That's why the fuel/air ratio is always changing. Since the path for the air is always there to go through the engine, you don't need a BOV. But the pressure of the intake does go up & down, which bleeds back out the way it came *and* through the engine. It's just that when boost pressure is high, it's easier for it to come back out the way it came (path of least resistance) when the turbo spools back down. No harm in that.

 

YouTube - 50mm Blow Off Valve.... On a 04 Duramax Diesel LB7

A doodoomax, but they do sound cool!!!!

 

They sound cool, in a fast and furious movie!

 

DWEEEEB!!!

 

Haha guess I'm alone here then lol