Maybe I'm missing something here but I just don't see the benefit of one on a diesel engine. Y'all more intelligent ones chime in on this.

Here's the thread of topic:

http://www.dieselplace.com/forum/showthread.php?t=182441

My posts start near the bottom of pg1

[Edited on September 18, 2007 at 10:32 PM. Reason : -]

9/18/2007 10:29:52 PM

only needed on very high cfm/psi setups, and even then it's mostly a precaution, not a requirement. even though they don't have throttle plates, stepping out of that much fuel and boost quickly can cause enough of a disturbance in the airflow to tear up the internals of the turbo.

think of it this way... the only way you're getting that much pressure through the motor is by force. when you stop that force, the inherent restrictions of the pistons, valves, exhaust, etc. is going to push back. not nearly like a closed throttle plate will, but you're also talking about flow and boost WELL in excess of gas motors.

[Edited on September 18, 2007 at 10:37 PM. Reason : oh, and the OP there is obviously a ricer and doesn't have any practical need for one...]

9/18/2007 10:36:15 PM

I like the term "barking"

9/18/2007 10:40:34 PM

^^yeah, i did change my last post to this:

Quote :

"On second thought, the only time I could see a BOV being beneficial on a diesel is when the engine is coupled to a manual transmission since the engine's RPMs would drop rapidly between shifts. Sorry, I'm thinking about a BOV on an automatic tranny diesel."

but on an auto tranny i cant find any reason at all to have one.

and yeah, i think you're right about that guy being a ricer. what a shame. now ricer's have found there way into real power.

errrrrr, wait. i was a ricer once.

haha

Quote :

"think of it this way... the only way you're getting that much pressure through the motor is by force. when you stop that force, the inherent restrictions of the pistons, valves, exhaust, etc. is going to push back."

i see what you're saying. that does make sense. but you're right, you gotta be making some serious boost to have that effect.



[Edited on September 18, 2007 at 10:45 PM. Reason : -]

9/18/2007 10:41:23 PM

I know this is a bit off topic, but I would like clarification on the new LMM motor. Is the throttle mentioned below exactly like that of any gas vehicle, or is it of some different, new design?



Intake Throttle Added
Another emissions addition to the Duramax is an electronically controlled intake throttle upstream from the turbocharger. While the engine is idling or the truck is traveling at low speeds with no load, the engine computer will limit the amount of air allowed to enter the engine to intensify the load. This will increase the temperature of the exhaust, which helps maximize the performance of the passive catalytic converter and the diesel particulate filter.

9/18/2007 10:47:29 PM

For some reason 2 of my friends both wanted a wrx and proceeded to ask me "do they have blow off valves" as if that was the most important feature to consider when buying a car. One then asked if I have one on my stock non turbo car. WTF

9/18/2007 10:52:16 PM

^^No, it's a throttle plate just used differently. This plate reduces the volume of air yet increases the pressure of the air (think of a garden hose with and without a nozzle. without a nozzle, you'll get a higher gpm of water due to less friction loss. with a nozzle, you'll get higher pressure due to the discharge orifice of the nozzle but less gpm.) causing the turbo to spin faster which generates more heat in the exhaust which in turn reduces emissions. You can really hear the effects of this on new "big rigs". The turbo sounds like it's screaming while sitting at idle.





[Edited on September 18, 2007 at 10:59 PM. Reason : -]

9/18/2007 10:53:02 PM

hmm not a technical as BBR but i thought blow off valves were to vent boost at a shift so u didnt ram psi in on engine deceleration. i thought it was more to protect the rotating assembly than the turbo but u make a good point. i just assumed diesels didnt have then because of the low rpms/high comp. ratios they usually operate at and they way theyre built. 5.9 cummins parts are gonna be a tad tougher than ur 2.0 ricer. do larger commercial diesels have them?

9/19/2007 1:26:41 AM

since a diesel lacks any gas style fuel/air metering devices, building up too much pressure in between shifts or a rapid lift off the throttle isn't really an issue until you're running BIG numbers.

many diesels (stock and highly modified) are adequately boost controlled by wastegates and fuel input.

the wastegates can mimic a BOV sometimes since they work from pressure in the manifold. when you let out of one pushing a lot of cfm/psi, it's going to cause a spike in the manifold pressure (remember, no throttle plates and you've got a drop in turbine pressure). sometimes that will exceed the wastegate actuator setting, and you'll hear it bleed by some. my powerstroke will do this pretty often of you fully spool it/let out under load.

9/19/2007 2:40:34 AM

The richer overall mixture helps increase the EGT's at idle the most with that upstream throttle on the newest duramax. Same fuel, less air = richer, which burns hotter.

9/19/2007 9:25:14 PM