bov's

i was just driving on the freeway beside a big rig and heard something that sounded like a bov. that got me thinking, is there any real point to one, there's no throttle body closing to create turbo stall and unless the extra boost (from flowing a bunch more cfm at low rpm) creates exhaust thats too hot, i see no point to it.

i don't know of many(if any) diesel trucks that use BOV, hosistly those engines are so heavy duty and strong, its not very easy to blow up the intake manifold anyway. they may use a wastegate, but if so its more likely to be used to limit power output and control emissions and gas useage. i bet what you heard where the brakes or a air shifter.

I don't know of any that use a BOV stock but some people that are pushing way over the stock boost will use them every now and again. But the kits are very expensive ($600-$700). Sierra is right about the wastegate too.

but i don't really see the point to a bov, if some of them use it is it because the extra boost at low rpms will cause an increase in exhaust temps?

thanks for the help, it probably was the shifter because he wasn't braking.

In diesels since there is no throttle, there is no need for a BOV. It could be used as a boost control device, but typically its a waste to make boost and then later bleed it off. That way you would get increased EGTs and exhaust restriction. Instead a wastegate is a wiser control device. It lowers EGT and restriction and still controls boost.

A BOV on a diesel would be an mistake. No help, and it comes with drawbacks.

but let's say you had a diesel that had egt's that were on the verge of melting the turbine at maximum boost. when you shift and your rpm's fall, the turbo would still be providing the same ammount of air flow, that would raise boost, increase egt's and melt your turbine right? that's the only viable place for a bov that i can think of.

Not really. Some diesels don't have wastegates. Their max boost is regulated by turbine housing alone. In engines like my 95 Powerstroke, there was no wastegate and it provided about 17 psi. If you chipped it and gave it more fuel, the boost rises.

So, in general, if you're close to cooking your turbine, fix the EGT problem. Lowering or controlling boost won't solve it.

when you take your foot off the pedal, the fuel stops. So when you shift you're actually cooling the turbine for a second.

oh ok, thanks. so there is absolutely no reason for a bov on a diesel.

Right. There may be a small variation in EGTs over the RPM range, but not significant. When your foot is to the floor you are telling the the injector pump (or computer) to squirt X amount of grams of fuel per stroke, so your foot to the floor at 1000 RPMs shouldn't make any more EGT than foot to the floor at 3000 RPM. It would still be getting X grams per stroke, just more or less frequently.

oh i don't think you understand what im trying to say, i was saying that the turbo would produce more boost right after a shift because it would be providing the same ammount of flow as when the engine was reving high but the drop in rpms would make that flow make more boost. that's what i was saying would raise the exhaust temps.

OOOOHhh. I see. Its more or less self-sustaining. When the tranny shifts up, the amount of air and fuel decreases because the injectors fire less frequently and its drawing in fresh air less frequently. So, the net amount of gasses that get pushed out the exhaust is the same, but slower and the pulses are less frequent. The net result is that the compressor speed drops keeping boost about the same.

Sorry bout that :)

oh ok thanks, that explains alot.

There are a few throttled diesels around. The general consensus is they did it to reduce NOx emissions on engines with high static compression.

But putting a BOV on them would only serve to scare the ricers.

There are a few throttled diesels around. The general consensus is they did it to reduce NOx emissions on engines with high static compression.

But putting a BOV on them would only serve to scare the ricers.

I'd like to see a dsl with a throttle (plate)

i was just driving on the freeway beside a big rig and heard something that sounded like a bov. that got me thinking, is there any real point to one, there's no throttle body closing to create turbo stall and unless the extra boost (from flowing a bunch more cfm at low rpm) creates exhaust thats too hot, i see no point to it.

I assume you have heard a engine retarder (jake brake) when slowing down.

Some drivers will hit the brake momentarily during shift by accident or on purpose, also there are some exhaust brakes (butterfly in exhaust pipe) then same thing can be hit momentarily and some will sound like a pressure build up of air or air leaking out, it is exhaust passing thru a small opening and sounds nothing like the popular jake brakes. Air compressor kicking off , air dryer exhausting, air controlled engine fan, ect.

I'd like to see a dsl with a throttle (plate)
Toyota 1KZ TE is a fine example and in current production

There have been many others throughout recent history.
Mercedes
Isuzu
Etc.

Are you sure it is not used for engine shut-down only?

Like a dsl pulling tractor? (emergency shut down)

Are you sure it is not used for engine shut-down only?

Like a dsl pulling tractor? (emergency shut down)

Very sure, I know two people who own vehicles with such engines. They control engine airflow according to pedal position just like a petrol engines throttle.

I didn't believe it the first time I heard about it either, as every diesel engine I'd seen and worked on to that point was unthrottled.

No kidding, that's crazy. I searched for that engine you listed and it did describe a "engine shut off butterfly" but I'll take your word for it. Still think it is pretty wierd,,

I once throttled engine with exhaust butterfly, but was a gas engine with carb wide open all the time,, crazy.

I once throttled engine with exhaust butterfly, but was a gas engine with carb wide open all the time,, crazy.

That's an interesting version of EGR.:grinyes: