Any possible way to rig a blowoff valve on an idi?

[jaluhn83]

There is no right way - a blow off valve is utterly and completely useless on a diesel.

On a gasser it vents to high pressure side of the turbo when you snap the throttle closed. The turbo and air moving through it has enough ineria that you otherwise get a pressure spike and cause compression damage / surging. The BOV unloads the compressor and prevent this as well as keeping the turbo rpm up a bit.

On a diesel you have no throttle so you'll never have this issue.

I'm making 18-20 psi of boost. Probably could get more if I messed with the wastegate, but I'm perfectly happy with that. I'm running a full moose pump. The combo seems to work well - no smoke issues to speak of and egts stay reasonably cool.

 

[79jasper]

Also could cause the turbo to over spin.

 

[S-west]

Well I'll take my chances with a bov, h1c are cheap. And with no wastegate and a junior moose I'm guessing I'll be around 20 then. Maybe a little less but I don't really care if I have high boost numbers or not

 

['94IDITurbo7.3]

There is no right way - a blow off valve is utterly and completely useless on a diesel.

On a diesel you have no throttle so you'll never have this issue.

I am sorry but you could not be farther from the truth with this.

 

[jaluhn83]

Please explain then.

 

[Hyde]

Mine is an external wastegate.

Just ran a quick thought for your BOV, run a normally closed say 1psi boost switch to control an inline valve on your vacuum source to the BOV. That way when you are on boost the valve will be closed, as soon as you hit 0psi the switch will close opening the valve and allowing the BOV to see vacuum. Just a quick thought not sure how well it would work.

 

[S-west]

That may work, but I thought the bov has to open while there is boost pressure, otherwise it's not doing much. I think the point of a bov on a diesel is to relieve the pressure when you aren't using it, to prevent problems with the turbo and so forth. Plus if the valve is switched open at 0 psi, it would prevent you from being able to build boost again. Or I'm just misunderstanding what your saying haha

 

[Hyde]

Better idea, micro switch that trips when the throttle returns to idle, also the BOV being open shouldn't cause it to not build boost, they have a very light spring that is supposed to open at the slightest amount of vacuum. Any boost should force it closed.

 

['94IDITurbo7.3]

Regardless if you have a throttle plate in there, if you are jamming a crap-ton of air into the engine and then all of a sudden it doesn't need all that air, the air has to go somewhere....w/o a BOV the air that wants to/needs to escape has to go back through the turbo, that will make the turbo actually start to spin or attempt to make it spin backwards(EXCELLENT way to break turbine shafts), even if the shaft doesn't break it is still extremely ******* the turbo internals. You put a BOV between the turbo and the intake mani....now you are deep in boost, let out of the throttle all the way, with the BOV properly tuned, the BOV now becomes the path of least resistance so the air charge can escape out the BOV rather than going back out the turbo.

Is a BOV absolutely mandatory on a diesel like on a gasser? Most defiantly not! Is it completely and utterly a waste of time on a turbo diesel? Not at all in my opinion if you are running a decent amount of boost.

 

[jaluhn83]

How's it not going to need a ton of air? Air flow through the diesel is a simple function of rpm - unless you're planning to instantly go from 2500 rpm to idle there's no sudden change in airflow. There's not *that* much inertia to the air or turbo and these engines do not change rpm that quickly.

You may see a slight increase in boost pressure but nothing comparable to what happens when you effectively instantly block the air flow into the engine as happens on a gasser.

I note that many early gasser engines had no BOV, and likewise to the best of my knowledge **no** turbo diesel uses one.

 

[79jasper]

What Eric speaks of is called turbo bark/flutter.
It's a big problem with the SD psds.

Just to give some idea, this is a duramax with a bov. No bark, just the bov. https://www.youtube.com/watch?v=qWFhno0lfVQ&feature=youtube_gdata_player

 

[kc0stp]

I know our old POS tow truck (and only tow truck) at work has turbo bark like mad when shifting but Ive never seen any proof turbo bark causes damage, but the big question on the damage side isn't if but how soon? 100k? 50K? turbos no matter what eventually will need a rebuild, how much if any is it accelerated by no BOV/turbo bark?