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Hello all, I was talking with a guy tonight about turbos, intercooler, wastegates etc. Trying to hone my knowledge about them.

My question is about blow off valves, I know that gassers need to have them but what about diesels? I was under the impression that diesels did not.....

thanks in advance......Props to Andre!!!!!!!!:smile: :smile:
 

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Someone please correct me if I am wrong! Blow off valves are for running high boost/rpms and then when the throttle slaps closed all of that boost has to go some where. Such as in doing a burn out at the track and shutting it down all that boost has to go somewhere or it will gernade your plumbing. A diesel 1 does not turn high rpm and 2 never goes high rpm to low rpm instantly and most importantly there is no throttle plate to trap all that boost in the plumbing. That is my theory on the subject. I think that is also why stock turbo cars do not have blow off valves not enough boost or rpm to hurt anything I think!!
Derek
 

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I just got done "restoring" a beat up 92 plymouth laser with a DOHC and a turbocharger on it. I was not pushing it really hard but shure enough when I shifted from 1st to 2nd my pipes exploded. Well they blew apart at a connector. Let me mind you this thing is in horrible mechanical condition. The wastegate might not even open for all I know. This car does have a BOV stock.
 

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Someone please correct me if I am wrong! Blow off valves are for running high boost/rpms and then when the throttle slaps closed all of that boost has to go some where. Such as in doing a burn out at the track and shutting it down all that boost has to go somewhere or it will gernade your plumbing. A diesel 1 does not turn high rpm and 2 never goes high rpm to low rpm instantly and most importantly there is no throttle plate to trap all that boost in the plumbing. That is my theory on the subject. I think that is also why stock turbo cars do not have blow off valves not enough boost or rpm to hurt anything I think!!
Derek
You are correct.
There are a few diesels out there with throttle bodies (toyota 1KZ series is a modern engine with them) but they don't have or need a blow off valve in turbocharged form.

Many stock petrol cars have recirculating BOV's which are very quiet (silent in some cases) as they vent air back into the air filter.
Of course the ricers like the loudest, most obnoxious BOV they can find. On a petrol fitted with a mass airflow sensor you can see them go so rich they blow black smoke when they vent. The ECU still thinks the air went through the engine.
 

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blow of valve on twin turbo

Saw this setup on a 94 Dodge 2500. Two wheel drive sleeper. Fella came to my house to pick up a B 5.9L oil pan he bought from me. Said he was at Rockingham NC drag racing. Notice he had a five inch exhaust with six inch tip. I look down and commented that he had no receiver, how did he tow his drag racer. I don't, I drag race this. Well, it sounded normal when he pulled in the yard. So up pops the hood, and I am staring at twin turbos with a blow-off valve. Wanna go for a ride?
Oh yeah. I was looking out the right rear view mirror, as the six inch side exhaust laid a cloud of smoke that looked like a dog depositing in your yard. Big black long turd of smoke, then that second turbo kicked in and all that smoke was blown away. What power.
Said he bracket raced, running consistent 11:58 at 105. Camper shell with slicks in the back. And got 21.5 MPG on his way down from wisconsin.
Blow-off valve and non-wastegated turbos. Studs and girdles. With a truck that drove like stock, till he romped on the throttle.
Had to constantly convince myself for the next couple of days that this was not for me...:rolleyes:
Wayne
 

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So up pops the hood, and I am staring at twin turbos with a blow-off valve. Blow-off valve and non-wastegated turbos. Wayne
U Sure you weren't just looking at the external wastegates?
I'm not new to forced induction, just new to turbo diesels...
Just curious...

Michael
 

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Yeah blowoff valves are usually activated by a pressure difference which you would not get with a diesel. On a gasser you have the vacuum ahead of the throttle body which will pull the diaphragm open.
 
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