93beater

ok im just wondering do our trucks have boost blow by's?
ok i know im dumb just curious??

BC847

If you mean Blow-off valve, no.





Dumb questions are easier to fix than dumb mistakes. Ask away.

93beater

hah thanks man, ya thats what i meant, so is there a need for one of is it just not needed?

BC847

As I understand things, the typical single turbo rig you may read about here doesn't, but apparently when one starts pushing the limit with radical twins and such, . . . .perhaps. May help control turbo-bark in those applications.

I get the impression thorough system design makes them redundant.


I'm sure the better informed will speak up shortly.

BearKiller

I will relate an adventure that I once had with a turbo safety plug.

I was cruising along in the snow, somewhere in Iowa, with a gooseneck cattle trailer in tow.

At that time, my truck still had the 6.9 Navistar, with an aftermarket Hypermax turbo.

Just cruising along, minding my own business, and WHAM!!!!!, something explodes under the hood.

Other than me filling my drawers, everything seemed to be in order, except I noticed somewhat less power and no boost on the gauge.

A rubber freeze-plug kind of thingie had blown out of the intake hat, not from high boost, but from old age.

It sure got my attention.

johnny5.9

Blow off valves are typically used in gasoline engine applications. This is because gas engines have throttle valves that close shut and cut off the engines air supply in order to lower rpm. When running at boost if you suddenly close the throttle the boost has nowhere to go. To prevent this boost from backing up in the intake tract and surging in the compressor a spring loaded valve is used to bleed off this pressure. This valve is how guys can crank up boost by adjusting the spring tension. Since diesels have no throttle the boost still can make it's way into the engine, granted, at a much lower rate when you let off the pedal. This scenario can still cause compressor surge (usually heard real bad in 6.0 l ps and duramaxes) but not usually to the same catastrophic result as with a gas engine. The waste gate in employed to minimize this in diesels. Instead of bleeding off manifold pressure the wastegate is vacuum controlled and causes a bypass valve in the exhaust turbine to open rerouting spent exhaust gas around the turbine thereby allowing the turbocharger to slow down very rapidly in response to the suddenly lowered rpm.