Blow Off Valve

[HillCountrykid]

Do I get a prize for having the correct answer?



Brian

 

[A Johnson]

I was working on a C series in a marine application once doing sea trials. I believe this was a 420 hp engine. We had the captain cut the throttle for some reason and I could see the turbo actually momentarily stop. You could also here the distinct "bark". This was quite a revelation as to the stresses the shaft goes thru.



I dont know anything about blow off valves and have no input on the subject. All I know is the turbo is under some mighty impressive stress at times.

 

[GDouglas]

On turbo gas engines at the dragstrip, we use a bypass valve around the compressor that is controlled by manifold vacuum. Under positive manifold pressure, the valve remains shut and when the throttle is lifted (throttle plate mostly shut) there is then a vacuum in the manifold that opens the bypass valve and therefore connects the discharge of the compressor back to the inlet side to give the excess boost somewhere to go so that the turbo isn't stalled or reversed. However, on our diesels there is virtually no vacuum signal in the manifold that we could use to operate such a valve.



Possibly we could rig some sort of valve controlled by our throttle linkage with our external vacuum pump as a vacuum source to operate such a bypass valve around our turbos.



I am curious to find out what you guys think about this idea.

 

[SmokinJoe]

Originally posted by GDouglas

On turbo gas engines at the dragstrip, we use a bypass valve around the compressor that is controlled by manifold vacuum. Under positive manifold pressure, the valve remains shut and when the throttle is lifted (throttle plate mostly shut) there is then a vacuum in the manifold that opens the bypass valve and therefore connects the discharge of the compressor back to the inlet side to give the excess boost somewhere to go so that the turbo isn't stalled or reversed.

I wonder when someone will address this issue? Even with stock trucks shifting gears with the manual transmission causes the Turbo to try to stop...

 

[Diesel Freak]

Originally posted by GDouglas

Possibly we could rig some sort of valve controlled by our throttle linkage with our external vacuum pump as a vacuum source to operate such a bypass valve around our turbos.



I am curious to find out what you guys think about this idea.

My thoughts exactly, but I need to fine a three way two position non pilot oprated 12volt solenoid valve.

 

[docdyno]

Sounds like a great idea. Early apologies as I too am not very turbo knowledgable. BUT- I work in engineering development and we make engine control systems and control components. It would be very easy to very accurately detect the condition you are describing during deceleration with an inexpensive sensor. We could then build a simple control algorithm (computer formula) to control a servo to open or PWM (pulse width modulate) the valve (Open and close it from our sensor input data) Now before you think I have gone off the deep end and excessively complicated this idea- It really isn't that difficult or expensive to do. The most expensive part is the engineering development- and for interesting "development" projects- The engineering could be real cheap! Anybody have any interest? If so, lets talk about control parameters. I can do the control part- What about the valve hardware?

 

[The patriot]

I think you guys are making this way harder than it has to be.

My last car before the truck was a Buick Grand National. The guys that ran these had blowoff valves, but all they were was a header flange welded to the side of the intercooler. On that went a cap, and some long bolts with springs on them. Viola!! Blowoff valve.

Very low tech (sorry not to wow you engineering types ) but it always works, and it's adjustable.

Eric

 

[Mark_Kendrick]

We are looking for a valve to be actuated at will not only by pressure.

 

[Diesel Freak]

Originally posted by The patriot

I think you guys are making this way harder than it has to be.

My last car before the truck was a Buick Grand National. The guys that ran these had blowoff valves, but all they were was a header flange welded to the side of the intercooler. On that went a cap, and some long bolts with springs on them. Viola!! Blowoff valve.

Very low tech (sorry not to wow you engineering types ) but it always works, and it's adjustable.

Eric

That is a relief valve, we need a blow off valve... there is a difference.

 

[Diesel Freak]

Originally posted by docdyno

Sounds like a great idea. Early apologies as I too am not very turbo knowledgable. BUT- I work in engineering development and we make engine control systems and control components. It would be very easy to very accurately detect the condition you are describing during deceleration with an inexpensive sensor. We could then build a simple control algorithm (computer formula) to control a servo to open or PWM (pulse width modulate) the valve (Open and close it from our sensor input data) Now before you think I have gone off the deep end and excessively complicated this idea- It really isn't that difficult or expensive to do. The most expensive part is the engineering development- and for interesting "development" projects- The engineering could be real cheap! Anybody have any interest? If so, lets talk about control parameters. I can do the control part- What about the valve hardware?

the sensors already exist... you could use the MAP sensor and the TPS, but that would complicate things for the installer. the easiest way is to use a simple 'and' circuit with two inputs... to simulate the MAP sensor and TPS... basicly two switches in series to operate the solenoid valve..... this could be done with simple discrete logic, but that too is overkill..... keep is simple guys... you are getting close.

 

[Diesel Freak]

SOMETHING LIKE THIS!

 

[Deezul1]

we 12 valvers are interested too if it isnt hooked to the engine puter. Sounds like a really great concept and I hope youall can make it work.

 

[Diesel Freak]

The 12 valvers will not be left out.

 

[The patriot]

I musta really missed the boat on this one...

Originally posted by Mark_Kendrick

We are looking for a valve to be actuated at will not only by pressure.

I have to ask, why?

 

[Lsfarm]

I'll give it a try

I hope I'm not mis-interpreting Diesel Freak's intentions.



Patriot: the problem is that the turbo is only up to speed and developing boost when the 'throttle pedal' is depresed, requesting power from the engine. When the driver lets up on the pedal, either to shift or to back off the power, the exhaust pressure isn't enough to keep spinning the turbo against the pressure on the compressor [engine intake] side.



The result is the turbo losing rpm, losing boost, and probably 'Barking' which may include a lot of stress on the turbo shaft. Maybe breaking or 'huffing' the turbo.



So if I have read this thread correctly, Diesel Freak wants to come up with a controlable blow off valve [either throttle postion of electronic] that will open when the throttle is lifted, which will allow the turbo to keep spinning fast [the valve will relase some intake pressure]. Once the throttle pedal is depressed again, the valve will close, and then the boost will be there much faster since the turbo hasn't slowed down as much if any.



This should give a lot more power available to the stick shift trucks which loose so much power [boost] with every shift. And will provide some protection for the turbo's shaft.



I hope the helps, and I hope the valve works.



Diesel Freak, correct me if I'm wrong!!



Greg L

 

[Diesel Freak]

Bingo!

 

[The patriot]

That's kind of what I thought,(same reason they put em in the old GN's) but I still think the one I wrote about would be fine.

Dont like electronics much..... as evidence of me owning a 12 valver.

Eric

 

[Diesel Freak]

This can be done without any electronics.

 

[KatDiesel]

I don't have a problem with losing boost Oh wait I'm an auto... sorry forgot.

 

[Mark_Kendrick]

Originally posted by KatDiesel

I don't have a problem with losing boost Oh wait I'm an auto... sorry forgot.

smart@$$!!!



It'd also be useful in ssaving turbo bearings on autos if it was built properly.



To be able to stop barking would be very valuable for everyone.