Engine/Transmission (1998.5 - 2002) Blow off valve

[FFSchooley]

Anyone out there know if anyone makes a blowoff valve for our trucks? I know you can get them for other vehicles, but havn't found any for our trucks. I constantly "bark" my turbo and sooner or later am going to break the damn thing. Any info on this would be greatly appreciated.

Brett Schooley

 

[Alan Reagan]

To my knowledge, there is not an off the shelf setup to do this. I looked into it quite extensively for several months and went as far as designing a system to do this but the parts are very expensive. The reason they are so expensive is because of the temperature extremes (going from zero boost to 40 lbs on a hot summer day) as well as the sealing properties required, the valve material, number of cycles desired (longevity), switching time, recovery time (closing back under throttle) and a few other odds and ends.



Other types are available for gassers because they operate off vacuum. We don't have that luxury.



Our system will have to operate on differential pressure between the output of the turbo and the intake plenum. When the intake pressure exceeds the output of the turbo by some constant (maybe 6 psi), the blow off is triggered. Why so much problem finding valves. Find one that goes 0-40 (or higher) psi, electrically driven solenoid relief valve that will close in micro seconds after loosing signal so you retain boost after quick lift situation. Also, the valve will have to operate in ambient from let's say 0*F to 250*F (winter/summer with no boost to full boost).



This can be done. The parts are just expensive. Oh, yeah..... don't forget to calculate the bleed off through a 1/8, 1/4 and 1/2 NPT so you'll know if you are getting rid of the air fast enough at high pressures.



Finally, don't try to do this by connecting a microswitch to the accelerator peday and triggering the relief valve when you let off or you'll bleed pressure every time you coast. That will stop the barking, but you'll be constantly trying to spool the turbo back up after you do this.



Adjustable differential trigger points is the right way to do this little job, especially if you are racing.

 

[willyslover]

FF... Pm your phone # to me ... one day next week maybe we can meet for a cup of coffee or a beer. .

I'm just east of ya

Gary

 

[Diesel Freak]

It should not be that hard to do... . all you would need is a Normally open pressure switch set for 15 PSI (boost) and a tie in to the TPS (or a micro switch on the throttle is series with the pressure switch) to operate a small three way valve to either direct boost pressue or Vacuum (from the factory vacuum pump) to operate the BOV.



it's actually quite simple.



or you could just refrain from suddenly lifting off the throttle at high boost.

 

[Alan Reagan]

Diesel Freak, It sounds like the NO switch would close at 15 PSI and then depend on lifting to trigger the blow off. It would work, but would have limited application. The differential pressure is what is causing the bark problem. If you aren't triggering off the differential pressure, then you would always blow off at every lift above 15 PSI if I understand your solution. That will probably stop the bark but my point is that if you are racing, hitting 30-40 psi boost, you don't want to suddendly bleed off pressure to 15 or whatever PSI every time you shift. I would think you would want to maintain as much boost pressure as possible in the system during a shift. You just don't want the intake pressure to exceed the output pressure of the turbo. So bleed off from a differential measured system would be short duration equalizers and not relief valves.



Also, you have to consider that if you tie into the TPS voltage, you are essentially putting another circuit of minimal resistance (assuming you are operating a switch or solenoid) in parallel to the TPS circuit. This in turn could change the resistance causing the voltage drop/measurement to be different than it was prior to the installation.



Just some thoughts.



Anyway, however you do it, what I found that getting the quality valves and pressure switches is not a trivial or cheap thing. Also, if you try either solution, you should go after adjustable set point pressure switches so you are not locked into a system you can't fine tune.

 

[Diesel Freak]

very true. . I have thought about all of that.



I understand tieing into the TPS is not a good idea... a micro switch in the throttle is a better idea. The 15 psi NO switch is just a starting point.



We could eliminate the whole thing if we could use a differential pressure sender with a LVDT... but the truck does not have an AC system. Also the exhaust pulses from the manifold would kill any bellows actuated piece of equipment in a very short time.

 

[Diesel Freak]

Temperature may not be a huge problem since the gas would be dead headed at the switch. All you would have top do is have a long enough line leingth to allow the exhaust gas to cool before the switch... . 3 feet of copper tubing would be more than sufficient.

 

[Diesel Freak]

http://www.whitmancontrols.com/catalog/viewdiffswitch.php3?partkey=895209188

 

[Diesel Freak]

The rest would be simple pneumatics. . a three way solenoid valve with the output directed on the BOV actuator.



The turbonetics Godzilla BOV with discharge horn (HONK) $466



A usefull and setable differential pressure switch $200



Three way non pilot actuated solenoid valve... no clue yet on price.

 

[Alan Reagan]

The switch looks good. I don't know if your price is accurate or not but it's not out of line with what I looked at last year for a good differential switch. There is no big mystery here on how to do this. It was just very expensive to find the right parts and last year, some of the right parts were not available off the shelf yet.



I sent Whitman a few questions concerning pressure and reaction time of the switch.

 

[Diesel Freak]

Time is a factor... I would like the whole system to actuate in less than 5ms... . a little optomistic, but I think with over 30 psi of boost helping things move it may work.

 

[kaffine krazed]

How about putting a one way check valve after the turbo?

 

[Alan Reagan]

I don't think you could find one with the right flange/fittings or proper pressure and you would have a fixed low set point for bleed off. It would also bleed off air on slow/slight throttle lifts that normally aren't a problem where backspin is concerned.

 

[FFSchooley]

Just to make sure I understand correctly, the idea of what you guys are saying is to have a sensor that detects the pressure difference between the intake and exhaust sides that will activate a solinoid opening the blowoff valve?

 

[Alan Reagan]

You are correct FF. Detect the difference and at a preset level provide an electrical signal to open the blow off valve.

 

[rrivelli]

Blow-off Valve

What are the "big trucks" doing to control barking? Do any of them use a blow-off valve? Or are they not producing enough boost to have a problem?

 

[Alan Reagan]

They don't normally operate at the boosts we have been discussing and they don't do sudden lifts off the throttle.

 

[rrivelli]

I'm a bit confused about what's being referred to as "sudden lift". If a tractor/trailer is pulling its load up a hill, doesn't the driver shift at max rpm, therefore max boost ?(although I believe you are correct, much lower rpm/boost than we're talking about). And if so, doesn't the driver "suddenly lift" his foot off the accelerator when shifting?



I'm having my 2001 2500 std cab 6spd 4x4 bombed in a few days, and trying to prepare myself for how to drive this thing without huffing the turbo, or breaking any other parts for that matter.....

 

[Alan Reagan]

Back when I drove the big trucks, I shifted without the clutch and that meant a gentle lift, not sudden. Even with the clutch, it is not an attempted speed shift but a rhythmic shift to allow the engine transmission syncronization to avoid grinding. In some cases, even double clutch action is necessary. Sudden lift would be like your foot slipping off the accelerator at WOT. With a tractor trailer, you would ease off, always having some resistance/pressure on the accelerator pedal. Otherwise, you would be picking up clutch springs off the pavement.