CRD blowoff valve?

TheBrandyMan · **Joined:** Sat Sep 06, 2014 8:40 pm **Posts:** 1

My buddy gave me a aftermarket blowoff valve and i was wondering if anybody out there has done the 2.8 CRD blowoff valve replacement? If so help would be greatly appreciated! Thanks!

geordi · **Posted:** Sat Sep 06, 2014 9:18 pm

There is no "2.8 CRD Blowoff valve replacement" because the CRD doesn't HAVE a blow off valve. It has a variable-vane turbo that controls the boost by changing the pitch of the vanes in the exhaust side.

flash7210 · **Posted:** Sat Sep 06, 2014 9:20 pm

Blow off valve?
I've never seen a turbo charged Diesel engine with a blow off valve. Most use a waste gate or in the case of the CRD, variable vanes in the turbo eliminate the need for a waste gate.

Blow off valves are for gasoline engines.

The Scott McLean · **Joined:** Tue Feb 15, 2011 9:19 pm **Posts:** 43

There is such a thing as a diesel blow off valve, but they are all computer controlled. Designed for very large diesels, that are used for racing. This provides relief from wide open throttle, full boost, to no throttle, low rpm. Because we do not have a throttle body, and our intakes are generally open, egr crap aside, there can be no pressure differential, to trigger the blow off valve. Instead, they use the map sensor, and throttle pedal position to trigger the diesel blow off valve. It was born from the racing side, where they have huge engines, and huge turbos, that do not want to slow down fast. Our little jeep does not generally need one, however I have recently seen a 250hp, ball bearing turbo build, that might. Do some searches, and research, you will come up with discussions about blow off valves. Originally jeep designed the egr system to act as a blow off type valve. Again wide open throttle, then off the gas, scenarios. I remember the discussion was popular when weeks introduced his elbow bypass of the egr system.

I purchased weeks system, and I am not too worried about my turbo. I rarely race with my jeep, and have owned many cummins, with much larger turbos then this one, with out the need for a blow off valve.

gmctd · **Posted:** Sun Sep 07, 2014 12:49 am

Correct - a BOV is necessary on gasoline engines because the throttle plate is used to control air flow thru the engine - add fuel corresponding to the air flow and you get the ~14:1 stoichiometric air\fuel mixture ideal for complete combustion - wide-open throttle plate + full fuel flow = max developed hp - increase the air flow (boost) with a turbocharger, more fuel can be added = more hp - end of run, foot off the accel pedal, throttle plate slams shut = whadaya gonna do with the 14psi boost, let it rupture the charge-air cooler hoses?

(A Diesel engine, with no throttle-plate, always pumps maximum air flow - add a small amount of fuel and it idles - add more fuel it begins to develop power - increase fuel, increase power - any excess airflow blows out the exhaust pipe)

Enter the Blow-Off Valve BOV, absolutely necessary on throttle-plate controlled performance gasoline engine systems.

The Flow Control Valve FCV on the KJ CRD engine, which is a type of throttle valve, is also used at shut-down to prevent the li'l JEEP from shaking like the RAM CUMMINS trucks - very upsetting to soccer-moms and -dads driving their first Diesel-engined vehicle - block the air intake passage, pistons don't pump and compress large volumes of air = crankshaft rotates to a stop smoothly like a closed-throttle gasoline engine at shut-down

In the highly unlikely event that the FCV slammed shut at full boost, a BOV valve could prevent a disaster - but, I have never even heard of just such a scenario, and, seemingly, as have not the VM and DCJ engineers, so the KJ CRD is not equipped with, nor is there any occasion for, adding a BOV.

Save yer money for an upgraded torque convertor - word up.......................

CATCRD · **Posted:** Sun Sep 07, 2014 11:47 pm

Former member Glend was the first to modify his EGR valve to function as a BOV. The factory and GDE tunes pop open the EGR valve when you lift off the go pedal quickly after hard acceleration. Cut the EGR pipe where it enters the valve from around the engine, cap off the exhaust manifold side and it becomes an instant electrically operated BOV, with the sound you'd expect, if you're into that kind of thing. There was a video floating around of someone who did it.

devilkin4 · **Posted:** Wed Sep 10, 2014 12:30 am

heres the link for the video http://s1213.photobucket.com/user/dudeb ... f.mp4.html

now my question is what if you completely remove your egr and fcv from the jeep wont you need a way to get rid of the pressure?

geordi · **Posted:** Wed Sep 10, 2014 5:32 am

FFS....

NO. The engine is CONSTANTLY INHALING massive amounts of air. There is NOTHING TO STOP THIS, so if you suddenly go from full throttle to zero throttle, what happens to that 21 psi of boost?

It passes through the cylinders just as it would have before - except this time it doesn't have any fuel added to it, and it doesn't go boom. It just goes in and out as normal.

There isn't any wall (throttle plate) for the boost to slam in to, there isn't any difference in the air volume or air path whether at acceleration or deceleration, only whether fuel is added or not changes.

DIESELS DON'T NEED A BLOW OFF VALVE. The fact that there is this function within the computer... Is most likely from a poorly-educated programmer that doesn't understand how diesel engines breathe compared to gasoline engines.

Glend · **Posted:** Wed Sep 10, 2014 5:54 am

Suggest you talk to Keith at GDE, as I did when I was doing my EGR valve conversion. There is good reason for GDE retaining the valve software to dump boost - it is called 'compressor surge' and will damage your turbo. The built up boost pressure tries to bounce back and exit through the intake (ie the turbo vanes).

And no I am not back but I do look in from time to time.

flman · **Posted:** Wed Sep 10, 2014 7:35 am

devilkin4 wrote:

heres the link for the video http://s1213.photobucket.com/user/dudeb ... f.mp4.html

now my question is what if you completely remove your egr and fcv from the jeep wont you need a way to get rid of the pressure?

Diesels did not have the EGR or FCV 20 years ago, they are emissions devices, why is every one fooled into thinking they are required?

gmctd · **Posted:** Wed Sep 10, 2014 12:46 pm

Real-world fact (not Diesel-fume induced imaginations often posted as 'fact'): '94 GM 6.5L TD and Diesels in other OBD1 passenger-type vehicles oem-equipped with pwm-type EGR intended to reduce oxides of noxious, also equipped with reactive catalyst-type converter\soot-trap.......................... :goink:

geordi · **Posted:** Wed Sep 10, 2014 1:16 pm

flman wrote:

Diesels did not have the EGR or FCV 20 years ago, they are emissions devices, why is every one fooled into thinking they are required?

This is a fantastic question. I think the answer is somewhere in the vicinity of a fundamental misunderstanding of how a diesel engine actually works differently from a gas engine.

Keith and I have talked extensively about that function in the computer. I had an SEGR device (completely unplugs the EGR electrically) from 30k miles when I bought the CRD. I also removed my FCV throttle plate and sealed the intake elbow on my CRD. The failures I had on the engine had NOTHING AT ALL to do with the removal of that "pressure release" nonsense.

Keith may or may not be playing it cagey about this, because he is selling a product that is most obviously designed for on-highway use, so he HAS TO legally retain the usage of the EGR system as designed by the factory. I do not fault him for this, I just choose to disagree (as many have) about the need for EGR on a diesel.

Regardless of EGR usage or existence: If you are at full boost and high RPM, and you suddenly go to zero throttle demand - The engine is STILL AT HIGH RPM and will ramp-down from that MUCH SLOWER than the turbo will. Fuel is cut when you come out of the go-pedal, air flow is constant and continuous.

There can be no compressor surge - what would cause that other than the intake suddenly stopping? If you shut the engine off ENTIRELY at high boost, then maybe there could be compressor surge, as the pressure would be hitting a brick wall of the closed and non-moving valves... But in a running engine? No chance.

mass-hole · **Posted:** Wed Sep 10, 2014 6:24 pm

geordi wrote:

flman wrote:

Diesels did not have the EGR or FCV 20 years ago, they are emissions devices, why is every one fooled into thinking they are required?

This is a fantastic question. I think the answer is somewhere in the vicinity of a fundamental misunderstanding of how a diesel engine actually works differently from a gas engine.

Keith and I have talked extensively about that function in the computer. I had an SEGR device (completely unplugs the EGR electrically) from 30k miles when I bought the CRD. I also removed my FCV throttle plate and sealed the intake elbow on my CRD. The failures I had on the engine had NOTHING AT ALL to do with the removal of that "pressure release" nonsense.

Keith may or may not be playing it cagey about this, because he is selling a product that is most obviously designed for on-highway use, so he HAS TO legally retain the usage of the EGR system as designed by the factory. I do not fault him for this, I just choose to disagree (as many have) about the need for EGR on a diesel.

Regardless of EGR usage or existence: If you are at full boost and high RPM, and you suddenly go to zero throttle demand - The engine is STILL AT HIGH RPM and will ramp-down from that MUCH SLOWER than the turbo will. Fuel is cut when you come out of the go-pedal, air flow is constant and continuous.

There can be no compressor surge - what would cause that other than the intake suddenly stopping? If you shut the engine off ENTIRELY at high boost, then maybe there could be compressor surge, as the pressure would be hitting a brick wall of the closed and non-moving valves... But in a running engine? No chance.

I've been doing some reading about the 7.3 PSD and it seems what they call compressor surge is when the turbo essential goes into cavitation, like a boat prop. Is their version of compressor surge differnt than what we are talking about here? It sounds like theirs is more of a performance issue rather than a turbo exploding issue.

WWDiesel · **Posted:** Wed Sep 10, 2014 6:41 pm

All the 2nd generation common rail Dodge Cummins Diesels came from the factory with NO EGR, FCV, CAT, or any of that other junk! I know, I own one and the waste gate has been blocked off since day one after I bought it new.
So all this nonsense about needing a blow-off valve or EGR valve to relieve pressure is a bunch of hogwash! :roll:

Just as others have stated; when you abruptly let off the throttle under hard acceleration, the first thing that happens is the fuel is reduced and the engine begins to slow down and the energy to spin the turbo is reduced very quickly thus reducing the boost almost instantly. If you have a boost gauge installed, you can observe this! Its amazing how quickly it happens!

My Dodge is 16 years old and still going very strong with no turbo related failures of any kind! And yes, on occasions when pulling a heavy load and you back out of the throttle very quickly, you might hear an occasional turbo bark as everything comes to a quick slowdown! You learn how to drive the diesel and try and avoid this.

Remember, the diesel engine is just a big ol air compressor that moves gobs of air through the motor, fuel is added to obtain energy or work out of the motor while all this air is being pumped through it... :wink:

geordi · **Posted:** Wed Sep 10, 2014 6:48 pm

Couldn't tell you what they mean because I am not familiar with the 7.3's design.

I've heard of it called "turbo bark" or that the turbo physically reverses direction because of the air pressure wanting to go the other direction. Cavitation is again something that would happen when you suddenly reverse direction and are causing bubbles (underwater) and a vacuum where there had previously been flow in the opposite direction - Water has significant mass to try and reverse direction, which is why you have that vacuum and bubble creation, b/c the suction from the propeller is strong enough to "tear apart" some of the water from the laminar flow that is moving in the opposite direction.

In the case of turbo boost that suddenly hits a blockage, their description of cavitation may be that the air destabilizes within the turbo as the pressure tries to reverse against the still-incoming-air, and causes buildups / reversals of the wheel / etc.

DIESELS DON'T HAVE A THROTTLE PLATE (unless the 7.3 has some stupid design choice for emissions) so this shouldn't be an issue ever.

If the engine is at high RPM (assuming for a moment that it was spun to high RPM by a really big starter or the like) and high boost into that intake... This is what the engine looks like when the go-pedal is released! No fuel. Just inertia spinning the pistons, opening the valves, and passing the air into the exhaust. While the much much lighter turbo wheel spins down from 100,000 rpm in less than a second, the engine takes at least that long to spin down from 4000 RPM back to idle. Inhaling air (as normal) the whole way down.

What extra pressure? How could the turbo go backwards? The engine is still doing exactly what it was doing a millisecond prior... Just without fuel this time, which is why the RPM starts to come down.

Drewd · **Joined:** Mon Feb 06, 2006 12:24 pm **Posts:** 902

OP, the veterans on this forum are yanking your chain because you are a newbie with 1 post. The original blowoff valve is to the rear of the turbo and while difficult to find is not impossible to replace.

This is the blowoff valve I have installed on my CRD http://www.youtube.com/watch?v=boQfUScLQT4 IT WORKS AWESOME!

gmctd · **Posted:** Thu Sep 11, 2014 3:20 am

WWDIESEL:
The '03 CUMMINS 5.9L 24-valve engine was the first Common Rail Diesel CRD engine to be offered in the RAM pickups - the next upgrade was the '07 6.7L 24-valve CRD engine - both use electronic injectors controlled by the ECM.

The pic in your sig is obviously a '94-'97 5.9L 12-valve or maybe a '98-'02 5.9L 24-valve, neither of which were produced with CRD fuel system - the 12-valve has a mechanical 6-piston inline injection pump timed to the camshaft - the 2nd-gen 24-valve has a rotary 6-piston injection pump with electronic timing control, also timed to the camshaft - both systems use six (6) individual injector pipes from the pump to each cylinder - both systems use mechanical pop-off type injectors.

FYI: A turbocharger consists of two seperate systems, linked by a common shaft:

- an exhaust-driven turbine with either waste-gate or variable geometry configuration, both of which bypass exhaust gasses around the turbine wheel to maintain desired boost pressures - the gasses are bypassed into the exhaust system, not into the atmosphere, which would be illegal and dangerous - these can also be used to prevent over-boost conditions

- a turbine-shaft driven compressor fan to compress intake air at atmospheric pressure into higher pressures - a blow-off valve would be necessary with throttle-plated engines to reduce boost by exhausting it into the atmosphere - thus, the loud 'farting' noise when the throttle-plate slams shut - this can also be used to prevent over-boost conditions in very-high
boost systems, such as the twin- and triple-turbo Diesel pulling tractors, with up to 300psi (iirc) boost

A waste-gate bypasses exhaust gasses back into the exhaust system - a blow-off valve bypasses boost pressure back into the atmosphere.

No KJ CRD engine was ever oem-equipped with a blow-off valve in the compressor system - early KJ CRD's had a waste-gated turbo - later and current KJ's have variable vane geometry known as VVGT

The EGR is not used to reduce boost - the FCV is used under certain boost conditions to reduce intake volume in order to allow exhaust gasses to mix\recirculate with intake flow to reduce oxides of noxious...........................

Almost fergot: Diesel trucks 2500 and 3500 chassis were not required to be equipped with EGR, but were equipped with a reactive converter\soot-trap - all 1500 trucks, SUV's, passenger vehicles were required to be equipped with EGR and other emissions devices to meet Federal emissions standards - the GM 6.5L TD was available in 1/2-ton SUBURBANS, BLAZERS, and 1/2-ton (1500) pickups and so was required to be equipped with several emissions-type devices - DODGE did not offer the RAM 1500 with the CUMMINS 5.9 engine, so it did not get the EGR, as did not the big INTERNATIONAL 6.9 and 7.3 in the FORD F250\350 lineup - by 2003, Federal required all Diesel engines in all street vehicles to meet all emissions standards

Vmcrdrod · **Joined:** Wed Mar 22, 2017 9:21 am **Posts:** 33

Just got the Turbosmart BOV from XDP TS-0304-1006. It works off of pedal current has an overboost relay as well as cruise control relay cost me $280 shipped. I’m using Sasquatch CAC hose port to run air for the solenoid and BOV placement somewhere upstream of the fcv. With a relay on the over boost ground relay in the connection to the controller one could in theory control run away by using a E stop lock closed switch to ground the solenoid should the condition present itself The only trick would be that 12 volts would need to be supplied to the solenoid to maintain an open. A second solenoid would be ideal with a constant ground and a switched 12 volt directly to the Batery in any case these BOV could serve as at least a viable choice if not a solution to the engine of run away theory. :ALONE:

Should have everything to install it in the next week.

PZKW108 · **Joined:** Sun Apr 06, 2014 5:23 pm **Posts:** 461

geordi wrote:

Couldn't tell you what they mean because I am not familiar with the 7.3's design.

I've heard of it called "turbo bark" or that the turbo physically reverses direction because of the air pressure wanting to go the other direction. Cavitation is again something that would happen when you suddenly reverse direction and are causing bubbles (underwater) and a vacuum where there had previously been flow in the opposite direction - Water has significant mass to try and reverse direction, which is why you have that vacuum and bubble creation, b/c the suction from the propeller is strong enough to "tear apart" some of the water from the laminar flow that is moving in the opposite direction.

In the case of turbo boost that suddenly hits a blockage, their description of cavitation may be that the air destabilizes within the turbo as the pressure tries to reverse against the still-incoming-air, and causes buildups / reversals of the wheel / etc.

DIESELS DON'T HAVE A THROTTLE PLATE (unless the 7.3 has some stupid design choice for emissions) so this shouldn't be an issue ever.

If the engine is at high RPM (assuming for a moment that it was spun to high RPM by a really big starter or the like) and high boost into that intake... This is what the engine looks like when the go-pedal is released! No fuel. Just inertia spinning the pistons, opening the valves, and passing the air into the exhaust. While the much much lighter turbo wheel spins down from 100,000 rpm in less than a second, the engine takes at least that long to spin down from 4000 RPM back to idle. Inhaling air (as normal) the whole way down.

What extra pressure? How could the turbo go backwards? The engine is still doing exactly what it was doing a millisecond prior... Just without fuel this time, which is why the RPM starts to come down.

Cavitation: cavitation occurs when water pressure is lowered below the water's vapour pressure, forming bubbles of vapour

This happen to a propeller without having to reverse, c'mon Geordi just look it up. It seem like your just assuming stuff from your own experience...….

When I'm under acceleration with my CRD and I let the throttle off WHY can I hear the vanes letting pressure go ( no air box) . There must be a delay in the process creating a moment of overboost ???

I worked on a racing Cat engine with a few thousands Hp @ over 100psi and it was fitted with a BOV !!!!

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

Just for my understanding, what are you referring to when you say "letting pressure go?"

The thing that BPV/BOV usually solves is compressor surge (sometimes called flutter, I think) which occurs in moments of high pressure and low flow. The common scenario for this is going to be a gasoline engine where the throttle plate snaps shut (like during a shift) and there is still high pressure between the compressor and throttle plate but little to no flow. That's this:

Aside from being bad for performance, it's also very hard on a compressor. Moving that direction on the map creates a reaction force against the wheel slowing it down. It also puts a massive thrust load on the turbo's bearings and fatigues the surface of the compressor wheel. Over time, it will wreck the bearings or start tearing the wheel apart.

On a diesel, X rpm = X airflow no matter how you slice it, right? I don't really understand how you can get this high pressure / low flow scenario to unfold on a diesel. It's a bit baffling to me!

Edit: Because I don't like to be baffled I've been doing some reading. It appears that diesels can suffer the inverse problem, which is a sudden loss of exhaust pressure when you lift. The result is similar. I see how relieving intake pressure to make up for a lack of exhaust pressure would relieve the problem.

CRD blowoff valve?

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