Turbo Back Pressure Relief System

[Diesel Freak]

Re: Re: bov

Originally posted by Alan Reagan

If I understand what he wants to do by venting the wastegate port to the outside, I believe it would need to be airtight to maintain pressure.



If the wastegate port is not air tight, intake air could be drawn through there under heavy load conditions rather than the filter.

Alan, not to pick nits here, but your terminology is incorrect.....



there is a lot of difference between a wastgate and a Blow Off Valve... . they are on opposing sides of the turbo... . please try an avoid confusion.

 

[Alan Reagan]

Re: Re: Re: bov

QUOTE]Originally posted by Diesel Freak

Alan, not to pick nits here, but your terminology is incorrect.....



there is a lot of difference between a wastgate and a Blow Off Valve... . they are on opposing sides of the turbo... . please try an avoid confusion. [/QUOTE]



"If the other plan was to bleed off back pressure on the inter-cooler side, that would be like installing a US Gear super duty brake back wards, and routing the waste-gate port outside, rather than back to the turbo. Now the price is around $500 - $1200. " That quote is from Sticks on page 4 where it is suggested to put in the US Gear AFTER THE TURBO.



I didn't dream that up. He is suggesting that as an alternative way to bleed pressure. I know where the wastegate is. I'm not sure this technique will get him where he wants to go and I'm not trying to confuse anyone. I'm just trying to answer the question about air tight. Point taken.

 

[Sticks]

Re: Re: Re: Re: bov

Originally posted by Alan Reagan

QUOTE]Originally posted by Diesel Freak

Alan, not to pick nits here, but your terminology is incorrect.....



there is a lot of difference between a wastgate and a Blow Off Valve... . they are on opposing sides of the turbo... . please try an avoid confusion.

"If the other plan was to bleed off back pressure on the inter-cooler side, that would be like installing a US Gear super duty brake back wards, and routing the waste-gate port outside, rather than back to the turbo. Now the price is around $500 - $1200. " That quote is from Sticks on page 4 where it is suggested to put in the US Gear AFTER THE TURBO.



I didn't dream that up. He is suggesting that as an alternative way to bleed pressure. I know where the wastegate is. I'm not sure this technique will get him where he wants to go and I'm not trying to confuse anyone. I'm just trying to answer the question about air tight. Point taken. [/QUOTE]



Whoa guys... I was just kicking out an idea for this new product. I have no need for one of these for my truck. I got a BOMBing vaccination a couple of months ago, guaranteed to keep my HP from going over 300. DD 1's and Edge EZ, and I'm done. I noticed the almost year long lag on the posts, so I threw out a concept to maybe assist with the R&D.



If there was a terminology error made, it was on my part, and I got my information from US-Gear by their "waste-gate design" on the afore mentioned item.



Happy developing!

 

[Alan Reagan]

Thanks, Sticks. I haven't done any research in a while because the parts were so expensive that I didn't think anyone would go for it. I'm not going to build something that will cause problems or that you can't depend on. I appreciate your response. I thought my brain had screwed up there for a minute.

 

[CoreyPerez]

I've been stuck on the location of this microswitch, and the idea has been tossed around about the gas. I actually think that the micro swich located on the clutch would be a better idea. You would have a lag time between when your foot comes off the peddle and when the peddle would bottom out, engaging the switch, where as when you push in the clutch, you are instantly activating the switch when the load is coming off the drivetrain.



Just a thought.



Corey

 

[Turbo Horseman]

Don't race cars need the check valve, or whatever its being called, because they are operating at extreme rpms (9k - 10k)? When they come off the go pedal, shift and then go again, it seems to me that they are likely dropping more rpms (creating more back pressure) than our engines can safely operate at.



If we're only pushing 3200 rpm, not going crazy with the boost pressure (<35 psi) and are bombed to a lesser degree, then how many of us would really need this thing-a-ma-jig-do-dad versus peace of mind? Now if you're MOAB (mother of all bomb(ed)(ing)(er) etc) then you would be barking for this imvho.



By the way, my turbo only whines... thankfully... so far... it refuses to bark. Unlike the dog, I like it when my turbo whines... its so cool.

 

[rkubicki]

Not beneficial to all trucks??

I needed a bypass valve in my VW race car to prevent the compressor's seals from blowing when the throttle was snapped shut under high-boost conditions... It seems more critical to have these on an application where you have a butterfly or some other type of throttle plate acting as a "dead-stop" for the boost pressure.



Our diesels don't have this plate so essentially when you snap the pump shut shouldn't boost pressure leak through the engine during the next intake cycles?



I have a smaller than stock turbine housing on my truck with some pump mods and I still cannot seem to get the turbo to "bark"... It seems like you would need quite a bit of extra pressure (well above and beyond stock ) before the open intake valve(s) would not be able to vent enough boost to prevent back-pressure at the compressor.



If you know your intake valve size, boost pressure and RPM at the time throttle is lifted then you could roughly calculate if a bypass valve is needed or not... . Or some pressure readings as close to the compressor as possible to monitor positive surges would work too.



While I have built my share of turbocharged engines, I am no expert on the subject by any means - so someone with more experience, please feel free to correct me.



Either way, I think its cool that you guys are trying something new and I can't wait to hear how the project turns out.



I have used bypass valves from Turbonetics in the past - they are quite nice:



http://www.turboneticsinc.com/catalog/bypass.html





Rob

 

[Alan Reagan]

Re: Not beneficial to all trucks??

Originally posted by rkubicki



Our diesels don't have this plate so essentially when you snap the pump shut shouldn't boost pressure leak through the engine during the next intake cycles?



Rob [/B]

When building boost higher than stock, with the wastegate disabled/modified to allow this boost, the sudden lift will cause the pressure to try to go to the lowest point of resistance which is back through the compressor side of the turbo. Without pressure being applied on the exhaust blades to keep the turbo spinning "forward" the pressure built up in the entire intake system (manifold, intercooler and plumbing) will not be bled off fast enough by the intake cycle. The sudden surge of backpressure to the turbo without exhaust gas to keep the turbo under load will cause the "bark" or backspinning action on the turbo. When doing the calculations you are talking about in your post, you would have to consider not only the volume of air in the system, but the mass (weight) of the air as well. By calculating the weight of the air which is the volume at a specific pressure, you would then know how much air you would have to get rid of.

 

[rkubicki]

Re: Re: Not beneficial to all trucks??

Originally posted by Alan Reagan

When building boost higher than stock, with the wastegate disabled/modified to allow this boost, the sudden lift will cause the pressure to try to go to the lowest point of resistance which is back through the compressor side of the turbo. Without pressure being applied on the exhaust blades to keep the turbo spinning "forward" the pressure built up in the entire intake system (manifold, intercooler and plumbing) will not be bled off fast enough by the intake cycle. The sudden surge of backpressure to the turbo without exhaust gas to keep the turbo under load will cause the "bark" or backspinning action on the turbo.

Ok, there are three things happening in the sudden lift scenerio that are worth mentioning:



1 - The engine decelerates, it does not instantly drop to idle... This can take up to 1 second to happen.



2 - While the engine is slowing down, it is not stopping its flow, there are still intake and exhaust cycles being performed. . Granted the engine's flow capabilities are a function of its speed but there is still positive pressure at the exhaust port that is working on the turbine blades.



3 - As the engine decelerates so does the turbo, retarding its output and moving out of its range of peak efficiency... Boost pressure does not remain constant in these conditions.





Having said that, the engine intake port will always be the point of lowest pressure, no?... . Its like trying to fill a bathtub with a bucket while the drain is open. . I would think you'd have to have a very large compressor on your engine before that would become a problem... By then backflow would be the least of your problems.



If the engine is still flowing air how could the turbocharger actually spin backwards??... You have a 5. 9L "air compressor" feeding from whats left of any intake pressure and discharging through the turbine housing... Compound this with the forward inertia at the turbo's shaft.





It scares me to hear folks mention removing or tampering with their wastegates... Wastegates serve a very important purpose - they prevent the turbo from overspeed which could cause compressor surge or turbo and/or engine failure!!



Turbos are designed to operate in a peak speed range depending on the characteristics of the compressor... If you overspin a turbo by defeating the wastegate you get to a point where the compressor's efficiency begins to fall... If not controlled, efficiency drops off and the compressor surges (becomes unstable) - Could this possibly be the "bark" you are hearing??



Sorry about such a wordy response... I have seen some beautiful engines destroyed from mis-controlled turbochargers... I'd hate to hear that happen to any one of your engines.



- Rob

 

[Alan Reagan]

Re: Re: Re: Not beneficial to all trucks??

Originally posted by rkubicki

Ok, there are three things happening in the sudden lift scenerio that are worth mentioning:



1 - The engine decelerates, it does not instantly drop to idle... This can take up to 1 second to happen.



2 - While the engine is slowing down, it is not stopping its flow, there are still intake and exhaust cycles being performed. . Granted the engine's flow capabilities are a function of its speed but there is still positive pressure at the exhaust port that is working on the turbine blades.



3 - As the engine decelerates so does the turbo, retarding its output and moving out of its range of peak efficiency... Boost pressure does not remain constant in these conditions.





Having said that, the engine intake port will always be the point of lowest pressure, no?... . Its like trying to fill a bathtub with a bucket while the drain is open. . I would think you'd have to have a very large compressor on your engine before that would become a problem... By then backflow would be the least of your problems.



If the engine is still flowing air how could the turbocharger actually spin backwards??... You have a 5. 9L "air compressor" feeding from whats left of any intake pressure and discharging through the turbine housing... Compound this with the forward inertia at the turbo's shaft.





It scares me to hear folks mention removing or tampering with their wastegates... Wastegates serve a very important purpose - they prevent the turbo from overspeed which could cause compressor surge or turbo and/or engine failure!!



Turbos are designed to operate in a peak speed range depending on the characteristics of the compressor... If you overspin a turbo by defeating the wastegate you get to a point where the compressor's efficiency begins to fall... If not controlled, efficiency drops off and the compressor surges (becomes unstable) - Could this possibly be the "bark" you are hearing??



- Rob

Nice response.

1. I agree with number 1.

2. The positive pressure on the turbine blades (exhaust side) is less than the air pressure on the the engine side of the compressor blades. Yes, there is still air being bled off, but not fast enough. Keep in mind that this whole problem is caused by excessive pressure in the system.

3. Correct again.



The intake is the point of lowest pressure because it is "pulling" the air. But using your analogy of trying to fill a bathtub with a bucket while the drain is open... . you are right. However, pour a five gallon bucket of water into a bathtub with the drain open. Water will be standing as it attempts to drain from the small drain (intake valves). Now do it with ten gallons immediately poured in. The small drain has a finite amount of liquid that it will past. If it had some other place to go, it would go there instantly, rather than wait for that small drain to clear. Same with the intake valves.



The forward inertia of the turbine/compressor shaft is not enough to combat the sudden burst of reverse pressure built in the system.



The bark is a result of instability in the system. Backspin is a result of a large mass of air under high pressure impatiently trying to find a new home.



Don't just think about pressure/volume. Convert that to mass. At 20 psi boost, out engines are moving 40 lbs of air/min. At 40 psi, they are moving 63 lbs/min. However, the volume is constant. Every two revolutions the engine takes in 5. 9 liters of air, no matter what the pressure. It's when you get this large mass of air with no place to go (not enough intake room to match production) that you get this instability and reverse air flow.



I am not a proponent of tampering with wastegates. But for those that race, this is a serious problem (backspin) because it will wring off the turbine shaft. There's not enough "space in the sytem to get rid of this mass of air. So if you put a blow off valve in, you bleed it into free space outside the engine.



BTW, when I first started working on this, I found that a 3/8 line was sufficient to bleed off enough air to stop the problem. It would do it in milliseconds. Why? Because it is only bleeding off what the engine can't take during the intake cycle. This is a very fast operation. The speed that it has to work is part of the reason the parts cost so much.

 

[dsherman]

count me in

 

[rkubicki]

Re: Re: Re: Re: Not beneficial to all trucks??

I need to lean down my responses or else we are going to be writing hour-long essays soon

Originally posted by Alan Reagan

But using your analogy of trying to fill a bathtub with a bucket while the drain is open... . you are right. However, pour a five gallon bucket of water into a bathtub with the drain open. Water will be standing as it attempts to drain from the small drain (intake valves). Now do it with ten gallons immediately poured in. The small drain has a finite amount of liquid that it will past.

I was afraid of that analogy coming back to haunt me ... I didn't mention this before but the bathtub analogy is flawed because the drain would have to be variable-flow and in relation to the amount of water being dumped in the tub... But my original point is that a stock turbo probably wouldn't be able to give us that "10-gallon" rush... A stock turbo with a tampered wastegate would do even less as it passes its high-efficiency speed and heads for the surge line - but it would probably make a noise and possibly destroy the turbo.



If you have a very large compressor then I totally agree with you that this system is needed.

Originally posted by Alan Reagan

Don't just think about pressure/volume. Convert that to mass. At 20 psi boost, out engines are moving 40 lbs of air/min. At 40 psi, they are moving 63 lbs/min. However, the volume is constant. Every two revolutions the engine takes in 5. 9 liters of air, no matter what the pressure. It's when you get this large mass of air with no place to go (not enough intake room to match production) that you get this instability and reverse air flow.

I can't seem to arrive at your 63 lbs/min number - even at 100% compressor efficiency and 4000 RPM!... The most efficient turbos won't come close to 100% efficiency... I have not seen the compressor map for our Holset but a safe guess maximum efficiency for it would probably be 70%... and a safer max RPM would be 3500 so the numbers would change to:



40 lbs/min @ 3. 8 PR, 70% efficiency, 3500 RPM and 40 PSI boost



By the way, does anyone have the compressor maps for the Holsets used on our trucks??... Last time I checked on their website I could not find them.



Rob

 

[glhs]

backspinning?

I've read this forum and keep seeing the term "backspinning ". Do you really mean the turbo is stopping and spinning backwards or just slowing down quickly? IMHO I don't think it's possible for it to spin backwards without a throttle plate like a gas engine to, (for lack of a better word) "confine " the compressed air. I would think we would see many more broken shafts if that were the case. I reaize I'm sticking my neck out here for a possible :-{} but it just doesn't sound possible. Kurt

 

[crawler]

"Backspinning"

Actually the compressor can be spun backwards or if not backwards then come to an immediate stop. When you let off with a good bit of boost you can hear the air rush back out your airfilter(aftermarket systems anyway). I blew up 1hx35 and 1 hx40 because of turbo bark. The hx40 actually shot the impeller shaft through my hood, when it snapped off.

 

[Alan Reagan]

n(lbs/min)= P(psia) x V(cu. ft. /min) x 29

divided by

(10. 73 x T(deg R))



Rob, The mass of air you are moving is reduced by the volumetric efficiency related to the internal construction/physics of the engine and not the efficiency of the turbo. Turbo efficiency deals more with the amount of RPMs required to reach a certain pressure, not whether or not the pressure can be reached. Inneficient turbos heat the air more than efficient ones. Then you are fooling with the T part of the equation more. As T increases mass decreases.



Mass is relative to pressure, volume and temp. Volume is set at 5. 9 liters or 359 cu/in every two cycles. If you set P = 20 because that is the amount of mass you are interested in, you have not made it absolute. At sea level you are at 14. 7. So add 14. 7 to your boost at sea level. For 20 psi P(psia) would be 34. 7. Higher altitudes, add whatever air pressure is appropriate. As you can see from the above formula, the only thing we have control over in our engines is the pressure (P(psia)). The temperature is in Rankine (outside air temp plus 460).



Instead of compressor efficiency, what you are thinking of is volumetric efficiency.



Theoretically if all was perfect, we could fill the cylinders completely with air. If we had 20 psi boost in the intake manifold, we would open the intake valves and get 20 psi in the cylinder before the intake valves closed. Unfortunately, this doesn't happen. With some exhaust remaining in the cylinder and the restriction offered by the intake ports and valves the actual amount of air that flows into the cylinder is somewhat less than ideal. The amount that does flow divided by the ideal amount is called the volumetric efficiency.

For your basic stock 24 V 5. 9L Ram, I think this number is around 0. 85-0. 95 (or 85% to 95%).

To take this into account when we calculate flow into the engine, we multiply the ideal amount of air by the efficiency to get the actual amount of air:



actual air flow = ideal air flow x volumetric efficiency



So you got me. I was doing a theoretical calculation or ideal air flow calculation. I use those to ensure the intake air filter is large enough to supply adequate air to the engine under heavy load (high RPM).

 

[rkubicki]

Originally posted by Alan Reagan

Rob, The mass of air you are moving is reduced by the volumetric efficiency related to the internal construction/physics of the engine and not the efficiency of the turbo. Turbo efficiency deals more with the amount of RPMs required to reach a certain pressure, not whether or not the pressure can be reached. Inneficient turbos heat the air more than efficient ones. Then you are fooling with the T part of the equation more. As T increases mass decreases.



Mass is relative to pressure, volume and temp. Volume is set at 5. 9 liters or 359 cu/in every two cycles. If you set P = 20 because that is the amount of mass you are interested in, you have not made it absolute. At sea level you are at 14. 7. So add 14. 7 to your boost at sea level. For 20 psi P(psia) would be 34. 7. Higher altitudes, add whatever air pressure is appropriate. As you can see from the above formula, the only thing we have control over in our engines is the pressure (P(psia)). The temperature is in Rankine (outside air temp plus 460).



Instead of compressor efficiency, what you are thinking of is volumetric efficiency.

Alan, forgive me if I twisted compressor efficiency and volumetric efficiency up in my last post. . However, both must be addressed to accurately calculate flow... As your very good description points out, a less efficient compressor heats the charge more than a very efficient one - so you would need to take this into account as well.



The ideal tempurature rise (Ti) from compressing ambient air at a given atmospheric pressure and temperature must be divided by the compressor efficiency to get the actual temperature rise (Ta).



Ta = (Ti / EFFc) where EFFc = compressor efficiency.



Lets take an arbitrary ideal temp rise of 90 degrees:



You can see that for a 100% efficient compressor, Ta = Ti = 90deg... . Assume a more realistic compressor efficiency of 75% and look what happens:



Ta = (90/. 75) = 120 degrees (rise in temperature).



We know that temp has an effect on density, which affects mass, wich affects flow... This actual temperature rise is then used to calculate your density ratio which is used to calculate your compressor flow.



IMHO, this number has a much greater effect on flow than volumetric efficiency... By the way, you get some of the density back when you pass the charge through an intercooler, but not all.

Originally posted by Alan Reagan

So you got me. I was doing a theoretical calculation or ideal air flow calculation. I use those to ensure the intake air filter is large enough to supply adequate air to the engine under heavy load (high RPM).

Not at all - I just like talking about the science behind turbos... To tell you the truth, if the Cummins engine didn't come turbocharged I probably wouldn't own one today.



So have you tested any prototype bypass systems yet?

 

[Alan Reagan]

You bring up an excellent point that I was having to deal with before I took my sabbatical to serve my country in the hunt for terrorists . The temperature is a critical component in this whole picture, something that drove the costs of components up significantly. The suddent increase in temperature coupled with the quick increase in pressure from say 0 to 40 psi drives component costs up very quickly. The system I was working on sensed pressure at the output of the turbo and at the intake. When the intake exceeded the turbo pressure by say 5 psi, the pressure relief solenoid valve would energize and bleed off. Most of these valves are commercially available but the operating range in pressure is usually 0-5, 5-15, increasing like that. Then they have to operate in temps from -20 to 200. Why so large? Because, the truck may be a daily driver and you still want it to work and hold pressure in extreme cold and heat. (The 200 was boost air temp, worst case that the valve might see)

 

[rkubicki]

Originally posted by Alan Reagan

You bring up an excellent point that I was having to deal with before I took my sabbatical to serve my country in the hunt for terrorists .

God bless you and all brave men and women who protect this great country!

Originally posted by Alan Reagan

The temperature is a critical component in this whole picture, something that drove the costs of components up significantly. The suddent increase in temperature coupled with the quick increase in pressure from say 0 to 40 psi drives component costs up very quickly. The system I was working on sensed pressure at the output of the turbo and at the intake. When the intake exceeded the turbo pressure by say 5 psi, the pressure relief solenoid valve would energize and bleed off. Most of these valves are commercially available but the operating range in pressure is usually 0-5, 5-15, increasing like that. Then they have to operate in temps from -20 to 200. Why so large? Because, the truck may be a daily driver and you still want it to work and hold pressure in extreme cold and heat. (The 200 was boost air temp, worst case that the valve might see)

Temperature is very critical... I calculated a 324 degree (F) temperature rise in that whole 40psi boost/80% vol eff/3200 RPM scenerio a few posts back... and that gets added to the current ambient temp!!



Most bypass systems I've seen have the bypass valve closest to the throttle (or intake on a diesel) - after the intercooler where the temps aren't so extreme.



Did you get a chance to check out that Turbonetics link? ... Those bypass valves are pretty nice and they are purpose-built for what you are trying to do.



Rob

 

[Alan Reagan]

The Turbonetics link looks good.

 

[CUMINNTSTRKN]

guys go here. https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=72621

jim