Turbo Back Pressure Relief System

[SteveH]

Re: Wild idea?

Originally posted by Vaughn MacKenzie

OK, how about this: When running high boost, the drive pressure (exhaust) side should be higher than the compressor side. SO, how about running a 2" or so pipe back from the compressor side to the outlet area of the exhaust manifold and stick a check valve in this pipe? As long as drive pressure is higher, everything works like normal. Drop off the throttle and drive pressure drops instantly, then the check valve opens and the pressurized air rushes back into the exhaust side to help support the pressure and still provide a bit of drive to the exhaust turbine. This would probably be enough to save the turbo, especially if you have air shooting back with 40-50psi helping it along, to at least keep the turbine from going backwards or having high pressure differentials. This setup would not allow exhaust to leak into the intake if the check valve is quality.



This wouldn't me a simple modificiation. Sound too far out??



Vaughn

At first this sounded good, Vahghn, but I think there is a problem. The exhaust side has a greater velocity of much hotter less dense air which should mean a lower pressure. Even without the hot less dense air, the air to the exhaust turbo would be higher velocity from expansion in the cylinders, and this would mean lower pressures. Increased velocity decreases pressure through a line, the principle behind an orifice plate operation and all flow meters using differential pressures. I still think that a good quality check valve in the intake side of the manifold would be a much simpler and troublefree operation. The check can always have a minimum flow orifice so it doesn't completely cut off the flow either direction. These are used all the time where I work and do the job very well, are trouble free, have no maintenance schedules, and have only a flapper or similar restriction for a moving part. Keep beating this around, the ideas are worth keeping up with.

 

[Little Bill]

A very simple, sturdy flapper valve just downstream of the turbo outlet is all you need. Only 1 moving part that is self controlling and instantaneous. The excess pressure in the I/C, pipes and intake will be eaten by the engine during the next few revs. If you don't like the idea of the engine absorbing the excess, then now is the time to try to vent it because now you have time. You could make your relief device simply by drilling a 1/4 or 3/8 hole in the flapper. This would allow the excess to bleed back slowly over several seconds.

 

[Diesel Freak]

Check/Flapper valve

hehe, now we are talking.



Using a check valve to stop flow reversion from barking the turbo should work. now all we need is to find a 4 inch check valve that will survive in a 350F to 400F high flow, high vibration environment. I have used wafer check valves (they open and close like butterfly wings and have an internal bleed orfice ) in semiconductor vacuum systems that may work for this application.



time to get out the parts catalog and do some looking.



-Cliff

 

[Vaughn MacKenzie]

Should work with lower drive pressure

Steve H, when it comes to HX40 turbos you are right, drive pressure in the exhaust manifold is lower than the intake side ( I was thinking about the HX35 which has quite a bit higher pressure on the exhaust vs. the intake side).



But there is an easy solution. . . selecting the right spring strength for the check valve flapper could solve this. Set it for a 20-25 psi differential so that it stays shut unless the exhaust pressure drops to 25psi less than the intake side. That would keep 'er closed udner normal acceleration and cruising, it would only kick in when needed. . . when you've pumped up the boost then suddenly let off the throttle. Even with a 25psi differential I think for the first instant the valve opens there would be sufficient flow back to the exhaust side to keep the turbine from backspinning. This only needs to work for a few milliseconds until the danger is over.



I think the main reason the HX40s have this problem has more to do with the fact the outlet is huge compared to the HX35 than anything else. The drive pressure is lower to begin with, and what drive pressure there is bleeds off much faster when you let off of it. The HX35 sorta acts like a balloon, filled tight with air and let out more slowly so there is no chance for backspin.



Sound like I'm onto it??



This check valve setup should be as close to the exhaust side as possible to minimize preturbo exhaust chamber volume or spoolup could suffer a bit. . . . probably not majorly critical though.



I just think someone needs to take my ideer and try it out!







Vaughn

 

[KWIKKURT]

With all these Great Minds coming up with new ideas to think over how do you expect me to get any sleep. My brain is going to be spinning all night!!





OK how about this I can live with a bark or two!!: Holset are you listening ... ... . How about a HX40 centersection with a BIGGER Shaft?????



Good night all.

 

[Alan Reagan]

Some of you guys are coming to the conclusions that are similar to what I'm finding in the marketplace. That is, there are several approaches to solving this problem but because of the heat, rapid change in temperature, vibration and varied losses across the intercooler, this becomes a complex problem to solve. For instance, if you are lucky enough to find a four inche check valve, it would have to be about six inches in diameter (external) to maintain proper flow (internal). Then, you have to get it manufactured to bolt to existing flanges. Nobody will touch that unless you are talking OEM manufacturing quantities. The toughest part of this whole deal has been to find the two parts needed to control the air pressure and get them to handle heat and vibration over the long haul. As I stated earlier, I refuse to even suggest parts that would fail early and often that people may go put on their engines. All of this dialogue is good. I seriously consider each suggestion. Right now, the way technology is, there is a severe restriction as to what approaches can be taken because of where the pressure sampling has to occur.

 

[Cooker]

I know this is a very old topic, but I was wondering if anyone has developed a product to fit the bill. I was informed that one is on the very near horizon from one particular company. I was wondering if there are others?

 

[ToolManTimTaylor]

http://www.hksusa.com/images/?id=1746



HKS Makes one for Big $$'s

 

[KWIKKURT]

Originally posted by ToolManTimTaylor

http://www.hksusa.com/images/?id=1746



HKS Makes one for Big $$'s

I would be sure to not be running Propane and / or Nitrous mix using the Popoff style valve. You might end up looking like a Iraq Tank or I guess you could call it the "Mother Of All Barks"... .

 

[DAWG-1]

I would be interested in a way to stop the turbo from barking when I can not let off the pedal slow enough. Let us know how this is going. Thanks, Sam.

 

[Josparkz]

Sure . I need one of those gadgets

 

[nickleinonen]

Originally posted by ToolManTimTaylor

http://www.hksusa.com/images/?id=1746



HKS Makes one for Big $$'s

i like the sound of the aftermarket blow off valves that the turbo ricers have. i could have a similar sound on a diesel. neato

 

[CRoth - BD-Power]

Originally posted by ToolManTimTaylor

http://www.hksusa.com/images/?id=1746



HKS Makes one for Big $$'s

Unfortunatley it doesn't work, we've tried it. But if someone doesn't believe me I'm willing to sell it.

 

[Cooker]

Mr. Roth,

Do you know of one that does work? Thanks.

 

[Sticks]

I just finished reading the entire thread. My mind started looking at the solution for this as an exhaust brake mounted on the turbo side. It obviously takes heat and vibration, can be wired to be instantaneous, and looks to be about the correct size mounted in the first inter-cooler pipe.



Is my brain thinking in the right direction?



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.



Alan, am I on the right track?

 

[Alan Reagan]

The exhaust brake on the turbo would be an effective relief but IMHO there would be two issues:



1. Too sudden a release. There needs to be release, but I believe it needs to be more gradual to prevent over spinning the turbo in the forward direction due to sudden depressurization.



2. The trigger to open the valve would need to be driven by measuring the differential pressure between the intake manifold and the output of the turbo and not connected to the throttle. You don't want release when you are running up through the gears under normal operation. You only want relief when the intake manifold pressure exceeds the turbo output by some predetermined value. That value needs to be adjustable.



A smaller valve would do the trick. I'm not sure that the exhaust brake is completely air tight when shut and it would have to be airtight to avoid pressure losses.



Hope this helps.

 

[Diesel Freak]

I gave up on this... . it is more trouble than it is worth. But if you want to build the system to use a BOV... go for it!

 

[Sticks]

Originally posted by Alan Reagan

The exhaust brake on the turbo would be an effective relief but IMHO there would be two issues:



1. Too sudden a release. There needs to be release, but I believe it needs to be more gradual to prevent over spinning the turbo in the forward direction due to sudden depressurization.



2. The trigger to open the valve would need to be driven by measuring the differential pressure between the intake manifold and the output of the turbo and not connected to the throttle. You don't want release when you are running up through the gears under normal operation. You only want relief when the intake manifold pressure exceeds the turbo output by some predetermined value. That value needs to be adjustable.



A smaller valve would do the trick. I'm not sure that the exhaust brake is completely air tight when shut and it would have to be airtight to avoid pressure losses.



Hope this helps.

To control the speed in which it releases, attach a small gas shock like on tool box lids/hoods.



The e-brake that is on my truck has a pressure sensor on it. All it does is activate an idiot light telling me to down shift.



Making it 99% air tight would not be too much work.



I have no need for one of these. I was just trying to toss a few ideas out. From reading the tread, my brain just put this together.

 

[Scrappy]

bov

I would think that the valve would not have to be air tight, just slow the air down some. I do know that I want something that will NOT come apart and send debris into the intercooler or worse yet the engine!

 

[Alan Reagan]

Re: bov

Originally posted by jvanwaardhuizen

I would think that the valve would not have to be air tight, just slow the air down some. I do know that I want something that will NOT come apart and send debris into the intercooler or worse yet the engine!

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.