Why not use blow off valves??

[JJohnson]

Hello gentelmen, I have a question or possibly a possibility for Cummins. I have a Nissan 300zx twin turbo with 425hp that is my project car. I have installed twin blow off valves for the turbos and have been verry impressed with the performance improvements. I blow off valve works like this- when the turbos spool up around 2000 rpm they build substancial psi on the exaust side as well as enormous vaccum(boost) on the intake side of the impeller. Well the minute you shift and release the throttle, the air that is rushing into the turbo is SUDDENLY shut off and the turbo impeller stalls and is subject to these pressure forces every time you are using boost and release the throttle. (almost constantly) The cure for this is installing a blow off valve that sences this positive pressure and purges it out of this small fist size unit and causes significantly less impeller fetigue and the greatest thing is your turbo is spolled up and waiting for your next gear! I am sure Cummins is much more familiar with this than I ever will be but it works wonders for my Z. Thanks for your time. Jace

 

[BigCarl64]

Somebody a while back had started a project trying to do exactly what you are describing. I haven't heard anymore in a while. I can't remember who it was.

 

[Cummins Corvette]

The blow off valve in a gasoline turbocharged engine lets off the excess pressure created when the throttle is closed. In a diesel, there is no throttle, and thus no sudden pressure serge when you let off the throttle. Maybe I am missing some thing, but I believe that is how it works. The turbo barking is from a LACK of drive pressure in the exhaust, and the turbo tries to reverse (I think). So a pressure sensitive valve is not the answer, rather a valve that purges the pressure when you let the pedal up. I could be way out of line here.

 

[ToolManTimTaylor]

Gee so am I

I am wrapping up my WRX 3" ehaust as we speak and have been working on somethinh but still is rudementary. Ultimatly nothing more than a Solonoid that senses a " 0 throttle condition" sent by the Apps sensor or TPS as most people call it but the mechanics involved are killing me. I fashioned a ice maker water solonoid into a piece of three inch electrical pvc (Actually a coupling) but when I plugged it in (Extension cord and loaded motor to build slight boost. sure it kind worked but man what a slow bleed off it was (Serious tea kettle sound) we need something super fast acting that has a huge orfice to bleed off that pressure REAL QUICK being all that air plumbing holds some CUft whereas my wrx holds an eighth of that at 16 lbs where the truck holds much more at 42 (Peak). as for the electrical ..... hmmmmm



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[Alan Reagan]

That was me that started the thread a while back. The problem I ran into was the cost of the components to do this. I looked at two approaches:

First, I looked at using an electronic differential switch to sense the pressure difference at the output of the turbo and the intake manifold. This will work, but finding a reliable bleed off valve was difficult. Main reason is because of the broad operating temperature range.



Second, I found a mechanical differential switch. It was more expensive but in my opinion is the way to go because it can be turned to individual engines/conditions simply by turning a set screw to adjust differential switch trigger pressure. The mechanical switch was also more ruggedized for environmental, vibration and temperature extremes. This is an expensive switch plus you still have to buy the bleedoff valve. Also, you have to consider that differential switches are normally measuring pressures at similar temperatures. In the pressure system, the ouput of the turbo is or can be considerably hotter than at the intake. Under high boost conditions you are probably looking at 150 to 200 degrees F difference not to mention that the overall temp at the output of the turbo could go from ambient (let's say 70*F at the turbo intake) to 260*F at 19 psi boost at the output of the turbo. Think about how much the temp rise is at 40 or 50 psi of boost. Yep, you can reach 400*F. Most manufacturers won't touch these extremes of temperature with the range of pressure being so low.



You have to be careful in selecting components. Vibration and/or temperature fluctuations can cause either the switch or valve to activate at an undesirable time. Also, there are harmonic frequencies that have to be considered on both the switch and valve to avoid unwanted activations or fluctuations in performance.



You have to be careful when deciding what will make this thing work. You could use the accelerator system and trigger when lift is detected. To me that's not practical because you may not be in a zone where reverse pressure is an issue and therefore the system isn't operating efficiently by bleeding off boost. I worked an approach where differential pressure was being monitored so that when the pressure at the intake exceeded the pressure at the turbo by "X" number of pounds (remember, the trigger point is adjustable), the intake pressure would be bled off. The design would bleed it off in under . 5 seconds under worst case conditions using a 1/4 NPT valve thus stopping the "barking" or turbo reversing action.



In parts alone for a dependable system, low quantities, I was looking at three to five hundred dollars. One of the main problems is finding valves that stay seated at low pressure that will remain reliable when working under high pressure and temperature. Most of the valves of this type are for steam applications. The manufacturers and engineers that I discussed this with indicated that they would have to change the seat gasket materials for the systems to work in an exhaust environment. That's the reason for the high cost.



It is simple to do. But it ain't cheap if you are going to do it right and make it reliable. Good components are expensive for this type of work.



Hope this helps.

 

[ToolManTimTaylor]

Hey Alan ,

I remember your post on this and you hooked me on something to tinker with at every oil change like you see above have been Futzin' arround with the idea (Mainly cause of all the stuff available to me at my shop). And One thing I kinda had a brainstorm on was when I opened a box that had a Solonoid actuated blowoff valve from Blitz. (Install in a 3000gt) but anyways that particular application was a custom built unit for a friend that he purchased a ways back. Anyways the reason for electric ($$ to Donuts) is the variable rate in which you can in a sence bleed off boost. My wrx for instance uses a conventional vac unit but now bleeds off at Part (5%) throttle which is anoying at anything below 5 psi at highway speed. So thats where an electric unit is sweet. It can be programmed to eliminate that "performance only" quirk / trade off. ONLY the main issues would be A. Cost along with custom machine work to adapt a flange that won't be huge and bulky (A curved baseplate to "Bolt up to a aluminium 3. 5 inch tube would be sweet) but As my experiment above was just an IN bay kinda fooling arround thing I noticed that boost had to be bled off in volume ..... Lots of it in fact where the ctd has plenty of that in its ductwork alone. Do you think it's possible to coordinate a relationship with two parameters? one being throttle lift and one being pressure reading (MAP sensing) with those two elements and some electrical circuitry this may work???

 

[jimnance]

Turbo Boost

Hey Alan, I hope you have upgraded to a racing crank. Saw a crank from a 300 ZX one day snapped in two. Guy was pulling about 25 lbs of boost when the crank sheared. :--)

 

[Alan Reagan]

Toolman, Your question:

"Do you think it's possible to coordinate a relationship with two parameters? one being throttle lift and one being pressure reading (MAP sensing) with those two elements and some electrical circuitry this may work???"



My answer: Absolutely. The throttle lift could provide a binary "enabling" signal to be utilized to enable the MAP sensing signal to open the bypass or blow off valve. Throttle lift could simply be a binary (0 or 1) signal created by a micro switch on the accelerator.



The problem then is the MAP sensing. You would have to use a differential detector to generate a signal when the pressure at the output of the turbo is LESS than the air pressure at the intake manifold.



If a "1" is generated on throttle lift and a "1" is generated when the differential pressure meets the above parameter, both "1" signals could be fed into an "And" gate (an electronic device that compares binary signals and gives an appropriate output signal:

0 and 0 = 0, 0 and 1 = 0, 1 and 0 = 0, BUT 1 and 1 = 1. You could only get a 1 signal out when both conditions are met: the throttle is lifted and you have undesirable pressure differences.



I'm sure we will have to go off line with this. I'll be glad to assist you any way I can. I was working on this and just about had the solution when I was called up on active duty with the Coast Guard.



Please, don't take my earlier post as the ultimate solution. It is just what I found as I worked through this problem. If I can help, or you want advice on the digital portion of your solution, don't hesitate to get in touch with me.

 

[ToolManTimTaylor]

Sweet.

Once things kinda calm down here ... ... ..... I would be happy to help out #ad