drive pressure test

[swankmetal]

hooked up an old oil pressure gauge to the manifold last night. it was kind of hard to read cuz it was bouncing all over the place under load. at wot, seeing about 33-34psi boost, i was seeing 75 psi on the other gauge. and my exhaust housing is very heavily ported.



i'm not sure what to think.

 

[cerberusiam]

I don't think an oil pressure gauge is going to give you a valid reading. If it is then those numbers are very, very bad. You might stop by your favorite hardware store and get a cheap air pressure gauge and use it instead. Interested in what you come up with.

 

[Greenleaf]

Hi Swank,



I'll tell you... the guys over on the engine due dad forum have been discussing how to attatch a boost gauge to monitor drive pressure.



A boost gauge,copper tubing and what ever else they were rigging up. Look for it in the thread about "little 55" or "how do twins work"



I'm not aquainted enough with the 'puter to post the link, sorry.



GL

 

[JLEONARD]

https://www.turbodieselregister.com/forums/showthread.php?t=119530

 

[JLEONARD]

I didn't see details of how they hooked up the gage... . maybe I missed it.

Why couldn't one simply remove the pyro thermocouple and plumb a pressure gage temporarily into that hole?

Is that where the reading should come from???

Jay

 

[cerberusiam]

Why couldn't one simply remove the pyro thermocouple and plumb a pressure gage temporarily into that hole?

That is my understanding of how to test the drive pressure. The drive pressure should be as constant as the boost and not need an isolator to take bounce out of the gauge but thats a guess. A chunk of copper tubing is used as a heat sink to keep from melting the rubber line. I would make it as long as possible to keep the heat to a minimum in the end where the hose is hooked or run copper line all the way to the gauge.



My . 02

 

[Old Smoky]

swankmetal - Might want to try a wastegate. Checking drive pressure is easy. You can use a regular boost gauge, with about 3-4' of copper tubing coiled up to dissipate heat so that the plastic hose doesn't melt. Just remove your pyrometer, or drill and tap another hole, and install a boost fitting. The drive pressure will rise before boost, the rate depends upon the turbine housing size, and the mass of the turbo rotating assembly. The peak will depend upon the size of the turbine housing and wasetgate setup (a very restrictive exhaust system can cause problems too).



We do alot of dyno tuning, it's scary to see the drive to boost ratios that some setups make. An ideal ratio would be near 1:1. Having a proper wastegate is about the only way to do this. You can actually gain power by having a wastegate that is tuned to your application. An example is a friends '03 cummis: With an experimental box it made 410hp with about 32psi boost and 44psi drive. When the boost was raised to 39psi, the drive pressure actually pegged a 60lb gauge, and lost over 5hp. You can see that the increased pressure looses efficency, and is harder on parts. More boost doesn't always mean more power. I have seen similar results with my setup. Currently it produces 62psi boost, with 63psi drive. I have a drive pressure gauge that I watch every day to tune my compound turbos. Its a good thing more people are checking this.



Mike

 

[swankmetal]

Might want to try a wastegate.



i've got one. just an old actuator that i cut the housing off of. kind of like a ghetto turbomaster now. still messing with it to get it figured out. if i cinch it down, i see over 40psi. oh yeah, i've got the wg port drilled out to 15/16 (from the stock 5/8) all the way through the divider.



or drill and tap another hole, and install a boost fitting.



thats what i did. and ran copper tubing all the to the gauge



(a very restrictive exhaust system can cause problems too).



don't have one of those



and the mass of the turbo rotating assembly.



sooo, a bigger turbo affects the drive pressure in what way?



cerberusiam, why wouldn't the oil pressure gauge work? i would think that it's the same thing, no?



I have a drive pressure gauge that I watch every day to tune my compound turbos



i'm thinking that i will make this a permanent addition to my growing "array". so i can tune my non-compound turbo.



dave

 

[cerberusiam]

cerberusiam, why wouldn't the oil pressure gauge work? i would think that it's the same thing, no?

No. Fluids don't compress, air does. The actuator and rise rates will be different. While it may "work" you won't get a true reading. Yes?

 

[swankmetal]

gotcha. think that could have something to do with the bounce?

 

[cerberusiam]

Unless you have a major leak I would think the drive pressure should be fairly steady. That would be my guess on the bounce.

 

[SRadke]

I expect an oil pressure gauge should be adequate. Pressure is pressure, the compressability of the measured substance should only make a diffrence in the gauge if you have an extreme flow restriciton or something else that would prevent it from moving quickly. You could have a problem with the gauge though, wouldn't hurt to try a diffrent one.



-Scott

 

[Mark_Kendrick]

The bounce happens every time an exhaust valve opensthe copper tubing will help cushon the bounce a bit and dissipate the heat.



Boost pressure is fairly constant because of the rotary compressor. So unless you have a diesel turbine you're gonna see a pulse

 

[swankmetal]

UPDATE



cleaned up the install the other night. got copper tubing coming out of the manifold, rolled a few times, behind the head to a compression fitting backed with a nipple, about 3" of rubber hose, to another nipple/comp fitting, plastic tube to the gauge. no more noise in the cab and no more bounce of the needle.



stuffed a 58mm wheel into the old h1c the other day too. now, at 40psi i've got about 49psi of drive pressure. boost comes on HARD, too.



dave