Turbine pressure vs manifold pressure

[Clifton]

Has anyone measured there turbine inlet pressure and at what psi was your manifold or pre intercooler pressure?

[Tony D]

I know JeffP did on his last-before-this-build-turbo setup.... (LOL)

 

My recollection was that Exhaust Manifold Pressure (measured at a tap in the spacer before the turbo) was 23psi at a manifold pressure of 23psi, from 3000 to 7000rpm.

 

Below 3000, I don't recall if he measured that.

 

This was very good.

[Guest Dorifto]

^ Uhh, I think he meant on the intake-side, not the exhaust-side.

 

On my friend's RB20-powered 240SX, we saw a 2psi drop from the outlet of the turbo, to the manifold. We think there might be a small boost leak at the intercooler.

[S15 200sx owner]

^ Uhh' date=' I think he meant on the intake-side, not the exhaust-side.

 

On my friend's RB20-powered 240SX, we saw a 2psi drop from the outlet of the turbo, to the manifold. We think there might be a small boost leak at the intercooler.[/quote']

 

Arh, no he doesnt,

 

Turbine sizing 101.

 

If you size the turbine side of the turbo too small, it creates too much back pressure in the exhaust manifold and on the engine, therefore restricting horsepower, this can be felt as the power delivery "hitting the wall" at the top end of the rev range.

 

By sizing the turbine correctly if you can keep the exhaust manifold pressure to less than boost pressure or no more than, then you can actually start making serious horsepower from a turbo charged engine.

 

Most people end up using turbos that are too small for their application, you are better off using a turbo that is 50% too big than one 50% to small.

 

Hope that helps

 

Clint T

[yo2001]

I don't think you can make less back pressure than actual boost intake pressure. That would be my guess though. I was always told to aim for anything less than 2:1 ratio. So 40psi back pressure or less on 20psi boost. Actually use an oil pressure gauge to measure the back pressure. You would have to used copper line until it's far enough away from the manifold. Or you can go with a new AEM boost sensor. 3.5bar or higher reading is what you need.

[Clifton]

Ya. I'm talking about the turbine side. I've also heard 2.0 and 1.8:1. I haven't measured my pressure before the intercooler which I need to to do be accurate. At 26 psi manifold I was had 35 psi with a P trim wheel and 45 psi with an O trim wheel. Both are with a .70 hot side a/r. The P trim adds about 700 rpms of lag. I am running the O trim for now. It's too much fun having a broad power band. It almost feels like a supercharged V8 the way it comes on now, atleast when comparred to the P trim.

[yo2001]

That's a good bit of difference btw O and P trims. There are different P trims circulating around so you might have better luck with something different. I've seen 3 different Ptrims from 12 blade, 11 blade and 11 blage gen III. The P trim also suppose to be taller for better windage to get the wheel to spin compare with an O trim with small exducer. I think the fine compromise btw the two is 10 blade stageV wheel. Or there are other GT turbine wheels out there like GT37 wheel which is like 10 bladed version of a P trim.

[Clifton]

That's a good bit of difference btw O and P trims. There are different P trims circulating around so you might have better luck with something different. I've seen 3 different Ptrims from 12 blade, 11 blade and 11 blage gen III. The P trim also suppose to be taller for better windage to get the wheel to spin compare with an O trim with small exducer. I think the fine compromise btw the two is 10 blade stageV wheel. Or there are other GT turbine wheels out there like GT37 wheel which is like 10 bladed version of a P trim.

 

I've seen 3 different P trims too. I have the on that looks almost clipped but wasn't. T netics looks almost like a GT wheel and the other looks like mine just a little more blade on it ( not the clipped look). I don't know if any other P trim will spool any faster though. I've seen alot of dynos of 3.0 motors (7M and 2JZ) with P trim/.68's and none spooled any faster, basing that of how fast the motor reaches 400 ft lbs. I will keep the P trim turbo (T72) for the VH45 unless I find a .58 P trim housing to try for cheap.

[Tony D]

WOW!

2:1, 1.8:1?

 

My training said something on the order of between 3 to 5psi more than what you see in the inlet manifold. Having a multiple of boost seems like a VERY undersized turbine wheel...

[S15 200sx owner]

WOW!

2:1' date=' 1.8:1?

 

My training said something on the order of between 3 to 5psi more than what you see in the inlet manifold. Having a multiple of boost seems like a VERY undersized turbine wheel...[/quote']

 

Yes i fully agree Tony, as i said above, to start really expoiting a turbocharger and making good power, manifold back pressure of no more that boost pressure is desirable.

[Clifton]

My training said something on the order of between 3 to 5psi more than what you see in the inlet manifold. Having a multiple of boost seems like a VERY undersized turbine wheel...

 

A P trim wheel is pretty big.

 

 

 

Yes i fully agree Tony, as i said above, to start really expoiting a turbocharger and making good power, manifold back pressure of no more that boost pressure is desirable.

 

I don't think it is possible though.

 

Come on, one of you guys tap an 1/8" thread into your manifold and run some copper line to a gauge. It's fun to test:mrgreen:

[S15 200sx owner]

A P trim wheel is pretty big.

 

 

 

 

 

I don't think it is possible though.

 

Come on' date=' one of you guys tap an 1/8" thread into your manifold and run some copper line to a gauge. It's fun to test:mrgreen:[/quote']

 

It is, you just keep going bigger on the turbine until you achieve it, thats assuming that your post turbo exhaust is big enough.

 

Once you get the manifold back pressure down, you can then start treating the engine as a normalling aspirated race engine in regard to longer camshaft duration, which = Big horsepower.

 

As under a normal situation (high manifold back pressure) you have to keep cam duration short to avoid valve overlap otherwise you get too much exhaust dilution in the inlet charge because of the higher exhaust pressure to inlet pressure and both valves open together (overlap)

 

I have experimented with all this stuff above in the past on my turbocharged "A" series engine in my Mini racecar, very old school now, but the theory is still the same.

 

Who's confussed?

[dapiper]

I measured 38 psi on turbine side with 18 psi boost (380 RWHP) and then changed out Flowmaster for Dynomax (all 3") and achieved 410 hp at same boost. Exh BP went from 7 to 2.5 psi. L28E N42 with Turbonetics H3 and 0.69 A/R. Cannot find run data to determine change in turbine BP, unfortunately.

 

I thought you divide boost psia by effy to calc turb BP, i.e. (21+14.7) / 0.7 = 51 psia = 36 psig.

[Clifton]

I measured 38 psi on turbine side with 18 psi boost (380 RWHP) and then changed out Flowmaster for Dynomax (all 3") and achieved 410 hp at same boost. Exh BP went from 7 to 2.5 psi. L28E N42 with Turbonetics H3 and 0.69 A/R. Cannot find run data to determine change in turbine BP' date=' unfortunately.

 

I thought you divide boost psia by effy to calc turb BP, i.e. (21+14.7) / 0.7 = 51 psia = 36 psig.[/quote']

 

Thanks. This is what I was looking for.

[Pyro]

I'm sure there are ideal set-ups for max hp and different ideal set-ups for street perfromance.

 

I'm confident my hybrid turbo has less back pressure and makes a lot more HP than the old stock T3. But I miss the quick spool and low rpm street torque of the high back pressure T3 turbo. However, at the track I would be saying the opposite.

 

Isn't it back pressure that spins up the turbo?

[S15 200sx owner]

I'm sure there are ideal set-ups for max hp and different ideal set-ups for street perfromance.

 

I'm confident my hybrid turbo has less back pressure and makes a lot more HP than the old stock T3. But I miss the quick spool and low rpm street torque of the high back pressure T3 turbo. However' date=' at the track I would be saying the opposite.

 

Isn't it back pressure that spins up the turbo?[/quote']

 

Not so much back pressure, but more so pressure drop accross the turbo, ie low back pressure after the turbine, this is why fitting a larger low back pressure exhaust to a factory turbo car makes so much difference in power, it increases the pressure drop from before the turbine to after it.

[jeffp]

First the intake side of the house. You will want to acheive the best flow through the system you can with the hardware you select. Keep the pressure from turbine to intake manifold as low as possible. That means the correct intercoler and pipe. You can run a little inefficient on the intake side if you have enough turbo to get to the numbers you want.

The Exhaust side, the back pressure should not, if designed correctly, not reach the cut over point on the back pressure. This 2 1/2 times exhaust back pressure to intake pressure is ok, is just bull. That includes ANY turbo application, and will only serve to increase efficiency of the system in ANY application. If you plug up the pump with excessive pressure on the turbine side, there will be no place for the intake to exit after combustion, so try to keep it at least equil.

[S15 200sx owner]

This 2 1/2 times exhaust back pressure to intake pressure is ok, is just bull. That includes ANY turbo application, and will only serve to increase efficiency of the system in ANY application. If you plug up the pump with excessive pressure on the turbine side, there will be no place for the intake to exit after combustion, so try to keep it at least equil.

 

Exactly! It would be like sticking a potato up your tailpipe!

[Clifton]

OK. I measured the pressure, pre intercooler(Ebay 12x24x4 thick). 30 psi. So I have a 4 psi pressure drop at around the 600 hp level. Seems high but without knowing what everyone else has it's hard to compare. Regardless, the P trim is running 5 psi higher than my compressor discharge. The O trim is 15 psi higher. I was checking only to see how my setup compares to others. It makes more power than I probably should have on the streets so power isn't an issue. I would love to know what the turbine pressure is on one of those GT35's. They spool pretty fast. I'll check the exhaust BP after the turbo next.

[Tony D]

Come on, one of you guys tap an 1/8" thread into your manifold and run some copper line to a gauge. It's fun to test:mrgreen:

 

Uh, why do I need to? Jeff P did it, and had 23/23 as I posted above. I will ultimately be running his setup turbochargerwise on my black car using a standalone EFI system, so given I have seen his testing setup I trust his numbers.