Measured backpressure on stock turbo
#1
Measured backpressure on 8 turbo (vid post 4)
Did a quick test on turbine pressure relative to charge pressure for those curious about backpressure on small turbo's.
Setup: VIII turbo with 10.5 HS, stock WGA with about 5psi preload over stock, stock cam gear settings, methanol injection, MBC, stock exhaust manifold and O2 housing, stock intake manifold, IC and charge assembly, temperature about 75 degrees.
compressor psi / turbine psi
Pressure was obtained by tapping into egr valve hotside and readings were taken from a pressure guage.
Eventually I will do the same test with delayed intake valve openening
Setup: VIII turbo with 10.5 HS, stock WGA with about 5psi preload over stock, stock cam gear settings, methanol injection, MBC, stock exhaust manifold and O2 housing, stock intake manifold, IC and charge assembly, temperature about 75 degrees.
compressor psi / turbine psi
10 / 10 (3700 rpm)
20 / 20
25 / 35
30 / 40 (4500 rpm)
28 / 42
27 / 45
26 / 48 (7000 rpm)
Rpm data is crude relative to pressure differences. Pressure will peak at 48 psi I believe due to pressure induced WG relief.20 / 20
25 / 35
30 / 40 (4500 rpm)
28 / 42
27 / 45
26 / 48 (7000 rpm)
Pressure was obtained by tapping into egr valve hotside and readings were taken from a pressure guage.
Eventually I will do the same test with delayed intake valve openening
Last edited by C6C6CH3vo; Feb 25, 2008 at 06:42 AM. Reason: added vid post 4
#2
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Good info. FYI if you were to do a pull from ~2krpm or so and plot backpressure vs rpm, you will see a increase in slope as the wastegate starts opening.
Assuming VE doesn't fall off a cliff beyond 7krpm, backpressure will keep rising beyond 48 psi.
Assuming VE doesn't fall off a cliff beyond 7krpm, backpressure will keep rising beyond 48 psi.
#3
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at those back preasures I would start looking for a new turbo, granted we run a v8 in our race car but none the less we had a very simalar looking chart in the start of our quest for a championship. We had tried 2 turbos both same GT4708 compressors 2 different exhaust wheels and 11 exhaust housings before we got the setup we wanted. our original peak preasures were 19psi boost @ 49lbs backpreasure making 849 hp at the wheels on a Dynocom dyno. Our final turbo and exhaust housing combined with a HKS 60mm wastegate neted peak power at 17psi boost at 21lbs back preasure making peak power of 978hp all gained by getting rid of the backpreasure. Downfall is lack of spool up time in a street car, but I am trying other ways of getting rid of the backpreasure by going overjill on the wastegates.
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at those back preasures I would start looking for a new turbo, granted we run a v8 in our race car but none the less we had a very simalar looking chart in the start of our quest for a championship. We had tried 2 turbos both same GT4708 compressors 2 different exhaust wheels and 11 exhaust housings before we got the setup we wanted. our original peak preasures were 19psi boost @ 49lbs backpreasure making 849 hp at the wheels on a Dynocom dyno. Our final turbo and exhaust housing combined with a HKS 60mm wastegate neted peak power at 17psi boost at 21lbs back preasure making peak power of 978hp all gained by getting rid of the backpreasure. Downfall is lack of spool up time in a street car, but I am trying other ways of getting rid of the backpreasure by going overjill on the wastegates.
With that said, bigger wastegates won't do a thing for backpressure. All a bigger gate will let you do is run less boost.
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There are definitely a lot of gains to be had by reducing backpressure. What's amazing is that so few shops/tuners/racers even measure it. So you're one up on the others right there.
With that said, bigger wastegates won't do a thing for backpressure. All a bigger gate will let you do is run less boost.
With that said, bigger wastegates won't do a thing for backpressure. All a bigger gate will let you do is run less boost.
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#9
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Sizing turbo compressors for an application is the easy part. It's the sizing of the turbine side that is the challenge to getting the best compromise with respect to power vs. response.
#12
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Will do JKav. I'm presently using a smallish .70 A/R TS T4, but that's going to be too small for what I want ultimately. I've already secured a 1.00, so we'll plug it in soon and see where that takes us.
As for the EBP, the Ford sensor might be a good idea. I'll have to look into that. I hadn't really considered the discharge press. I may end up needing too many fittings to squeeze that one in, although I'd like to run the EPB and EGT from the same manifold tap in order to make all as practical and easy to retrofit as possible.
As for the EBP, the Ford sensor might be a good idea. I'll have to look into that. I hadn't really considered the discharge press. I may end up needing too many fittings to squeeze that one in, although I'd like to run the EPB and EGT from the same manifold tap in order to make all as practical and easy to retrofit as possible.
#13
The 48 psi backpressure itself does not scare me with at least 26 psi on the charge at 7K, what scares me is what it would be beyond 7K when boost tapers even more.
I'm anxious to see how decreasing overlap slightly will effect this, like about 2 degrees delay on intake.
#14
I'm wondering if there in any profit by just increasing the turbine housing if there is one available larger than a 10.5. Hate to go through the trouble and expensive of a new turbo when mass flow is the primary problem. A test with a 9.8 would give a good indication.