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Old 09-30-2008, 02:54 AM   #1
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Default measured exhaust backpressure and turbine inlet pressure

Anyone measure these numbers?

I think my fancy metal cat took a **** from all the oil burning due to a leaky turbo seal... it used to show ~ 4 psi at redline and 10 psi of boost ...

But the turbine inlet pressure numbers look good...


GT2560 internal wastegate
ETD shorty manifold
BEGI custom divorced pipe downpipe
TDR i/c
2000 motor

turbine inlet pressure (includes exhaust backpressure)
4000 RPM/5 psi 6 psi
4000 RPM/10 psi 10 psi
6500 RPM/5 psi 10 psi
6500 RPM/10 psi 20 psi

exhaust backpressure measured behind turbo

4000 RPM/5 psi 1-2 psi
4000 RPM/10 psi 3 psi
6500 RPM/5 psi 3 psi
6500 RPM/10 psi 6 psi

Last edited by JasonC SBB; 10-01-2008 at 12:45 AM.
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Old 09-30-2008, 04:24 AM   #2
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interesting - can you share how you measured the egbp ?
I am also looking to measure that
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Old 09-30-2008, 12:48 PM   #3
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Went to plumbing store, bought 1/8 MPT - 1/8 compression fitting.
Bought 1 foot 1/8" copper pipe.
Bolted fitting into top of turbine 1/8 NPT tapped EGT hole
Cinched down pipe into fitting.
Used a length of 1/8" vacuum hose to driver's seat and a 0-30 psi pressure gauge.

If you want to see how compression fittings work look here at the exploded view:
https://www.miataturbo.net/forum/sho...0&postcount=21
There's the same kind of adapter there, but a larger size. Note the copper sealing ring, called a "compression sleeve".
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measured exhaust backpressure and turbine inlet pressure-tip-setup.jpg   measured exhaust backpressure and turbine inlet pressure-tip-adapter.jpg  
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Old 09-30-2008, 02:20 PM   #4
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wow !
thats incredible - props to you ! I always wanted to try that but I feared the heat of the exhaust gas and I also anticipated that the pressure there would be about 4 times what you measured !
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Old 09-30-2008, 04:41 PM   #5
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No issues with the exhaust heat to the gauge? or is something else needed? I'd love to try this with some muffler swaps to go with dyno pulls.
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Old 09-30-2008, 04:48 PM   #6
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Very cool!

There is no significant flow of exhaust gas through the gauge, so the main heat transfer enemy is conduction down the pipe. If one uses a long length of copper tubing to allow it to air cool, followed perhaps by a rubber hose, then it works. The same idea works for O2 tail pipe sniffers on dynos.

Pressure drop is also negligible down the tube. Simply put, no flow means no pressure drop.
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Old 09-30-2008, 06:45 PM   #7
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Wow those are incredible numbers! I always figured on average they'd be a little higher than that
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Old 09-30-2008, 10:55 PM   #8
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Yeah, you definitely gotta do something about that post-turbine pressure. Pretty stinkin' high...
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Old 09-30-2008, 11:12 PM   #9
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if you can get away with it, i think it would be cool to remove the cat and redo the test of post turbine pressure
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Old 09-30-2008, 11:40 PM   #10
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Yeah oil is bad on catalytic converters.

+1 to Mach929, I'd like to see the numbers without the cat in place.
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Old 10-01-2008, 12:44 AM   #11
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Quote:
Originally Posted by Mach929 View Post
if you can get away with it, i think it would be cool to remove the cat and redo the test of post turbine pressure
I have a bung post cat just for that. I just have to get under the car... it'll be a few days, I just wanna keep driving the car for now, I missed it. M3 isn't getting driven at all LOL.
Last time I measured it, it was 1-1.5 psi max IIRC... with the next smaller bodied magnaflow muffler than I have now...

I measured backpressure because when I was installing the downpipe, the brick in the cat was clunking around when I shook it... dammit that cat cost me ~$100.. I'm sure it's more than that now.
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Old 10-29-2008, 07:14 PM   #12
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OK I had a louvered core 2.5" glasspack installed, louvers pointing rear:
https://www.miataturbo.net/forum/t26866-2/#post325138
Exhuast is quieter than with cat.

Backpressure is 40-45% lower and I get:

at 10 psi of boost:
4000 RPM 2 psi
6500 RPM 3.5 psi

Is this acceptable?
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Old 10-29-2008, 07:25 PM   #13
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Quote:
Originally Posted by JasonC SBB View Post
OK I had a louvered core 2.5" glasspack installed, louvers pointing rear:
https://www.miataturbo.net/forum/t26866-2/#post325138
Exhuast is quieter than with cat.

Backpressure is 40-45% lower and I get:

at 10 psi of boost:
4000 RPM 2 psi
6500 RPM 3.5 psi

Is this acceptable?
Resonators and glasspacks, especially, break in. Give it a few weeks. When I put 3 glasspacks and a magnaflow, it was silent at idle (from 5 feet you could NOT hear the exhaust) and quieter than stock under cruise and acceleration. For a few days. After a month it's loud. Or to me it's loud. Louder than stock anyways.

Those number look better ut back pressure still seems kinda high. 1-2 PSI would be good I think. It climbing on you like that doesn't seem right. But your's is 2.5" not 3, so that's probably about right. 3 would perform better for sure.
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