SR20DET builds boost but feels NA - Miata Turbo Forum -Boost cars, acquire cats.

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Old 08-26-2016, 01:50 PM   #1
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Default SR20DET builds boost but feels NA

I am asking this question here because this is the community I am a part of even though I imagine a Nissan forum may be more appropriate. Plus, most of you are mad smart with car stuff so...

I have a friend who has a 240sx "race car" that weighs about 2700lbs dry. It has a garrett 2854 turbo at 18psi, aftermarket EMS, SR20DET "red top" motor.

It feels slow. We haven't had it on a dyno but it feels far too slow for the boost levels it is running at. It doesn't feel markedly different between wastegate and EBC.

The car has felt slow ever since he got it. It felts slower than it should have with stock ecu, piggybacked/chipped ecu, two different turbos (new, verified good), two different exhaust manifolds. Boost pressure (wastegate 6-8psi and ebc 18psi) is referenced to the ECU from the manifold.

We have:
swapped ecus from stock to Haltech and back
checked dwell
checked cam timing
checked to make sure the correct cams are in the right position (exhaust and intake not switched)
verified timing marks on damper mechanically correct to TDC
switched injectors
swapped turbos
swapped exhaust manifolds
checked engine compression (150-160 across the board)
swapped spark plugs and wires
appropriate AFRs at full throttle/boost
swung the timing about four degrees forward and back with NO discernable change in power.
It IS a shitty BOV, but if the BOV or if there was a boost leak why would we be hitting 18psi by 3,000 rpm or so?

What are we missing?
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Old 09-07-2016, 11:32 AM   #2
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Bump?
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Old 09-07-2016, 11:41 AM   #3
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Clogged exhaust. Best guess right now.

What afr are you seeing?
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Old 09-07-2016, 01:46 PM   #4
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Exhaust is 3" from DP to tailpipe. No cat or muffler. Exhaust has been checked for crushes and obstructions. AFRs are correct (11 to 12ish from memory) checked against the standalone AFR gauge in the shop.
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Old 09-07-2016, 01:58 PM   #5
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If the BOV is shitty and leaking you can still hit your target boost, but that means the wastegate might be still almost completely shut and the turbo is overspeeding in order to produce that pressure, and it's way out of the efficiency zone so it's just blowing tons of super hot air and not making any more power.
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Old 09-07-2016, 04:07 PM   #6
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Quote:
Originally Posted by Arca_ex View Post
If the BOV is shitty and leaking you can still hit your target boost, but that means the wastegate might be still almost completely shut and the turbo is overspeeding in order to produce that pressure, and it's way out of the efficiency zone so it's just blowing tons of super hot air and not making any more power.
This, ask me how I know..... Actually don't.

Blcok off the BOV to test if youre brave, or get a known good and try again.
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Old 09-07-2016, 11:59 PM   #7
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Cool. We will gather the tools to do a full pressure test of the charge pipe system and test the car next time it comes in to the shop.

The reason we discounted it to this point was that it makes boost so quickly and holds 18psi at a very reasonable duty cycle on a 10psi actuator.

one other thing we want to check is wither or not the camshafts are correct. One of our first suspects were cams out of time, but it's been checked over and over. We half suspect that the motor was assembled with some odd assortment of parts that don't work correctly with factory assembly procedures.
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