'94 BEGI S pre-4k bog - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-26-2008, 06:35 PM   #1
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Default '94 BEGI S pre-4k bog

Last year I bought a BEGI-S for my '94 to get some base numbers, then upgrade bit by bit to see what each "upgrade" can net this particular kit. Started at 97rwhp stock, up to 171rwhp non-intercooled with Bipes and 190lph pump and just recently intercooled.

Before I dyno it intercooled, I'm still trying to debug why it bogs below 4krpm. It happened immediately after installing the intercooler so the only change would be cooler air/denser air. Throttle response change was not really noticeable.

Before the intercooler it would start pulling pretty darn good from 2500rpm on up, but now it's quite weak until 4krpm then gets going nicely.

setup:
190 Walbro
BEGI-S (non-separated gasses) GT2554 (intercooled) 8psi
stock injectors
BEGI FMU
Bipes ACU
Base timing set at 12 BTDC (i believe)

Bipes settings: (aggressive)
Airflow to Retard: Open Open Open = max retard 4
Airtemp to Retard: Open Open = 1 degree retard for each 65 degrees F)
RPM Map: Closed Closed = Start Retard RPM 3000

I've gone through different Bipes settings, played with the FMU but with no luck. I've returned it back to the settings I had pre-intercooled to start over.

Any ideas on this bog? I want to dial this out and dyno before moving to larger injectors and MSPNP.

Thanks!

d
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Old 05-26-2008, 06:38 PM   #2
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If you don't have a wideband you need one. That should be your next purchase. I bet you're just going lean or really rich and that is causing it to bog.
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Old 05-26-2008, 06:40 PM   #3
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What does your fuel pressure look like? How much boost? Where are you getting the signal for your wastegate ad FMU?

That should be a lively turbo below 4000rpm. I doubt it is the BIPES, I would suspect a fueling issue.
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Old 05-26-2008, 06:43 PM   #4
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I never looked into the O2clamp but is this issue corrected with the O2clamp?
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Old 05-26-2008, 06:51 PM   #5
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ah, forgot to mention, thanks for reminding me. We do have an Innovate wideband at the shop that is telling us that it's running lean, which led me to play with the FMU. I admit that we've never tuned the FMU before so we were green here. Trying both ends of the spectrum of adjusting both the needle valve and the main diaphragm we still experienced the problem.

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Old 05-26-2008, 07:16 PM   #6
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If it's running lean then that is your problem. It needs to be running at 12.5:1 in boost or richer. But not richer than 11:1. It will continue to bog until to fix that.
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Old 05-26-2008, 07:51 PM   #7
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Quote:
Originally Posted by cjernigan View Post
If it's running lean then that is your problem. It needs to be running at 12.5:1 in boost or richer. But not richer than 11:1. It will continue to bog until to fix that.
Well, then the only thing adjustable is the FMU, or to decrease the boost. Do you have any experience tuning the FMU to get more fuel at low RPM? is that even possible with the BEGI FMU?

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Old 05-26-2008, 07:57 PM   #8
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yes, you increase the preload with the top screw adjustment. But then you need to back off the needle valve.

What did you set the pressure, with the vacuum line to the OEM FPR disconnected, at?
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Old 06-02-2008, 07:54 PM   #9
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sorry to get back so late, i've had to loan the car out to a customer while we fixed their blown engine

I've had the pressure set from 60-75psi with the line off and played with the needle valve in various positions.

Is there a way to calculate what the pressure should be set at if I have the boost set at 6, 7, 8, or 9psi? How should the needle valve be adjusted with the main diaphragm adjustments?

thanks!


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Old 06-02-2008, 10:19 PM   #10
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wideband. go buy one.
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Old 06-02-2008, 11:41 PM   #11
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How does it respond from a rolling start at 4k and above?

I'd have to add my out of the *** guess that it's lean tip in. If you're moving over to a MSPNP, not sure what you want to get out of fussing with your AFPR.
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