Xede, GT2560, 12psi - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-20-2008, 11:36 PM   #1
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Default Xede, GT2560, 12psi

Took the car to Gas Head Motorworks in Houston this morning and they spent about 2 hrs working on my bitch to idle decently and about an hr on the dyno.

For the last 2 weeks it would have a very lumpy idle with the AC on and stall when the RPM dropped much below 1K. Tip in was jerky and it was difficult to cruise at low 1st and 2nd gear speeds below 2K rpm. WOT felt great, though. Also a CEL was always lit for misfire.

They moved the 02 sensor further down since they suspected it was getting too hot and screwing with my air/fuel. It helped the idle immensley and Clint was able to smooth out the idle after that.

Going from his shop to another shop (where the dyno was) he drove and had me adjust settings at various RPM and load. This helped driveability immensly.

Only gained a few peak HP and torque but everything under the curve was smoother and better.

I don't have a scanner but it was on a dynojet:
227 hp @ ~ 6600 RPM
218 ft-lbs @ ~ 3800 RPM
air/fuel stayed between 13 and 14 but dipped close to 12 at 3600 RPM
temps were in the low 90's this afternoon

Great shop, Clint and Kevin are awesome and know their Miatas.
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Old 05-20-2008, 11:40 PM   #2
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Is that RWHP, uncorrected? Your AFR was not 13-14 while at full boost, right?
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Old 05-20-2008, 11:41 PM   #3
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How was AFR measured? I know I wouldn't want to see 13-14 AFR under boost.
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Old 05-21-2008, 12:02 AM   #4
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AFR measured with a wideband. One hooked up to the dyno/tailpipe and another at the the downpipe.

Yes it was 13-14 under boost. What's typical?
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Old 05-21-2008, 12:08 AM   #5
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13-14 is most commonly seen are piston melting territory.
Most people shoot for 12-12.5:1. While 13:1 is seen as dangerous and 14:1 is preposterous if you see that as a safe AFR for in boost.
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Old 05-21-2008, 12:10 AM   #6
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low 12's is desirable. if you have a cat a tail pipe sniffer will show half a point leaner than actual but that still puts you at too lean.
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Old 05-21-2008, 12:16 AM   #7
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Wow that's frightening! Wouldn't I be getting detonation if it was at such an unsafe threshhold?

Guess I'll have to work on this a little more.
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Old 05-21-2008, 12:25 AM   #8
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I'm surprised your engine has even survived.
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Old 05-21-2008, 12:29 AM   #9
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We did 8 pulls.
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Old 05-21-2008, 12:37 AM   #10
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Quote:
Originally Posted by Jesse H View Post
AFR measured with a wideband. One hooked up to the dyno/tailpipe and another at the the downpipe.

Yes it was 13-14 under boost. What's typical?
At what RPMs did you see boost? Maybe those AFRs where prior to going into boost. Still, better safe than sorry so check it as soon as you can.
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Old 05-21-2008, 01:23 AM   #11
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It starts to really spool at ~3300 RPM and full boost at 3700 RPM. AFR's stay 13.5 to 14 from 4K to redline.

Definately going to address this tomorrow, thanks for looking out guys.
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Old 05-21-2008, 01:29 AM   #12
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Quote:
Originally Posted by Jesse H View Post
It starts to really spool at ~3300 RPM and full boost at 3700 RPM. AFR's stay 13.5 to 14 from 4K to redline.

Definately going to address this tomorrow, thanks for looking out guys.
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Old 05-21-2008, 01:41 AM   #13
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Ya, I really like Gashead too. Clint and Kevin both do an outstanding job. They squeezed out 230 whp on mine.

Nice numbers you made, but hopefully 13-14 isn't the AFR you were running at full boost. Maybe the wideband was reading off?
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Old 05-21-2008, 02:56 AM   #14
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Point is that real tuners should know that 13-14AFR is WAY too lean under any amount of boost. Hell a bunch of knuckle heads on some forum know that it's bad m'kay. Doesn't matter if the reading was off or not. They could have cost the guy a motor.

Tuned indeed.
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Old 05-21-2008, 03:07 AM   #15
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To be fair, if you had an EGT gauge that was reading correct engine temps, and the guys did tests at both 12.0:1 and 13.0:1 and 14.0:1, and the 13-14 range made more power with acceptable EGTs, then I would be OK with it.

Somehow I doubt you have an EGT gauge, and somehow I doubt those tests were done. Does that shop have experience with turbo tuning, or are they mostly an NA shop?
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Old 05-21-2008, 03:09 AM   #16
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The shop is one of the most notable Miata shops in the Houston area. Though they couldn't figure out how to tune an AEM F/IC with IRTBs, I do get my alignments there.
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Old 05-21-2008, 03:22 AM   #17
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Quote:
Originally Posted by Savington View Post
To be fair, if you had an EGT gauge that was reading correct engine temps, and the guys did tests at both 12.0:1 and 13.0:1 and 14.0:1, and the 13-14 range made more power with acceptable EGTs, then I would be OK with it.

Somehow I doubt you have an EGT gauge, and somehow I doubt those tests were done. Does that shop have experience with turbo tuning, or are they mostly an NA shop?
I agree but that's doubtful at 12psi on a relatively small turbo with 9.5:1 static compression.
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Old 05-21-2008, 10:03 AM   #18
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Sorry, any dyno operator who lets a pull continue when things get above mid 13's is nobody I'd take my car to.

The last dyno-day here in Hampton Roads, we had a Voodoo'd '97 where the operator aborted at around 4000rpm when there was a steady rise above 13:1 and was clearly on it's way to dangerous. He said, needs more fuel and we'll try again. Next run, aborted at about 4500rpm where we ran out of fuel... etc.. etc... We maxed out pots over several runs until it would stay rich enough.
I was impressed beyond words... we all know what happens to a shops' reputation when they start blowing up motors.
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Old 05-21-2008, 12:11 PM   #19
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Quote:
Originally Posted by Savington View Post
To be fair, if you had an EGT gauge that was reading correct engine temps, and the guys did tests at both 12.0:1 and 13.0:1 and 14.0:1, and the 13-14 range made more power with acceptable EGTs, then I would be OK with it.

Somehow I doubt you have an EGT gauge, and somehow I doubt those tests were done. Does that shop have experience with turbo tuning, or are they mostly an NA shop?
Not all knock is audible either. Just because EGT are in line doesn't mean that damage isn't happening.
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Old 05-21-2008, 12:22 PM   #20
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Ok I just got off the phone with Clint. He wasn't basing his AFR off the dyno's WB but the one at the downpipe, pre-cat. The unit looked like an Innovate LM-1.

He said he kept AFR's in the low 12's.
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