GT2560 - 261 ft-lbs, 272 hp - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-19-2011, 02:15 AM   #21
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That's pretty late for full retard. In my experiments, staying advanced that long hurt my spool a lot. In fact, by staying fully advanced longer I could delay hitting my boost target by 1500RPM IIRC. Whee I guess
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Old 09-19-2011, 04:10 AM   #22
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I wonder if the Blox manifold on my car helps to smooth out the spool-up spike that you see, Jason. Look at the Excel chart - the torque uptake is much smoother with the Blox manifold than it is with the stock manifold.
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Old 09-19-2011, 04:38 AM   #23
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Jason, after looking at your boost vs. RPM plot again, you've got something going on that is hurting spool. 10psi at 3500rpm is really, really slow.

https://www.miataturbo.net/diy-turbo-discussion-14/i-want-your-spool-data-26641/

Put your boost curve into that thread - you are spooling up really, really slowly.
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Old 09-19-2011, 11:20 AM   #24
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It's not hard to do a full retard run
a full advance run
and a few runs in between.

I guarantee more advance below 4000 will improve that spool situation.

Perhaps I *do* need to dyno my car on october 15 to do some VVT data pulls...
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Old 09-19-2011, 12:44 PM   #25
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Hmm the post I typed last night didn't show up.

After thinking long and hard, I suddenly remembered the giant O ring in the compressor housing (sealing against the CHRA), has been broken for years. It's in there, it just doesn't complete an entire circle. The replacement has been sitting around for years. So, I have a small boost leak. This maycontribute to the slow spoolup, along with the wrong VVT setting ~ 3200 RPM. I'm glad that Ian's data is there to compare against. Without it I'd have been blissfully unaware of a spoolup problem.

Tomorrow I go in for (left) knee surgery (ACL recon), so it'll be a few weeks before I can drive a stick.
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Old 09-19-2011, 12:52 PM   #26
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Ummm, that's a pretty significant issue. Id get that replaced asap.
You know you're probably pushing way more pressure and overspinning the turbo to keep up with that boost leak right? Just my .02
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Old 09-19-2011, 01:43 PM   #27
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Quote:
Originally Posted by JasonC SBB View Post
Tomorrow I go in for (left) knee surgery (ACL recon), so it'll be a few weeks before I can drive a stick.
Ouch, good luck buddy. I had that one about 5 years ago, same knee. I found the secret to driving a stick was to not tell the doctor the car is a manual. That way he can't tell you not to do it. Also, your crutches will easily fit between the seat and rollbar.
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Old 09-19-2011, 01:48 PM   #28
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Quote:
Originally Posted by Savington View Post
Jason, after looking at your boost vs. RPM plot again, you've got something going on that is hurting spool. 10psi at 3500rpm is really, really slow.

my 1.6L with china t3 spools better.
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Old 09-19-2011, 01:54 PM   #29
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Here's a great way to analyze a dyno plot.

BMEP (in psi) and BMEP per MAP in psi per atmosphere of MAP

BMEP (in psi) = tq (ft-lbs) / displacement (L) * 2.47

BMEP per MAP = BMEP / MAP (in atmosheres)

BMEP per MAP = BMEP / MAP *101 (if MAP is in kPa)

The magic number is 180 psi at torque peak.
This translates to 73 ft-lbs per L per atmo of MAP.

Here's the importance of BMEP
http://www.epi-eng.com/piston_engine..._yardstick.htm

The resulting BMEP/MAP is an indication of VE and correct ignition timing.
In my curve above, the plot from 4000-7000 is VE
The reduced VE below 4000 RPM is due to the the wastegate being closed, TIP is higher to accelerate the turbo shaft.
Attached Thumbnails
GT2560 - 261 ft-lbs, 272 hp-bmepplot2.gif  

Last edited by JasonC SBB; 09-19-2011 at 06:50 PM.
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Old 09-19-2011, 02:03 PM   #30
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Quote:
Originally Posted by 18psi View Post
Ummm, that's a pretty significant issue. Id get that replaced asap.
You know you're probably pushing way more pressure and overspinning the turbo to keep up with that boost leak right? Just my .02
Small leaks are more significant at spoolup than at high RPM tho.
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Old 09-19-2011, 02:04 PM   #31
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Quote:
Originally Posted by Savington View Post
Jason, after looking at your boost vs. RPM plot again, you've got something going on that is hurting spool. 10psi at 3500rpm is really, really slow.

https://www.miataturbo.net/showthread.php?t=26641

Put your boost curve into that thread - you are spooling up really, really slowly.
Hmm, I think I broke it after this boost plot which I posted, 10 psi by 3000 RPM:
https://www.miataturbo.net/showpost....3&postcount=12
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Old 12-11-2011, 03:22 PM   #32
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Quote:
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Haven't I told you that this isn't correct before, Jason?

Purple line is my first built motor (84mm 8.6:1, BP4W head, GT2871R). Blue line is my second built motor (83.5mm 8.6:1, VVT head, GT2871R) with VVT at full retard.



Now look at the old motor vs. the new motor w/ VVT advanced under 4500rpm (huge low-end gains) and the Blox manifold installed (huge top end gains). VVT is at full retard from ~5000rpm up, just the same as it was in the blue/purple chart - if VVT were causing the top-end gains, they would have appeared in the blue/purple chart - but they didn't. The lighter lines under it are the lines from the previous visit, which was VVT and the Blox manifold at 14psi on 100 octane.



All four torque curves synthesized into one:



See how the torque curve extends flat to 6000rpm on both of the Blox curves, but the torque drops at 5000 on the stock manifolds? Now look at your torque curve - the torque drops at 5k.

VVT does not have any effect on high-end torque - the intake manifold makes that difference, and I've never seen any data to disprove that.
Just to clarify, all the above "stock intake manifold" plots above are with the VICS manifold (including the VVT head plots), right? No 01/VTCS manifolds mixed in?
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