Crazyness under boost around 4500 rpm at 8psi - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-19-2009, 03:56 AM   #1
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Default Crazyness under boost around 4500 rpm at 8psi

I had a fun trip to the exhaust shop today, I was able to get the car up to 8.2 psi. I'm using 1.8 injectors on a 1.6NA with a t28 turbo. Around 4600 rpm the car seemed to stall a bit, but once it got past that 5000 or so it just started charging again. I'm wondering if my transition from 100 to 128 kpa is to large a jump. I think my Max kpa was something like 156, so maybe I just need to scale my ve table down from 230kpa max to around 160 to 170 kpa, and then try and smooth out the transition.

If I'm seeing 80% Duty cycle on 1.8 injectors at 8psi, any chance I could safely run 9 or even 10psi after getting this tuning issue sorted out.

Both the msq and log are attached if anyone cares to review them.

BTW I was quoted 250.00 to build exhaust system, with me providing the muffler, and my old high flow cat. The shop is also going to build me a test pipe. I'm not as into the test pipe, since I will have one coming in the future. Just wondering if anyone had any thoughts on this price. I sort of think is not a bad price considering the flanges. The exhaust will start after the after the downpipe. They will modify my current cat to fit, and then build start with fresh piping from that point.
Attached Files
File Type: xls datalog200909181304.xls (1.15 MB, 55 views)
File Type: msq Base_Turbo_Tune_JJS_megasquirt200909131331.msq (35.0 KB, 55 views)

Last edited by apariah; 09-19-2009 at 04:07 AM.
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Old 09-19-2009, 04:59 AM   #2
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Looks like overboost is kicking in. msq says you have it at 152kpa. 8psi is ~ 155kpa.
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Old 09-19-2009, 05:05 AM   #3
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Boost spike and hitting over boost.

Get bigger injectors for more boost. I wouldn't feel safe going over 80-85% duty on any injector just to have head room. And whats up with the max RPM of 11600?!?

I got 2.75 from downpipe back to a 14" resonator to a split at the back axle for duals for 130ish. Flanged DP and at the diff. Included about 6 hangers and about 2 hours time. Just to give you an idea. But then again the shop does all my exhaust work I need and I tip them well

Last edited by DXO; 09-19-2009 at 05:20 AM.
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Old 09-19-2009, 12:43 PM   #4
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I agree, I was trying to remeber where I saw the issue, I was not looking at the MSQ at the time, the machine I'm using does not have mega long view installed so I couldn't verify the exact number. I

As far as overboost kicking in, since I have not set overboost, I didn't think I even turned it on since I don't have the GM Boost solenoid, is it on by default. May be set to initiate when you reach 80% duty cycle on your injectors>

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Looks like overboost is kicking in. msq says you have it at 152kpa. 8psi is ~ 155kpa.
I have no clue where 11600 max rpm is coming from, that looks like insanity to me. However it might be the max rpm setting in MLV.
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Old 09-19-2009, 02:13 PM   #5
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The crazy max RPM was just a fluke. Happens occasionally.

The Overboost Protection setting is set at 152kpa right off the bat in the pnp base maps.

Overboost Protection cuts fuel for a brief second, (the massive drops in PW and duty cycle in the log when boost spikes) in an attempt to prevent more boost.

Think of it as a rev limiter that activates when you have too much boost.
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Old 09-19-2009, 03:53 PM   #6
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Can I take that to mean if I raised this default overboost protection, my stock setup would probably produce more than 8psi with the current wastegate actuator.

I guess its best to leave things as they are for now until I can get larger injectors.

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Originally Posted by ssmith View Post
The crazy max RPM was just a fluke. Happens occasionally.

The Overboost Protection setting is set at 152kpa right off the bat in the pnp base maps.

Overboost Protection cuts fuel for a brief second, (the massive drops in PW and duty cycle in the log when boost spikes) in an attempt to prevent more boost.

Think of it as a rev limiter that activates when you have too much boost.
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Old 09-19-2009, 05:48 PM   #7
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Is the wastegate at its lowest setting? You could probably loosen it a bit and be fine. Right now its just spiking, If you increase the overboost to 9.5 psi you probably wont hit it again.

Last edited by ssmith; 09-19-2009 at 06:12 PM.
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Old 09-19-2009, 06:14 PM   #8
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The wastgate is probably at its tightest, I adjusted overboost to a bit higher and everything was great I went up to 6500 rpm no prob.

Last edited by apariah; 09-19-2009 at 08:33 PM.
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