datalog: AIT, boost - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-29-2007, 12:41 AM   #1
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Default datalog: AIT, boost

Just looked at a log from the last time I took the car out to log some full throttle boost runs. Ambient was 80f, air intake temp was 28.4c/83f at the start of the boost run - 1700rpm. AIT rose to a peak 44c/111f at 7000rpm. Boost onset was 1900rpm, peaked 13.8 psi at 4000rpm eventually falling off to 12.2psi. I've got a tiny spearco cored IC - core is 3x16x6. Anybody have any similar data?

Also notice how much the boost falls off after it peaks at 4k rpm. It settles down to just over 12psi around 6k rpm and holds that until the end of the run at 7k. I've seen worse, and I've seen better, but better is usually on an external gate. I'm running an internally gated t3 .48AR turbine. Am I seeing the internal gate trying to "catch up"? I've moved the signal hose over to the manifold and got identical results. - rob
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datalog: AIT, boost-log.jpg  

Last edited by m2cupcar; 04-17-2007 at 04:48 PM.
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Old 03-29-2007, 01:27 AM   #2
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It takes more initial force to open the wastegate (compress the spring) than it does to keep it open once it has moved. So what is happening is it is overcoming the spring force and surpassing what you have it set to. Then it settles to an equilibrium.
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Old 03-29-2007, 08:27 AM   #3
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Add a helper spring...The spring in the can is too weak. =>The exhaust gasses are producing the power to open the wastegate.
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Old 03-29-2007, 09:58 AM   #4
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thanks guys- I should have known that given how many times I've read it
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Old 04-16-2007, 05:47 PM   #5
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Default helper spring installed and tested

Quote:
Originally Posted by m2cupcar View Post
...Boost onset was 1900rpm, peaked 13.8 psi at 4000rpm eventually falling off to 12.2psi. ...
Got my helper spring setup and made one datalog run (green=rpm, other=boost). Definitely saw some changes. First off I got boost onset at under 1400rpm - and this was with an older map that had one degree ign retard overall compared to the prior. Peak boost was over 1 psi higher and maintained a higher level than previously to redline. There is also a rise near the end of the run, whereas previously it stayed flat. The boost curve still follows the similar "spike and fall" pattern, but more importantly I've decreased the differential from peak to droop by almost a full pound of boost. Next step is to tighten up the spring.

My helper springs set up consists of a small link on the flapper arm with the spring running to a turnbuckle eye bolt, which runs through the wg can bracket and is double nutted on the other side. - rob
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datalog: AIT, boost-afterhelper.jpg   datalog: AIT, boost-helperspring2.jpg  
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Old 04-17-2007, 01:19 PM   #6
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Default helper spring 2

Just made another logged run. This run had the rod/spring tightened about 3/16". The boost curve is again similar, this time a greater differential between peak and low, and the overall boost at mbc stop to redline is higher. It looks to me that what I'm seeing now is something that can be helped by the spring, but not resolved. Perhaps a limitation on the stock internal gate design? Comments? - rob

dashed line = boost, bottom green = rpm, orange = AF, green = AF target
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Old 04-17-2007, 02:01 PM   #7
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Rob,

Have you tried the link's boost control?
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Old 04-17-2007, 02:25 PM   #8
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Yes. I spent a good amount time trying to get it work (and doubting my IQ) only to figure out that I've got a dead component on my link board.

I know where the component is located on the board, just need to confirm the exact specs (have the location) and then swap it out.

Decided to run the mbc just so I could drive the car and get it tuned, rather than working on one more thing that keeps the car sitting in the garage.

* Something else I noticed on the logs was that I have no spike when I'm running through the gears. Only spikes when I do a boosted run from a low rpm. Perhaps another indicator that there's more at "fault" than the actuator.

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Old 04-18-2007, 12:09 PM   #9
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Good info.

I know from my dyno runs that the spring did help smooth out my boost curve above the 8-9 psi range. It definitely wasn't a perfect fix at the time though. My wastgate looked like it was still leaking a lot above 9. I figured it just needed to be messed with a bit which i didn't have the time to do before more runs.

I think I've messed with mine as much as I can. I just need to get a couple of runs in to se if anything has been resolved.
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Old 04-18-2007, 12:43 PM   #10
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yes - as with most simple/cost effective solutions, this requires quite a bit of fiddling with and will never be perfect, but seems to yield a nice improvement for the cost IMO.
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