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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 05-23-2007, 11:28 PM   #1
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SO I DID some math for a hp goal. around 190 whp would be nice. I figured i needed about(9-10psi boost) 413cc of fuel at 115psi with tan tops; fuel rising 6 to 1. if i did my math correct I can run 9-10psi boost at 413cc of fuel at 80psi with supra green tops fuel rising 3 to1. when running bigger injectors(green tops) do i delay fuel rise until about 1 to 2psi of boost.

is any of this this correct?
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Old 05-24-2007, 12:42 AM   #2
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SO I DID some math for a hp goal. around 190 whp would be nice. I figured i needed about(9-10psi boost) 413cc of fuel at 115psi with tan tops; fuel rising 6 to 1. if i did my math correct I can run 9-10psi boost at 413cc of fuel at 80psi with supra green tops fuel rising 3 to1. when running bigger injectors(green tops) do i delay fuel rise until about 1 to 2psi of boost.

is any of this this correct?
With my T25 .80ar and 305's, I'm running 12psi w/90-100psi of fuel pressure, and 14* base w/Bipes pulling 7*... makes 190whp. It would easily make over 200whp if the stock ECU didn't cause it to run absurdly rich above 5k.
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Old 05-24-2007, 01:26 AM   #3
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Is there any way around the rich mix above 5K?
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Old 05-24-2007, 04:01 AM   #4
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Is there any way around the rich mix above 5K?
-Run way lean below 5K.

-Squirt it.
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Old 05-24-2007, 09:50 AM   #5
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Is there any way around the rich mix above 5K?
Not on the stock ECU.
You can help it out a lot, but a dyno is really the only way to fine-tune it. A wideband and street-tuning will get you most of the way there.
After 5k, the stock ECU simply dumps in a crap-ton of fuel for safety.

If the graph was elongated a little more, you could really see the wall it hits when the AF starts on it's way back down. At 5k on this graph, it looks like it just gently starts going rich... but it really jumps off the cliff rich.
https://www.miataturbo.net/forums/sh...&postcount=117
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Old 05-24-2007, 09:56 AM   #6
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the ECU switches to a predetermined fuel map at 5k. so when using large injectors and high fuel pressure you get lots of fuel dumping in up top.

you can fine tune the fuel before that point, but after it becomes difficult. If your building a setup below 10psi or so it's fine, but after you need a bit more injector to start fueling for high power level is where it becomes tricky.

I know I was leaving some HP on the table with the same setup, but I was comfortable with a 12.5:1 AFR between 3-5K and a 11:1 AFR between 5.5-7K
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Old 05-24-2007, 12:23 PM   #7
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you can just max out the stock map by running small injectors and have the thing run good past 5K rpm and perfect everywhere else as well. But your math fails to consider that you will run a max DC of 80-85% on stock ecu so unless you get your BSFC down to around .5 instead of the normal .55-.6 we see alot of times with WI or some other super cooling method you might run short doing things that way. This is all a question of effeciency of the turbo and IC so the max enthalpy in the intake is relatively low. Thus you will have no knock burn fuel more effeciently and make more hp.
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