1.8, gt2554r, 420cc, ms3, 12.5psi - Miata Turbo Forum - Boost cars, acquire cats.

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Old 07-08-2015, 07:45 PM   #1
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Thumbs up 1.8, gt2554r, 420cc, ms3, 12.5psi

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Old 07-08-2015, 08:34 PM   #2
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Looks good. What is your duty cycle on those 420s? I'm getting uneasy on my 440s at 10psi.
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Old 07-08-2015, 09:32 PM   #3
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At 9psi the tuner mentioned it was around 80%. 12.5psi is the max he could get out of the injectors while keeping it safe.
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Old 07-09-2015, 11:50 AM   #4
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Safe means different things to different people. I don't know your duty cycle but I wouldn't consider over 85-90% duty cycle safe. Changes in ambient temperature or pressure from the conditions on the day it was tuned can lead to the ECU demanding more or less fuel at the same rpm and load. With many injectors roughly 85% DC can be the threshold beyond which the injectors don't close before being energized to be reopened. They are therefore always open and no additional fuel can be added if longer opening times are requested by the ECU. This can lean out a mixture at high RPMs and loads.
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Old 07-09-2015, 12:04 PM   #5
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Steve's right.
Food for thought though: what I've noticed is there's usually quite a big "cushion" between what the MS (and other ecu's) say is "maxed out" and the the actual physical limit.

While some see this at 80%, most can go to 100, I've even gone to 125% on EV6 injectors before actually physically running out of fuel.
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Old 07-09-2015, 01:48 PM   #6
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<p>&nbsp;</p><p>What fuel system, as in NA with 44psi referenced, NB 60psi atmosphere, or some other?</p><p>EDIT: found on your other thread: 1997 Miata.</p>
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Old 07-09-2015, 04:17 PM   #7
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I trust my tuners judgement on the duty cycle.

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Originally Posted by DNMakinson View Post
<p>&nbsp;</p><p>What fuel system, as in NA with 44psi referenced, NB 60psi atmosphere, or some other?</p><p>EDIT: found on your other thread: 1997 Miata.</p>
Correct, stock 97 fuel system excluding the RX8 injectors.
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