Spark Plugs and Plug Gap for E-85 and E-85/pump blends (blowout issues) - 3000GT/Stealth International Message Center
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Old 07-10-2019, 10:16 PM   #1 (permalink)
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Join Date: Jun 2016
Location: Southern California
Drives: 91 3000GT VR4
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Default Spark Plugs and Plug Gap for E-85 and E-85/pump blends (blowout issues)

Hi All,

Main Question: What are recommended spark plugs and gap when running 50/50 blend of pump 91 and E-85 mix at about 15psi? Potentially full e-85 in the future. Stock ignition system.
Copper or platinum?
Heat range?

More info: I seem to have always had an issue with spark blowout with this car, but I never really felt the need to run more than 11-12 psi because the car was my daily for the past 11 years. Well now that I have another daily, I have been experimenting with running E-85 blends, doing some of my own tuning/logging, and turning up the boost.

I replaced the plugs and wires with a 3sx tune up kit ( Ė MSD wires and platinum stuck NGK plugs. This helped a bit and I can now get to around 11-12 psi just fine with no blowout. As soon as I go even slightly higher, I can feel the blowout and see it in the logs. Its minor at ~13 psi and mostly under high load and high RPM. But if I try to go to ~15 psi itís enough to make the car stutter and AFRs spike. When I put these plugs in I gapped to 0.028íí (basically what I have seen on stealth316 and other places that should be good to 15 psi easily).

This is my first time running any amount of E-85 and although I donít think that is the reason for my blowout (I experienced it long before on only 91), I know it could affect the gap required for the plugs. I plan to pull my injectors and get them flow tested/cleaned and put new plugs in at the same time. I donít mind running copper now since I drive the car <1000 miles per year at this point. I will probably never go above 15-16psi, but I may eventually go full e-85. I am leaning toward doing stock plugs again and gapping down to 0.024íí, but am not sure if copper would be a better option since I donít need longevity anymore.

If I replace the plugs and I still get blowout, then I figure I will proceed with considering the source of the issue to be ignition coils or PTU. Anything else to consider?

Full mods list below.
Gt-347 Turbo Kit (~13g)--RC 550cc Injectors--Denso Fuel Pump--Apexi S-AFC II--Turboxs Boost Controller--3sx Air Filter--DNP Stainless Intake Pipe Kit--Turboxs BOV--Autometer Boost Gauge--AEM UEGO Wideband O2--EK2 Downpipe--Gutted Precats--Testpipe--Polished VR-4 Plug Wire Cover, Valve Cover, & Plenum--Stage 2 Twin Turbo Clutch Kit--Full Bomex Body Kit
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