Mitsubishi 3000GT & Dodge Stealth Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
447 Posts
Discussion Starter #1 (Edited)
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?
Gap?
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 had a shop replace the plugs and wires with a 3sx tune up kit (https://www.3sx.com/3sx-tune-up-kit-ignition-spark-plugs-msd-plug-wires-gaskets) – 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 it’s enough to make the car stutter and AFRs spike. I told the shop to gap these plugs to 0.028’’ (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 don’t 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 don’t 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 0.024’’, but am not sure if copper would be a better option since I don’t 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.
 

·
Registered
Joined
·
447 Posts
Discussion Starter #2
Never got a response here but figured i would post a follow up in case someone searches.

I changed my spark plugs on Saturday and also pulled my 550cc injectors to be flow tested and cleaned. I was running the NGK PFR6J11 Iridium plugs. These only had a few thousand miles on them. However, even after putting those plugs in with new wires, I was still getting blowout. Even though i told the shop that installed them to gap to 0.028'', i found that 4 were 0.031'' and 2 here 0.035''. That actually made me feel a little better, because i am pretty confident now that the 2 with the larger gap were the source of my spark blowout - it didnt seem bad enough to be all 6. I also measured the resistance of all the spark plug wires and they were well within spec.

I ended up going with NGK 4091 R5671A-7 after reading some threads and the notes here (https://www.rvengeperformance.com/2019/05/19/3000gt-dodge-stealth-performance-spark-plug-recommendations/). I gapped them down to 0.026’’ and will see how that goes. I am feeling pretty confident now after finding 2 plugs with a large gap, switching to copper non-resistor, and lowering the gap.

I did find quite a bit of deposits on 4 of the 6 plugs (not correlated with the two that had the larger gap, I checked). Key picture is below and more full size are at the link here (https://imgur.com/a/OCUDSHs). I think perhaps the white specs are from a E-85 fuel stabilizer I was adding a little bit of since I started running 50/50 E-85 and pump 91. I also know my VSS are pretty shot because I get smoke on decal, so that could be contributing to some buildup as well. Picture shows spark plugs in order – front of engine on the right side.



Any thoughts on these? Nothing looks terrible, but interesting that 2 look much cleaner than the rest.

Will post another update after i get the fuel injectors back, put everything back together, and try running 15psi again.
 

·
Elevate
Joined
·
1,120 Posts
.024 on NGK racing coppers and carry on with your life. I believe you'd want a 7 heat range. maybe 8 on e85 but idk how that works since you're not running much boost

lots of guys on e85 running .018 (but with high boost). I run .024 on 93/meth and 21-22psi, no blow out. Magnacore wires. I've never messed with the platinum or iridium plugs as there seems to be no need when proven builds are pushing 6xx-7xx hp on coppers without any ignition hiccups.

I'm not sure with what boost level, but I know e85 guys usually run those Kenne Bell boost-a-pumps when it's time to up the boost
 

·
Registered
Joined
·
447 Posts
Discussion Starter #4
Quick Update:

Finally got the car back together aftering changin the plugs to the copper NGK 4091 R5671A-7 gapped to 0.026''. (I was waiting for injector flow test and clean). Took the car for a quick test drive and no more stuttering or spark blowout. Seems to pull hard on the exact same boost (13-14psi) that was blowing out pretty bad before.

I was worried about going small gap because of people complaining about idle, but ill never look back now. Coppers at small gap FTW (and yes i know 0.026 is not that small, but compared to stock).
 
1 - 4 of 4 Posts
Top