Forum > Forced Induction

reading plugs for turbo apps?


I've done some reading around and i dont understand a couple things.  I know that a turbo needs cool down time after running hard but how do you read plugs and accomplish this without getting false readings?

One thing i read said to take the engine to where ever you wanted to check and coast the engine to a stop and THEN shut the engine down.  Isnt this just going to give you the ignition readings for idle on the ground strap instead of what you were trying to look at?

My app is not boosted at the moment and wont be turbo but while i was on the dyno, i would run it WOT and shut the engine down when i got to the rpm where i wanted to read them.  Once the engine is shut down, there is no more fuel and no more heat being generated and that should give the most accurate reading correct?

I never realy thought about that one, but it seems as though you could always cut the fuel, leave the car in gear and coast down.  Thiw will kill the combustion events when you want, and keep the oil pump turning to keep the turbo lubricated so it can spool down.

I am sure I am missing some details in this thought process though.

Might want to try to maintain the same throttle opening for a bit as the added vacuum could cause some undue strain on the rods and possibly the bearings.

Hmmm.  This is a great question.

Killing the engine under boost a couple times doesnt kill the turbo instantly. I'm sure I did it like 30-40 times on my old setup, no problems.

Evans Performance:
+1, you can do it occasionally without any issues.

This is the best, least damaging way to do it.

1) Have a spare plug ready - ANY plug that will work in the motor at idle.
2) Get to the RPM/boost you want to read
3) Turn of the key while holding it WOT
4) Stop using your lefty or heal-toe like a jdm racer
5) quick like a bunny swap the spare plug with a fresh one.
6) fire the beater back up with the 3 brk7's and the shitty autolite or whatever
7) let it idle while you attend to the sparkplug-shaped burns in your hand because you're a nog that forgot a shop rag.

Its a mechanical oil pump, nogs, so it gives pressure with ignition or not. When the motor freewheels to a stop (with TB open), boost is removed w/o surge, and you still get full oil pressure. This alone will cool the turbo enough where the 1-2 minutes you're stopped won't cook any oil, unless you run 260F oil temps at idle like the OG's. As for post-pull idling, your motor doesn't care if it idles with a heatrange 9 or 4 plug, it just needs to fire. A really bad or different plug may give a lumpy idle while you're "reading".


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