Spark Plugs

[robertisaar]

so, i was looking up plugs the other day, thought about something odd.

since cylinders 5 and 6 tend to run the hottest, think there would be any benefit to using 1 heat range colder plug on just those two cylinders?

much like anything that pops into my head while i should have my attention elsewhere, it's probably more trouble than it's worth, but thoughts?



i assume this issue affects the LQ1 as much as the gen1/2/3 OHV engines as well?

and is the 3500/gen4 stuff subjected to the problem to a lesser degree?

[ericjon262]

so, i was looking up plugs the other day, thought about something odd.

since cylinders 5 and 6 tend to run the hottest, think there would be any benefit to using 1 heat range colder plug on just those two cylinders?

much like anything that pops into my head while i should have my attention elsewhere, it's probably more trouble than it's worth, but thoughts?



i assume this issue affects the LQ1 as much as the gen1/2/3 OHV engines as well?

and is the 3500/gen4 stuff subjected to the problem to a lesser degree?

my thought, on obd2 applications, the fueling can be skewed to compensate for that to a degree. on obd1, it might be worth a shot, really depends on how much power, and how many steps exist between heat ranges.

[Superdave]

I've thought about this as well but to validate it you'd need to test with an EGT probe.

It's a great idea, I think it could help in a racing application. Probably not worth it for a street car though.

[robertisaar]

my thought, on obd2 applications, the fueling can be skewed to compensate for that to a degree. on obd1, it might be worth a shot, really depends on how much power, and how many steps exist between heat ranges.

that would throw off O2 trims though, using fuel to cool it down.

i don't think the P66 V6 PCM has an individual cylinder trim in its code, but it could be added in.

I've thought about this as well but to validate it you'd need to test with an EGT probe.

It's a great idea, I think it could help in a racing application. Probably not worth it for a street car though.

would an EGT probe really be necessary? we know they run hotter(or at least gen1/2/3 do), wouldn't pulling the plugs and comparing them after running them for x miles/passes give a good indication of how different they're acting per cylinder?

[ericjon262]

my guess, is that the cylinders in question run hot because they are lean, due to unequal air distribution. so changing the injector skew could change fix the lean issue and even out the temperature difference. I think that's also why the 3500 has the large tube inside the intake extending about 1/2 way back, and the gen 4 engines have the V in the back of the plenum. to aid in distribution so the engine doesn't have hot spots. (at least due to distribution)

what I hadn't thought about was coolant, which I do have a solution for too, but that's quite a bit more involved then a tune...

[robertisaar]

from what i can tell, it is all(or mostly) coolant.... the RWD guys have to flip the intake around, so if there were any flow problems with the intake, now 5/6 are actually 1/2.... but i think they still have the hot cylinders issue.

[caffeine]

An infrared thermometer could help indicate which cylinders are hot and how much difference there is. And doesn't require a bung in the exhaust like an EGT

[carbon]

I think that's also why the 3500 has the large tube inside the intake extending about 1/2 way back...

And the oil squirter for the #5 and #6 pistons...

[Superdave]

I think the issue is more air distribution than cooling. 3500 "should" be better but who knows.


IR thermometer could work but you'd have to do it while under load on a dyno.

[Roadbastard]

Why do those cylinders run hotter?

[caffeine]

Running lean (less air distribution too those cylinders) would make them run hotter

[dskopek]

from what i can tell, it is all(or mostly) coolant.... the RWD guys have to flip the intake around, so if there were any flow problems with the intake, now 5/6 are actually 1/2.... but i think they still have the hot cylinders issue.

I am running a turbo on a RWD setup with the manifold flipped and under normal unboosted running #1 always runs hotter then any others, I have so much fuel in the motor under boost and so little time under boost I don't see any problem yet.