Plug Info

[blk91]

Hello all,
I Bought a 92 supra not to long ago and it has a semi built motor, with what I was told to be lightly ported heads with oversize valves and weisco pistons. Motor idles sort of uneven and was missing a bit on the top end now and again I was thinking the plugs were fouled or needed to be replaced and was going to have them replaced as I was upgrading my intcooler and would have the IC pipes off, Anyway I was told by the shop that the plugs were 2 heat ranges colder then the stock plugs and they were not sure what to replace them with. Also they said the fact that they are 2 ranges colder could be causing the miss as well, They also said they looked to be in like new shape and were not fouled at all. The car is running 91 octane gas and running about 1 bar on a non ct based 60-1.
Does anybody know if i need to be running colder plugs? I feel like its overkill but Its not something I know much about I have added forced injection to allot of 350z's before and know they run a range colder when boosted. Which I why i cant see a factory turbo car running 2 ranges colder.
Any info would be great Kanan

 

[wiseco7mgt]

It could be a lot of reasons it runs a little rough not just plugs. Have you checked all the vacuum lines yet for any holes or that they are correctly hooked up? have you checked the afm to see if its excessivley dirty inside?
Hows the timing , is it set right?
How about plug leads?
Any valves riding maybe if the engine has been rebuilt ?
Theres heaps of things it could be just start with the basics and narrow it down.

 

[GrimJack]

As I recall, the rule of thumb is a range colder for every extra 100 hp you're putting out.

So at a guess, I'd say 1-2 ranges colder is probably about right for your engine.

 

[blk91]

Plug wires are new, I have had 2 bad afms and they didnt seem to manifest like that when i had them. But to be honest the main reason I felt it was the plugs was simply because three or four people have said so when riding in the car, I also need to have my wide band installed to see if maybe its a AF thing.