Sorry guys this question must have been ask a dozen times already, but I can't seem to find an answer. Just finish my B series 85X89 14.5:1 compression, but not exactly sure which spark plugs to put in yet. Just trying to get it ready for tuning. Any advise will be greatly appreciated.

 

I would guess an 8 heat range at that compression ratio and build. If you're running stock ignition, just go with stock or slightly smaller gap. If you have a high power coil, I'd start at the stock gap and increase it ever so slightly to see where it likes it on the dyno or maybe .005" in total over stock if you just want to adjust once and go. Testing and tuning is the only way to get an absolute answer for a heat range and gap size.

 

I am an old guy, back in my racing days, you would pull a run, get past the 1/4 mile at full throttle, kill the engine without letting up off of the throttle, get towed back to the pits and read the plugs, change the gap or the plug based on what you were reading from the last pass.

 

With ethanol or other additives in the gas now plug reading doesnt work the same. Ahhh brings me back to my carb tuning days reading plugs. The dead end empty street behind my neighborhood used to be my test strip. My motor now IDK what to do plug wise. I took my plugs out after 5,000 kilometers and they are white almost unused looking rather than a nice tan. Do plugs just take forever now days to color or is it wrong? The plugs I pulled out of my motor were black when I opened the crate so I figured Id change them out with fresh ones. The heat range I have now is actually 1 hotter than what they should be, I went to the store and say I need them for a 98 ITR of course not thinking USDM are less compression and such which use a 6 heat range rather than 7.

 

This is still the best way to do this, by making a full throttle pass and then shutting down the engine and pulling the plugs and reading them. The color mark on the ground straps location will tell you if your plug is the correct heat range, the white insulator will tell you if your timing is good and air/fuel is good. You have to know what to look for but this is the absolute proper way to do it.

 

i would have to agree and say 8 would be a good heat range to start with. might need to go higher. they say to start with the coldest plug that doesnt foul up the engine

 

Go 8's i run it, gap to .035

 

heat range 9
gap 0.9mm

 

x2......

 

8's or 9's will do you fine, just gap it to .035..if it doesn't blow the flame out, go more, until you start to break up..
i'm at 13.0CR and i run 8's..i had 7's in for the break in, but went with 8's cause i knew i'd beat on it alot..

 

Thanks guys for all the good info. I will try both 8's and 9's, hoping to get this thing on the dyno soon.

 

What' 8's do yall run? Got a part number handy? The only 8's my local O'reillys carries is in an Iridium plug, I'm on a cooper 7 now, and it's still a bit white on my ground strap

 

I just looked up the 4554's which are the R5671A-8 for a heatrange of 8


Can you guys go in a little more depth on how to read the plug? I can read the ground strap, will it tell you anything else other than you are running the right heat range? How do you read the porcelain to figure out if you are running too much timing or not?