spark plug recommendation

what heat range plug you guys recommend for n/a sb 13.4:1 compression? i used a 7 ngk on last combo with 11.3:1 and 7 ran a little dirty with that. Ice Ignition and crank trigger.

I ran ngk 9 in my 13-1 alum headed 520 ci.rb and they seemed to work great compared to the 7,s.but everything about this motor defies common logic.

ok, a 9 is colder than a 7? i was thinking maybe a 7 or 8 would be a good range. i will keep that 9 in mind thou.

what does "dirty" mean? are there deposits build up on the center porcelain/ electrode? usually a plug is too cold when you have missing under light loads and the plug can't keep the center clean.


Joe

Define "dirty",,,,,,,,ae you reading after a high gear jaunt??

when I say dirty I mean dark brown to black. never foul but just dark in color. the shell is always black at the base of the threads using a 7. street and track. o2 numbers seem to always be in range(12.5-13.1wot) 14.5 idle.
iv never been able to do a hard run clean cut pass. they shut the track down til your out of that area at the end of the track.
this engines going to the dyno and I need to get some plugs. what do you recommend?

There`s guys runnin 7`s up 14.1.1 but I`d go # 8`s.......

Can`t always blame the plugs and need to check out the ign. and carb...................

this may sound bizzar but has anyone ever tried putting several different heat ranges in a motor at the same time then comparing how they look.

Yep, years ago I left Cabs house w/a few different plugs in my 360 and read em and went w/Autolites before switching to NGK`s.........

ok Dom. ill get some 8's and see what they look like after dyno time. Dom, how did the autolites work out for ya?

never thought about doing that, but its sounds like its worth a try.

They never did BUT, I`ve got my carb tuning skillz coming around so maybe that would change but not willing to start over when plugs are a major part of the tune...........at least the POROPER ones......

I'm going to try Autoite 3910 in the B1 motor I'm dynoing next month, it has right at 13.0 to 1 compression They have worked well for me in many motors on pump gas with lower compression, I'm one of those guys that likes to run my motor lean with the coldest plug I can keep looking good, clean with no color or speckles The ignition timnig, AFR, and the spark plug heat and tip type all contribute to what the spark plugs look like IHTHs

ever have any luck with the champion cx series with the cut back strap?

I have never run the champions but have run the AR series in autolites with the cut back straps,,AR3910 in my small block with 13.0 to 1.0 comp, work's good for me.

AR3910, ok. any street driving on that?

no, track only, 13. to 1 comp and sunoco supreme fuel, 112 octane, ran them for years with no failure's, even with extended idle time they never hiccuped.

I've never seen a set of them, let alone bought a set to use I'm usually looking for the best bang for the buck, not the latest, greatess, trick race part of the year AKA I've never thought about trying them, I have used some of the C57YC and maybe a set of the C61YC, if that is a good Champion part number I drove my low compression pump gas Duster on the street with both the AR3911 and AR3910 with no fouling or missing problems running Oregon 91 octane pump swill I ended up trying and using Champion RC12Yc and RC9YC alos, both worked okay, the RC12YC seemed a little hotter than I liked so I ended up using the RC9YC due to the lower cost at the local parts stores on special compared to the AR3910 or 3911s

the ngk 7's would stay clean at the track,but after some street time would be very dark in color. this was on pump gas 11.3:1 compression.

Yes, the CX plugs are all I use on the dyno motors. Bulletproof plugs with the cut back strap. Extra piston clearance also. They are fairly cold plugs though, race only, not a street plug.

I run NGK 9's in my 14.8-1 572. After a clean cut power run they look perfect. However driving around the pits they're way dark. Never seemed to bother it down track. Same plugs 300 passes. Made it's best passes ever this fall.
Doug

which heat range cx plug would you use in 13:1 gas engine?

are the ngk r5671a-8 resistor type?