Spark Plug Heat Range

So, my recent build is a 500 stroker RB block. Bought it as a .040 over 12.5:1 domed piston motor. For my build I went with a -6 cc dish piston with the Stage 6 heads that should give around 10.5:1 compression. Motor had a Autolite Racing R3933 plugs in it. I'm running 110 fuel, but went with a step up hotter AR3934 plug. Think this is an ok heat range? Or should have stayed with the colder plug?

what was the reason for going to the hotter plug?


Joe

The 3934 is the same as a NGK -8. And I run -8s in a 14:1 motor. You could probably run a 3935 in it at 10.5:1

Is there a reason you have to run a non projected tip?
If not the ar3911/10 is the normal projection plug.

ar3933=ar3910

ar3934=ar3911

I guess I am old school, but read your spark plugs to see if heat range and timing are correct.

I went with same plug that was in the motor, but a step hotter because I was lower compression. But they may have had these non projected tip plugs in it due to the domed pistons, and maybe I don't need them with flat pistons I have. What's people running in the old stage 6 heads...for those still running them? Motor is together, so be hard to check now I think.

I run NGK #8 on NA and NGK #10 on nitrous with my stage 6 heads with 12.2 to 1 compression on VP 110!

Is it a 5671 or a 5672 (which tip)?

I use 5671-10, non projected tip! Same with the 5671-8 also!

Are your heads aluminum or iron?

Mine are AL

Usually aluminum heads on BB Mopar's act like they've lower the compression ratio one full point and increase the heat needed on the detonation thresholds when compared with the same compression ratio as used in iron headed motor.
My message is BB Mopar usually like a little hotter plug than colder, especially on the street. Colder plugs will be darker, perfect plugs (heat range, ignition timing and dead on air fuel ratios) from a well tuned motor should look like they are almost new.
You need to watch yours and see if they are going black, brown or lite tan under normal light throttle street driving
If their dark looking, use the next hotter plug
On your deal I would use NGK # 7 or the Autolite 3923 or maybe the next hotter 3924, Champion RC9YC ( I think, hope , that is the correct # for 3/4 reach with the 5/8 body size ) should work well also
Do you know that there is a federal law that can put you in prison for up to 10Yrs for using leaded fuel on the public streets if you are caught and convicted?
That is the main reason I switch to E85 on my race cars and hot street cars

Dark, light, brown, black, tan, white. Initially more influenced by air fuel ratio than heat range.

Make an educated guess as to what heat range you may need. (to get close) Dial in fueling, or at least get close.

Then look at jwb123 post, at least in reference to heat range.

I have always used projected on flat top motors and seen some gains vs the non projected.