Projected tip or non projected tip spark plug

I have a 460 with Domed pistons and iron CJ heads. Compression is around 14:1 run VP 113 fuel with MSD 6AL with Blaster SS coil. Motor runs upper 7,000,s down the track. Witch plug will work best and why, projected tip or non projected tip such as an Autolite AR 24 vs an Autolite AR 134. I do have to index the projected tip plugs for dome clearance.

Thanks,
Dennis

72puller wrote:I have a 460 with Domed pistons and iron CJ heads. Compression is around 14:1 run VP 113 fuel with MSD 6AL with Blaster SS coil. Motor runs upper 7,000,s down the track. Witch plug will work best and why, projected tip or non projected tip such as an Autolite AR 24 vs an Autolite AR 134. I do have to index the projected tip plugs for dome clearance.

Thanks,
Dennis

A "rule of thumb" for me is; if the piston is a flat-top or dish, I use a projected tip plug. If the piston has a dome, I use a regular tip plug.

Thanks for the reply Randy. I assume it is because of flame travel with the plug tip being unshrouded above the dome.

72puller wrote:Thanks for the reply Randy. I assume it is because of flame travel with the plug tip being unshrouded above the dome.

I can't really say about the unshrouding but, a projected nose plug in SOME domed piston applications will physically interfere with one another.
My "rule of thumb" is not just about Fords.

Sometimes, (as in small block Chevrolet 18 degree applications with a flat tops), a regular nose plug actually makes more power than a projected nose plug and it probably has something to do with intake wet flow in the combustion chamber.
That is why you test different stuff ...

Thanks

rmcomprandy wrote:

72puller wrote:Thanks for the reply Randy. I assume it is because of flame travel with the plug tip being unshrouded above the dome.

I can't really say about the unshrouding but, a projected nose plug in SOME domed piston applications will physically interfere with one another.
My "rule of thumb" is not just about Fords.

Sometimes, (as in small block Chevrolet 18 degree applications with a flat tops), a regular nose plug actually makes more power than a projected nose plug and it probably has something to do with intake wet flow in the combustion chamber.
That is why you test different stuff ...

the p/j plug in a dome or flat 18* sbc , puts the spark near center of the bore

Dennis I would not use a projected tip. I think the AR 134 would be best maybe a 133. I use the AR 133's and change them about two times a season just because. If you use a projected tip it "may not" need quite as much timing.

Bret