autolite 425 plugs...what's hotter?

[claybill]

i am running autolite 425 plugs...this is the plug with the long threads...

took them out to do a compression test and everything was pretty sooty. but it wasnt an honest run....engine never got warm enough..but wondered if anyone knows the next hottest plug number......

but i can go over to NAPA tomorrow am and order something from their chart..

i am running a fenton aluminum head..dual stock carbs B&B..comp is 120 exact cyls 1 thru 6.

bill

[greg g]

shouldn't worry about new plugs till you get the carb issues ironed out.

[1955 plymouth]

I know the plugs we use for Harley-Davidson motorcycles get colder as the number gets higher. EX: 6r12 would be a hotter plug than the 10r12.

The reach should not detrmine the temp or burn rating of the plug. You should be very careful using a longer reach plug in any application, your pistons could come real close to the top of your combustion chamber and smack the plugs, also if the threads go past the end of the threads in the head they could build up carbon and make it really hard to remove from the head later on, possibly even pulling the threads with them or breaking off in the head.

Hope this helps a little.

[Plymouthy Adams]

the length of the ceramic is the determining factor on the heat range..

[claybill]

took al of the advice from the last thread about my carbs...YES. i learned something..and it was just balancing the vacuum out by turning the air set screw in and out AND doing the same with the other crb...learned a few things.. i needed a PUSH! and got one from TIM and others. i always thought the screw should be the exact on both carbs..not so...thye vary.....anyway i got it close,..and smooth. will try a longer drive tomorrow 200mile run.

i'll stop on interstate and get a plug reading mid way. might be running ok.

the dairyland region of POC is touring MAT KENSETH #17 NASCAR's garage in cambridge wisc sat at 10am...then lunch and talks about our national in june...

plugs....the aluminum fenton H/C head is cast thicker than the iron head for obvious reasons....a longer thread plug is required. it ends up even with the head. i know the porcelain area is the key to heat range. some plugs read up and other plugs read lower...i think hotter plug would be a number lower...

thanks to all for patience.

bill

[Don Coatney]

This might help.