PRO1 aluminum dart heads BBC.

[MR509]

I have a set of dart 345cc pro1 heads on my 509 bbc motor and would like to know what is the best type and heat range of spark plugs to use.

Motor is a 509 gen six block with 13.5 to 1 compression.

Cam is 714 solid roller crane.

Carb is a dominator 1150 jet size 95 square no power vavles and 37 squirters.

This combo is in a dragster and hooked up to a power glide trans.

The reason i ask is i just bought this thing and the owner told me the piston would some times hit the spark plug and close up the gap enough to make it start missing.
He said that he had to use a washer under a couple of the plugs and then it was ok.

NGK spark plugs come with washer already on them.

Let me know what works best with this type of head.

Also this is a great website, my first time on it.

Thanks Billy.

[Awesome Bill]

That has nothing to do with the spark plug other than using an extended tip, which you don't want. If the compression is around 15-1 and on gas, AR3932/AR3933 indexed, 14-1 AR3933/AR3934 indexed, 13-1 AR3934/AR3935 indexed. If you put the ground strap between 10 and 2, you won't hit anything. It is possible you might have to run 1 silver washer on each to pull the plug back out. I have seen that some times. But, you will still need to index all the plugs.

[MR509]

That has nothing to do with the spark plug other than using an extended tip, which you don't want. If the compression is around 15-1 and on gas, AR3932/AR3933 indexed, 14-1 AR3933/AR3934 indexed, 13-1 AR3934/AR3935 indexed. If you put the ground strap between 10 and 2, you won't hit anything. It is possible you might have to run 1 silver washer on each to pull the plug back out. I have seen that some times. But, you will still need to index all the plugs.

Thanks Awesome Bill.

Billy.

[want-a-be]

If you have this engine apart you could clearence the pistons a bit for the plugs. Usually called a fire slot by the old timers. You won't need much. PM me and I can walk you through it if you need it.
Indexing the plugs is usually a must in this situtuation. I've seen the pistons so close to the pluggs that they would actually hit the plug while installing them, and wipe the electrode to the side ruining the plug. Had to make sure the piston was down in the hole when installing the pluggs and the index them in.
If your running extended tip pluggs going back to nonextended will help alot. Depending on how closely your tuned you might have to jet some, and/or move 1-2 degrees of timing.


Thanks, Don