I need advise on spark plug heat rating for my stock twin.

I will be using alch injection and 15-16 psi of boost on stock twins.

Scott

 

I am running all 9's...

 

Cheers. Thats ok then. I use 9's all round. I have had no probs but wanted to check

Scott

 

At least all 9s....you may want to even move up to the NGK iridium plugs...EIX10s...

 

All 9s

 

I would think 9's. That should be sufficient. But you will definetly notice if they arent powerful enough. In that case, do what rynberg has said.

 

How are your stock plugs looking when you remove them? If they're showing signs of excess heat, there are plenty of alternate plugs that can fit, you've just got to look around.

Personally, I've tried Autolite AR3934 and AR3932 copper plugs (equivalent to NGK 8 and 10 heat range, respectively) on my car, which is mostly stock. They wore out a bit quickly, and my car doesn't generate enough heat to need such a cold plug, but my point is that you can find colder plugs than 9 if you look around a bit. If you plan on using NGK Iridium plugs, look into the BKR7EIX, BKR8EIX and BKR9EIX. The Autolite and the NGK BKR*EIX use the smaller 5/8" hex, so you don't need a special socket to install them. I haven't been able to find a colder Iridium plug that fits without a special socket, but I haven't looked at Densos yet.

-s-

 

all 9's here too...