Ok, I know I'm about to start a firestorm, but I'm searching for that last bit of horsepower. I have an NA 524cu.in. BBC with 10.1:1 Compression, good size cam, 1000cfm custom carb, MSD 6M ignition with their HVC II coil and distributor. I'm somewhere in the 650 to 700hp range.. I have been running Autolite AR3932 plugs and saw an ad on JEGS for Brisk spark Plugs. I called Brisk USA and they developed a surface gap plug specifically for the Lamborghini large displacement marine engines. So I ordered a set and giving them a try so far the biggest difference is idle and acceleration is improved, the jury is still out on top end. I'm interested in any findings anyone else has come across with different plugs.

First problem is your ar3932 is way to cold for your power that's equal to a -10 NGK. You would never feel the difference in acceleration unless you had a fouled plug to start with. Try this on a dyno not in your boat you can see what it is actually doing back to back. I have big doubts that they are worth anything for power or most cars across the country would have them from the factory.

why worry about the plugs when the MSD ignition will take a dump soon anyways? just kidding....... or not.

actually i think most of these fancy plugs just drain your wallet. didnt motortrend do dyno tests and found almost no difference?

R5671a-7

Ok, I don't have any issues with fouling plugs even though I do extensive river cruising for hours at idle with a big cam and carb, I also run my plugs for up to 2 seasons. I must be the only person who can get an MSD ignition running well on OSO. My Brother-in-law worked on a program with Ford on spark plugs, they were able to gain 40hp in a 300hp motor by re-engineering the plugs. Indexing can get you 7-8hp, which I do also. My engine builder saw a 40hp jump going from a regular coil to the HVC II blue coil I'm running on the dyno. When I was a kid I had a go-kart racing engine on a mini bike that had 13:1 compression and would run over 10k rpm and spark plugs in that motor were night and day different. F-2 Speedy, so the NGK crosses to the AR3935 which is 3 steps hotter than I run. What compression and HP are you running? What are the water temps you run in, and what temp does the motor run at on extended hard runs? I also boat on big water and may run 30+ miles at or over 5000 rpm so I'm real careful running hotter plugs.

try ar3934

It was the recommended plug from AFR for those heads, haven't had any problems with them loading up or fouling. I bought an Otoscope to check my plugs with and based on the band on the electrode they are cold. Haven't seen any reason to run hotter plugs. The only reason I change them is so I have a fresh set to check the carb jetting with.