We ran my BBC on the Dyno yesterday after we made a few changes in the heads, and cam. This is a mild engine, but was making power up to about 5200 before it started dropping off. We were just not making enough power. After fooling around with a few things, I took the flame arrestor off and added a velocity stack. We got 30 HP on the next pull, and exhaust temps, which were not bad, dropped further. I'm running a standard 4 inch high by about 8 inch diameter arrestor. Anyone got any ideas what to use and still be compliant with the law?

9X5 K&N Marine.

Several others here have reported the same thing as you. Some have gone to the K&Ns on the dyno and did not see the decrease...

O K,
Who handles K&N Flame arrestors besides Rex Marine?

CheckmateF1 just went through this with his HP500, now a 509. He tried several different Flame Arrestors, and the K&N was byfar the best, and it looks the best too. Do a search for his results.

I got my K&N's from CP Performance

Me too.

30 hp !!??!! Holy crap... wheres that cp #

Was that on a efi or carb??

Is the base of your flame arrestor flat, or does it have a smooth upward slope as it goes from the outside in towards the carb? I was told that a flat base creates turbulence at the carb - isn't the one on the HP500 a flat base? That's what I thought CheckmateF1 was dealing with.