my 509 9.5-1 compression with rpm rect port heads & custom cam for 5800rpm peak has a holley strip dominator manifold with a 850 holley. would it be worth the money to change to a dart, brodix etc? which manifold would you suggest? looking for 15 or more hp to make it worthwhile. the boat is a 26 american offshore so top end hp is the goal.

I'm running almost the same set up as you including the strip dominator intake.The reason I chose it was because I seen a test where it's power band starts at a lower RPM than the other single plane intakes. Personally I don't think it would be worth the money to change. Also I run a 1" spacer between the intake and carb.In my 850 holley I run #84 jets all the way around. Engine has been in the boat 8 years now and still runs very well.

try indexing the spark plugs.i ran a 2 inch spacer under my carb.also try taking some of the timing out thats good for some top end power.

When I was building my 540 engine for my eliminator, a 2" HVH super sucker was worth 16 hp on the dyno.

Chris

Did that spacer have the 4 holes in it or was it wide open? Do you remember where you got it from?