I have the exact same boat, 90 Scarab 21' with a 350 Mag. I see 53-55 mph (GPS) at 4800 RPM. I'm running a 21 degree Mirage prop. I doubt your hitting 62, but if you are, DON'T change a thing!

-Rob

Thanks for all the replies..This is my first adventure with these power boats.. Now I have messed around with old hot rods for years. That is my thinking. If you are not turning the RPM's you think you should then something is wrong..A small block can take 5300 all day. I understand how to get that out of an rod but this boat thing I am still learning. The single plane in my opinion would give you mid to high range power..Now here we go again, I am thinking in terms of a rod..If I cannot increase rpm's on a boat that i cannot..I just thought I would throw it out there and see what everyone else thought..Thanks for all the replies.

Get a 502...

4600 is the perfect rpm range for that engine, if you want to turn a 21-23 pitch prop into the low 5000 range your gonna need to add about 100 hp or more

[QUOTE=khubard;3624191]a small block can take 5300 all day. no it can't. you are used to hot rods. run it up to 6500 and shift. this isn't a race car, it is a truck, loaded with bricks, pulling a horse trailer, uphill at 60 mph. what an engine will put up with for 10.5 seconds is astronomically more than what it will take for 30 minutes.

You could always put a alpha one ss drive on it that would help.

[QUOTE=dereknkathy;3624406]In addition to the above post, your limited to the RPM range of your cam! Boats and cars are completely different. A good dual plane is good to 5500-6000 rpms. Your a LONG way from that rpm range!

Boats like cubes, lots of cubes, not rpms.

Endeavour, you are right...That is why I am trying to frigure out how to get more RPM's

KWRIGHT, educate me. What is so good about a Alpha one SS Drive. Where do i find them