How much horsepower to run 70mph?
 

How much horsepower does it take to push a 30 ft scarab to 70 mph? My boat has the 330 hp motors with freshened up oval port heads, some lunati cams and air gap intakes. I'm guessing I have 360 or so per side? Were right at 60 mph now with 21 pitch props.

I'd like to see 70 plus next summer. Boat still has the trs with merctrans II. I don't want to change them out at this point. How much more horses do I need with my existing setup? Thanks for any and all input.

Figure about 20-25 hp per motor per mph......10 mph needs 200-250 hp per motor. Your not looking at changes to your motors.......your looking at COMPLETE new/bigger motors to get there.

Like T500 stated.

Unfortunately the cheapest way to get more speed is to sell current setup and buy a new boat with the wanted speed. It is so hard to keep my emotions out of my toys. They get too much money they shouldn't.

What RPMS are your engines turning with the 21 pitch props? You'll need that as a guideline for prop selection when you upgrade the engines...

I would think that a set of 500' s would get that boat there. What rpm are you seeing 60 at now? I would guess around 5k?

Thanks for the input guys. It's turning 4250-4350 rpms right now full throttle. These 330's arent supposed to go past 44-4500, I'm thinking because of the cast crank and rods.

I was thinking of having my engine builder friend get me some forged cranks and rods and then build these 454's to 500+hp. But I wasn't sure if that'd be enough power.

I hear what you're saying but I just spent a lot of time and money (mostly time) on this old resin bucket. I guess I'm gonna keep it a while.

If it were me, Start looking for a pr of 500HP's ;)

Or pull motors, and have them built to 500 HP(+ or - a couple)

I had a 30' scarab (1984) Tried to duplicate the merc 420's as best i could....So im guessing i was in the 400hp range....best i got out of my boat was 69.8 on gps.....that was a TRS setup with the velvet drive trannies too...

What ratios is the trs setup? 60mph, 4300 rpm and 21's don't add up