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

Not sure on the ratios. But that's what the tachs are saying and the speed is from gps. I'll check on the ratios tomorrow.

my guess is you need around 5000 rpm with 1.5 ratio to run 60 mph with a 21 pitch...

Thats what I was thinking.

Looks like I need to look at the props again. I'm sure they're 21 pitch. I'll report back tomorrow guys lol.

Here's the prop, 21 pitch..

http://i159.photobucket.com/albums/t...ps668d6b5a.jpg

I saw 60 mph on my friends app on his phone. The likelihood of both tachs being off the same amount I would think would be very low.
Did they make different ratio TRS drives?

01scarab29 built twin 383s around 400 hp and is in that MPH range.

In the 60 or 70 range?

Just spin your props in, that will get ya close.........:party-smiley-004:

I think he's low 70s

My 31 Scarab Viper ran 76 mph with 500 carb engines approx 470 per side .26 labbed b1's for props.

like captyarr, mine is 29Scarab twin 383's, 400hp/425tq dyno and tune by Bob at Full Throttle Marine ,,,, ran 73 at 5400 ,,,, before rebuilds 350's 300hp/?tq it ran 67 at 4900 ,,,,, boat weigh's 6500/dry ,, about 7300 fuel,gear,2 adults

1989 Scarab 31 Excel with 454 Mags, Comp Cams Extreme Marine cams, lifters, springs, push rods, roller rockers, Edlebrock RPM Airgap intake and Holley 4150 750 CFM carbs with 23 pitch Mercury mirage props and I run low 70's at 5200 rpm. I ran 65-67mph with the stock engines. Going to try 25 pitch to see what that does fro me.

Just as a comparable, I'm running HP500s in my twin step 33', and am seeing about 82 (perfect conditions, light load) at 5200 RPMs with 28 pitch props.

1988 30 panther, 29 pitch 3 blade with cup , bravo 1 outdrives 1.5 ratio, 70 MPH at 4250 RPM. Motors make 425hp at that rpm WOT and its close to WOT at 70 MPH GPS. With 177 blowers the 330hp 454s make 600ft lbs torque at 2500 RPM through 4500 RPM and 457hp at 4500 RPM with cam change. Rev limiter set at 4700 RPM.;).

Lol, my 30 TRS Panther (same hull as yours) ran 72+/- depending conditions witb a little warmed over Merc 420's labbed 3 blades, approx 450hp. So 420/side with labbed props should get you 70.

Now just shy of 80 with ~570hp.

Thanks for the information guys. I've been talking to my engine guy about making mine 500 hp over the winter. Which I'm thinking should get me over 70 mph. Rookie, which transmissions are you running? and aren't you running blowers now?
Thanks again.