Scarab 29 Top Speed
 

1997 Scarab 29, Twin 383 Mercuiser Mags (350HP each, stock), Bravo 1's with 23P Mirage props spinning out. I am only getting 65-66 mph @ 4,900 RPM's with drives out, tabs up. Shouldn't this boat be going faster? This model supposedly does 67-68 mph with stock 350 MPIs which I believe were rated at only 300HP vs the 350HP of my engines. Suggestions on getting more speed? Different props? I feel this set-up should be going 72-73 mph.

Bought the one out of NJ? Are the props Mirage, or Mirage Plus? Gear ratio in drives is 1.5? Yes, you should be able to run a bit above 70 with your power.

If you have 1.5 drives your slip is at 7.2%
Getting your rpms up to 5200 with same slip you would be hitting 70 mph
Reduce slip to 5% gets you to just under 72 mph

Are the motors tired, have a lot of hours?

make sure your trim tabs are going all the way up the 29 scarab i had had a spacer in the cylinder and would not let the tabs come all the way up put a straight edge on bottom of the boat to the tab and check that way and i can tell you a 2 or 3 inch shorty will really wake that boat up as far as ride and speed

Yes, I got the boat from NJ I was looking at. It's on Lake Norman now, in North Carolina, and will also be seeing time in Tampa, FL. I think the props are Mirage Plus but I'm not by the boat right now to 100% confirm. Drive gear ratio's I'm not sure. How do I check that?

The motors should be good. They are 2012's and have about 180 hours. All cylinders were strong when tested during the survey.

Rev limiter?

Mercury rates the 383 Mag at 4,800-5,200 RPMS. I think I'm turning about 4,900.

BTW are you reading the speed with a GPS?

Yes, the boat has a Raymarine system installed and it has GPS. I probably should double-check it with phone though too.

You can count the teeth on your gears if you take the drive off or put motor at top dead center on the timing mark, put in forward gear, mark you prop location, rotate the motor with a breaker bar one full rotation, see how far your prop traveled (should be 1 1/2 turns) That's a 1:1.5 gear. That's how they used to tec our boats in APBA Factory classes. Don't forget a 1.65 gear is pretty close.

Might be easier to pull the coil wire or plugs on the coil, put in gear, then jump the slave solenoid. Crank it over several times counting the prop and the crank

Edit: make sure to feed the drive water when doing this, no reason to take a chance

Couldn't you just take the drive off and rotate the drive shafts one turn

Yes but rotating the engine only takes about 5 minutes at best with a friend.

My only concern would be bumping it exactly one rotation. A 1.65 gear could be confused if you were not exact IMO. I'm not a mechanic just someone who has been through Tec many times in APBA LOL

Rotate the motor at least 10 times, this will be easy to determine by dividing the crank vs the prop

your Scarab should be around 70mph. I have a 2001 twin small blocks 23 mirage plus, stock it ran 67-68mph at 5100rpm. As TRC2 said, check for spacers, mine had them also, would let the tabs come up to parallel. They are 383's now and best it has run is 74mph. I have 3 sets of props that "I" have had the check to be true and correct. 23 mirage plus, 25 mirage, 26 hydromotive 4blade. the 25mirage have been redone again to mirage plus specs. in next few days I will run all 3 sets and get good numbers of RPM, Speed, Slip.

What’s your top speed I got a 29 with motor with each putting 355 hp I hit 64 bravo drIve 23 mirage

I believe the motor spins 1.5 times for 1 prop revolution if I am not mistaken.