Not long after the purchase of my1997 Scarab 29 i realized the transum was rotten. Pulled the vortec scorpion MPI engines and did 2 new 383s with just under 10:1 compression with Comp Cams XR276 cams with straight 4" exhaust thru EMI manifolds and aluminum raisers. We lifted the engines 2" and did a prop change to bravo 1 four blade 24p. Im still learning the mefi burn software but at end of season we achieved full throttle with good o2 readings. After all the changes we've gained a net of 4MPH to 69 MPH up from 64. Current full throttle now with the 4 blade props is 4850-4900 rpm. Ive been racking my brain since September and cant pin point the lack of improvement. At this point im asking for help. Any suggestions or thoughts are welcomed.

thanks aj

Did you originally have the 350 or 383 black scorpion engines ? On your new builds, did you keep the mercruiser tunnel ram intakes ?

You are still to deep. Try to borrow a pair of -2 lowers. And a set of Rev 4 23p I would have raised those motors as high as you could have and spaced the drives down if needed. That way you could have just bought spacers instead of lowers.

What did the Dyno show for target RPMs on build?

^^ what he said... 64 mph with that prop at 4800 rpm sounds close. So to go faster you need to spin a bigger prop that rpm or sin that prop faster, Which one will your motor do??

I did keep the factory induction system. And the motors have not seen dyno time. The props are spinning inwards also.

Need more rpm. A dyno to would help to prop it better but I personally would try going down in pitch and see what you can spin them to.

That's why I said try the rev4. A 23p is more prop than 24 bravo but goes through the water much better and the boat will probably have a better attitude. I'd try spinning in and out back to back and see where it gets you.

How much are you estimating the hp gain per engine???? A 5mph gain is probably about a 75hp gain per side.

If you have 1.50 ratio drives, your prop slip is very low at only 5% which is pretty unlikely for any straight V bottom boat.
I'd try some 23 Mirage Plus props spinning out and see what happens.

Thanks for answering my second question. Could you answer the 1st ?