How much HP is my motor making?
 

OK, I've got another motor question for you guys. I've been thinking about building a 400 small block for my boat (1985 21' Scarab) but the motor I've got in there right now seems to run great and makes decent power. It's a Jasper marine 350, but I'm not sure if it's one of there performance motors (300 HP) or one of there stock motors (260 HP). It's got a Holley 750 carb and an Edelbrock Performer intake. With a 3-blade 22P turbo prop that has been sharpened and had some extra cup added to the blades, the boat will run 59 mph on the gps( about 63 mph on the speedo) at 5000 rpm's with only myself in the boat and a half tank of fuel (about 20 gallons). What kind of power do you think this motor is making? Also when is the Thunderbolt rev limiter supposed to kick in? Thanks

Nobody even has a guess as to how much? It's either 260 or 300. Will 260hp push a 3400 lb. boat to 59mph with a 3-blade 22P prop with the motor spinning 5000rpms?

Based on your information I would guess your motor to be the 260 HP version. Take a look at
You can fill in some of the variables and calculate top speed, horsepower, etc.

Good luck!

Davetop speed estimator

My 84 210 XL used to run 56-57 with 22 Turbo Stock 260 Hub exhaust. I would say you have 260 {Faster hull under Scarab}

I agree birddog.

I had a 79 210XL/260hp. When loaded with a zillion pounds of junk it still ran 52 (real speed) with a 21p standard Mercruiser stainless.

The Scarab is both lighter and a faster hull. He has some mild bolt-ons in the form of the carb and intake that should help him a smidge, but I'm still thinking he has the 260. We could be wrong, though. A true 60mph is a strong runner.

I'd call Jasper and ask the apparent differences or if there is a model# designation visible on a tag or something. It may indeed be a 300.

I don't guess I've helped at all...

Unless you have a new ignition system, you won't have a rev limiter. Of course, it can't hurt to try and find it! :eek: :D

I'd try to find out what components were used to build the existing motor. If they turn out to be some good stuff, then it would be cheaper to put a blower on the motor.