Vintage jet boat

[cjprofessorguy]

I have a 1973 21 foot Kona jet boat with a 455 Olds Hardin Marine 390 horsepower v8 with a Jacuzzi 12WJ pump. I have 2 questions- first, what type of performance should I expect from this big old jet boat, and second, if I change the intake to an Offenhauser twin 4bbl setup, how much performance increase will I see and what cfm carbs should I use in a twin setup? Thanks a bunch!

 

[mkast]

Re: Vintage jet boat

Find out the camshaft specs.
Most cams don't have the lift or duration for dual quads.

 

[cjprofessorguy]

Re: Vintage jet boat

Well i figured it had a pretty good cam in it to make 390 hp in '73 from a 455. Any suggestions on how i find out what cam is in it?

 

[haulnazz15]

Re: Vintage jet boat

390HP doesn't seem like much of an extreme build for a 455. If you were around 425HP-450 HP I'd say you had a pretty beefy cam in it.

 

[MikDee]

Re: Vintage jet boat

Have you tried it yet? You need to give us a baseline, your rpm range, & top speed.