How much power can an L48 make?

enkeivette

enkeivette

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Mar 30, 2008
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Upgrading only the exhaust and intake manifolds and the cam.

Thinking about putting my stock 78 L48 into a boat, cheap project. I would probably use upswept headers with an attached muffler, the biggest flat tappet cam that would make sense and a single plane intake, if it would make sense. With the stock HEI and Q-Jet.

Any intake recommendations? Cam recommendations (Solid or hydraulic, don't care)? This would be attached to a Jet Drive.
 
Bird about got it right on the HP end of things....but....

having driven a few boats in some varying weather, and some varying size of waves and hulls....it is MY opinion that as with cars, for most effective performance....it's all about TORQUE, screw HP readings....

gimme 1000 ft lbs at 2000 rpm, and a HUGE prop, and I will scare hell out of you with ski boat speeds.....

:devil::nuts:
 
I think with a Jet hp is more important. A jet hits full rpm quick and then the boat takes a while to catch up, not like a prop where you need lots of grunt to get it moving.

Bird, cam specs? Single plane?

I just sold my wave runners so I'm pretty serious about this, need a new project, like yesterday.
 
The old GM #151 cam from the 327's of the 60's is good. Stick with a dual plane.
 
enkeivette said:
I think with a Jet hp is more important. A jet hits full rpm quick and then the boat takes a while to catch up, not like a prop where you need lots of grunt to get it moving.

Bird, cam specs? Single plane?

I just sold my wave runners so I'm pretty serious about this, need a new project, like yesterday.
Click to expand...

Interesting, I wonder why.....never owned a jet boat, didn't know that...

seems like a strange reaction as we still pushing water with a 'prop' arrangement,

:clobbered:
 
If I had to speculate I'd say the prop in a jet only has to fight the water in the jet, while a typical prop has to fight the static ocean.
 
After the cam the quadrajet is going to be your limiting component assuming it is the L48. If you can get a 650 DP or 750 vac sec and a good dual plane you are about done on the intake side. If you can get a used LT1 intake you have the holy grail in my opinion. Bird's cam suggestion is probably about as big as you can get w/o changing springs etc.
 
A boat needs to run at a steady RPM too. Turning it 7000 won't help unless the jet has been modded. A full on prop will spin a hole in the water. (cavitate). Figure on a cam with a peak torque that matches the jet pumps best efficency RPM.
 
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