I have a Bosch fuel injected 383 in my boat. I am wondering how I can get more midrange torque out of it. It is in a Jet boat where the jet unit is only rated to 4500 RPM, so I dont need HP above 4500 RPM what I would really like is to make about 50 -75 ftlbs more torque from 3500 RPM to 4500 RPM that would put it right around 500 ft lbs. Can this be done? Reliability is very important and I need to be able to run it on pump gas. Any ideas?
Thanks

 

I would start by getting a custom ground cam. specifically for your needs.

 

That is exactly what you need to do. The great thing is that reliability and low RPM operation pretty much go hand-in-hand.

Another thing you will want to consider is your intake. I would suggest you talk to a professional to see if they can set you up with a cam/intake combo that would give you the maximum low-end power.

 

For 4500 RPM, I'd consider doing a modified tuned port induction system based on a Scoggin Dickey TPI Vortech intake manifold, some AS&M runners, a set of ported Vortech cylinder heads and a 52mm throtle body.

Put in a Comp Cams hydraulic roller retrofit cam in the 218/224 degree range, or else the GM Hot cam package, some 28 lb injectors, and you should have a pretty nice and torquey engine that is nice and flat in its powerband between 3000 and 4500 RPM.

 

What about changing the jet pump impeller to make it twist to 5,000-5,500? I would imagine that would be cheaper to do.

We had a mild tunnel ramm'ed 468 w/ a berkley jet in our last jet boat and it twisted about 5200. We only had it running that alst part of boating season and sold it w/o the motor and got a 25' Checkmate Convincer.

 

Thanks for the replys so far. The boat is a river sled with a Hamilton 212. It weighs about 4000 lbs and is designed for running white water in rivers. The 212 is a volume pump made for hauling loads and grabbing aerated water, the pump is only rated for 4500 RPM. What I want is to be able to turn a bigger impellar so that I will have better midrange and load carrying capacity, but I dont want to loose any top end. I.e I need more power.

I will look into a cam and intake. that seems like a fairly sane addition that wouldnt be too hard to put together. How much torque should I expect to gain with such a change?

I am contemplating a Supercharger, any thoughts there?

Thanks again for all the help.
MTRR

 

How much you gain from a cam and intake depends entirely on what your current setup is. If you happen to have a motor that was designed for power up high in the rev range then a swap could get you loads of power down low.

If you want to add a supercharger then go ahead and do it before you spend money on the cam and intake, as both should be matched to the use of forced induction.

Sounds like a cool boat by the way.