Last March I bought a 1979 Trojan 36 for a reasonable price needless
to say however the engines ran fine for the sea trial but it was all
down hill from there. I feel I paid a fair price for the boat and I am
considering replacing the Chryslers with New Crusader 8.1 engines
along with new gas tanks.

I have however not been able to find much information on what I can
expect on performance out of new engines on this boat. I am not sure
what I was exactly burning per hour on the Chryslers but I suspect it
was about 27-35 GPH. (One of the engines I was running most of the
year had low compression on 2 chambers. ) My cruising speed was about
20 -25 MPH at 3100 RPM when it was running.

I will be going from 330 HP to 385 HP and I am not sure if that should
help fuel economy. I am sure the fuel-injected engines should be more
fuel efficient but I am not sure by how much or what to expect, any
Ideas?

On Thu, 04 Nov 2004 02:32:40 GMT, (John) wrote:
Last March I bought a 1979 Trojan 36 for a reasonable price needless
to say however the engines ran fine for the sea trial but it was all
down hill from there. I feel I paid a fair price for the boat and I am
considering replacing the Chryslers with New Crusader 8.1 engines
along with new gas tanks.

I have however not been able to find much information on what I can
expect on performance out of new engines on this boat. I am not sure
what I was exactly burning per hour on the Chryslers but I suspect it
was about 27-35 GPH. (One of the engines I was running most of the
year had low compression on 2 chambers. ) My cruising speed was about
20 -25 MPH at 3100 RPM when it was running.

I will be going from 330 HP to 385 HP and I am not sure if that should
help fuel economy. I am sure the fuel-injected engines should be more
fuel efficient but I am not sure by how much or what to expect, any
Ideas?
===============================================

Twin 385s should burn 35 to 40 gph at cruising speed (70% of wide open
throttle). This assumes that the props and gear reduction are correct
for your boat/engine combination. You may need to change both, as
well as going to larger prop shafts.

Speed normally varies as the square root of horsepower for a planing
hull, ie, 4 times the power for twice as much speed. The real
question then becomes, how much power were your old engines
developing? My best estimate would be a 8 to 12% increase in cruising
speed, perhaps a little more if the old engines were really clapped
out.