Engine problems

[chase8]

One of my buddy's here on the forum has a problem I was hoping some of you motorheads could help with. Couple yrs ago he didn't get the boat winterized in time and the utah cold cracked the block on a stock merc 350. I'm not sure exactly which 350 it had in it but it was trashed so he decided to get it replaced. After weighing over his options he decided to spend more money and have a 383 stroker built for it. The marine dealer contracted the job through a reputable marine engine builder here in utah. Now the problem is this. With the stock set-up he was running before he was getting between 55 and 60 mph @ about 4800 to 5000 rpm. The stock engine was rated at about 260hp. He was told this stroker would produce around 400 hp. So we took it out recently and the thing is a pig. The best it will do is 47 mph @ about 3800 rpm. We ran the stock 21 pitch prop as well as a 22 and it didn't seem to make much difference. Now he seems to be getting a bit of a run around. We are being told that the ecu may need to be reprogrammed and that the engine is not getting the right air fuel mix. I'm thinking that someone screwed up. This engine runs great. It purrs all the way throught the powerband, and has no hiccups or hesitation. But it runs more like a stock 305 instead of a 350 or 383. We are testing it at an altitude of about 4300 ft.

[ratso]

One of my buddy's here on the forum has a problem I was hoping some of you motorheads could help with. Couple yrs ago he didn't get the boat winterized in time and the utah cold cracked the block on a stock merc 350. I'm not sure exactly which 350 it had in it but it was trashed so he decided to get it replaced. After weighing over his options he decided to spend more money and have a 383 stroker built for it. The marine dealer contracted the job through a reputable marine engine builder here in utah. Now the problem is this. With the stock set-up he was running before he was getting between 55 and 60 mph @ about 4800 to 5000 rpm. The stock engine was rated at about 260hp. He was told this stroker would produce around 400 hp. So we took it out recently and the thing is a pig. The best it will do is 47 mph @ about 3800 rpm. We ran the stock 21 pitch prop as well as a 22 and it didn't seem to make much difference. Now he seems to be getting a bit of a run around. We are being told that the ecu may need to be reprogrammed and that the engine is not getting the right air fuel mix. I'm thinking that someone screwed up. This engine runs great. It purrs all the way throught the powerband, and has no hiccups or hesitation. But it runs more like a stock 305 instead of a 350 or 383. We are testing it at an altitude of about 2300 ft.
Go to the Gearheads Section.

[Havasu47]

If the engine is fuel injected, you can't run a stock ECU designed for a 260 HP 350 and expect it to work on a 400 HP 383. This is just scratching the surface of probable problems.

[BajaMike]

You need a lower pitched prop....try a 19.....if you are only getting 3800 rpm, it's probably the prop.
What drive does it have??

[Beer-30]

You need a lower pitched prop....try a 19.....if you are only getting 3800 rpm, it's probably the prop.
What drive does it have??
BM, he tried the 21 that was on it before the new motor, and it was slower.
Engine is being limited on the intake. If it has the regular "throttle body" type intake, that is your limiter. For a 383 or even a hot 350, it is like a restictor plate.
The later model "Monsoon" type Vortec intake was good for around 325HP, but not much more. He may be looking at aftermarket EFI.