Rebuild engine or repower

[Kthien915]

Is it more cost effective to rebuild a engine and upgrade it or buy new engines ?

I have twin 454 7.4l motors that I believe are a good platform to rebuild and update. Looking to get at least 600hp out of each. Still have a bit of life left in them I'm just starting to get a build sheet together and trying to narrow down cost.

 

[HubbaHubbaLife]

.... this will be a great thread!

 

[Husqy510]

I'd perform a leak down and if they check out, you could easily upgrade those motors to close to 600hp. It wouldn't be cheap, but it'd be a lot.less than two new motors.

 

[obnoxious001]

Is it more cost effective to rebuild a engine and upgrade it or buy new engines ?

I have twin 454 7.4l motors that I believe are a good platform to rebuild and update. Looking to get at least 600hp out of each. Still have a bit of life left in them I'm just starting to get a build sheet together and trying to narrow down cost.

With twins, I suspect you are running outdrives? The reason I ask that first is the type of drives will have some determination of what RPM you want to run the engines, which in turn limits where you want the power curve. Type of fuel and size of the boat (how much of a load there is on the engines) will also need to be taken into account.

Aside from compression, cylinder heads and camshaft do the most for making power. Last week I ran one of my engines at Westech dyno, 460 cubic inches (.030" over 454) that made a respectable 608 horsepower with stock iron 990 heads at 6500 RPM, but that was with 11 1/2-1 compression and AV gas, for a little 18' jet boat. That engine does have a solid roller camshaft. To make that much on pump gas you would need to spend more money on a good set of cylinder heads.

 

[Kthien915]

Yes I have out drives Bravo ones, I'd like to be able to cruise at 3800- 4k range. I'd love to stay with pump gas but I know that might not be practical with a 600 hp target. The boat is a 32ft hallett heavily built. I also thought about changing the props from a three blade to a 4 blade . I'm told 4 blades are better for cruising speed and for heavier boats.

 

[obnoxious001]

Yes I have out drives Bravo ones, I'd like to be able to cruise at 3800- 4k range. I'd love to stay with pump gas but I know that might not be practical with a 600 hp target. The boat is a 32ft hallett heavily built. I also thought about changing the props from a three blade to a 4 blade . I'm told 4 blades are better for cruising speed and for heavier boats.

If you increase cubic inches with a longer stroke crank you may get closer. I did make over 600 hp with a 9.6-1 iron headed engine, but once again the peak power was around 6300,, too high for the outdrives. A pair of 540's would easily make the power, but you would not be using any of the existing 454 parts.