38 Foot deep vee.What differences will be seen going from 420hp 502's to 800hp 632's?
At the same speed will fuel useage be the same?
Forget the drives,maintenance etc.Just interested in your thoughts on fuel burn.

More Hp, & Cubes = more fuel

The only problem with horses is if your going to work them you have to feed them.

An 800 HP 632 engine is going to have a much greater BSFC (brake specific fuel consumption) than a 420HP 502, period!
The 800 hp engine is going to allow you to cruise at a faster speed or lower rpm than current 502 and that will save some fuel while running but the higher horspower potential of the 632 at speed will use a lot more fuel than the 502, but the speeds will be much greater. You see where I am going here?

Best Regards,
Ray @ Raylar

So say both are running @ 45mph,will the 632's use more fuel than the 502's.Guessing that the 502's are turning 4000 and the 632's maybe 3000 or less.

My guess is at the same speed, the bigger engines will use about the same amount of fuel. Will you always go the same speed? Not very likely

Okay so if at the same speed they both burn the same amount but running the big motors "faster" will use more fuel.Going from A to B i will get there quicker so therefore they won't be running as long.
I'm just trying to work out if i pull the small motors and fit the big.I already have both sets.
I use this boat around the islands and out to the reef.
If the both would use the same amount at the same speed i would be happy and do the swap.

Yup! I found that out when I went from my Scarab to the Apache.... I assumed I would be spending a ton more on fuel.

When I had the Scarab I'd burn 30 gallons per hour at cruise, which was 3700 rpms or 50 mph. Engines were 502", NA about 500-550 hp.

On the Apache (6 ft longer and a lot heavier), I burn 40 gallons per hour at 3700 rpms but now I'm running 61 mph at those R's. Plus, if I want to slow down to say 3200 rpms (50 mph) I will actually burn a little "less" fuel than the Scarab did at 3700. Engines are 580", blown, 830 hp.

So for 6 ft. in boat length, a couple thousand extra pounds, roughly 300 hp difference per engine and 10 mph gain in cruise, my fuel costs have largely remained the same.

However, get above 4200 rpms when the boost kicks in and all these figures quickly go out the window!!

Do get to buy one of your 502s off you if you swap them out?

632's big wheels and 2 speed trannys with OD