What do you think of this combo
 

I bought a Black Thunder with a wild engine combination. 540 ci, Cam Motion solid roller 248/253 dur. 690 lift 112 center. Holley Pro Rams with 2-750 dp's. Msd ignition. With extension boxes and labbed 24 bravo 1's the boat goes 69 mph at 5000 rpm. Empty or 7 people and 1000 lbs of fuel same speed. Seems very odd to me.

YOUR HP IS WAY LOW WITH 24 P BRAVOS....WHAT ARE THE RPMS SUPPOSED TO BE
THEY SHOULD BE SCREAMING

Do the MSD boxes have rev limiters by chance ??
See if they have a 5000 rpm chip in them.
I would think that you should be able to hit 5600 to 5800 rpm real easy.

6000 rpm chip. And I should add, the previous owner said it had 8.5 to 1 comp. Is it a bad combination?

What heads?
Compression is on the low side for sure.
Is this a 43'er??

Have you checked to see if the carbs are opening all the way? Wide open throttle fuel pressure? Do you know what your ignition timing is at WOT? How do the plugs look after 10 seconds wide open?

The heads are GM iron sq. port pocket ported and intake matched by Tyler Crockett. 2.25 intakes.

It is a 43.

The carbs do open all the way. It doesn't seem to matter though., the boat does't go faster it just makes more noise.

The ignition timing is 16 at idle and 36 at 3000.

Plugs are a little rich if anything.

The engines do burn a quart of oil about every 4 hours.

The cam sounds too big for that low of compression. You would gain power with a smaller cam or raise compression to match cam / carbs. Then start buying high octane fuel..............:(

what gear ratio in drives.

YOU do have the tabs up and the drives trimed - right.
Please don't shoot me - we do get those problems sometimes.

The drives are 1.5. The compression may even be lower. That's just what the owner told me. He had blowers on it but got tired of blowing up outdrives.

DonMAn,
Just a question here but what does compression ratio have to do with cam size ?
Isn't that how you make the power when you don't have CR . You build cylinder pressure with the cam.
My old 502 with 8.5:1 made 625hp on the pump with a pretty big solid roller.

I would personally yank those intakes and put on a Brodix with either a 850 or a 1050 dominator.

I have a new pile of parts in the garage that should be on the boat by Sunday. I'm going with the combination Teague recommended in the April Powerboat. Crane 651, World Products intake, 1050 Holley. This winter I'll have the blocks redone with about 9.5 to 1 comp. It's just hard to believe that other combination works so poorly.

26 Scarab
 

The engine can't start the compression cycle until the intake valve closes. A long duration camshaft will delay the closing of the intake valve. This really shortens the compression cycle considerably. A shorter compression cycle lowers the compression in the cylinder.

A good performance engine should have at least 155 to 165 pounds of compression (87 octane fuel, 34 degrees total advance). Less cranking compression than this is really hurting performance.
An engine with a tight quench and a cool air/fuel mixture can run as much as 190 pounds of cranking compression. (92 octane, 34 degrees total advance).

Sincerely
Dennis Moore