1995 Checkmate 253 with 700HP
 

A buddy has a 253 with a 700 HP 540 CI engine going in. has anyone had this type of power in this hull? he was curious where to start with prop size and what can he expect at WOT...thanks for any info.

Did he dyno his engine to know what RPM it makes peak power? Best bet if you don't know that is to start with original prop he had to establish a baseline and go from there.

I built a 548 for my 253 checkmate and over propped it for year and half and was disappointing in power it made and it never climbed to RPM it should (6300). Dropped down to a 23p hydromotive QIV and engine was happy and broke 80 mph.

My favorite props by far on that hull was Hydromotive QIV with cut diffuser and cup added. Almost zero chinewalk and far reduced porpoising over a Bravo I prop.

we put 800hp 540ci in an 25 active thunder its an absolute blast to drive and many will tell you here winding it up is better than overtorqueing the drive if you put good guts in that big chunk of iron then twist it up ...we run 6500 -6800 can exceed 7000 but so far have chickened out 90 is enough).....different props and rotations do make a huge difference try a left prop to cancel engine torque some hulls like that some don,t (the shifter is reversed so its tricky testing if you like it you just move the cable on the shifter on the helm)

I had a 1997 253 with 1200hp. The drive was 1:36 ratio. We turned the engine to 6200-6300. I ran a Hydomotive 4 blade 28 pitch prop. It's hard to know what your friend should do if he didn't dyno the engine. It will require a fair amount of testing with different props. I did turn mine left to counter engine torque. This hull will want to chine walk a little in the 75 to 90 range.

I found this in the Checkmate forum archives from a member on here named Vinny. This post was from 2009 I think. I was modifying a 259 Convincor at the time so I always read his posts. If I remember correctly he was spinning this prop over 6000rpm.

"I have a '99 259 with a 700+ hp 540. I can run 85 with the right conditions. Running a -2 Imco, spinning a 25" P5-X."

Kunkels Marine in Mansfield Ohio has been there, done that and have a wall of props from doing it.
They were Checkmate dealers forever and did most of the testing that the factory was quoting.

The above suggestions are spot on that you need to know more about where that motor makes power.

Get that info then call Jason or Harold Kunkel and they will set you straight.
They had 251’s running 120’s 30 yrs ago.

And they will tell you, torque is more what you’re after than, HPs.

Thanks for the info guys. He did dyno the engine. Peak torque was 697 at 4200 RPM. Peak HP was 701 at 5900 RPM....he has a 1:5 Bravo...was considering switching the shift cable and running a LH prop as the boat did torque roll before.

Thanks for this info, its nice when someone already did the leg work on the hull your using! Appreciate your time.

Any updates?

Well, he put the boat in the water and used it a few times to work out any bugs. Then planned to start making full passes to dial the prop in. Unfortunately, the fuel pump he was using couldnt keep up with the engines needs and he leaned out and burned a couple pistons. The ole' Holley Blue pump isnt designed for 700+ HP apparently. Long pulls in a boat are much different than 1/4 mile passes in a car. SO the engine is back together now, so testing will commence in the spring!

Looking forward to the results. I feel like that's an area that most often gets over looked is the fuel delivery support. Not just the car or injectors etc.... But the actual lines and fittings coming from the fuel tank itself. You can only pull x amount through a certain diameter fitting and tube setup regardless of the pumps and other items installed.

I should mention, He did start at the tank and replace lines, fittings and all. This wasnt just a fuel pump update. Expensive overlook, but its done right now.

It was suggested to me to run 1/2" inside the tank and to the fuel pump. And I'm only projected to make 550 HP. (carbed)