BY U BOY

IDLE IN GEAR IS 700RPM RUNNING A HYDROMOTIVE LABBED 24P. BOAT IS RUNNING 68 WITH NO TRIM AT 4500. PROP TESTING IN THE MORNING NEED TO GET TO 5100RPM.

dlbCheckmate

Mike, I am also running a 251 Checkmate (87) but I have a 468 with ported heads and run 78 mph on GPS (25 pitch 4blade Hydromotive prop) I had heard originally heard that Checkmate built two versions of the hull. One had some hook for less HP. What Motor combo did yours come with originally?

Mike Paula

That's interesting......... it started life as a 330hp. how is your bottom? the hook is right at the pad area.

Mike Paula

Dont know where I am with no trim but with positive trim at the sweet spot it will pull 5000 rpms. with The 23p hydromotive. If I over trim it rolls over and drops the bow and revs up to 5200 rpms and drops to 56-57 mph.

BY U BOY

I WAS PULLING 5000RPM WITH THE 23P BEFORE I MADE SOME CHANGES. WENT FROM A 330HP 454 TO 525+HP 454 I WAS RUNNING 59.9 GPS NOW I AM AT 68 WITH MORE TO GO I THINK I SHOULD HIT 73MPH.

Kidnova

I've been running a ZZ502/502 in my 23 Wellcraft Nova for 4 seasons and no signs of reversion. 1 season with stock Merc exhaust...no signs of reversion. 3 seasons with Revolution Marine exhaust and no signs of reversion. Running a labbed 25P Mirage generally turning 5050 to 5100 RPM's. Will do +,- 68-70 MPH any day all day. Best WOT so far is little over 73 gps.

The Nova has a slight hook probably about +,- 18-20 inches up from the transom. 4 foot straight edge shows the hook is about 1/8 inch deep. Haven't checked/measured for a while but think thise numbers are pretty close. Prop shaft center is about 7 3/4 in. below the bottom of the boat...way deep by totays standards.

23 Nova's are not known for a fast/efficient hull. I would think your 251 would be several MPH faster at WOT than a similarly powered 23 Nova. I'm sure the bottom paint is holding you back some, like Griff said.

Sounds like you have the ZZ heads along with the ZZ cam. What are you running for a carb, and how is it jetted? Your turning a 23P at 5000 to 5100 RPM's. A ZZ turns a 23 at over 5600 R's. When I tried a 23 I pulled back on the throttle at 5600 while it was still climbing. If your going 60 MPH turning a 23P at 5050 RPM, your prop slip is around 19%. That's very high. Could be the bottom paint plus not trimmed properly ?

Mike Paula

I am using a 502 GM performance Short block.The Heads are the same as a zz502. I would have thought I would pull more RPMs than it does. I have a flowed 600 holley with the same jetting as the stock zz 502(dont have spec here with me).


EDIT:Not a 600 I meant 800!!!

BY U BOY

A 600 SEEMS SMALL I HAVE A 750 AND MY ENGINE IS SCREAMING FOR MORE FUEL AND A SCOOP. CHANGED JETS ON THE WATER TODAY AND STILL NEED TO GO BIGGER. 83 PRIMARY 85 SECONDARY. LOOKS LIKE I NEED 85 88 OR LARGER.

dlbCheckmate

Mike, mine is flat no hook at all. It has a little chine walk with a three blade but you can drive through it. The four blade took it all away. I wanted to try the Imco shortie and see what it would do for me. Then if it helped I could move the motor up some more with the box. Havent gotten the chance yet. I'll answer your email soon.

Dave B

Kidnova

Like By U Boy said, 600 cfm is likely too small. I'm not carb smart so I rely on books and guru's for help. According to the "carb chart" in Dennis Moore's book, a 650 on a 502 is good for 4500 RPM's. An 850 on a 502 is good for 5800 RPM's. I'm sure there are variables but, have to believe those numbers are in the ball park. FYI...my ZZ502 came with a Holley 850. That's gotta tell you something. I'm sure someone here who is more knowledgeable will chime in on the carb thing. But, I'd say your 600 is way too restrictive. You could call Dean Nickerson to discuss what you need for a carb. If you call Nickerson's have all available engine info available.

What's your compression? I know you said you have ZZ type heads but what size are the valves? And what intake do you have?