Hard Charger

Ok I have a 93 Sonic 28 ss w/ a single bb. Last week installed new/ rebuilt Gen 6 502. 600 hp
bored 30
srp forged flat tops
moly rings; first ring gaped at 28 thousands, 2nd at 26
merlin heads
teague hyd roller valve train.
cam is 610/ 632 lift 236/ 244 dur @50 112 cl
cloyes adjustable timing gear. cam was degreed in at 112
merlin air gap intake
holley 800
msd distributor (ready to run) msd coil
ngk plugs -9 series
imco powerflow exhaust w/ extensions, no silent choice
bravo 1 w/ 1.50 gears

First sea trial results. 61 mph gps at 4,900 rpm using 26p b1 lab. Prop slip is 24%! moved the timing up and down a little, slight improvement. Fuel pressure was always above 6 psi.

I know the quick fix is trying different props which I'll try out soon. However I believe this motor should be able to turn a lab 26 b1 to the desired 5,800 rpms.

What's wrong with this setup? Is the factory X dimension creating to much drag from the drive sitting so deep? I believe the prop centerline is close to 7" from the bottom of the hull.

TexomaPowerboater

What was the previous power/hp and how fast did it run?

Sport 280

Deep drive and 4 blade prop on a non stepped hull is not a good combination. Try a mirage + 25 pitch three blade. But with that much slip the engine should turn more RPMs. If you advanced the cam to much top end will really suffer. Was the cam installed according to the cam card? Was the 600 hp from a dyno? Your combination is very close to a Merc HP500 which makes about 470 hp. Not a lot of power for a heavy single engine boat.

Early sonics are fairly heavy boats. You will likely need a prop you can spin at 5400 RPM to get power from the combination you listed, maybe even a 23.

But what were you running before the new power? Prop, Horsepower, rpm?

You need something to compare to the new setup.

f311fr1

My 28 ss with 502 Mag had a Mirage 23 pitch 3 blade. The drive is probably too deep. I should have some 23, 25, and 27 pitch right hand props. Shoot me a PM and I will check in the barn.

Hard Charger

Dang power keesp going out. So let's try posting again.

Previous motor was a clone hp500. tried various props and the overall best one was a lab bravo1. Best speed was 63 mph on gps, 4850 rpm 1-2' chop light load using a lab 26p b1.

New motor has more compression, better valve train, iginition, heads, etc. Cam was degreeded in per specs. It makes more power than the latter.

Thats why it doesnt make sense. Almost exactly the same rpms and speed. It feels like you hit a wall at 4,900 rpm, just stops pulling.

GTOFFSHORE

What is your timing set at?
You may have a very deep drive but more power is more power.

pacalim1965@yaho

540 with -2 imco shortie

Hard Charger

Great response. Thanks for your insight on this matter.

Hard Charger

Timing is 35 degrees overall.

bigblue

I love the sarcasm. And what?? A whole new setup isnt in your budget this year???

Starting a little lower in pitch would be a good start. Know any buddies that can lend you something to try? Or perhaps a local place for trial and error. A lot of guys reccomend BBlades. I may be giving him a call too! Best of luck to you.