Steve Zuckerman

Ray,
Lots of questions.........I'll make a few observations. Gears in our boats are our 1 speed trannys. 1.65s I would call 1st, 1.50s 2nd, 1.36s 3rd, and 1.25s 4th. Since we only have 1 gear, we have to pick the most efficient gear for our boats speed and horsepower/torque range. 2nd gear (1.50) is what 90% of sub 100 MPH performance boats run efficiently. 1.50 gears allow more propeller pitch because they are delivering more torque to the propeller than 1.36s or 1.25s, which is why you have dropped down in pitch to recover lost RPMs.
I have a friend here who just changed from 1.35s to 1.50s in a 28' Profile tunnel, went up in pitch to a 34" and gained 10 MPH. Think about that...........he went from 3rd in a 100 MPH boat to 2nd, and gained a lot of speed.
Ray, this is a good experiment. Nothing ventured, nothing gained as they say. I wish it had worked better for you. We would all be doing the same if it had.
Regarding the handling issue, I would have to watch your boat run. Are you trimming differently, say more to get your RPM back? If so, that's probably causing some of the chine walking. Keep us posted.
Regards,
Steve

raytart

Hi Steve

Thanks for your reply. The answer to your question is YES. I am trimming out more to get the rpms up and I also need to drop the tabs down in order to keep the boat settled down. (which in turn scrubbs off speed) I'm having a tough time trying to figure exactly what is happening. I'll post a photo so you can see it running' Sorry NO video.

Ray

Steve Zuckerman

Ray,
Sounds like your before and after speeds are pretty close??
It's not unusual to have to give up pitch if you go up (down numerically) in gear ratio. I guess the bottom line is Mercury knows what gear ratios their motors like, and it's hard to fool physics.............
When I was racing, I had several friends try different gear ratios. If they went up in gears, they always had to go down in pitch and vice versa. I never could tell that it made much difference. I just stuck with the 1.87s that came with most of their racing (and stock) outboards, and they worked fine. I've been to the old Lake X, and believe me, they tried 'em all.
Regards,
Steve

raytart

Should have left well enough alone!
Point well taken. If it aint broke... don't fix it!

Steve Zuckerman

Ray,
The attitude of your boat looks great........bow up, riding on the end of the step and pad, with "dry" chine all the way back.
I am starting to see how you guys are getting the big #s some of us were a little skeptical of. Your conditions, nice surface chop, sea level, salt water (yes the jury's out on the salt H20) are nearly perfect. Plus your air and water temps probably average a good 10 degrees cooler than down here. All good things for performance enhancement.
I would go back to the 1.50s, that I recall (?) you were running 80ish with, and play with props/gearcases/spacers. I would also try to get some air to the engine compartment. Isn't the Monstaa guy who made the nice air intakes for Sick Nordic near you?
No harm in trying the gear change. Like I said before nothing ventured, nothing gained. This one just didn't work, and some modifications don't.
I should also mention that some friends here with BIG power (900ish) are running 1.35s in their Heat, and it did work well, as in 100MPH, before they had motor issues.
Regards,
Steve

raytart

Steve

I'm not ready to throw the towel in yet. I sent the 26 pitch to the prop shop for labbing. Hoping to pick up about 400 rpm and hopefully 2-3 mph. I'll keep you posted. My speed is actually a bit faster with the 1.36 setup. If I gain rpm like I hope to, the speed should follow. Best speed with 1.50 was 77-78 at 5200 rpm. I'm now at 77-78 with only 4800 rpm.

Ray

raytart

HERE'S AN UPDATE WITH THE 1.36 GEARS AND 26 LABBED B1

Livorsi GPS speedo

525efi 1.50 gears-its/xr drive-28 bravo with added cupping)
At 2500 rpm went from 25 mph to 32 mph
At 3000 rpm went from 35 mph to 41 mph
At 4000 rpm went from 50 mph to 60 mph
At 5200 rpm went from 76 mph to 78 mph


RESULTS WITH 1.36 GEARS LABBED B1 26 PITCH
DRIVE SPACER IN (GLASS SMOOTH WATER)

At 2500 rpm 34 MPH
At 3000 rpm 46 MPH
At 3500 rpm 56 MPH
At 4000 rpm 65 MPH
At 4500 rpm 73 MPH
At 5000 rpm 79 MPH

PROP STILL NEEDS TWEEKING TO GET TO 5250 RPM
SO CLOSE TO 80 IT'S KILLING ME!

bobl

Your prop slip numbers are phenominal. I have the exact same boat and drive setup, with 1" spacer and my slip numbers are at best 14-15%. That's with a 29" Hydromotive P5X, they are even higher with a Bravo 1 prop. Must be some really good water you run in. I'd really like to understand the difference. I think Steve's numbers are similar to mine also.

raytart

Bobl

No B.S. here either. Just telling it like it is.
When I get a chance I'll post a pic of the tattle tale speedo.

Ray

You should move to Long Island just to get a few more mph.
Ha Ha

Steve Zuckerman

Ray,
Sounds like you are making progress. Good luck.
Bob, I have mine down to 13% with the 28P5-X using go-fast.com's calculator.
May be the lower unit, your ITS box, the deck difference, or a combination of the three.
Regards,
Steve