28 w/280s
 

Guys,

Looking for some setup advice...

Current setup = 28 with twin 280s. Mids are 15" and powerheads are stock. Preferred props are currently 14.5 x 32 four blades, spinning out, with motors toed in (prop shafts closer than nosecone). Speeds are unimpressive at 105-106mph. Tried spinning in but lost speed and only ran 103 (with the 14.5 x 32 props and motors mounted straight). Have tried a set of three blades that are faster but the boat blows-out and the rear end starts to get real loose...!

Based on what I have read on here a lot of people prefer 15 x 34 four blades (but with 300 motors). Most also spin their props in. My setup question is this: with a pair of 280s are these props something to try? And would toeing the motor out whilst spinning in be something to reconsider? Also, why do most of you run 15" vs 14.5" dia. props?

Feel free to share any 28 + 280 setups you run or know have run in the past... I'll take any info I can get!

What's you prop shaft height?
You can usually run the props higher with a bigger diameter and not blow out.

BTW... prop shafts closer than the nose cone is toed out.
Think of it like your feet, if your toes are closer together than your heels you are toed in.

also, watch your trim angle as most outboard cats run best with neutral or very little positive trim
What rpm are your turning when running the 14.5 x 32s @ 105-106?

subscribed

Running at 8,000 rpm and prop shafts about an inch above the bottom of the hull. Tried 30p props but the motors wouldn't turn them.

What gear ratio? 8000rpm turning 32's does not add up unless the ratio is high like 2 to 1

I thought they were 1.87s. What doesn't add up? The props have been re-worked...so maybe the #s I was told are off?

Seems like your engines should be higher, if you can keep water pressure. My guess would be 1 3/4 - 2 inches above the bottom.

I assume these are the race ecu's? They have 8200 rev limit. the sport ecu's are 7500 I think?

supercat, correct.

What are your motor heights and water pressure???

According to my calculations with 10 percent slip which is a little high at 8000rpm and 32" pitch props you should be running 117mph. Are you saying you can spin 32" props but not 30" Props?
Turning 30's will only make you turn higher RPM's and possible go slower.
Raising the motors will increase speed and rpm but i would first try and figure out why you have a 19% Slip with the motors only an 1" above the bottom. Are they on set backs? If so how far back?
I would guess the props are not 32's but maybe a true 30. Could have been reworked.

Hopefully this covers most of what you guys have asked: motors are mounted on 5" jackplates, water pressure is well above 10psi, and the props have been re-worked. They're supposed to be 32s but it looks like they might not be(?). The 30s never worked out. Not sure why the numbers are so bad but the boat has seen 106mph with those props. Any ideas??

106 w/ros ecms is god awful. Where are u you located?

I do know that when I ran un labbed props I lost 5 to 10 mph. The rpm's were up but so was the slippeage.

Yes. Have only ran Merc lab props.

Stock 280 ECU's redline at 7750rpms.

Sounds like you may have a set of 2:1 gearcases. If you drop the cases, the top of the sportmaster should be stamped with the ratio. 1.75, 1.87 or 2:1... 32's and 8k at 106 works out to about 12% ish...