Chestah Cheetah

iTrader: (1)

Got a slight problem here that just might help me pick up a couple MPH once resolved.

2006 Howard Bullet
2006 525EFI With Whipple Stage 1 ECM Program
Teague Platinum Drive with Imco Standard Lower 1.36 Gears
Bravo 28P and Bravo 26P
91 Octane Fuel

With either prop, the motor only winds up to 4900RPM. This is our wall. The guess is we need to swap the gears to 1.50. What are some thoughts on why we can't get full RPM?

class6

Try a un-Molested 555 1st

Griff

The gear ratio should not be an issue. The 26 should spin +/- 400rpms faster than the 28 no matter what the gear ratio.

Is the tach reading off a smartcraft or analog guage???

Uncle Dave

Sounds like a bad ECM program or that you may have some kind of guardian stopping it form revving out.

How old is the fuel? If its detecting knock typically you wont be able to rev.

Who is the engine guy that built it? Id go to him first.

UD

F-2 Speedy

iTrader: (6)

The stage 1 Whipple tune for the 525 EFI nets you 25-30 hp, which puts you around 550-560, trying to spin a B1 28 is tough, I think what your seeing @ 4900 is correct..........I had 625 hp in a 540 cu in and they would spin a 28 B1 5200

Chestah Cheetah

iTrader: (1)

Agreed on the fact that the 26P should net 400RPM's. Both props are used with unknown origins and whether they were labbed or modified in any way.

The tach reading is from a Vessel View 4 .

A full tank of fresh 91 octane in the tank (the Whipple ECM upgrade requires 91). The motor was built by Mercury Racing, no other builder involved.

Not sure I agree here. I have had the same exact boat and motor combo in the past, spinning a 28P to 5250 was no problem on a pure stock 525EFI.

The differences between this boat and the last boat are Bravo XZ with 1.50 gears vs. a Teague Platinum with IMCO standard lower running 1.36 gears. This boat
has the ECM upgrade the other boat did not. We are not hitting the rev limiter, getting the same exact top speed with both props (which also tells me one or both have been labbed somehow). So gears are not the problem? What other theories?

F-2 Speedy

iTrader: (6)

That's right off Whipples website, so believe what you want.......change the gear or prop, your trying to spin a 28p with a 1.36 gear with 550 hp, it wont add up in my book

Chestah Cheetah

iTrader: (1)

I apologize, I understand what you're saying now.

The 1.36 gears are most likely the culprit here? Is it safe to assume switching to 1.50 gears would get this combo to full RPM range?

CDShack

Before I deal a lot of money on a .14 gear difference I'd try a 24' and see if it changes. If you're still at 4900, easily tells you have other problems. It not, prop into the gear ratio.

Uncle Dave

Yup its a its cheaper to put a smaller prop on that to re gear it.

I would think he should be turning the 26 at least a few more RPM than the 28.

UD