Less pitch with extension boxes?
 

My boat, stock, spun labbed 26p Bravo1's on -1" lowers, 1.50:1 ratio to 72-73 mph @ 5200rpm. I now have 28p Bravo 1's on -3" lowers with neutral Imco boxes 1.5:1 ratio.
The motors have aluminum heads by Edelbrock & the cam Tyler Crockett supplied for his 454/502 Mag MPI upgrade package.
When I had my Whipples I could spin the same 28's to 5300+ @ 94 mph on 1.34 gears, same boxes & drives I have currently.
I was expecting 5500 rpm with the gear change and Whipple removal. I can only obtain ~4900/4950 rpm & 74 mph.
It just doesn't seem like I should be spinning the same 26p wheels I had back in stock form with an estimated 100 additional hp I currently have.
What am I missing here?

to many changes at once....I think its about the 100HP and nothing else, that sounds about right with the RPM !

Okay so I do not see a problem. Do the math.
RPM X Ratio X Pitch X 0.0009496 = MPH (no slip)
4900 X 0.666=3263.4
3263.4 X 26=84848.4
84848.4 X 0.0009496=80.57204
80.57 - 8% slip = 74.12 MPH
So if you speedometer is correct at 74 MPH you are at 8% slip.
I do not see a problem unless you are not in the designed operating WOT range for your engine.

Yup, I was expecting more RPM. I think I overestimated my hp in N/A form or underestimated when supercharged. Either way, I have a lake boat again & I'm getting happy with that.

I agree you should be spooling those 26s at a higher rpm. Are you estimating 100hp per side or total increase?

Just curious, why did you pull the whipples?

Your prop slip is obviously less than before and its pulled your motors out of the cams power range, I have fought the same problem when I run my boat with blower belt off. You get spoiled having a flat torque curve that goes on forever with a blower and its harder to prop for N/A, we just forget that over time, Smitty

Jason,
We'll talk tomorrow AM.

B

I am curious to see what comes of this, I have the same thoughts with mine and some things just don't make sense in my head.

Yours seems pretty straight fwd to me unless you have a weird tuning glitch. You made hp at 5600 or so, your running a un-labbed prop and are 600 or so rpms below the power band if I remember right, you really need to try a labbed prop that gets your rpm's right where they need to be, Smitty

Yes, I'm tracking the RPM part it's the drive height that gets me thinking.