xcpilot

Using a cupped 30 Bravo 4 and hitting the rev guard hard at 5450 @ 93mph. Thinking it may be time for a 32? Not sure where to go, any suggestions. Power from a whippled 496 with forged internals, CMI headers and 7lbs of boost. Thanks.
BTW this was my first day @ 7lbs of boost......WOW!

Linster

Can you get the rev limiter raised? If so, I would have it raised to 5800. Is the 30 stock? If so add about .020 cup, no more. The 32 takes a lot of work to get them to hook up right. Never seen 2 of them run the same. They have a good amount of slip.

Steve Zuckerman

Raising your limiter should also give you another pound of boost, and horsepower comes with boost. With forged internals you should be OK @ 5800/5900. I wouldn't run it there all day, but for occaisional blasts, it's OK.
A 30" P5-X or Herring 5 blade (really are 30" pitch, and the extra blade will pull Rs down some too, with more efficient slip #s) would be a good test if you can find one, or a 32" B1 with cupping similar to your 30".
Sounds like you have your boat dialed in nicely. Congrats.
Steve

CB-BLR

Somewhere the math is off...
at 29 pitch.. which is what a 30 is stock.. slip is at 6.7%
at 30 pitch .. slip is at a little over 9%

It is hard to believe that a Bravo prop has slip that low ... Hmmm

Anyway... I agree with Steve... demo a Hydromotive 30 P5x. Hydromotive has a demo program. Going up 1 inch in the hydromotives pitch will reduce rpm aproximately 150-170 rpm.

That is my favorite all-around prop.

I regularly spin a labbed 30 p5x at 5600 rpm to 92.8 mph which equals about 12.2% slip

Sounds like your boat is running pretty darn good.


Chris

90mphRAGE

Read the post for prop ~600 hp rage. I run approx same 750 hp (whipple 500EFI) & turn a 32 labbed 5400ish & 90ish. My prop slip calcs are around 17-18%. Slip drops with my labbed 28 to about 15-16% on the 5750 limiter @ 84mph. 32 labbed should be what you need. I don't see how 93 is possible with that prop & that rpm. Desert Rage & I have compared/tried many props with comparable hp & consistent results.

CB-BLR

As I said... the math doesn't add up.

Either the GPS is wrong, or the tach is off (which is quite often the case), or this is a fuzzy number for speed.

Something doesn't add up.

I am glad the boat is running well though, and that you are having fun... that is what it all about in the end.

Chris

Nordicflame

iTrader: (4)

I do see where you hitting the rev limiter at 5450 so the tach seems right I suppose.
However I don't recall any mention of this detail ; Is this with a GPS speedo?

CB-BLR

A non-GPS speedo would make sense.

Chris

bobl

He said the 30" prop was cupped. It's possible to knock a couple of hundred rpm off with heavy cupping, so that could skew the slip numbers quite a bit.

bobl

The 496 whipple moter I built for 22 Daytona made peak HP at 5500 RPM. That was with a Raylar blower cam. The stock cam would probably peak sooner. The 496's don't seem to like a lot of rpm like a 502 based engine does. I'd try to prop for no more than 5500 unless you have dyno numbers telling you otherwise.