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Discussion Starter #1
Guys

I have a 25'7 Effect.....a 502 Whipple BBC that throws off 900 HP on the dyno...I am running a 32 P prop and at 5,000 RPM I am in the low 90's. I have the XR Brovo Drive with 1:50 gears

Question: Can the boat and engine pull a 34 P prop to get more MPH? What are the pros and cons of running the 34 vs the 32?

Thanks
 

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mud slinger
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2,012 Posts
Guys

I have a 25'7 Effect.....a 502 Whipple BBC that throws off 900 HP on the dyno...I am running a 32 P prop and at 5,000 RPM I am in the low 90's. I have the XR Brovo Drive with 1:50 gears

Question: Can the boat and engine pull a 34 P prop to get more MPH? What are the pros and cons of running the 34 vs the 32?

Thanks
What rpm's can they motor turn?
 

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AKA Blownjet 468
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1,205 Posts
Guys

I have a 25'7 Effect.....a 502 Whipple BBC that throws off 900 HP on the dyno...I am running a 32 P prop and at 5,000 RPM I am in the low 90's. I have the XR Brovo Drive with 1:50 gears

Question: Can the boat and engine pull a 34 P prop to get more MPH? What are the pros and cons of running the 34 vs the 32?

Thanks
I HAD almost the same setup-stock 502/[email protected] prop, 5400rpm-96mph
I heard the 34p props are a different animal, and to stay away from them- also means
more strain on the drive- what exactly are you trying to achieve?
 

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Discussion Starter #7
Like the most of you, I am looking for a little more speed....you see/hear all the time set-ups with 1/3 less HP than I have and you will hear numbers in the 90 MPH range....I was simply thinking I could put 2 more pitch (to the 34P) and see the mid or upper 90's MPH. I am running 5 lbs of boost on a GT Performance build....not looking to go ape-shit, just want near the 100 MPH benchmark

I guess I should toss the wifey, kids, all their chit and see what I get
 

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mud slinger
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2,012 Posts
Like the most of you, I am looking for a little more speed....you see/hear all the time set-ups with 1/3 less HP than I have and you will hear numbers in the 90 MPH range....I was simply thinking I could put 2 more pitch (to the 34P) and see the mid or upper 90's MPH. I am running 5 lbs of boost on a GT Performance build....not looking to go ape-shit, just want near the 100 MPH benchmark

I guess I should toss the wifey, kids, all their chit and see what I get
You have to big of a prop on it if you cant hit the rev limiter.
 

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Prop down until you are at the rev limiter if you want more speed. Maybe try a five blade if you can get a loaner. You should easily hit 100 with that much HP and that hull. Good luck. I think you will go slower with a bigger prop.
 

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32 DW X-CAT
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Comment:

Well with a 1.50 gear ratio and 900+/- HP you should easily pull this propeller. You probably hit the rev limiter pretty quick.

In fact at a liberal 18% slip ratio you should be right at 99MPH with this propeller.

Some of the LIMITED information your providing is not the proper manner for obtaining top speed.

I do not recommend having people in the boat when your propeller testing. Second, you need to have the boat at WOT and trimmed for speed versus cruising. Typically a hull like yours likes a little chop on the water and into the wind should get you the best top speed.

Good luck!

KAP
 

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there seems to be a lot of issues here with prop, drive height and RPM's. You should prop the boat to hit max RPM's or at least very close to it. Talk to Robbie Racer about the 257 Carerra. he has done everything to his to obtain the speed he is going. The motor is loaded way heavy now and you need to get it to perform. You are only using about 700-750 HP of your 900Hp that you say it has at 5000 rpm's.
 

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Do you know at what RPM the motor makes peak HP? You want to prop at or very close to that RPM. I'm guessing it will be above 5000 RPM and the fact the limiter chip is 6K should give you a hint. :D
 

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Sorry, I missread your original post. Like many have said, run a smaller prop to get the rpm's where they should be. Not only will top speed improve but acceleration and overall handling will be greatly improved.
 

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AKA Blownjet 468
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forgot to verify- are you saying that 5000rpm is all you can pull? what IS the max rpm
you have seen with this "900hp"? not talkin' smack, just curious, I could pull 5400rpm,
with my labbed 32p* with "substantially less power" GPS speedo, 96mph.......;)
 
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