25p worked to 24p and cupped.

[SickSation]

Ive got an 01 sunsation aggressor 25. Its got a 454 with a 25p reworked to a 24p and cupped. Im getting around 70mph at 4250 RPM. If i go to a smaller pitch prop to raise rpms will i gain top speed or just raise rpm and speed stay about the same? Boat plains very quick with the current setup.

 

[cigdaze]

From seeing the pic last night, I saw that you have a 7.4 MPI 310HP (not to be confused with the 454 MAG). The 7.4 MPI has a WOT rpm range of 4200 to 4600. You're on the low end of this, so a smaller pitch prop should get you a little more rpms and get you closer to the engine's peak abilities (perhaps slightly more top end). Planing should technically get better with a smaller prop, albeit I don't know exactly what was done to your prop, so it could be apples to oranges going with a smaller stock prop.

Generally speaking 3-blades are faster top end, 4-blades offer better planing, mid-range cruise, and better holding "bite" in rougher waters.

The choice is yours, but I always prefer to be at the upper limit of the recommended rpm range, so if it were me, I'd be looking for another prop to get you closer to 4500-4600 rpms. This will be especially helpful for those days when it's a bit rough, and you have a full load of people and full fuel.

 

[SickSation]

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Sorry... yea, not a 454 mag. 3 blade prop. Ive heard reworked props arent always the best to run. The marina behind my shop has loaner props. I might just grab a 23p and 25p and see which performs better. Does cupping make much of a difference? I run on the ohio river so we see alot of midly rough waters due to all of the barges and general boat traffic.

 

[cigdaze]

Nothing at all wrong with reworked props as long as it's been done by a competent professional.

Reworked aka "labbed" props will always perform better than their stock counterparts. Stock props are basically just cast, polished up, and sent out the door. Amongst other reasons, the blades are generally thicker than they need to be, the edges are blunt and square, and only minimal cup is provided. Prop professionals will lab-finish your prop to precisely suit your needs and your boat and try to get as much performance out of a prop as reasonably possible while maintaining sufficient strength and life expectancy.

Yes, cupping can make a difference in the way a boat holds its bow. If I'm not mistaken cupping should help planing time and provide bow lift.

If you have a worked 25 now, chances a stock 25 will only deteriorate your existing performance.

I'd try a 23P 3-blade, and both 22 & 24 pitch 4-blades, shooting for 4500-4600 rpms.
I'd venture to guess that a labbed 24 pitch 4-blade or a stock 22 4-blade will be your best all-around prop. Since generally most of us don't spend all day at WOT, find the best cruise prop you can. Best way to find out is to try 'em and see.

 

[Trim'd Up]

Is that speed GPS? 70 seems a little fast for a 7.4 in a Agressor. The numbers don't work out either. A 25" spinning 4200 with no slip is only 66mph. A labbed 25 mirage will probably be your best bet. My buddy with the same combo usualy runs a 23" right on the rev limiter, and the stock 25" is a little slow out of the hole and low on RPM's.

 

[cigdaze]

Is that speed GPS? 70 seems a little fast for a 7.4 in a Agressor.

I didn't want to burst his bubble, but ya, that's quite optimistic.
Assuming 1.5 ratio drive, 24P prop, 4250 rpms, even at 0% slip (which is unattainable), the mathematical speed should be 64.4mph.

A labbed 25 mirage will probably be your best bet.

That's what he has now...rpms too low.

 

[SickSation]

........

Right now the boat has a 25p that was labbed to a 24p and cupped. I havent had it that fast yet. I just bought it saturday. Ive only had the boat out 1 time and ran 65 on speedo. Water was too rough and im a newbie when it comes to any speed on the water over 45mph. The previous owner told me it will run about 68-70 on gps at 4250rpm in perfect conditions using the trim tabs. Im not fimiliar with trim tabs yet because my old boat was an 18ft rinker so this is a new world to me. I knew the engine had a few hundred more rpms, but i am far from an expert on this topic. Thanks for the info.

 

[SickSation]

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It also has a stepped hull... Dont know if that makes much of a difference.

 

[Trim'd Up]

I didn't want to burst his bubble, but ya, that's quite optimistic.
Assuming 1.5 ratio drive, 24P prop, 4250 rpms, even at 0% slip (which is unattainable), the mathematical speed should be 64.4mph.


That's what he has now...rpms too low.

A 25" turned to a 24" with cup added. Sounds to me he would be right back at the RPMS of a 25" stock or close. I know that my buddies boat is all over the limiter with a stock 23" mirage, but a stock 25" plus won't spin the RPM's. Maybe a 25" mirage non-plus, they have less cup and usually turn a few more RPM's.

I didn't think the aggressor had a true step ever, just that kinda half step from the chine to the inner strake. That area wouldn't be in the water at speed anyway. I may be wrong on that though.

 

[SickSation]

.............

Not sure about the hull. Heres a pic.

 

[jeffswav]

I just took a look at your info. The boat will probably run 58 MPH GPS on a good day if you have the standard EFI 454. The "Dream O Meters" are all about 3 MPH fast. You are also overproped for that setup. If the Mirage you have now is hooking up to get on plane then I would try a 23P mirage. Check your RPM at WOT and shoot for about 4600 RPM. Here is a link to that you can check out. Most boats are about 10 or 12 percent slip. Your outdrive should be 1.5 ratio. http://www.rbbi.com/folders/prop/propcalc.htm

 

[bbladesprops]

All great answers and suggestions!

We have test propellers if you are interested, give us a call.

Brett

 

[bbladesprops]

All great answers and suggestions!

We have test propellers if you are interested, give us a call.

Brett