prop selection for a 259

[vinny p.]

I have sitting on the fence on this question for the last month or so. Maybe the experts here can give me a push so I will fall to one side of the fence! I have a '99 259 Convincor, 454 magnum, Gil exhaust, adjustable fuel regulator, Teague flame arrestor, MSD ignition. Of course, all this means is that the motor is still basically stock. I am currently spinning a 24" Bravo 1, I tried a friends 26" Bravo. Below are the results. Now, all speeds are recorded from my stock speedo, we all know that they are not accurate means of measuring speed ( I wish I was really going this fast!!) But, it will be good enough to compare speeds with different props. Both props are stock out of the box.

24" Bravo 1 26" Bravo 1
r.p.m. m.p.h. r.p.m. m.p.h.
3500 50 3500 55
4000 58 4000 64
4500 65 4500 70
5000 74 could not pull above 4500

As you can see, my cruise speed vs. rpm picked up with the 26", but I lost a considerable amount of top end. My stock motor obviously does not have the h.p. to pull the bigger wheel. What I was thinking of doing was getting a Labbed 26" Bravo. I should have a better cruise and top speed with the labbed prop vs. the box stock prop. The question is, will I get my top speed back to where I was with the stock 24"??? Anybody think I may actually pick up speed over my stock 24"??

 

[vinny p.]

I have sitting on the fence on this question for the last month or so. Maybe the experts here can give me a push so I will fall to one side of the fence! I have a '99 259 Convincor, 454 magnum, Gil exhaust, adjustable fuel regulator, Teague flame arrestor, MSD ignition. Of course, all this means is that the motor is still basically stock. I am currently spinning a 24" Bravo 1, I tried a friends 26" Bravo. Below are the results. Now, all speeds are recorded from my stock speedo, we all know that they are not accurate means of measuring speed ( I wish I was really going this fast!!) But, it will be good enough to compare speeds with different props. Both props are stock out of the box.

24" Bravo 1 26" Bravo 1
r.p.m. m.p.h. r.p.m. m.p.h.
3500 50 3500 55
4000 58 4000 64
4500 65 4500 70
5000 74 could not pull above 4500

As you can see, my cruise speed vs. rpm picked up with the 26", but I lost a considerable amount of top end. My stock motor obviously does not have the h.p. to pull the bigger wheel. What I was thinking of doing was getting a Labbed 26" Bravo. I should have a better cruise and top speed with the labbed prop vs. the box stock prop. The question is, will I get my top speed back to where I was with the stock 24"??? Anybody think I may actually pick up speed over my stock 24"??

 

[vinny p.]

My chart didn't post how I typed it out. The spacing is off. I will try to post the results another way.
24 Bravo-----------------26 Bravo
RPM----MPH-------------RPM----MPH
3500---50--------------3500---55
4000---58--------------4000---64
4500---65--------------4500---70
5000---74----------could not pull to 5000

I hope this works.

 

[Shameless]

Vinny,
Sorry I do not have exact numbers, i am sure Rick does, but check to see where your peak h.p. rating and peak torque rating is, and I bet you will find your answer.

 

[checkmate243]

Vinny p.-For every pitch up you gain you should see about 200 rpm loss on the tach.The trade off is used to reduce rpm but keep the same speed.In your case 5000 rpm is in what I call the safe zone for that motor set-up.I would try 25 pitch first!The speedo is only for looks get a GPS.I drive to the GPS and tach.You will find much better info in your testing.The trick is to spin that 26p like your 24p prop.To do this look at spending a 26p out to the PROP SHOP for blue printing and balanceing.To save money try asking your local checkmate dealer to lend you some prop for your testing.Just a thuoght.

 

[checkmate243]

Hey is web site for cals.
http://www.rbbi.com/folders/prop/propcalc.htm

 

[vinny p.]

checkmate243;
That is where I think I am heading with this. I want to try a labbed 26". I think I will get good results from it. I know what you are saying about GPS, you are right. But, remember, my speedo is the constant here. The only change I made was the prop, so any changes in speed on the speedo are relative. I was hoping to find someone who has tried this before I spend almost $1,000 for a labbed wheel.

 

[Shameless]

Vinny,
I was not too clear by what I meant by checking your h.p. rating. Simply put, I do not believe you have enough horsepower to turn that prop unless you were to raise your x-dimension.

 

[BayviewRick]

Vinny,

You start getting into those big "wheels" it takes some serious horsepower to spool up and get you out and gone. I honestly believe your going to loose more than you gain. Where do you live? We have a couple lab finished props that Tom uses on his personal boat,we can try them in Spring and see the results before spending the $$$. Even with 600 plus hp in his Fountain Fever, if it's a little humid or three/four people in the boat, she'll struggle out of the hole, reaching top rpm's. I'll put Tom on this subject when he gets back, he's out of town doing an ice recovery. It's a long story, but Toms an ice diver and gets called upon by the DNR,Munincipalities statewide throughout the winter. Rick

www.Bayviewmarinecenter.com

 

[vinny p.]

Thanks Rick!! I live in Long Island, New York. Any information will help and certainly be appreciated.

 

[Shameless]

Watch out Rick, a guy named Vinny from Long Island, could be trouble!

Just messing around Vinny! Great looking C-mate!