Prop testing : looking for opinions
 

I'm thinking of moving up in pitch to bring my RPM's down and hopefully gain some MPH.

My current set up is a labbed 26 Bravo one spinning thru a 1:5 gear ratio. My RPM's are 5600-5700 and I have run a best of 80.7 on GPS.

I wonder if I will gain anything by switching to a 28 Bravo one ?

ya up 2 pitch sounds right, your rpms sound a bit high.

is this 28 gonna be labbed?

if not you might have even speeds....

labbed is a different story, let the pros comment on this.......
I'm going to post a topic on props right now for my boat...

26Scarab,
If you're sucessful in moving up in pitch, and wanting to sell the B1-26, let me know.
80.7 is moving pretty good for a 26 Scarab, you must have some impressive power!!!!!
Jon

Jon,
I will let you know. The prop is in pretty decent shape, there are a couple of nicks in it though.
Yes I have a N/A 540 roughly around 675HP.

26scarab,

You NEED a 28P prop!!!

I think you'll gain about 3 to 5 mph.

Well I'm picking up a 28 Bravo and will test it tonight.

I don't know about 3-5 but anything more would be cool:)

I'd also be interested in the prop,if you want to sell it.

You might want to try a Hydromotive 27 as well. I have a friend who is running in the nineties with that hull who believes that it runs best (and most stable) with some stern lift.

I remember you have oval port heads on that motor which may mean you have big torque in the lower RPM range. I think as you increase in pitch your "seat of the pants" acceleration will be less and you may pick up some speed. I would maybe even try a 30 Bravo and see how it does. If the torque is high enough in the 5000 RPM range you may be pleasantly surprised that your motor will not lug down as much as expected when the larger pitch props are run. This could result in some significant gains. If your motor is set up for high RPM then the larger props will lug her down to much and the speed won't be there. Keep us posted on your results and good luck with your testing!

Well I tested it last night...not very good results.

It did plan very good but I made to passes.
1st pass had a max of 4800rpms and a speed of 73.4
2nd pass 5000rpms and a speed of 75.9.

I guess the 26 stays .

Laster,
I've tried a Hydro before and it was too much stern lift , the boat was pretty squirrely.
I'd like to talk to your friend, how much power does he have to get into the 90's ?

Chuck, that rpm difference really surprises me.
that cam must be pretty peeky, sounds like the 26" just let's it get into the power band and then really screem. do you have the dyno curve to post. us engineers like to bench engineer with data.... NEED MORE DATA........:D

you could slightly cup the one you have too. effectively adding 1/2 to 1" of pitch. who did the labbing?

Chuck, where did you borrow a prop from. I've been having problems finding someone I can get a couple of props from to test.

Rob,
Yes I was surprised to, but with the 26 being labbed already the rpm spread does kind of make sense.
Here's the dyno data from my 502 which had the same components as the 540 with less compression:

4600rpm 561 ft/lb 493 hp
4800rpm 567 ft/lb 506 hp
5000rpm 569 ft/lb 541 hp
5200rpm 571 ft/lb 574 hp PEAK TORQUE
5400rpm 566 ft/lb 590 hp
5600rpm 560 ft/lb 614 hp
5800rpm 556 ft/lb 620 hp
6000rpm 552 ft/lb 625 hp


Jr.
Call Lenny at Millennyum Marine 468-7361

TOMCAT has a program that takes this power curve and overlays boat speed knowing your hull efficiency ( 80.4 @ 5600) that will estimate if another pitch will improve the top speed. the program assumes equal prop efficiencies.

now that I see this. you are not falling off your power curve, so you may be at your best point now. One could argue that dropping pitch may increase your speed because your power curve is still climing, but that, I think, is the opposite of what you were considering for reliability.

Rob
Seems like i did a pretty decent job of dailing this boat in !:D
I will probably just leave it alone and use it for the rest of the summer. I think the motor is coming out this winter to freshen it up (100hrs:rolleyes: ) and I will probably dyno it . Then I will really know if I'm close on my tuning.

Thanks Chuck, I'll do that.

freshen at 100 hrs........???? Hell its barely broke in! :-]

Lab the 28 and you should pick up the 300 rpm that you need. I just went from labbed 26 bravos to unlabbed 28's and the rpm's went from 5600 to 5100. I intend to get the 28's labbed soon and then the 26's will be available.

SteveJohns,
I would rather take it apart then have it come apart :D
I run this motor HARD , even though it gets valvesprings and lifters (big solid roller) every season I would still like to go thru the short block.


Anyone have a labbed 28 Bravo one RH that I can try ?

OH --- I also saw the same speed with both props. So when I lab the 28's I should gain 300 rpm and 2-3 mph.

Tinker,
I lost 5 mph between the two props:mad:

That is because you went under your torque curve. I was still in my torque curve or was creating enough to overcome the extra load. (Twin engines)

Your TQ curve is increadibly flat. I've allways maintained that a smaller pitch prop spun faster is more efficient that a larger pitch spinning slower. Is your case just proving this?

CobraMarty,
Yes I seem to be proving this on this boat.
Even when I had the stock 502mpi (64gps) I stepped down from a 23 Mirage to a 22 Hydro and the boat picked up almost 2mph.