Prop Help
 

What's up fellow Formula owners?
It's getting much closer to boating season here in northern Ohio, with that being said I need to get some help on testing props asap. I dropped new power in my float and need to test a couple props, how can I test props without going out and buying two props? I want to test a Mirage Plus 19 and 21. Does anybody have either they are wanting to sell? Any help and our places to look for props would be appreciated! The new power is a new 357 Mag MPI from Michigan Motorz, 325 hp. Should be night and day vs my very tired original 260 hp engine.

Call Bblades, They have program. It cost 45$ to test a prop for 15 days. The 45 bucks will be subtracted from the price of the prop you buy, so if you test two and buy one, the whole thing has run you 45$ + the 525$ of the M+ prop you buy. 45$ very well spent and Bblades have competitive prop prices. Get the solid hub version.

The Revolution4 is a very nice alternative to the M+ if you consider a 4 blade.

A good friend of mine (who knows much more about this stuff then me) said a 4 blade could cause outdrive issues do to the slip ratio. Reason being, I stayed with the alpha drive (the engine is 300 hp at prop and right at the limit of the outdrive). He suggested going to the Mirage plus. Thoughts on this? I am trying to get as much speed/performance as possible. The 242 is a big boat for it's size, with a single screw, full gas and people a 21p may be to high to get out of the hole. But a 4 blade would also help with that... Let me know what you think on this.

Thanks,
Matt

Hi Matt.

If you keep your drive in good condition and don't thrash it, I don't see a big problem with the Alpha and Rev4. Torque kills drives and Merc put it behind the non-mag 454s.
That being said, the M+ would most likely be the fastest and a good choice. Unless your prop sits really deep, the Rev4 will be better in terms of mid range efficiency though but slower.
With a 3 blade, the number to shoot for is 52-54 mph.

Needed info.

Bottom condition?
What is your drive ratio?
Top GPS speed with the 260 @ ? rpms?
Former prop?
Max reccomended rpm range for your old and new motor?

This info makes it a lot easier to determine a good starting point + your old prop might be good for baseline testing.

I have a few more thoughts, but provide as much of the info in the questions above you can first.

Anders

Anders,

The drive ratio is 1.47, I am assuming that by bottom condition means the hull of the boat condition? Sorry, not sure if that is what you mean. the bottom of the boat is not painted, the hull is in very good condition. Top speed last season was 39 mph on gps at 4200 rpm, ran a rev 4 15 pitch prop. I lost about 3 mph however the hole shot was MUCH improved from the 4 blade 17 pitch aluminum prop I was runnning before (top speed with that prop was 42). New motor is rated for 4800-5000 rpms. The prop does sit pretty deep for a 24 ft boat, draft is 32" with outdrive up.

Hm. I'd have thought it to run a bit more, like 44, but then again, it was with an alu prop. The ones I've run had 330/454s and ran around the 54 mark. All in all, the two M+ props to test are the 18" M+ and the 19"M+. Which one works the best is depending on a few variables, but the 21" in no where near the right pitch. You'd have to run 58-60 just for that. 1 inch does not sound like a lot, but depending on slip ect. and the somewhat narrow rev range of your engine, it's not a straigh forward answer to say which one is the best. See what you like. My personal best bet, would be the 18" but you might think differently. Just to begin with, test the 18", and if it's too sluggish, go 17", if too low, go 19" and if juuuuust right, buy it.

I have an 87 242LS with the 454/alpha, my engine was a remaned with about 350hp. I run a bravo 1 4 blade 22p that was cleaned up a little and runs great 56gps is the best I have seen.

post a pic of your 242 from huron ,

How do I post pics? I am not a paid member.

http://s1073.photobucket.com/albums/w396/rossman4040/

Pics from the complete overhaul, the cabin is being gutted and pimped out as we speak. Not bad for an old girl, 1984.

I always liked the lines of that boat. Sweet project.

BTW, yes, by bottom condition I did refer to paint, nics, hook ect.

AO Razor, Ive been told to test a 19 &21 mirage plus. Just curious why you say a 21 will not work.

Matt

Matt.

Because you would have to run 58-60+ mph for that to work. Was that Brett @ Bblades who suggested the 21"??? Not to be down on your boat, but you'd need a 454/385 minimum to even begin seeing those numbers on a regular basis.

Here's some figures with your drive ratio and rpm rating with a 21" prop.

At 5000+/- rpms which is at the top of your rpm range.

10% slip = 61 mph, 12% slip = 60 mph, 14% slip = 59 mph and 16% slip = 58 mph.

And at 4800+/- rpms, which is at the bottom of your rpm range.

10% slip = 58 mph, 12% slip = 57 mph, 14 % slip = 56 mph and 16 % = 55 mph.

Deffinetly start with the 19". If you look in one of the previous posts, there is one with a 454 and 350 hp running 56 as best number.Therefore I'd say he runs 54+ on average with the B1 4 blade. Yes the BBC weighs more than your SBC, but the heavy Formula likes the torque of the BBC.

Anders

Rossman that looks great, hope to see it at the islands

oh6662b....you will see me.....every weekend over ther...lol

Hi Rossman

How is the testing coming along?

Wish I had something to report, not testing till next month. My cabin is being gutted and redone at this time. I will keep you informed....its a wee bit chilly on ol lake erie