prop question for a formula 242 ls 350 260hp
 

hi im new to the forum and the boating world, I realized my boat is a heavy tank haha and with a single 260hp motor it will never be a rocket ship but I was wondering if anyone has some experience with these boats and could give me a little heads up on if a different prop could give me a few more mph, trimmed up on glass water im lucky to hit 40mph it is completely stock with 350 hours on her. im looking to maybe put a thu hull exhaust and a different prop to hopefully get 45 mph, as for whats on there now I meant to take a look this morning before I left for work but completely forgot, (still half asleep haha) but any info and help would be greatly appreciated thank you!
:ernaehrung004:

I ran home and took a look its a mercury marine vengeance 14" diameter and a 19 pitch not sure of my rpms at WOT my tach is not working put I plan on fixing that this weekend

What rpm are you running at WOT to get 40

...uh...yea. This might be important. :lolhit:

Somewhere over idle rpm.

My tach is broken I plan on fixing it this week :silenced: what should I be running at WOT?

LOL.

4600-4800. Try to get to 4800.

I didn't know how important a tach was on a boat! Lol I'm a newbie :( I'll figure it out as I go:) I'll get some rpm numbers and keep you posted:)

Thanks for saying that, Do you knowhow to use the trim (down ) for planing (taking off) and then to trim (up) to loosen up the boat for cruise and then some more usually for top speed ? Tach and speedo (gps favorable) for top speed ?

If you have trim tabs - basically same thing in conjunction with drive trim ?

Yes I was told about trimming down the engine for take out then trim up for cruising I would hear the engine smooth out and could feel the boat pick up speed I do have trim tabs but I didn't touch them I'll try that too and see if that helps and I got my speed from my gps since the speedo is the other gauge that doesn't work lol

As others have said we need several important pieces of information.

Tach/RPM at WOT

Drive ratio

Prop diameter, pitch and number of blades

Unless your boat is grossly over propped or mis-trimmed it is unlikely you will see a 5 mph improvement with a prop change and/or thru hull exhaust.

I can tell you that thru hull exhaust will net you zero performance increase (that is readily and consistently measurable) for your setup. If you like the sound thats one thing, but don't expect any significant improvement in performance.

Easy.. Motor has 350 hrs on it in an underpowered boat. Prob has a lot of wide open throttle time and is whooped. Pull motor, put in a 383 stroker kit and put on a 23 pitch prop. 50 mph boat.

Chris

Haha if I could I would... Maybe in the future but right now I can't afford to drop thousands on a motor lol

The below will take you down the quickest path and least money spent..

1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

That would be over-propped with that boat size and motor.

I dont think so.. 23 pitch 3 blade with a 383 and 24 ft boat would be perfect but that is not the direction he is going anyway.

Chris

With a 1.5 ratio that combo would be lucky to spin 4600 rpm. Likely lower.

I had a 24x7 heavy hull with a 330 7.4 mpi that turned a 21p right 4800. It would have been faster and turned a 23p if had a 383 400hp. It would be like throwing your girlfriends fat friend out of the boat and adding 70 hp. I know it would have turned 23

Chris

Ok finally have some numbers I'm running only 3800 WOT on smooth water with only me and a little over half a tank of fule with the motor trimmed up I currently am running a 19 pitch mercury marine vengeance

I would check the timing on the motor first then get a different prop. Just by a cheap aluminum until you figure which one you need. If timing is 10 degrees then try a 15 pitch from here

http://www.pbsboatstore.com/quicksil...9GkaApE28P8HAQ

It says these props are only good for 50 mph but I doubt you will be that fast any way. And your only out less than 100.00 the 17 pitch might also be an option. I actually might have one you can try for just shipping and would sell you for 50.00 if you are interested. Let me know and I will dig through my props.

Chris

Ok I will Check the timing, should be 10 dregrees at idle? And I have a few extra props that came with the boat I will look to see what he gave me but if I don't see a 15 or 17 I will let you know, thank you ! :)

Also if I bring it up another thousand how much more speed you think I will get gaining another 1000 rpms? My speedo said 35 I didn't check it with gps yet I will tomorrow

You might get 8-10 mph.. How well does it plain off with the prop that is on it.. ie takes forever or jumps on plane.

Chris

I checked my prop supply and I have a Turning point brand prop that is a 14.25 by 17. It was used 2 times I had it on a bayliner 2452 which is a Massive Heavy Sled. It had a 5.0 220 hp merc and did 38 with that prop but was hard to get on plane. Your boat is lighter and not as wide so it would probably work. I only found one prop that gave good hole shot with that boat and it was a big ear 15 inch prop.

Chris

If it's Mercruiser Thunderbolt IV set the timing to 8 for stock 10 for better and 12 if you know how to identify detonation which you'd then back out of if you hear it. The distributor and controller will add 22 or 24 degrees as you increase engine speed. There are 2 modules. You can look on the edge of the device to see the advance value if you know where to look.
Then important, reset the idle back down to 725 neutral, which will equal 675 in gear. So's you don't ruin the gears as they engage.
You can also do all in timing by setting it with 32 degrees max timing. You do that with a dial light and rev it to the rpm where it stops advancing. Just do it warm and only briefly run the engine to high rpm, Unloaded engines at high rpms aren't so good.
Maybe 34 degrees if you dare or if it has aluminum heads.
I just got a Formula this season too, Thing crushes chop compared to my old boat. Weighs a lot more and feels good out in the broads of Winnipesaukee.
My boat's a little smaller than yours and has a little bit more on the HP, but effectively darn close. It uses a 19 pitch and does OK. I'd suggest a 17 for yours knowing that. You want to get the rpms.

10 is stock not 8. Dont try 12 on a boat..

Chris

Well it says 8 degrees in Manual 9. The big blocks are 10.

Pure conjecture. The problem with your analogy is the big block makes the same or more torque at a lower rpm than the small block. Show me verified data that the 383 would swing a 23" prop in that size boat. I've tried 23" Mirage, Mirage +, labbed and non-labbed in stroker SBC boats in the 21' size range and they would not in anyway shape or form pull 4800 rpm. I love SBC, but they won't swing that size prop on that boat unless you dropped the gearing or it had a blower.

There's no replacement for displacement. But I'm doing a stroker at some point too. Unless I can talk my brother into selling me his 454 that he's hoarding.

NHGuy my boats on winnipesaukee too! I have it parked at my parents place right in the channel if you're heading into paugus bay from weirs last condos on the left after Naswa. Maybe you could swing by and help me time it lol jk but I'm having more issues now :( anywhere from 3/4 - WOT it will sputter and fall on its face like its being fuel starved, runs good at 3000 and under but anything over that it will sputter.. If I throttle down and run at 3000 it will be ok but if I throttle up it'll sputter again.. If I go back to idle for a bit and come off plane it'll run at WOT for about 10 seconds then die out again. I changed all the plugs wires cap rotor fuel water separator and the fuel filter in the carb.. They didn't look to bad. I just ordered a fuel pump so that's my next guess lol one thing I didn't try was taking the gas cap off to make sure it's not a clogged vent.. Any suggestions???

curious as to what you came up with for a prop size and pitch. assuming you go the thing to rpm more than 3000

I'm still running the 19 pitch... The most rpm I'm running is 3800 but I'm starting to think that the tach is wrong.. Most I can get with it is 40... I'm going to double check to make sure the tach is correct and probably stock up on some props this winter and just enjoy it for the rest of the summer and test and tune next year

have 2 19P props. one aluminum one SS. i can get the aluminum up to 4400rpm but speed is 41. can get the SS up to 43 but the rpms are at 3750. gonna try a 17P this weekend hoping to get 4500 rpm and 45 mph

Please keep me updated I'm very curious! Is the 17p ss or aluminum?

I had a gps on my phone and ran it out the other day. Got 45 mph at 4450 rpm. With an aluminum 3 blade 19 pitch Michigan wheel prop. I was heading into a 10 mph wind. My boat has a 97 350 Mag with Weber afb carb, Alpha 1 Gen 2 1.5 ratio and vortec heads of unknown chamber size. The boat is a big load 4000 lbs plus, 22 degree deadrise hull. 1987 Formula 223LS.

Keith P, I have been day dunking this year out of Fays Marina in Smith Cove till I can get my old boat sold. That's just a couple minutes south of Governors Island for you from the Weirs. If you see me out there wave. My boat is that color so many are, off white topsides, black upper sides, maroon lower sides. I have one visual thing not too many old Winnnipesaukee Formulas do, a maroon bimini.

How did you solve the 3000 rpm wall?
My 89 Baja used to do that before I went through it and replaced the wires, cap, rotor, module, fuel lines.

You can get some ponies with Vortec heads and a better cam. But a big block would really be the ticket in a 24.

Don't bother with that marine salvage yard in Meredith. Guy gets 50% of new on tired out old stuff. And he won't even negotiate a thing.

I always see a maroon 223 parked in the channel on the right when im heading out to the main lake, not sure if its yours or not.. im always at braun bay just hanging out cant miss me I think im the oldest boat there haha blue and white 86 formula with the flat glass windshield. I replaced the cap rotor and plugs... no change.. ended up taking the fuel feed pipe out and the check ball valve was full of gunk, cleaned it out and its been fine ever since! but according to my tack WOT is only 3800 not sure if my tach is off. I bought a cheap one at pep boys to get by and there were settings on the back I never touched.. but with a gps on and trimed out at WOT still only getting between 38-40... the boat came with a ss vengeance 19 pitch prop on it, I want to make sure the RPMS are accurate before I go switching to a 17 cause I don't want to over rev the engine

AZ242LS is yours a 5.7 too?

Keith P. My parents place (now my brother's) is the community beach on Moultonborough Neck that you see as you make a left into Braun Bay if you come over the top of 5 Mile Island.
Nope, I avoid Weirs Channel unless it's a weekday or I need to go people watching.
I like to hang out at Timber Island, in the crook facing ENE, no sand but much smaller crowds. Sometimes we run over to Long Island Bridge so the dog can hop out.
On windshields, I am lucky to have wraparound.

Good going, finding that fuel issue. Running lean can detonate & ruin your engine.

yes