85 272ls. 54mph
 

Trimmed and as far as the throttle will go, can only go 54 at 3400rpm. Twin 350. 3 blade knifed props, not sure what the pitch is. Shouldn't I have more left to go?

What pitch are the props?

Either your tachs are both wrong or you are way over proped. That speed at 3400 sounds like 23" props....and at 3400 you are just getting into the peak of the torque curve. Check the last 2 digits on the part number...thats your pitch.

You're over-propped. Size the props to see upper 4k rpm's.

Besides speed. What harm am I currently doing to the boat if any?

Not really any serious harm in the short term...but you are for sure burdening the engines. Just for comparison...my 255 w/twin 350 Chevys, which is very close in size and weight as your 272 is turning 4300 RPM at 54 MPH and 5100 at 62~63.

I'm running 19" pitch and should be running 21"....I am slightly under proped....I keep my RPM at a max of about 4700~4800 by backing off.

Take a look at those props and let us know what you are running. If you are running Alphas with 1.5 gears your numbers should be close to mine.

Quicksilver 48 89804a5. 23p

Over proping bogs the engine making more heat and detonation. Long term......boom.
You should see about 4,400 to 4,800 rpms on stock motors.

OK...(the math still works) your running a 23" pitch...way too much prop. I'll bet your 27 is a pig out of the hole...especially with a load.

See if someone local can hook you up with a pair of 19" on loaner (even if they're aluminum) to see where that puts you.

I'm guessing your optimum is going to be a Mirage Plus Stainless in a 19" pitch.

What part of the country are you in? Check craigslist in your location and search under boats for "prop" in "title only".

Hey Sprink do you think you can send me an email at [email protected]. I have a few questions regarding your boat and time spent around the Formula Miami facility.


Sorry not to thread jack.

Mike...mail sent.

Thank you.. Does Diameter, 3 or 4 blade make a difference. Cupped? Knifed?

Heres a Picture of boat..

Nice looking Boat...same exact set up as my '86 272LS that I had 25 years ago...except I had a teak swim platform with 320 EFI power.

[IMG]http://i705.photobucket.com/albums/w...es335Large.jpg[/IMG]

...so I'm familiar with what you have.

Anyway...all props are cupped. If you have cleaver props and they are 23" you are really fighting an uphill battle...the cleavers don't work well until you are on a plane and in your case 23" is just too much bite.

Seriously...I think 19" props are your best overall prop pitch for your boat. Again..see if some prop shop near you can let you try a pair of used 19" and see how the boat performs the way you use it...then you'll know.

BTW....where are you located?

Kenosha Wisconsin. Was out this weekend, 8 people at 1250lbs, dog out of the hole but planed out again at 54. 14" dia or 15's you think. Thanks for your help. Appreciate it. Still haunt hooked up with any locals to talk to. Would love to hear it at 4500 Rpms. I have tru hall not the silent thunder, which I have heard are better to have, thunder have leaking issues. Just got buff the bow an she'll be like new.

Well, I bought 2 mirage plus 19p... outa the hole like you wouldnt believe,But 3700 rpm max at 51mph.. Now what...checked the gear ratio, 1.47's on both drives...Baffled...any other concerns that will make me puke?

Well...at this point I think it's obvious that your tach is bad. Go to BAMmarine.com ...they are OSO sponser and read through thier data base. Take a look at their top speed calculator. Your boat is probably very responsive and I'm guesing cruises very nicely between 35~45 MPH with plenty of throttle response throughout the speed range. Get yourself a cheap tachometer and hook it up near your helm. Your going to see about 4900~5000 +/- RPM at 51~52 MPH...which is where stock 260's with 1.47 No 1 Alpha's put you in that boat. You are proped correctly.

What I find interesting is that BOTH tachs are bad or for some reason giving you an eroneous reading. There might be a resistor in the tach feed that isn't supposed to be there. I suspect that some one has mistakenly put a resistor wire in the line between the tach and the coil output. I wish you were closer to me and I would hook up with you and help you sort this out.

Maybe some of the other members that have your same boat can shed some light on this for you...don't worry...there isn't anything wrong with your set up . We've just got to figure out why you're getting a screwy tach reading.:eek:

Stay tuned..someone will jump in on this. You might also want to post this info over on the tech forum to draw in a broader audience.

Fivept0, I think I ran across you on lake michigan a few weeks ago I was in Kenosha WI, I was in the red 242 ls with a 271 fastech. Very nice boat if it was you!!! I would also check the tachs you should be able to spin in the upper revs with the 19p. When I had the small block in mine a 19 pitch marige would put me right at 55 mph around 4800-5100 rpm depending on the gear and gas. Give or take a few mph as I didint have a gps at the time.

if you need a original tach to try out, I believe I still have mine some where, from when I upgraded.

That was us. Nice boat!!! I have a couple autometer race tachs that are mechanical, will one work for testing? Also in neutral , I can rev up to 5k, not under load. Maybe I shouldn't be doing that. Lol. I like running the cleaver 23p. Went to an inland lake with em, hit 59.6 on flat water. Met a guy here in town with the exact boat but black n red who is borrowing me some 21 cleavers this weekend. By the way next weekend is the air show in milwaukee We arecruising up together Saturday if your interested.

"Also in neutral , I can rev up to 5k, not under load. Maybe I shouldn't be doing that"

Yea..don't do that ...'cause you are probably pushing 6000 with no load!!! Alpha water pump impellers don't like that kind of stuff...among other things.

A mechanical tach will work but you have to have a way to drive it along with a cable...not good with a boat. Go to Auto Zone or somewhere and get a cheap electronic tach. Also check for that resistor wire. If I were doing it ...I would run 20' of primary 16 ga. wire temporarily from the coil up to the back of the tach and check it that way.

Running right at 60 with 23" cleavers is telling me that you are "spot on " with tune on your rig.