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272 Top speed & Prop questions

Old 03-06-2003, 08:46 AM
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Default 272 Top speed & Prop questions

I have a 1986 Formula 272; stock small blocks (70 hours on rebuild). When running the factory 23p 3-blade cleavers, WOT was about 4200rpm. Last summer with 4 adults and fully gassed, GPS said about 59 mph. Props had a tiny little “ding” on the tips. Is this speed typical for an older 272?

After reading some of the threads on this site, my real concern is that the rpm’s seem low and that I may be risking engine damage due to the low rpms at WOT due to overstressing the engines. I did call Formula and they said they were shipped with 23's.

That said, with how I use the boat most often, I am not overly impressed with the cleavers – they are lousy under 2700 rpm.

I have a pair of 4 blade ss 21p props (not sure of mfg) that I prefer to run with. Top end isn’t as fast as the cleavers, but overall performance is so much better. WOT with them is a little over 4000, but they easily lift the boat onto plane, and keeps it there, which keeps my young daughter happy. A 2700 rpm cruise returns a little under 40 mph.

Anyways, I am a little curious on what others are getting from their 272's.

Chris
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Old 03-06-2003, 11:45 AM
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BB,
I have an 89 272 with big blocks and 25 Mirages turning 45/4600 rpms. You should also be in that range at wot.
Cleavers were a good idea that didn't work real well. The only thing they were really good for was top end.

I'd try to find a pair of 23" or 21" Mirages to try. They should improve your performance at the low end over the cleavers and also give you a better top end than the four blades.
At 59 mpg you're in the ball park for your top speed. I think a little more could be sqeezed out of it
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Old 03-06-2003, 03:30 PM
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i have a 272 with 330hp bigblocks
64.9999mph on gps at 4500-4600 - with 25 pitch, just where the 330 should be
can not seem to hit 65, anyway........

the 260hp small block should be set up to run to 4800 lightly loaded (ie by your self) this is it's peak power.prop for that.
otherwise like you said, you are straining the engine and drive line, and if alpha drive, will blow
.
if you get the engine to its peak power point while at WOT, you should see your top speed, even though you may take less pitch to do that.
check your timing of your new engines. make sure they are running properly. then look to pitch the props to get to 4800
Darin at houston prop may have some insight for you or some props to trade or consider.....


what horsepower are these small blocks suppose to be at.
stock mercruiser cam specifications?, or an automotive configuration?

theoretically, if 660hp moves mine to 65mph, then 520hp should move your boat at 57.7 (squared law behavior of deep v hulls)

this would be with an appropriate prop that runs your engines at 4800rpm (where 260x2 hp is made)

if you have more power than that. and it looks like you may, then you should see more speed if getting to 4800. three bladed props (non cleavers) seem to have enough prop area for our boats. 4 blades just waste power spinnign the extra blade area through the water ( for our boats)

Last edited by Rambunctious; 03-06-2003 at 03:35 PM.
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Old 03-06-2003, 07:16 PM
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With BBC’s back there, I cannot imagine the engine room being any tighter than it is now. Bravo’s would be nice. I bet your boats sit low in the water – half my ‘bird is under water sitting at the dock. How much weight do the BB’s add?

When I said top speed was about 59, I meant WAY over 58 and a half. I wanted to toss my buddy out to see if I could see the elusive 6-0. Like my brother says, boats like ours have 3 speeds: the one you tell the insurance company, the one you tell at the bar, and the one you read off the GPS or radar.

My engine’s were rebuilt to stock Mercruiser specs. If it helps, they had 160 lbs compression in all cylinders – they were all pretty close. And sheepishly, I haven’t checked the timing in ages. I will be busy this spring.

One thing that I’ve wanted to do is connect another tachometer to the engines and confirm that my tachs are reading correctly. This year.

I just checked the 4 blades, they are Turbo 2+2, M14 1/4 x 21’s. Maybe you could tell me about them. They were a gift. But I just love the way they perform compared to the cleavers. The previous owner had them on a 272. They do have lots of blade area and know that can have a detrimental effect on top end. But where the cleavers seemed to have two modes: cavitating or hooked up, these 2+2’s are always pushing. I’ve got 3 23p RH cleavers downstairs as well, I wonder if they are worth anything in a trade? Darin have a phone number?

I can’t wait til spring; I cleaned off 26 inches of snow couple of weeks ago.

Now that I’ve dusted off the memory banks, …. I have a couple of observations that I would appreciate comment on:
- how easy is your power steering? I would call mine “firm”. I would like it less firm.

- My driver’s seat/bolster position absolutely sucks. Too close to the wheel. I wonder how easy it would be to move it back a few inches. I have major muscle cramps for a few days after the first ride of the season. You can’t really stand, nor can you really sit.

- The convertible top is useless. It would be great if I was a midget. I cannot even sit in the seat with the top up (I tried). I’ve got full canvass and side windows too. What a waste – I have never used them. Even if I could sit in the seat with the top up, I wouldn’t be able to look out the windshield. Maybe this top was added on afterwards. I have a hard time believing Thunderbird put tops like this on a boat. Are you guys running with a bimini? If so, do you have dimensions, mounting tips if I decide to buy one.

Don’t get me wrong, I love this boat, and always get compliments about it. Thank you Don.
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Old 03-06-2003, 08:46 PM
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BB,
I have a bimini and full enclosure ...plastic up the front and sides with canvas in the rear with a window. I also have screens for the sides for overnight stays
I can stand up under it and I'm 6'. it was a Formula top but had it remade locally two years ago , also modified slightly. I can run with it but keep the speed under 40 . Saw a bimini rip a windshield frame off last summer just glad it wasn't mine. Made a run from Phila area to Balto. 2 seasons ago and stayed at the Inner Harbor East Marina. The enclosure came in real handy. Gave us a lot of living space.
And NO you don't even want to see a big block engine compartment. Bravos have the sea water pump under the exhaust manifold on the drivers side and it is one real PIA.
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Old 03-11-2003, 10:58 AM
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Well here goes.........
I just bought a bimini....8footer made for Brand X but to make it fit I installed sliders just outside the side windows inboard of the antenna mounts, put mount poles for the rear support. when folded up it kind of has that "radar arch" look.
I can see how a convertable top would suck, unless you are 12 yrs old(or less than 5 foot tall.
Check for the bolster mount bolts in the frame. Mine has several holes where you could move the seat aft a few inches. Yes mine is tight also, thought of getting a tilt wheel assy, but was afraid of adding any length th the helm to add it.
I used to have a Mariah 20 ft 260 h.p. 5.7L running the turbo 2+2
Was told more than once that there were better props for a sterndrive. I'm running Mirages now and am happy, just need more pitch. The Mirage will give you good bow lift if you are running in relativly flat water.
The 2+2 is going to be a lot better in the mid range cruising speeds, just because it has more blades, but the 3 blade Mirage will probably give you more top end with a respectable midrange.

With a better intake/carb set up and a set of headers from Stainless Marine or IMCO it might just wake the boat up to more what you want.
I had real good luck with a pair of 7.4L Got an extra few MPH.
Plus it reduced the weight of the boat in the rear so it doesnt sit so low in the water.
Aluminum intakes and exhaust are fine if you aren't going to run in salt water.
Yes your RPM's are too low, if they are accurate. Plan on in the spring cool air with a half tank of gas by yourself... running just over the max rated rpm for your motors per the dataplate on the top cover of the carb. That way in late summer with the heat you won't be too low in your RPM's and "straining" your motors, causing them to overheat. Mercruiser runs the RPM's real conservative to be able to reduce warranty claims, adds life to the engine if you don't spin them very fast. So you want to run at least the top of their recommended range. It will give you reserve when loaded.
Good luck!
OPIE
By the way.. Mopower has a killer enclosure. seen pictures of it.
Can't wait to hear your numbers with those 540's.

I know I spent more than my .02 worth Sorry

Last edited by OPIE272; 03-11-2003 at 11:15 AM.
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Old 03-11-2003, 11:27 AM
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Originally posted by OPIE272
By the way.. Mopower has a killer enclosure. seen pictures of it.
Can't wait to hear your numbers with those 540's.

Yeah Opie , Me too. Engines still aren't done ,All prepped , heads are done(ported , polished , bowl blended and gasket matched). Whole works still needs assembly and dyno and time's running short
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Old 03-13-2003, 05:57 PM
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Yeah....but the thrill of the run when you get them broke in.
I received those light bulbs so if you need one let me know.Just a note for bulabula....If your docking lights burn out.. to get the original lamp it's approx $30
I have them for $10 in a power spot lamp that is 3X the candlepower instead of the flood light that you can barely see your hand in front of your face, OEM replacement.
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Old 03-14-2003, 11:10 AM
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Opie,
How are the lamps on heat do they run a lot hotter? I would be worried about deforming the housing. If that is not the case I would love a set as I think the factory bulbs suck unless you need to see your tow hook
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Old 03-26-2003, 01:16 PM
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1986 272 SR1 with original 23 pitch cleavers/twin 260 hp:

On GPS
-3000 RPM/38mph
-3500 RPM/43mph
-4000 RPM/52mph
-4600 RPM/57mph

Last edited by Unchained; 03-26-2003 at 01:18 PM.
 
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