Formula 27PC Complete Power plant rebuild

alldodge

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you could go with custom S-pipes to use the silent choice.

When I worked at Champ, we used to make all of EMI's heat exchangers

S-pipes, don't know if there would be enough room. How would they be installed?
 

alldodge

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Guess the S comes from the diverter to Y-pipe connection. If I had Gils instead EMI there would be more options. Gils even have diverters which are sealed off through the diverter to help with reversion, seen them on 525 and 600's. The one here is also appears to be a Gil which has been custom modified.
corsa5.jpg


I just bought these and may be able to do the same with a custom fab shop. Don't know if I want to go that route, but sure like being able to close the exhaust down. Wonder what it would cost to have the two made up? Guess I could call Corsa
EMI-152 plus 3in.jpg
 

Scott Danforth

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the cost is significantly less if you do not need it polished

the elbow above is about $50 worth of materials, $30 worth of labor to manufacture, and $300 to polish. then throw on margin, SG&A and you have a $900 pair of elbows
 

alldodge

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Don't need polish, just need to find a shop which can fab the thing. Going to need to find before I install the engine back. Sure would be nice to keep the diverters. The new pipes cost another 950, so paying a more would not be an issue to get what I want, but these hundreds are leaving my wallet way to fast :(. Chrome looks nice but I could care less. Have a real good weld shop in town but don't know if they work with stainless. Heck they are nuclear weld certified so my guess is they know how.
 

Scott Danforth

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the tubing is 316L SS, so is the plate. there are plenty of 316L SS pre-bent mandrel tubes that can be purchased. the plate will most likely be laser cut, and hit with a belt sander after welding to flatten.

I would find a custom exhaust shop and have them make it. Heck, that is how CMI got started
 

alldodge

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Good point, looks like Jegs and others have 4" in 304 SS 4ft sections for about 80
 

alldodge

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316 is better for corrosion than 304

Agree, has more nickel in it, but finding it is the issue so far at a decent price. Found a couple places but at 50 to 70 a foot is a bit much. I'm total fresh so 304 will work
 

Scott Danforth

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alldodge

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Thanks, don't have a TIG only stick and MIG, also not that good with either one. Farm welder only kind of guy.
 

Tail_Gunner

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To find tip speed, you need to know (prop) RPM, and circumference (pitch doesn't matter)

With a 15" (1.25' dia) prop, you would have a circumference of [Pi] times D[diameter] or 3.1416 x 1.25' = 3.93 (feet)...........roughly 4ft.............

@ 5600 RPM is approx 93 revolutions per second................ (5600 divided by 60 )

THEN divide by the drive ratio (1.66) ======> 3373 prop RPM or approx 56 prop revs per sec

The tip of one blade would travel approx 4ft (the circumference) every revolution

Since the blades make a "round-trip" 56 times per second, the tip speed is approx 56 times 4' or approx 220 ft/sec

[there's also the speed through the water which would make the actual speed and direction (vector) of the prop tip through the water not exactly in a perfect circle......)


Now the real question is what RPM, speed, blade angle and load produces cavitation. That requires you to know a few more "things" like blade area, number of blades, viscosity of the liquid, diameter, RPM, and a whole lotta math! yada yada yada!


I found some info on cavitation of marine propellers including one that was written by some guy for his PHD dissertation!! (OMG!!)



I'm gonna have to defer to Bruce on that stuff!! I'm only an EE from 1978. I'm great with Ohms and Kirchoffs Laws........but not all that great with Computational Fluid Dynamics!

Im building a new project boat and this question has been on my mind for quite some time.AllDodge once went to the prop forum's asking the very same question as to prop rpm level's and it brought back a old experience. After exhausting all of my source's i believe it goes to the type of prop and the mfg's design intent. I guessing it center's around how aggresive the angle of attack is and the prm level's the blade will reach.,,On my small boat running at 4900 rpm the prop never showed sign's of cavitation and is the wot rpm limit for that boat drive combo at 5600 rpm its burned pretty good...Do prop mg's take this into account when building a prop aka 1.66 gearing say a slip factor of 10% netting 4900 rpm one can design a prop with a certain degree of attack angle...go to a higher rpm and lower the angle or vice versa. Most I/O's run at 4800 and there are spefic prop's for I/O's the baypro 2 i have is tops on I/O"s...Just as there are prop's that do well on O/B's which do run at higher rpm level's and probably prop speed also.

I have a little 22' offshore type ive been tinkering with and found a unusual pick for a prop...a 4blade bass boat prop that gave me 8% slip medium diameter high rake. The previous props where slipping as much as 15% and they were offshore type's and running at high rpm....Drop that bass boat prop on there and bang 8%.. .but it was designed for high HP high speed boats running at very high rpm

It's not always talked about but i think angle of attack and rpm level's are very crucial in design...ever see a large diameter prop work well on a fast bass boat???
 
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alldodge

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Good stuff Tail Gunner,, we keep discussing this and maybe by the time I'm ready to put the engine in we will have decided. Angle of attack, blade diameter, thickness, rpm and number of blades all work in the stew. Eddie Young mentioned he would estimate that going from a 2.0 to a 1.65 would be like adding 5 degrees of pitch. With a 2,0 drive it would be like going to a 29 degree prop. They don't make a 29 but you get the idea. So with a 1.65 I should be able to go to a 19 pitch with current HP. Eddie suggest waiting until he dyno's the engine and determines how much torque and power were making.

If I remember correctly the original boat used the 2.0, engine at 300HP and a 20 pitch prop set. Installed the 502MPI with 415HP and went to 24 pitch props. If the engine comes back as 525HP I don't see going up to 28 to 30 pitch. Hope the change with the 1.65 or 1.81 will put me using my same prop sets.
 

Tail_Gunner

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I have to do something to get my mind off all of your eye candy.....You could just fabricate something of that nature and then ceramic coat it...Personally i like the chrome,,,, a llttie splash of blue on the engine..etc etc etc...These type's of threads are not good for me.
 

alldodge

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Yes know what you mean. If you want to see something that could take you down the other road is look at my transom work. The more I look the more I have to rip out. I'm hoping I find the end soon, other wise this might turn into a mute point. Will have a complete new power plant but have to junk the boat. Don't think that's going to happen but it sure is getting rough
 

NHGuy

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I agree this thread is fun, we get to live vicariously through you. I don't envy the transom work but I want you to remember how happy it will make you when it's sorted and you are tooling around in the boat.
Here's a scenario, you are cruising at middle rpms on a beautiful afternoon and some twit wannabe starts to pull into your comfort zone. Maybe you used to back off because your boat wouldn't accelerate that well. After the boat is done you can either back off or bust on by, easy peasy, push throttle, feel the torque, hear the engine, smile. It's good to have choices!
I just love to go from an easy loafing plane to 3/4 or 7/8 throttle for a burst.

ps. grammar and spelling police say"moot" point.
 
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alldodge

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I agree this thread is fun, we get to live vicariously through you. I don't envy the transom work but I want you to remember how happy it will make you when it's sorted and you are tooling around in the boat.
Here's a scenario, you are cruising at middle rpms on a beautiful afternoon and some twit wannabe starts to pull into your comfort zone. Maybe you used to back off because your boat wouldn't accelerate that well. After the boat is done you can either back off or bust on by, easy peasy, push throttle, feel the torque, hear the engine, smile. It's good to have choices!
I just love to go from an easy loafing plane to 3/4 or 7/8 throttle for a burst.

ps. grammar and spelling police say"moot" point.

It's all about the simple moments and the :D :D :D :D :D and look back and think your tooooo slow :D
 

alldodge

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Was on a thread at OSO on the issue of diverters and the OP had 525's. The end result was to install turn downs. After thinking about turn downs I think I'm going to go the same route. You have open exhaust when running and when you slow down they are as quite as non-diverter thru hull.

Got my new +3 up tubes today
Photo447.jpg
 
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alldodge

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Waiting for the stuff to come in to start the grinding so did a bit of work. Replaced the broken anodes on the new transom assembly, removed the exhaust boot and installed the exhaust block off plate.

Photo487.jpg
 

Mischief Managed

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If I remember correctly the original boat used the 2.0, engine at 300HP and a 20 pitch prop set. Installed the 502MPI with 415HP and went to 24 pitch props. If the engine comes back as 525HP I don't see going up to 28 to 30 pitch. Hope the change with the 1.65 or 1.81 will put me using my same prop sets.

Going from 415 HP to 525 will yeild roughly 12% more top speed. Assuming your desired WOT RPM is the same, you just need 12% more pitch. I'm guessing the top RPM will go up a bit (reducing the need for more pitch), so go up 2" in pitch to 26s (8.3% more pitch) and then get them cupped if need be to get the RPMs down. No need to change drive ratios. 26" B3 prop sets are really easy to find.
 
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