propellers for a new user

[ford351c594]

So I posted a pic in my new member thread.

I also mentioned that I am in a mist of a repower since the starboard old 260 hp mercruiser seized. we were at full cruise when it did so that made for an interesting 10 seconds and and long trip home.....

I am in stalling gen 1 sbc 383 all forged internals. built by white brothers in Tennessee. They are rated at 455hp at 2200 feet above see level. I'm in New Orleans so at see level. He said I should expect to see closer to 475 to 500. I'll know for sure as they are going on the engine dyno end of the week or beginning of the next.

They will be mated to VD's 1.5x1 1017s. I have 1.25 shafts. ( could be an issue, hope not as they were just installed a little over a year ago)

Also, I am going to speak in MPH not knots. Boat would do 30mph at 3400 rpms. That was also max rpm. Cruisted at 22mph at about 2800rpms. Currently running 17x16s that have been reworked to 16x13 with high cup. NOT MY CHOICE lol that is what was on it when I bought it.


so after all of that my question is what have some others ran on 28's with higher HP?

[Tony Meola]

Might be tough to find a 28 with that kind of HP.

You need to think about the clearance from the tip of the prop to the hull. Too close and you will actually errors the glass away from the prop wash. I am drawing a blank but I think the rule of thumb is that you need to take 20% of the prop diameter as clearance from the hull.

If you do a site search you should be able to find the formula.

[Kevin]

My first concern would be are these engines made for a boat? Compression, cams, limited duty verse constant duty.
To your question, you will need way more prop but depends on rpm/power curve.
I think my diesels are rated around 360 torque. I use 1 1/8 shafts been running them since 2006. No issues.
Curious to hear more about your progress.

[Yannis]

My 240hp yanmars just about fit in the space provided. I wonder how 500hp can fit in there. Even if you raise the deck.

[Carl]

Used to be a 28 with 502's in dads marina. Boat was donated to ship chaplin and 1st thing they had done was have yard pull those motors as it was unmanageable docking and in tight quarters in general.

I just asked the guy that ran the yard back then, he had no idea how boat was setup. He just pulled motors, installed a set of running takeout 350's, reduced wheel size, pitch and called it a day.

[Carl]

My 240hp yanmars just about fit in the space provided. I wonder how 500hp can fit in there. Even if you raise the deck.

Yannis- One thing about us guys on this side of the Atlantic...we can always figure a way to squeeze a bigger motor in. In this case a 350Small block...hell we put them motors in our motorcylces.

http://www.motorcycle-usa.com/2005/11/a ... uick-ride/

https://www.youtube.com/watch?v=QfARvNKsgow

[MarkD]

Ford 351:

Old 260's only turned 3400 WOT? That is 1000-1200 rpm light so maybe those engines were working hard and the starboard one decided to call it a day:) I think those 383's will fit fine (basically a built small block, if I am correct) but you may want to verify deck height to make sure they fit. Either way, with those ponies under the deck, the boat should loaf along at 25 knots if you get the wheels correct. Best of luck - keep us posted.

[Navatech]

My 240hp yanmars just about fit in the space provided. I wonder how 500hp can fit in there. Even if you raise the deck.

Increasing HP doesn't necessarily mean increasing the physical size of the engine... Getting more are (and therefore more fuel) into the engine will also do the trick... Also, gas engines are usually significantly smaller then diesel engines of the same HP...

As another example, the engines I have in my Bertram are the so called Detroit Diesel 8V92TI... Each cylinder has a volume of 92 cubic inch... That's 1.507 liter for you... For a total of 736 cubic inc (12.06 liter)... The original (non Turbo) version of these engines put out 400 something HP... The TI in my engines designator stands for Turbo Intercooler... That pushes the HP up to 575 HP... Some engine marinizers (e.g. Johnson & Towers) have taken the same basic engine and have pushed it to 800 something HP...

GM has a 6.2 "small block" V8 that puts out more then 600 HP... It's called the GM LS9... A pair of these will cost just over $50,000...





These are special racing engines hand build in a special plant (each is done by a single worker)... Would I put them in a boat even if I had the $$$?!... Nope... They're (really) good engines for what they're intended but when you push them that far they won't last in a boat... The more HP you push out of a given engine the less life you'll get out of it...

[Yannis]

Funny, IKEA started selling motors ?

[Carl]

GM has a 6.2 "small block" V8 that puts out more then 600 HP... It's called the GM LS9... A pair of these will cost just over $50,000...

Why do that when you can get a mopar 6.2 supercharged hemi crate motor at 707hp for just over 22k.


also not for marine...yet.

[scot]

Any gas engine (V8) needs to be propped in such a way that insures the engine can turn 4600-4800 rpm WOT. If the engine can't reach these rpm's, it will be very short lived.

The rule of thumb for prop to hull clearance is 10% of prop diameter, I like a bit more. Props in pockets can run a little tighter so I've been told? Diameter is the efficiency of the set up, not pitch. Small dia + higher pitch = less efficient, less mid-range speed (cruise) but more top end. Larger dia + less pitch = more mid-range speed, more efficient but less top end, take your pick. Efficiency is all about reducing the % of slippage.

What counts is how much power the engines are making around 3000 rpm's, where they will spend 95% of their life. Small block Chevys make big numbers higher in the rpm range. A stroked 350, i.e. a 383 will make good mid-range power and excellent torque numbers, so it's a great candidate for an upgrade and fits in the same space. You will be able to turn more wheel and cruise faster than a stock 260hp no doubt, but it still won't run with the outboards. Also, your stock gears may not be up to those HP numbers, check that out. I would hesitate to bolt those engines to a BW 71 series, 72 series maybe. A set of ZF63s, or 220s with a down angle would be a much better match, assuming the engine bay configuration can manage a down angle gear.

Talk to your engine builder, make sure he understands your engine's are going to be living their life at 3000. Make CERTAIN the cam he is going to put in your motors will not pull water back into the cylinders with the manifold / riser set up you are going to run. This is a cam duration thing. The bigger the cam, the farther away from the exhaust stream you have to introduce the water. This is a BIG problem with radical cams and stock risers. The last thing you want to do is start the engines and load the cylinders with water, which by the way he will claim no liability for.

Good luck, they will sound nice!

[ford351c594]

yes, they are marine 100 forged internals, with custom ground cams from Howard's. Built by white brothers in Tennessee. They do great work. I originally wanted 100 forged 350 and they told me it was basically a waste of money not make them 383 if going 100 forged on the internals. Both are also gear driven, no chains. For an extra $100 seemed like the way to go. And the custom ground cams were only $40 more than an off the shelf. Used white brothers heads and rockers that match the roller cams. And a low profile cyclone intake with quick fuel carbs. Actually if I added correctly, big if, be 3/4 of inch shorter than the 350's coming out.

They arrived today actually!!!

[ford351c594]

my main purpose of building the engines was originally for forged internals for durability. Then one thing led to another and this is what happens. LOL

[Navatech]

They arrived today actually!!!

They look good and the specs sound impressive...

[Navatech]

my main purpose of building the engines was originally for forged internals for durability. Then one thing led to another and this is what happens. LOL

There's actually a term for this: Scope creep...

[Carl]

Always nice to open a hatch and see Shiny New!

Best of luck with the new powerplants and enjoy!

[Hyena Love]

I'd prop for a cruise of around 24 at 3000, if it will still reach max rpm. Its real tough to push that hull at much more than about 24 or so in the typical small but close chop of the GOM during the run out. The most frequently spoken sentence from my crew on the way out is "Hey Idiot, slow the F down." Many days we are rolling out at a mere 18 knots.

Coming home, whole different deal running down swell.

[MarkD]

Time to replace the hatches with plexi glass - those are nice looking engines, you will want to "display them":) Looking forward to hearing how they perform.

[ford351c594]

what a disaster. The engine builder accidentally sent the wrong distributes. super waste of time at least i noticed something was fishy before we attempted to run them. was setting first engine up on dyno, and unboxed distributer..... Called them and super great customer service. correct ones are in route. Apparently they send out 2 sets of engines that day and the ignition parts got mixed up from my two crates and the other dudes two crates....... kinda wish I would have revived the 671 blown 502 however! :)

[Carl]

Sucks, but at least you found out before you set in boat and tried....

Crap happens, at least they were good about it and your be on schedule again shortly.