Max horsepower

I don't see how you could be any more stern heavy than my rig. But mine does not porpoise at normal trim angles. If you over trim without the hammer down, yes it will porpoise. I haven't seen one yet that wouldn't if you put in too much trim.. MY .02
 
fixit said:
my 91 v20 is running a 300hp mpi small block with a bravo leg in mine.
i turn a 18" mariage plus prop and my WOT is 5200
really stern heavy and had to put tabs on it to stop it from porposing

its a heavy boat with all the downriggers, radar arch/rod holders, 6" full canvas top, stereo, 9.9 kicker, dual batterys, prawn puller with traps etc etc etc

my max speed is around 42 knots, but cruises ar 30knots at 3200 rpm getting 2.5mpg according to the smartcraft gauges. jumps up on a plane in 2-3 seconds. i could have saved some weight and probably gained top end with an alpha leg but found a complete bravo package instead
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you need a higher pitch prop, bring it down to around 4800-4900 at WOT
 
RidgeRunner said:
I don't see how you could be any more stern heavy than my rig. But mine does not porpoise at normal trim angles. If you over trim without the hammer down, yes it will porpoise. I haven't seen one yet that wouldn't if you put in too much trim.. MY .02
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I/O Bravo, way heavy
 
THEFERMANATOR said:
A high five is a good prop for getting on plane, thats it. What prop you need has alot to do with how you plan to use the boat. I like the large diameter mirage type props for most uses myself. Not the fastest, but good holeshot, faster cruise speeds, and good economy because of excellent bite.
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Thanx for shearing, I'm used to the Mirage myself as I had one on a Formula 223 I used to owned.

I want good overall use but with as high top speed as possible, and that shouldn't be a problem with 250 hp?
 
RidgeRunner said:
To finish Ferm's thought I use a 3 blade Mirage copy made by Quicksilver without the PVS (vent holes) 21 Pitch. Not the fastest but great all around performance. Big round eared blades with some cup on the trailing edge for extra bite. Good bow lift, good cruise, both speed and mileage wise.
I had an EFI once. Sold it to a guy on here. Those motors drink lots of petrol...
It was the fastest motor I ever tried on my V-20 at 61.7 mph officially turning a 23p Tempest to the limiter at 5800 RPM.. Lots of prop slip but the stern lifts a little more with the Tempest and that prop likes trim. See signature picture of the 250 EFI strung out on the Suwannee River a few years back. That was when I weighed 270 lbs. Now that I am 175 lbs. I am sure I could reach 62 ;-) :beer:
Click on the picture to see how much boat is actually out of the water. The keel is touching water just in front of the console. Aired out for a old F-20 fisherman.View attachment 6316
Looks awesome! :clap:
It looks like you have a bracket on, is that good or bad for top speed? My boat doesn't have a top, so I'm gonna reach for the 62 mph mark, or 55kn as we say!
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I think it helps to get the propeller into cleaner water, maybe a little top end gain. I never ran the boat without the bracket, so I do not know for sure..
 
spareparts said:
you need a higher pitch prop, bring it down to around 4800-4900 at WOT
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4800-5200 is the normal wot operating range for an mpi motor. its actually 5170rpm when its stripped down and empty of fuel/light, and 4900 when loaded up with gear and fuel. --- just perfect imo

fyi the bottom of my swim platform sits about flush with the water
 
Speaking from experience, if its an injected engine, it starts pulling power at 4900 or so. Put one in a few years back, and found it to be PICKY about propping. If you went a hair low on pitch, it would pull power, a hair to much pitch and it would bog out, but get it JUST right and she would boogy.
 
The real problem with propping is that there's so much more to a prop than just the pitch, and all of them effect how the engine preforms. You have pitch, diameter, rake, cupping, prop material, type of blade, blade tip, number of blades, and of course, position of the blade in the water, just to name a few. (there are more) And each and every one of those items can and will effect the overall performance of the engine and the boat. :ski:
 
fixit said:
4800-5200 is the normal wot operating range for an mpi motor. its actually 5170rpm when its stripped down and empty of fuel/light, and 4900 when loaded up with gear and fuel. --- just perfect imo

fyi the bottom of my swim platform sits about flush with the water
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nope, its 4800-5000, just put a brand new 350 MPI in a boat today, its got the rpm written on the cover. Ferm is correct, that motor starts pulling power at 4900, I like to prop them out so they run 4800 at a light load, WOT
 
cat motors like the one you linked, turn to 5200, cats hurt the power so they turned them harder to make the lost power up. Non cat motors turn to 5000 before they start pulling power.
 
I know mine said it could go to 5200, but it sure started laying down above 4900. Propped it to run at 4700 and it went about 9 mph quicker than it did at 5150.
 
The outboard manufacturers will advise that if the motor isn't propped to reach max rpm, the engine is not running properly, and damage possible.

Over propped, lower rpm.........engine is working too hard and strains.
Under propped, higher than recommended WOT rpm, and spinning too fast.

Some of you may disagree, but that's the general standard .
 
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