is this boat over propped

[recoil]

hi guys we have a winner 1976 ish we think ?

question is we've rework the engine from 260hp to 330hp , the boat has a alpha one out drive , problem is were running a prop that's 14 1/4 by 23in pitch 5 blade stainless steel , trouble is its struggling to get me out the water on the deep water start , now iam 6ft 4 and 18 stone , but i would think that 330hp would rip your arms out ,
are we over propped and if so any suggestions on a good size prop
the boat will top out at just over 55 mph

 

[180shabah]

Re: is this boat over propped

What are your WOT RPMs with the 23" prop?

 

[recoil]

Re: is this boat over propped

about 4200 rpm at w o t

 

[steelespike]

Re: is this boat over propped

There was a thread on the forum regarding the need to change gear ratios
when modifying a motor for more hp.Whether your 70 hp increase qualifys I don't know.Do you know your motors max rpm rating.My guess is your present 4,200 is slightly on the low side.What size/weight is your boat?
Are you trimming in for hole shot?A prop with bow lift could slow hole shot.

 

[hwsiii]

Re: is this boat over propped

Spike, I agree with you, he is definitely overpropped. He probably should be getting closer to 4,800 RPM or more with the changes in cam and everything else he had to do. If you would like a more detailed analysis of your setup we need a lot more information.


H

 

[180shabah]

Re: is this boat over propped

4200rpm, 23", 1.5 ratio and 55mph all look good together.

Dropping to a 19" prop should put you in the neighborhood of 4600 rpm, top speed about the same with improved hole shot.

300hp in a 17'er should be able to yank you all over the place when skiing.

 

[hwsiii]

Re: is this boat over propped

Recoil, you are showing a prop slip of 10% right now, which is pretty goood. But if you are running an expensive high five prop I would expect better, you can get that with a good 3 blade SS prop.

Prop Slip

Prop Change

Shabah is right about the pitch change, except you only want to go down in pitch to a 21" if you stay with at least a 4 blade prop.
And in my opinion Shabah is definitely right about it should jerk a skiers arms off when you takeoff. If you are getting 330 HP my assumption is you have a cam in it that is not suitable for a boat, as it has the wrong duration or lift. Although some of the time it helps a lottt to change the gear ratio when you increase horsepower, like Spike said.


H

 

[180shabah]

Re: is this boat over propped

except you only want to go down in pitch to a 21"

OOPS!! somehow I subtracted 2" twice. Agree with 21" NOT 19". Thanks for the save hwsiii.

 

[hwsiii]

Re: is this boat over propped

No problems Shaba, like I tell everyone. I NEVER make a mistake, UNLESS I am breathing.


H

 

[recoil]

Re: is this boat over propped

hi guys here's a list of the work that's been done
dart cylinder heads ported to 30 degrees SS valve increase of 40 hp
marine cam
flat top pistons
edelbrock manifold
eagle billet steel crank
engine fully cleaned cylinders buffed all ports cleaned
new felco pro gasket set
new holly petrol pump
did a pressure test on one spark plug port 210psi cold
will check w o t next time we run boat , but i think your all right about the prop it came from Ron hill in Texas i believe and i also think its over prop i will try and borrow a high five 21in pitch should i lose a inch of the prop or leave it as it is ?
thanks all

HOW DO YOU GO ABOUT CHANING GEAR RATIO AND WOULD YOU TAKE IT UP SAY 2.1 OR TAKE IT DOWN SAY 1.1

any help much appreciated thanks

 

[hwsiii]

Re: is this boat over propped

A 1" drop in pitch should raise the RPM about 400 RPM.

Excuse me I meant to say a 2" drop in pitch.
H

 

[recoil]

Re: is this boat over propped

hi hwsiii
so if i drop the prop to a five blade ss 13 1/4 by 21in pitch the boat will pull better out the hole shot the engine wont have to work as hard better fuel consumption and the same top speed
am i right on this cheers recoil

hi guys i thought id post this " if you can try and ignore the two numpties in the front " LOL this was take in February are winter months let me tell you that day with the wild chill was bitter cold , any way you can see on the speedo and rev counter , if you can say with it till the end and let me know thanks again guys

 

[hwsiii]

Re: is this boat over propped

Recoil, yes to your questions about speed and acceleration, but I will reiterate again that I believe even with a 23" prop you should be able to pull up a 600 pound Gorilla if everything is working right in that motor. In my opinion something is very wrong at this time.


H

 

[recoil]

Re: is this boat over propped

what could be wrong m8 , carb or ignition

 

[hwsiii]

Re: is this boat over propped

Recoil, I wish I could tell you, but I would check everything including carburetion and electrical. What make and model of boat are you running this motor in.


H

 

[recoil]

Re: is this boat over propped

hwsiii
the boats pictured at the top its a 1976 we think winner wildcat , its about 18ft , i don't think its over heavy for a sports boat , like i said in earlier post the engine is just about brand new with all the work that's been done on it .

 

[steelespike]

Re: is this boat over propped

Is the speed by gps?Seems it would be faster It appears the hull would be designed for speed though is presently unknown.Of course you are dragging a lot of structure through the air.

 

[hwsiii]

Re: is this boat over propped

Recoil, if it is a 1976 Winner Wildcat I show a base weight of about 2,100 pounds, with the addition of all the towing gear I added another 300 pounds for an allup base weight of 2,400 pounds.
With fuel, assorted gear and 2 people I come up with about 3,000 pounds.
I also show a recommended Wide Open Throttle of 3,800 to 4,200 RPM and a gear ratio of 1.32, Verify this please.

Boat Weight

My Prop Picker show you need about a 22" to a 25" pitch prop depending on the gear Ratio.

Prop Picker

I show a prop slip of 10% at a gear ratio of 1.5:1, but I show a prop Slip of 21% at a 1.32:1.


Prop Slip

This is not going to sound right, but if you can borrow a very high rake, heavy trailing edge cup, progressive pitch 25" pitch in a 3 or a 4 blade prop try it, I believe you will pick up some speed but you will definitely lose quick hole shot.

If you can give me the RPM and speed numbers from 2,500 RPM up to WOT in increments of 250 RPM, I will run an analysis and try and see how the prop is reacting with the boat at different RPM.

The only thing I don't understand is why you have no low end torque for pulling up a skier. But with the numbers you give me maybe we can see if a lower unit gear change will help. But definitely make sure what gear ratio you have now, try pulling the plugs and turn the motor after marking the prop to see what gear ratio it is now.


H

 

[MikDee]

Re: is this boat over propped

Nice work on that motor, & old boat. That old of a boat is a semi-vee bottom I believe, a vee in the bow, to an almost flat stern, usually they are 10% faster then a vee, or deep vee bottom, with the same horsepower, but are a bit hard riding in the rough, by design. IMO, your boat should be faster, I agree with hwsiii I think there's something wrong? In the video, it sounds like it's not revving up enough, I would check to make sure your carb is opening fully, and be sure you're getting full spark advance.

 

[recoil]

Re: is this boat over propped

hi guys thats for all the info
i will pull the spark plugs out at the weekend and see how many turns i get to one revolution of the engine , until then thanks to you all
ps the speed is gps but its exactly the same as the air intake speedo on the dash .