1985 allison prop - setup help

[sasquitch]

Hello everyone, I need help! I have a 1985 allison xst. It has a mercury 220 motor converted to carbs (wh22s).The set back is 6" and the motor height is 3 1/2" below the pad. The prop is a A5 26p quicksilver chopper. I have plugged the top two holes in the water intake. The water pressure is 15-20 mid and w/o. I ran it Sunday and got 5500-6000 rpms but only 61mph. I got some info in the tech forum. I still don't understand the slip factor? I was told that the chopper is a surfacing prop. Does this mean it will slip until I get it up high enough to surface? Or does the slip come from cavitation from the over the hub exhaust ? I don't have the funds for a nose cone lwp at this time. How high do I need to raise the motor to get the most out of what I have? and how high is to high for a stock 1989 200hp lower unit? The setup I was running was 4 1/2" below the pad -Wh34s carbs (stock on the 175hp motors ) same 26p prop and it ran 5500-6000 rpms and ran 60 mph. I thought raising the motor 1" and adding a fresh rebuilt set of wh22s would have gave me a little more than what I had before. Thanks for any help! Brad

[150aintenuff]

first the 220 laser was a play on ##### its a 200 a strong one but still 200, the WH22 just gave back the 20 HP the wh34's take out due to small bore vs big bore.. you slip is un godly...... you should be way over 75 with that combo at 6K..... try a trophy as its designed to semi surface, you can go to about 2.5" below with the top 4 holes blocked off before ya run into nose cone teritory as long as you keep 12-15 PSI ( 10 minimum at WOT) you are safe to go up if needed.... but i suspect your already to high for your existing propeller and its condition... try a different one before you go changing the height again..

[sasquitch]

Thanks 150intenuff, What pitch,3 blade or 4 blade trophy should I try. What is the purpose of a surfacing prop? I would think the more the prop came out of the water the more slip it would have. The 26p chopper gives my boat huge bow lift. How does raising or lowering the motor effect bow lift. I need less bow and more stern lift. Will the trophy give me more bow lift or less? Thanks Brad

[150aintenuff]

a touch les s bow lift than the chopper and definatly more sternlift, props that are designed to surface are alot more efficient than those that arent while surfacing, the most efficient propeller only bites from 3oclock till 9 oclock in the rotation... or less and slip is solely a function of the stamped pitch of a propeller versus the forward movement of the blade in actual inches.. a chopper is best suited surfaceing, and a trophy is best suited semi surfacing like you are currently set up. id start with 24P trophy, you should see 70's or better at 6100 RPM with it.... if you dont something is seriously wrong..

[sasquitch]

Thanks for your help. I will be looking for a trophy, I've got to do something 62mph in a allison with a 2.4 is weak! How much should I pay for a used one. Thanks again Brad

[150aintenuff]

250ish for a really good used... less if condition is lower.. new at jacos they are mid 3's

[sasquitch]

I have a oppurtunity to buy a 28p bravo one from a friend. Would this prop help with my slip problem. Also there is a prop shop in my area that says they can add cup to the chopper and help the slipping. Will cupping help or should I buy the bravo one. Thanks for any help or suggestions. Brad

[150aintenuff]

chopper is not the correct prop on your setup.. a bravo isnt either... they are more biased for heavy sterndrive boats or heavier outboards AKA 3.0L or 3.2L that have the torque to turn the 15.25" blade a lil 2.fo doesnt turn those props very well at all... to much blade area, a good buddy on the boards (silverbullet02) has a 150 promax on his XTB 21 and hits 72 mph with a 25 trophy, which is 13.75" diameter 4 blade, over/thru hub this will be one of your best options for a starting point to get descent slip numbers, and to begin tweeking. i personally wouldnt touch that 28 bravo for your boat, look for a 25 trophy or tempest and get your slip down first, a good slip % for an allison is roughly 8-10% anything beyond about 12% on an allison and its WAY to much the A botes use power VERY efficiently and consistantly show low slip values when the setups are rite your botes short on setback, has wrong prop for engine height, and isnt effectivly using the design of the propeller, thus the high slip %'s

[sasquitch]

Thanks again 150anitenuff. I've been looking for a trophy but not much luck in my price range. I think I will break down and buy one . Is there any advantages to the trophy plus ? Also are the 2" jack plate spacers from Bob's a good option, to buying a new jack plate. If you had a choice between a tempest or trophy with my boat what would you buy.

Thanks again for your help. Brad

[steve20DC]

i sent ya pm about a trophy. i have one in your price range.

[patchesII]

if i were you i would be putting my money towards a nosecone. then you could run the prop you currently have. your combination of motor and hull is very capable of running fast enough to have blowout issues. if you do get a prop to bite like it's supposed to and assuming your motor is making advertised horsepower you're gonna be in blowout territory. my dad had one of those hulls in the late 80's with an xr2 on it and it would run fast enough to blowout with the standard gearcase

[sasquitch]

Hello, I just wanted a little more advice. I bought a 25p trophy and ran it today. The prop has one pvs hole plugged the others open. The prop is 4 1/2 " below the pad. I lower it from the setting of the 26p chopper I had on. The boat ran 63mph at 5800rpm. I don't know what slip that is. The hole shot is 150% better it gets on pad at about 4500rpm. The chopper would plane until around 5200rpm. I have a problem, when running 5800rpm the water pressure is at around 15psi and then for no reason it drops to 8psi. when I back off the water pressure goes back to 15psi. If I run it longer than a few sec. at 5800rpm the pressure drops. I stopped by my local outboard shop. The tech said to raise the motor? He says the trophy is sucking more water than the chopper and raising the motor will help? I don't know if that sounds right. I thought maybe I have problem with the water pump. What should I be running at 5800rpm 4 1/2 " below the pad ? Thanks for the advice on the trophy 150anitenuff . It is definitely a smoother faster hole shot and I think with a little adjustments it will be faster on top end. Thanks for any help. Brad

[150aintenuff]

trophys like to slip Just a little and then once your hull lifts, and your throttle imput stops it hooks up, lifting the boat, and also changing the water profile flowing from the back of your hull, personally it sounds like the engine is falling into a air pocket as the boat lifts and accelerates at 5800 to ultimate top end with the current setup,


you had better watter pressure before you lowered the motor , raise it back up your entering a rising airpocket caused by vacuum of the hull notch area as it slides through the water, your short setback, and low height is the cause of the pressure drop go back where it was, and possibly even up an extra pinch keeping water pressure minimums in mind


4 the record I always ran my trophy with either 2 sealed 2 open, or 4 medium vents

[150aintenuff]

currently for the record you are at 16% slip.... down from 22%

[sasquitch]

Thanks for the help. I will raise the motor.I was thinking of buying a set of Bob's 2" jack plate spacers. Do you think 2 " is enough or should I buy a 10" jack plate. Does anyone have a picture of Bob's spacers installed .