Who runs a 155 pump on their SJ?

JustinB

JustinB

Proof I has a brain \l/
Location
Oxford, MS
Since I have a 155mm pump sitting around, I have been giving some serious thought to swapping it into the SJ I am building. All of the searching I have done tells me that the Mag pump is "better", but I dont have one of those just sitting around.

Who has a 155 pump and likes it? What mods to the driveshaft will be needed with the WDK pump shoe? I'd basically be putting an entire WB2 driveline in my Square.
 
JustinB

JustinB

Proof I has a brain \l/
Location
Oxford, MS
wsuwrhr said:
What kind of power are you making? Or what engine are you running?


Brian
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Engine in signature: 64x 760, milled head, full Protec "A" wetpipe, dual 38's. I was thinking the 155 pump will give me the bottom end I will be losing with the 64x compared to a 61x cylinder
 
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kevbo

kevbo

Location
dfw
This is one of my upcoming projects. I think that I can get better hookup and thrust from 0-15 mph over a 144 pump. Mechanically the swap is very simple, a SJ driveshaft will fit and the pump bolts in. Im going to machine the shaft to use the same bearing as an 1100 because axial loads will be higher with a 155 disk. A B2 pump shoe would be very handy, I will probably make my own to match the widened inlet and SJ grate. Skat makes low pitch swirl props for the XL700 that should be perfect. I should have thrust/speed/rpm numbers compared with my 144 by the end of summer. The "bottom end" your trying to get is a throttle response issue, pump load will play a big part. Using a 155 is only an attempt to gain pump efficiency at low speeds.
 
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Waternut

Waternut

Customizing addict
Location
Macon, GA
I'd love to hear how this works but I think it's going to be a shot in the dark as I really doubt many people have tried it.
 
kevbo

kevbo

Location
dfw
Waternut said:
I'd love to hear how this works but I think it's going to be a shot in the dark as I really doubt many people have tried it.
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Yamaha have already tried it in their B2 and XL700/760. The 155 will have lower blade angle than a 144 consuming the same power. Less pressure drop at the inlet and over the blades should make more static thrust. This is strictly for low speeds, I expect to lose some top speed. If I get positive results with a 701 the improvement will increase with larger twins.
 
W

waxhead

wannabe backflipper
Location
gold coast
The blade is bigger your swing more weight further out. Nothing
to do prop pitch. That's an entirely different thing than what I am
talking about
 
Berky

Berky

Location
Fl
It seems like the 155 could be more efficent at low speed if you stuff the hub of the pump, it's all about volume and velocity, ya I bet the bigger prop will give a bit of flywheel effect but it's less than 10%.
 
Waternut

Waternut

Customizing addict
Location
Macon, GA
Little bit of math for you guys... The amount of extra metal on a 155mm prop compared to a 144mm prop is approximately 250mm cubed or 0.015 inches cubed. I'm estimating on the high side due to lazy calculating. The weight of steel is 0.29 lb/cubic inch so that means that you gain a whopping 0.004 lbs on the outer diameter of the prop. So the actual weight of the prop isn't going to make one lick of difference. The only real difference I see is the outer diameter of the prop is now grabbing water and that will put an extra load on the engine but that's why you pitch down in the first place so it should balance back out IMO.

The biggest problem I see is that there will be less pump pressure and it may be hard to keep the pump loaded up. Kind of like going the opposite way of a mag pump.
 
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