How do I determine what props I should be using?

[ktobias]

Hello all. I have a 2000 Sea Ray 340 Sundancer that was repowered recently with Mercruiser 383 Stroker MPI's. Same v-drives and currently running same original 3 blade props.

On WOT I am only reaching 4350 RPM's and I understand WOT for these engines are 4800-5200.

What I do not understand is how to find specifically what the best prop I should be using is? Everything I read talks about trial and error. I am hoping there is a better way, or someone who has already gone through this, since I pay $500 for each block and haul not to mention the high cost of new props.

I know they need to change. Just have no idea what I should be changing to. Any advice would be greatly appreciated.

Thanks,

Keith

 

[Lazy Daze]

Something else is going on here. That's a HUGE drop in performance/loss of RPM. Go to Sea Ray's website and look for the prop matrix for your boat. I suspect the difference in props from a big block to a small block (of that era) would only be an inch or two. Assuming this, for now, that is NOWHERE near enough to cause that type of RPM drop. Did you get full RPM's with your 454's?

Has the boat been sitting in the water for a while not being used? If so, a dirty bottom can easily account for that perf loss.

 

[hottoddie]

If the engines that were removed were big block 454s the 383s may on paper produce similar rated HP they will not produce the same amount of torque as the big blocks. You could have your existing props reworked and remove about 2" of pitch to get the rpms in range.

I'm curious what cruise and top speed you are getting with the 383s? You may be able to run them as is and rework the props over the winter haulout.

 

[Motoguy2158]

Hello all. I have a 2000 Sea Ray 340 Sundancer that was repowered recently with Mercruiser 383 Stroker MPI's. Same v-drives and currently running same original 3 blade props.

On WOT I am only reaching 4350 RPM's and I understand WOT for these engines are 4800-5200.

What I do not understand is how to find specifically what the best prop I should be using is? Everything I read talks about trial and error. I am hoping there is a better way, or someone who has already gone through this, since I pay $500 for each block and haul not to mention the high cost of new props.

I know they need to change. Just have no idea what I should be changing to. Any advice would be greatly appreciated.

Thanks,

Keith

I have 2002 340 with the 6.2s. The stock props were (3) blade 17 x 19 with a medium cup. The ZF transmission ratio is 2:1 ratio. The 6.2s are rated at 320 HP at the prop as compared the 7.4s being 310 HP. The big blocks do produce a little more torque. I switched to (4) blades Acme props this year. The are 17 x 17 with a medium cup.
Both sets of props got me right at 5000 rpm. I have (2) sets of the (3) blades if you need a different set. Not knowing what props you're running or what engines and transmission they had previously makes this a mystery.
Based on the SeaRay web site here's what i found"

The standard motors that year were:
7.4 MPI with 310 HP turning a (3) blade 17 x 16 cupped prop @ 4600RPM 1.50:1 ratio
T 454 magnum with 380 HP. turning a (4) blade 16 x 16 cupped prop @ 4600 RPM 1.50:1 ratio

Now throw in the 6.2s that should have a 2.0:1 reduction and the wrong prop.
Houston , we got a problem.
Do some research on what you have for sure. A prop guy might be able to set you up with a prop
that will work if you still have the stock transmissions and ratios. If they were switched out with the engines then i suspect you have another issue.

 

[Brite Idea]

I'll second four blade props for that boat. You have Bozzler & Sweezy near you pop in there with your current data and see what they suggest.