Prop question on a 27 Sport

[superhatz]

I bought a Magnum 27 sport with 350 MPI bravo 1s and the owner said it goes 60mph on GPS with 26inch 4 blade stainless props......but only 3800rpm.

My questions are?

What size prop do I need to get to run what RPM?.....24 inch.....5000rpm?

Also.....is there a good way to sell or trade for the right props.

BTW: I am seriously exited about this boat and I will post many pics when I get back with it this next week.

Thanks.......:)

[myfinancialadviser]

I would suggest going to your local marina / dealer and testing out several different props. Ive got 383's in mine and am running 3 blades, ive got a few engine mods so at wide open i can turn 5500 safely, and run 73 mph. I think you may be mis-proped with those 4 blades.

[Voodoocanoe]

I would suggest going to your local marina / dealer and testing out several different props. Ive got 383's in mine and am running 3 blades, ive got a few engine mods so at wide open i can turn 5500 safely, and run 73 mph. I think you may be mis-proped with those 4 blades.

Is yours the orange and white one "Old School" ?

[Forrest]

26" pitch four-blades sound pretty stout for that Magnum with 350s and a 1.5:1 gear ratio. A 26" four-blade is like a 28" three blade so I would say the you are way over propped. If you want four blades, which should work well, I would start by trying a pair of 22" pitch props which should get you a thousand or more RPM. Remember, the Magnum 27 is a fairly heavy boat for it's size and type and for that reason, a four-blade, stern-lifting prop will probabaly give you better all around performance and effiency over a three-blade prop.

Lets see pics!

Is it time for a Magnum get together yet?

[superhatz]

Thanks guys.....

What are used props like this worth?.......

BTW: I bought the white (light grey) one on the magnum marine site. I'm going to California to pick it up this weekend.

[anotherScott]

Hey Forrest, as I recall you have 12 blades hanging off the back of your boat! What kind of top speed do you see with that set-up? I have 3 blades on TRS drives with slightly worked 350's and just hit 70. Do you think 4 blades would make a significant change in attitude or top end of my boat?
Mine is a 1974 Sport which saw fresh water for the first time last week up at Lake George, New York.

Magnum get together????

Scott

[Forrest]

Scott, four blades will usually give you better all around performance and handling than three-blades especially in rough water; however, only testing will really answer that question. If you go to from three-blades to four blades, you will need to drop a couple of inches in pitch to get the same RPM.

On my DPX setup, I'm going to require some prop tweaking to get it in the 5000 rpm range. Here is what I posted in another thread about that:


The 383s for my Magnum that I built, dyno on the PC (Performance Trends Engine Analyzer v3.2 (http://www.performancetrends.com/EA30.htm )) at 365 HP @ 5500 RPM and and right at 400ft/lb torque @ 4000RPM. I'm running "E2" props on the DPX drives with 1.59:1 a gear ratio and only turning 4700 RPM at just over 70 MPH. E2 is the lowest pitch prop available for the DPX drive, so the next step is to send them off to good prop shop for some tweaking in order get me in over 5000 RPM. Otherwise I'll need to change the gear ratio, but that is unbelievably expensive on the DPX drives and for that reason, I don't see that happening. All and all, the DPX drives have transformed this Magnum 27 into an entirely new boat. This Magnum has seen drastic improvements in performance and handling, from the DPX drives over the original Volvo 280T drives, from idle to top-end with improved fuel economy.