I have a 1990 Formula 242ls with a 454 mag and Stainless Marine exhaust. I'm currently running a 23 Mirage (non +) and turning 4500-4600 RPM and seeing 56 MPH on GPS at WOT (a 2 MPH and 200 RPM increase since adding the exhaust). I'm cruising at 3500 RPM and 41 MPH or 3000 RPM and about 34 MPH.
I'm looking to maintain or increase top speed and improve cruising efficiency (if possible). My thought is I need to turn more RPM's as I really have to have everything just right to hit 4600 RPM. A friend has suggested a labbed 22P Bravo I, which makes sense. Any other suggestions would be appreciated.
I have calculated your slip at 15% which is the normal range for a 3B propeller. You do however need to get your RPM up to 4900-5000 RPM at WOT to achieve max top end. I would recommend trying a Mirge Plus possibly a 21P for starters to baseline with. From there we can take a look at your numbers.
I would consider the Revolution 4 line. Test a 21 and then consider blueprinting the propeller. The Mirage will raise the rpm's but won't improve your top end and the mid range will actually decrease. Your mid range slip #'s are in the 19+% range.
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Brett Anderson / BBLADES Professional Propellers
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Chewy, my 242 has the 454mag but they say 4600rpm max unless I am wrong, I see 55gps with a 4 blade bravo 22 pitch labbed w/alpha 1.47 my numbers are very close. Is this as good as it will get?
Thanks for the info. I'm pretty sure the peak RPM range is 4600-5000 RPM on my engine (1990). A couple of questions... are you running stock exhaust manifolds? What RPM's are you turning at WOT?
Last edited by chewymalone; 06-19-2006 at 03:25 PM.
I had a 89 242LS with a 454 magnum. Prop that came with a boat was a 21P mirage (non plus). Top speed was 55mph @ 5200 RPMs (too many RPMs). I tried a 23 pitch mirage+ and it was too much prop, could only get 4300 rpms. Bought a 22 pitch Bravo I. Top speed hit 56 mph @ 4800rpms. Engine had 730 hours so I think it was a bit tired. Most recently the engine hydrolocked with salt water. Anyway I found that the 4 blade got the boat on plane faster and ran smoother. Cruise speed @ 3000 and 3500 was faster too. I think 3500 was 40mph. I sold the boat but still have the 22 Bravo I. You might check with a prop retailer...sometimes they have loaner props to try first. In terms of top speed in this boat, I think unless you start adding big power you are not going to see much more from switching props. Check over at the Formula owner's forum...the topic has been discussed at length. I was just about to install a 502 longblock but decided to sell as is. With a 502 I think I'd be lucky to see 62mph. 6mph for $9K! That's too much
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