Labbed Props_0001

Comment by Brad J on April 20, 2009 at 1:35am

David, I curious to know about the props you are running and what you are getting out of them. I think I read on one of the posts that you are turning around 5,000 rpm at 65 mph with 23 pitch props. I’m currently running 21 pitch cleavers which gets me a great whole shot and right around 65 mph at 4 grand. My boat has the stock twin 350s with 260 hp.

I always thought if I could the rpms up I would get a higher top end, which is my priority. I’m interested in the Mirages but have been questioning whether to go with 21s or 19s. After reading that you are getting 5,000 grand with 23s with similar twins I’m questioning whether going up in pitch is the right way to go.

Intuition would say that going up in pitch would lower the rpms and top end; however, cleavers and full blades are completely different. I’d appreciate your experience with running the full blade 23s.

Thanks.
Brad

Comment by Brad J on April 20, 2009 at 1:36am

Also, what made you decide on the Thunderbolts?

Comment by David on April 20, 2009 at 7:52am

Brad, I've run an old set of cleavers, a pair of Hydromotive Intimidators and the Thunderbolts. The Thunderbolts are essentially Mirage props. 233's like a lot of bow lift and the round ear props provide that. The cleavers are old technology while the Hydromotives are more of blend between cleaver and round ear. If you go up in pitch you will lose rpm, probably about 200 rpm per inch of pitch. By what you are describing I would guess that either your props are more than 21", or the tachs and/or speedometer are not accurate. 4,000 rpm is lower than optimal. I think stock engines should turn about 4,500 rpm for best performance. My engines are also slightly modified, Dart heads, performer intakes and stainless marine exhaust so I am generating more horsepower than the stock 350's. Since I have 2" more pitch and 1,000 more rpm it makes sense that the top speed would be higher. I've also run 24" pitch and I felt the 23" gave better overall performance. Brett Anderson at B Blades labbed my props. The biggest change is more efficient cruising speeds and fuel economy. Many places will let you try and exchange props. I would try a set of 19" and 21" Mirage or Thunderbolts to start with. If you can test them on the same day you will get the best comparison. Look for how many rpm will keep the boat on plane, mph at 2,500 and 3,000 rpm (or whatever rpm gives you most comfortable cruising speed), holeshot and topend speed and rpm. Write down these numbers then try the next set. I'd also do this with your cleavers to use as a baseline before you test. Make sure your loads (fuel & passengers) stay the same during the test. Like I said before, I think Mercruiser recommends about 4,400 to 4,600 rpm at open throttle.

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