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Old 03-08-2002, 05:10 PM
  #21
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Dueclaws has hit the smoke and mirrors right on the head. When talking about corrected dyno versus prop shaft HP is where things get hazy. Most of the engine building world uses corrected dyno HP to compare the output of different engine combos. A 500HP makes 470 at the prop of a bravo drive at around 5200 engine RPM. What is the loss through the same drive at 6100 engine RPM? Is it measured on a prop shaft dyno or is it estimated? If it is estimated why not just give the corrected dyno HP which is a known value? This will make it easier for potential "do it yourself" customers to build an engine that will give them the performance they are looking for. My engine builder doesn't have a bravo or b-max drive between the motor and his dyno. I think the only reason Merc started using prop HP is to make the numbers look better for the insurance agents. I think most of the boating world wants to know corrected dyno engine HP.
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Old 03-08-2002, 05:21 PM
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My last boat (DCB Mach 26 twin 2.5's) was featured in HotBoat and was on the cover of the 04/00 issue. The boat was tested with 1/2 tanks (50 gallons) and two large males on board. The boat was tested at Havasu with my labbed props that I used on the boat, so I would say that is pretty "real world". The boat radared at 102 and some change. I have driven the same boat to 106 with just my girlfriend and I and light on fuel. I can say that the test they did on my boat was honest in regards to speed and handling.

I have another friend that had his boat tested in HotBoat as well. this was also a Mach 26 with a Teague 740 and bravo drive. The boat radared at 112 and some change. I can tell you that he has run his boat at Havasu at about the same speeds. So in my experience HotBoat has been truthful about speeds. That is my .02
 
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Old 03-08-2002, 09:06 PM
  #23
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While it appears many fellow OSO's understand the point I've tried to make, some will never get it. Again, to compliment Scott and the AO, I believe the speeds with 900 crankshaft HP. However, when HB reports those speeds with "blown 750 Owens racing engines" and you are used to "corrected Dyno numbers" or crankshaft numbers, thats when I say wait a minute. To me, the difference between a BLOWN 900 and a BLOWN 750 is huge, especially when multiplied by 2. I completly agree with Wette Vette's take on the "various" ways to measure hp...we need a standard for a baseline. Since all dyno's correct to standard conditions it seems crankshaft hp would be the most accurate. Although dyno "race" headers, and the lack of any accesories would certainly skew the numbers to the optomistic side of things relative to a "installed" marine application. If the testers or owners really don't know the numbers then print ESTIMATED or UNKNOWN. Just my more than .02. This has been a fun thread!
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