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Originally Posted by onesickpantera
(Post 3741788)
Mercruiser engine(aka black engines) were rated at the prop. 502 mag - 415pshp, 454 mag - 385pshp, 496HO - 425pshp, etc.
Mercury racing engines(aka blue engines) were rated at the crank. HP500/500EFI - 500 cshp, 525 - 525 cshp, etc. It's confusing because the black engines were always over-rated and the blue engines were under-rated. A 502 Mag was suppose to be 415pshp but was usually around 390hp at the prop and 425 at the crank. A 500EFI was usually 510hp at the crank. And we all know the 525s are stronger and I've heard 540hp to 560hp. Which led people to believe they were rated at the prop. |
Originally Posted by onesickpantera
(Post 3741788)
Mercruiser engine(aka black engines) were rated at the prop. 502 mag - 415pshp, 454 mag - 385pshp, 496HO - 425pshp, etc.
Mercury racing engines(aka blue engines) were rated at the crank. HP500/500EFI - 500 cshp, 525 - 525 cshp, etc. It's confusing because the black engines were always over-rated and the blue engines were under-rated. A 502 Mag was suppose to be 415pshp but was usually around 390hp at the prop and 425 at the crank. A 500EFI was usually 510hp at the crank. And we all know the 525s are stronger and I've heard 540hp to 560hp. Which led people to believe they were rated at the prop. |
A Bravo XR "eats" approximately 10% of the HP you feed it. (marine/wet exhaust sea pump/ water pump and alternator take their toll as well)
The arneson is not only stronger and less parasitic in nature (no 90 degree xfer) ,its a true surface piercing drive itself which is inherently more efficient and running cnc milled props. There are numerous studies here with guys that dyno their mills (assuming you dyno through marine exhaust and a water pump ) then hook up to a propshaft dyno - and run again which is why you can 3rd part validate the 10% Bravo loss. Wow...70 on a small 29 with twin big block - blows chunks. Not at all impressive considering I can run mid to high 80's on a regular day with three guys and a full tank - and 90 when I pull the radar arch off and run on a cold day with a single 700 on a 28.8 ft boat. Uncle Dave |
Originally Posted by soldier4402
(Post 3741814)
insurance purposes maybe. A good set up in car should net you around a 15% loss from crank to wheel and boat should be the same Give or take.
Plus in an auto you can run an open loop O2 sensor and tune in real time- all the time whereas in the boat the o2 sensor is out of the loop after primary tuning. UD |
Originally Posted by Uncle Dave
(Post 3741860)
A Bravo XR "eats" approximately 10% of the HP you feed it. (marine/wet exhaust sea pump/ water pump and alternator take their toll as well)
The arneson is not only stronger and less parasitic in nature (no 90 degree xfer) ,its a true surface piercing drive itself which is inherently more efficient and running cnc milled props. There are numerous studies here with guys that dyno their mills (assuming you dyno through marine exhaust and a water pump ) then hook up to a propshaft dyno - and run again which is why you can 3rd part validate the 10% Bravo loss. Wow...70 on a small 29 with twin big block - blows chunks. Not at all impressive considering I can run mid to high 80's on a regular day with three guys and a full tank - and 90 when I pull the radar arch off and run on a cold day with a single 700 on a 28.8 ft boat. Uncle Dave |
Originally Posted by Wildman_grafix
(Post 3740354)
How fast did that boat run?
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Originally Posted by soldier4402
(Post 3741814)
insurance purposes maybe. A good set up in car should net you around a 15% loss from crank to wheel and boat should be the same Give or take.
|
Originally Posted by Uncle Dave
(Post 3741860)
Wow...70 on a small 29 with twin big block - blows chunks.
Not at all impressive considering I can run mid to high 80's on a regular day with three guys and a full tank - and 90 when I pull the radar arch off and run on a cold day with a single 700 on a 28.8 ft boat. Uncle Dave 700hp single vs 800 twins(400 x 2). The weight of a big-block with rigging is about 1500lbs which is about 7-8 mph. Stepped bottom vs straight. Steps usually add about 10% more speed so another 7-8mph Now add in better modern prop technology allowing you to run a higher X dimensions which is good for what, another 2-4mph? So that's 16-20mph difference. Obviously all hulls are different but these are fair estimates IMO. |
Originally Posted by onesickpantera
(Post 3741954)
That makes sense to me.
700hp single vs 800 twins(400 x 2). The weight of a big-block with rigging is about 1500lbs which is about 7-8 mph. Stepped bottom vs straight. Steps usually add about 10% more speed so another 7-8mph Now add in better modern prop technology allowing you to run a higher X dimensions which is good for what, another 2-4mph? So that's 16-20mph difference. Obviously all hulls are different but these are fair estimates IMO. |
Originally Posted by soldier4402
(Post 3741961)
makes sense. I am wondering if there is a good HP to weight ratio table out there. For example does 10 less pounds net you 2hp and .5mph or something
That is 20HP =roughly 1MPH ..so if you want to pick up 5 you need 100more to the prop 10MPH = 200HP Im sure there is a pound per MPH ratio, but I dont know it. UD |
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