Scott B

Dude, wanna put down the pipe a moment and explain that??

BadDog

I understand Scotts logic completely, on paper. How much difference it makes is debatable and is likley offset in one way or another, by size of gear teeth and other mechanical differences.

As far as his statement envision smacking a canoe paddle into the water horizontally, now try it with the paddle at a 90 degree angle to the water.

BadDog

Woops, Cooltoys logic...

50boat

ive ran 750 hp on a 96 42 fountain four 4 years no down time yet,,, afrend runs 875 hp blower mots on a32 baha no down time,, 40 baha tripplehp 500 trashed --7--- drives in 14 months. ithink its the hole shot ore air time that does it. although i love to jump cruser wakes like a jetski. so how knows

cuda

Scott, is this for the Critter?

Scott B

X boat

jaroot

honestly scott, i could just "detune" the 16 to make you feel better

Root - die alpha die

Scott B

LOL, I'm already hearing rumours about your winter detuning project..

When do you want my SSM's for the dyno pulls BTW??

ECeptor

Here is some info on old vs new Bravo 1's - http://go-fast.com/mercruiser_bravo_sterndrives.htm

As to the big prop vs little prop discussion above, it's all about the damage to the powertrain - powertrain being everything from the engine flywheel to the prop.

Here's the deal - powertrain damage is quantified as load^exponent times rate. In a mechianical transmission like a boat drive it's torque^exponent times rpm. The exponent used depends on the failure mode and can be either 3.33, 5.66 or 8. So, let compare a couple of way of putting 600hp through a drive. First is a warmed up 540ci belting out 600hp at 5000rpm which requires 630 ft-lbs of torque. Second is a high winding 502 producing the same 600hp but at 6000rpm would require 525 ft-lbs of torque.

OK, now let's use the lowest exponent, 3.33, and see the difference in damage between the two set-ups.

The 540 is 630^3.33*5000=1.05E13
The 502 is 525^3.00*6000=6.87E12

Therefore the lower rpm 540 would have +53% more powertrain damage than the higher rpm, lower torque 502! This change in damage relates 1:1 to the life of the drive.

Moral of the engineering story? If you want to keep you drive alive, keep the torque low and rpm up to get the power to the prop!!!

I almost forgot - this is ASSUMING the drive is sufficiently designed so the failure is in fatigue and not low cycle. Put 1000hp in front of an Alpha 1 and all bets are off!