What makes the idea marine engine? One were the HP and Torque Peak at the same RPM? I know that my Power Stroke in my truck has lots of low end grunt making it good to tow with. However with a boat should the two try and peak at that same RPM for the top speed.

Jon

hp = torque x rpm

so i am trying to think if they will ever actually be at the same rpm, I think this would be only if the torque takes a nose dive at a particular rpm, where the rpm increase was cancelled by the torque decrease, (therefore your hp won't keep increasing after this top torque point)

this motor would run/dyno like it hits a wall. kinda like cruise control i think.

my best Swag ( sophisticated wild ass guess) would be a motor that makes peak power at the lowest rpm possible because spinning low pitched props at high rpm just waste energy turning the metal blades through the water. high pitch props at lower rpm seems to be the most efficient.

of course you can only make so much theoretical power at a low rpm and given displacement. there is only a given amount of fuel/air energy available.

Nah, in fact, would be really difficult to achieve what you speak of. Simultaneous Peak-gasm would require torque curve to drop dramatically as soon as it peaks. Not desirable. Torque is an indicator of combustion efficiency. Horsepower will almost always peak at higher rpm than the torque peak simply because hp is a function of torque x rpm (times a constant of 0.00019).

While it is easy enough to develop a cam profile to cause torque to drop off at a certain rpm, a flatter curve is far more usable.

Any thoughts??

Jon, I listen to Rambunctious ramble on like this all the time. We work together, boat together, and have lunch together often. He's one of those sophisticated anal redneck engineers you hear so much about. LOL!!!

I've always been told you want your peak hp at your goal rpm for a given motor. In my case, 5100 rpm. And your peak torque several hundred rpm below that. In my case, max tq is at about 4500-4600 rpm. Cam choice and compression are the biggest factors you need to deal with to get the tq and hp where you want them. That's not saying other things are not really important too, but if you're not making power with your air to fuel mixture, you're lost to the back of the pack!!!!

Did that make any sense or am I starting to sound like Rambunctious???

yea, what Mc said(not waterfoul) .....hey!! that's what i said too

mike quit picking on me, you may need me tomorrow night

I think you have all played a little to much with the wackey tie stick So we want torque to hit a couple hundred below the max RPM???

Jon

So I've been told Jon.

If you look at enough dyno sheets you will see that on the average the torque peak is 1000 to 1500 RPM below the HP peak. This is just the way it works out. Simply put, more cam moves the whole curve up with peakier peaks. For a boat, flatter is better. With a 6 speed peaky is ok.

This is the formula relating horsepower and torque:

torque= horsepower*5252/rpm

They are ALWAYS numerically equal at 5252 rpm.

TQ is what is actually measured and HP is calculated from it .

HP = TQ x rpm/5252