Horsepower VS Torque
 

I have changed a few things on my motors, and an unexpected thing has happened. My peak HP is 586 at 5100 rpm (goes flat as intake restrictions take over )and my torque is 606 ft lbs at same rpm. I am foggy on the subject, but I always thought that at peak HP, torque should be at least 100 ft lbs less than HP. I think it might be called over square ??

My peak torque is at 3700 rpm, 658 ft lbs. At my 5500 rpm limiter, hp is 580 and torque is now lower at 560 ft lbs.

These numbers come from Mark at Precision marine, so they are accurate, if not understated a bit.

Or do I have a better setup this way for top end speed, as that's is all we are after ??

Horsepower is torque. If you're making 580HP at 5500RPM, the only way to make more torque there, is by making more horsepower, and vice versa. HP is simply torque output . HP = Torque x RPM ÷ 5252

Have you ever tried more camshaft in the engine, to determine if it is indeed the intake manifold holding it back from making more peak power?

Got plenty of cam. It is the heads. They worked fine under boost pressure, but now N/A and struggle up top at max rpm. I know about the equation, just trying to see how the numbers work in a boat app, versus car/truck. I am still playing with props to get some better top speed. I had always thought that there needed to be more horsepower at 5100 than torque to get to a higher top speed.

At peak,I had 20 more hp than tq number,,My boat ripped up top.I'd spin those 28 pitch props really nice.
I'm always for making/holding the most tq in the upper rpm's so it can still push that brick thru the water.Of course,stepped hulls have it easier and I bet can do things w/ a little less tq to maintain/accelerate at speed.

Not sure how you can make "more HP than torque at 5100".

An Engine making 600HP at 5500rpm, is simply making 573 ft lbs at 5500RPM. If you're making 700hp at 5500RPM, you're simply making 670ft lbs at 5500RPM. It doesnt matter if its from a 454, a 598, or 632.

I always hear how "I need more torque to push my heavy boat thru the water at wide open throttle". Well, that also means you need more HP to push your heavy boat thru the water. Its not possible, to make 700 ftlbs of torque at 5500, and only 500 horsepower. it doesnt work that way.

HP vs Torque number spread, goes up with RPM. A 600HP engine at 5500, will make 27ft lbs less of torque, at 5500. A 600hp engine at 6000RPM, will make 75ft lbs less torque at 6000rpm. A 600HP engine at 5300, will make 5ft lbs torque at 5300RPM. A 750 Supercat race engine that makes 750HP at 7500RPM, will be making 225 less ft lbs torque, at 7500RPM.

core math says different.:D

but your right about the numbers.you need tq up high.

Smitty what are you running for heads, cam and intake?

A restriction in the intake tract will hurt torque as well as horsepower. Sounds to me like you are in need of a cam change. I prefer square motors in boats they seem to run the best. I would try a larger cam...