I just find it hard to believe that 550+ isn't easily attainable... 400 definitely should be a walk in the park, but only a chassis dyno will tell, maybe I'll get to that someday.
Well, if you want 550 hp you need to make more than a "gob" of torque.
First, a formula:
T = HP x 5252/ N
T = Torque (LbFt)
HP = Horsepower
N = Speed (rpm)
Lets plug in some numbers:
550x5252/3400 = 849 lb/ft
Look at that number - 849 lb/ft!
That's a pretty decent number for even a hot Max/stroke/cummins!
That would be one helluva number from a 6.x, definitely not "easy".
I just can't see the design delivering that, being a tractable daily driver or surviving long if it did.
There's just too many thermodynamic limitations in it. Too much heat into the head, not enough into the piston.
So, lets spin it higher and see if it gets any better:
3600:
550x5252/3600 = 802 lb/ft
802 lb/ft, not much better there either....
4000:
550x5252/4000 = 722 lb/ft
Still a waaay too high a torque number and we're really bumping up against the rpm limits of the design. Especially if you want it to live.
Don't forget, to make these numbers, you're also moving your torque peak to the rpm you need for your HP goals which means you could be looking at some serious compromises lower down in the RPM range where you live every day....you just won't know that until you build it.
Engines keep building HP after the torque peak, but it's a loosing battle. More RPM = bigger HP numbers but your lb/ft are dropping off on the other side of the peak. You make the difference in rpm. But the higher you go, the more your torque drops off and then you're beginning to flirt with rpm limitations....
All Hp is a calculated value, even on a dynomometer. All dyno's measure torque and calculate HP.
The numbers can be worked backwards (as we have see here) to figure out what parameters you need to meet to achieve a desired HP or torque goal.
Big HP requires either big torque or lots of rpm......or a combination of both.
Heath's LSR can claim big HP numbers because the RPM he spins the engine at makes a difference in the formula:
500x5252/5000 = 525 lb/ft
Much more believable/attainable numbers from a "hot" 6.x.
Roughly 100-110 more lb/ft than claimed by GM at the end of the 6.x model run.
GEP now claims 440 from the Optimizers with their support system.
110-odd lb/ft more torque from a knowledgeable enthusiast like Bill (with the experience and resources he has at his disposal) it not unreasonable to believe.
High RPM is how those little 4 cylinder Hondas can make big HP numbers. They can only make so much torque, so they spin the bejesus out of the engine and alter the formula in their favour.
Remember HP is work, work is calculated. Torque is twisting force, force can be measured.
Don't get me wrong, I would like to see a 6.X throw down big numbers, but the ones we're looking at here (849 lb/ft) are just not going to happen without a budget equivalent to the space shuttle. Even with that kind of cash it would still be doubtful.
I'm not trying to be a bummer here, but the numbers are the reality. When they're starring you in the face, it's hard to deny the reality of it.
Figuring out your target is easy.
It's physics and math, nothing more. Those are the rules of the game.
That's why guys chucking out a HP or torque number for a 6.x and adamantly stating it's attainable or they
will make it gives me a little internal giggle sometimes. They just don't fully understand the physics of what they are saying.
But as I said, the theory and figuring out the target is easy.
Building the hard parts and getting there is a very different story.....
artay: