longer lever to move the mass

[Joe Mendelis]

In David Rehers article on RPM and gear he talks about engines making the same power at different RPM and using different gears.
He says an engine that makes the same power higher will be able to run more gear and multiply torque more down the track(not verbatim).

One thing he says that really stands out is where he says with more gear it's "like a longer lever to move the mass". I can easily understand that more gear reduction gives you more torque at the wheels. What he does not mention is the lower rpm engine has the same gross torque as the higher rpm engine. (at the wheels) Not discrediting Reher whatsoever. He is an excellent engine builder.

You can not multiply Horsepower, but people are still saying you can! Jay allen mentioned being ridiculed for his formula HP x RPM = "downtrack power"

I don't care if the head engineer for Ferrari F1 tells me it's possible to multiply horsepower, I will never believe it because it can't happen.

Why did the other post on RPM get Locked?

[bob cook]

I thought it was interesting also. What happened?

[SchmidtMotorWorks]

What he does not mention is the lower rpm engine has the same gross torque as the higher rpm engine. (at the wheels)

Here's the quote,

A higher revving engine also permits the use of a numerically higher gear ratio to multiply the engine’s torque all the way down the drag strip. Let’s say an engine that produces 1,000 horsepower at 7,000 rpm is paired with a 4.56:1 rearend gear ratio. If this engine is then modified to produce 1,000 horsepower at 8,000 rpm, it can now pull a 4.88:1 or 5:14:1 rearend gear without running out of rpm before reaching the finish line. The numerically higher gear ratio gives the engine a mechanical advantage by multiplying its torque by a greater number to accelerate the car faster – in effect, it has a longer lever to move the mass.

Joe, I think you correct, the formula of horsepower already considers rpm..

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[bobqzzi]

You can not multiply Horsepower, but people are still saying you can! Jay allen mentioned being ridiculed for his formula HP x RPM = "downtrack power"

I don't care if the head engineer for Ferrari F1 tells me it's possible to multiply horsepower, I will never believe it because it can't happen.

You are correct

[putztastics]

This was for a dirt track car about 85 mph on the straights and 75 in the turns.

[BillyShope]

Here's a way to visualize the effects of gearing:

Consider a plot of acceleration versus speed. Now, impose a curve which goes to a value of infinite acceleration at zero speed and infinite speed at zero acceleration. This curve represents the maximum performance which can be achieved. In other words, the maximum acceleration is proportional to the maximum horsepower divided by the product of vehicle mass and speed. To generate a specific curve, 12075 times the max. horsepower and divided by the product of the mass in pounds mass and the speed in miles per hour will yield the acceleration in feet per second squared.

(Actually, of course, the horsepower mentioned is the horsepower available AFTER air resistance has been overcome, so the curve value goes to zero acceleration long before infinite speed is achieved.)

So, whatever you do with gearing, the results have to lie below the limiting curve.

[Racer7088]

Yeah we all know David Reher isn't crazy and he is obviously talking about holding onto your powerband for a lot longer time in rpm which will allow later shifting and or a lower gear and more average power. Rpm is easily acheived in all forms of racing if that's all you wanted. You can lame out the ramps and the cam and reduce lift at the valve and run much smaller and lighter valves and then certainly turn more rpm all while losing a significant amount of power and you will slow way down. Hell you could just shift way too high on any given car and we all know that's not the path to decreased ETs!

More average power equals more acceleration all else equal. People turn more rpm in the quest for horsepower in the form or more not less so I think everyone knows that. In the realm of displacement fixed engines which is most all of racing the main way to increase power is through rpm. There's also efficiency through design of chamber and pistons and rings and better sealing and less friction and so on and so on but I take Reher's article at that. He obviously doesn't think that losing power and gaining rpm is the way to go fast since they don't do that sort of thing. They are turning more rpm and making power out longer and increasing the average power through extended rpm and that makes pefectly good sense.

Some people were mincing his words to make it sound like he thought you could "multiply" power which we all know is completely ridiculous!

[BillyShope]

In school, they broke down the "horsepower equals torque times RPM" business to what they called the "pLAN" equation. The "p" stands for cylinder pressure, the "L" is the stroke, the "A" is the piston area, and the "N," of course, is RPM. So, "pLA" is equivalent to torque and you're back to the "torque times RPM" equation. But, the pLAN version gives a little insight to what's going on. There was, in the same book, a tabulation of piston speeds encountered by a range of engines during normal operation. These included everything from model airplane engines to huge stationary engines displacing thousands of cubic inches. But, amazingly, the piston speed was essentially the same for the full range of engines!

So, you can consider "LN" to be essentially a constant.

Now, suppose you're designing an engine of a particular displacement. That would mean, if it was a single cylinder engine, that "LA" is also a constant. But, you could halve the "L" value and double the "N" and have the same power from an engine half the size. Obviously, there's an advantage, then, to multiple cylinders.

Hotrodders often fall into the trap of thinking of multiple cylinders as a way to increased displacement, but there are other advantages. Consider a couple of sports cars from the fifties: the Austin Healey 100 and the Ferrari. The Healy used a huge 4 banger with a long stroke, but the Ferrari used a 12 cylinder engine.

And, as someone has already pointed out, simply spinning the engine faster doesn't do much good if the VE has gone south. Back in the sixties, there were SBC's and even Mopar slant sixes that were hitting 10k rpm through the traps, but...and correct me if I'm wrong...I don't thing that's commonly done today.

[Joe Mendelis]

This was for a dirt track car about 85 mph on the straights and 75 in the turns.

Putztastics, that is a very good example of the benefit of gearing. All I'm saying is if you now take that dirt engine and make it make less torque at a higher (same power) and put more gear in it, the numbers in your chart will be the same. Putting more gear in the car until it reaches peak performance is undoubtedly the way to go.