Somebody explain.

[IntegraR0064]

Originally posted by GTStang


Also when i speak of stroke i'm not talking bout the 4 stages of a Carnot cylce.

Carnot cycle?!! What do you drive, a refrigerator?

[Someguy]

EX. 347(Stroked 302) will create more hp but will not create as much torque as hp but will move the torque curve more to the end of the curve.
Where as a 351 will have equal hp as the 347 but will have more torque that is in the beginning of the torque curve to the end.
This lil example does not even begin to explian everything that is involved in this but I hope it clears up things I was talking bout

Its the other way around (as Texan said). Stroking the 302 to a 347 provides for a great increase in leverage on the crank (ie torque), but it does not lend itself to high RPMs because of the rod ratio. The 351 design lends itself much better to high RPM use, and higher hp for torque.

[MBTN]

There are so many factors that come into play for power. Why does a Ferrari 360 makes 400HP with 3.6 liters yet the Viper only makes about 460 with 8 liters?
Ferrari: Dual intake manifold, flat-plane crankshaft, titanium connecting rods, variable back pressure exhaust (i think), Variable valve timing, 5 valves per cylinder, aluminum block and pistons, dry-sump oild lubrication the list goes on...

The Viper has a simple 2 valve per cylinder V10. So despite its massive size, it only makes 60 more HP than the Ferrari engine. However, the sheer size means torque up the ass, unlike the Ferrari engine.

You must remember that HP is work over time. A smaller engine "works" faster, so it can make a lot of HP relative to it's size. A big engine has large moving parts, so it doesn't "work" as fast, but can make big torque.

Hope this helps...

[Someguy]

The Viper used duel intake manifolds also. But anyway...

HP = RPM * Torque/5252

So 500 ft*lbs of torque at 2626 RPMs and 250 ft*lbs of torque at 5252 RPMs both equate to 250 hp.

Anyway, spin a 427 SOHC up over 7000 RPMs if you want to watch a big engine "work fast".

[MBTN]

Well true... but a smaller engine CAN (not always does) spin faster. Spin a 3.6 V8 to 8500....

[Hudson]

While a Ferrari 3.6L V8 might put out more specific power than a Chrysler 8.0L V10, the LARGER engine actually gets better gas mileage. You may not care about this fact, but it does show that the Viper isn't necessarily tuned for all-out power.

[Someguy]

That's true. The gas milage for the LS1/LS6s are amazingly good on the highway with that deep 6th, while the smaller, higher specific displacement, Italian 3.6 is just plain horrible. We'll leave sex appeal out of this.

Anyway, the 427 SOHC is 35 years old but still made more power and more torque. 658 hp @ 7500 RPMs and 575 ft*lbs @ 4,200 RPMs even with a 7 ft long timing chain.

[Hudson]

The SOHC motor wasn't a standard production engine.

[Someguy]

Yeah it was, just very hard to get. It was intended for NASCAR so they had to sell a certain number of street cars equiped with them to make it legal. With a small carb and less wild cam they were crammed into Galaxies.

Some other teams cried "no fair" and so the OHCs were weighted down with mandatory ballast. Eventually OHCs were made illegal for NASCAR, but a rellatively small number of them were sold as the stock motor in cars.

Its like saying the GNX isn't a production car.

[texan]

Or the Chrysler Hemi for that matter, someguy. And it was at least as impressive as the cammer in terms of high RPM output.

[ivymike1031]

Originally posted by Someguy

HP = RPM * Torque/5252
So 500 ft*lbs of torque at 2626 RPMs and 250 ft*lbs of torque at 5252 RPMs both equate to 250 hp.

I always feel compelled to speak up when I see the aforementioned formula for shaft horsepower without mention of the (implied) units... In this case the only unit that wasn't stated in the formula was torque, which would need to be input in ft*lbf for the equation to work.

Of course ft*lbf was stated in the example calculation, just not in the formula...

[Someguy]

Originally posted by texan
Or the Chrysler Hemi for that matter, someguy. And it was at least as impressive as the cammer in terms of high RPM output.

Yeah, the whole point of it was to go head to head with the Hemi. Just goes to show that even NASCAR at one time had a use.

I always feel compelled to speak up when I see the aforementioned formula for shaft horsepower without mention of the (implied) units... In this case the only unit that wasn't stated in the formula was torque, which would need to be input in ft*lbs for the equation to work.

Of course ft*lbf was stated in the example calculation, just not in the formula...

Okay, we can go though the whole sheeml:

Power = Work/time

Horse power is some what arbitrarily defined as:

1 hp = 550 ft*lb/sec

Not 550 ft*lbs of torque per second, but the application of 550 ft*lbs of work in one second, or the application of 550 lbs of force over a distance of one foot in one second.

But since our engine rotates the force it applies is a in the form of a moment or torque and its speed is relative to the unit circle, we need to convert RPMs to radians/second. So we multiply by 1 minute/60 seconds * 2Pi radians/revolution which gives us:

hp = torque(in ft*lbs) * Revolutions/minute * 1/550 * 1 minute/60 seconds * 2Pi radians/revolution

For convenience we want to keep power in terms of RPM and ft*lbs of torque, so we do some house keeping, so we end up with:

hp = torque(in ft*lbs) * revs/minute * 2Pi minutes /(550*60 seconds)

Collect our units and we end up with:

hp = torque(in ft*lbs) * RPM * 1/(5252.11) (minutes*radians)/(seconds*revolutions)

Radians are dimensionless and the minutes and revs cancel, apply our deffinition of hp, and our final solution is:

hp = torque * RPM * 1/5252 (hp)

Are ya happy now?

[ivymike1031]

yep.


I'm sure you would believe the number of people I've run into online who think that the "5252" is somehow fundamentally linked to calculating power for a shaft (other units? what other units?)...