I was told that shorties give you more torque and the long tubes give more horsepower. The rule of thumb is you sell horsepower and drive torque. If thats the case why don't people use shorties more often?

 

IM not sure what you heard is correct, long tubes usually give more HP ant TQ from what Ive seen, read etc. Plus some guys dont come up with any power from long tubes, so why would they try shorties? Next, not last, is that the shorties ive seen for the vette are almost as much as the long tubes. JMHO, :cheers:

 

I think you mean "peak torque" and "peak horsepower". If you have more torque at any RPM, you have more power at that RPM as well. So saying one gives more peak torque and the other gives more peak horsepower is equivalent to saying one gives more torque at low rpm (where it adds to the peak torque value), and the other adds more torque at high rpm (where peak horsepower is, so you get a higher HP figure).

Really you want more torque at all rpm. Imagine one engine that has 300ft-lbs of torque at 7000rpm, and a 8000rpm redline. Compare that to another that has 300ft-lbs at 3500 rpm and a 4000rpm redline. Assume they both have the same rear-end ratio, and transmission ratios of 2:1 in 2nd, and 1:1 in 4th. When the first car is at 7000rpm in 2nd gear, the other car is at 3500rpm in 4th gear (which is the same vehicle speed in each car), both have 300ft-lbs of torque at the engine. Neither car can be in a lower gear than they are, because they are close to redline. The first car will have twice as much thrust, because the gearing multiplies the engine torque value. The first car also has twice as much horsepower, because power~torque*rpm.

The higher the rpm your engine makes torque at the better, because you can use lower gearing to obtain more thrust at the same vehicle speed. And high torque at high rpm means big horsepower, while high torque at low rpm means low horsepower.

Getting back to the header question, I don't think shorty headers make significantly more torque than LT headers at any rpm (not near peak-torque rpm, nor near peak-hp rpm).

 

MIles is correct, especially about the effects of torque and horsepower.

For simplicity's sake, I would add, though, that the general rule is that short tubes work better at high RPMs and long tubes work better at lower RPMs. For this reason many people will say shorties add HP and long tubes add torque, but as you can see from Miles' post, that really isn't true.