damn, I swear I have typed this explanation out like four times but never have saved it . OK, so here's the speech again in layman's terms, hope it covers everything (and accurately)...
HP= a measure of forced over time, where 1 hp is equal to 550 lbs lifted one foot in one second. Expressed in terms of torque, 1 hp equals 550 ft/lbs per second. Noticed this measurement is time based.
Torque= the measure of instantaneous rotational force an engine can produce. Notice this measurement is not time based.
hp= torque x RPM / 5252
torque= hp x 5252/ RPM
With these two basic equations, you can figure out how much hp or torque you have at a given RPM with either measurement. Notice that because of this equation, an engine can NEVER make as much hp before 5252 RPM as it can torque, and the opposite is true above 5252 RPM. Any dyno chart you ever see where the two plotted curves don't cross at 5252 RPM is a bogus dyno chart.
What's important to understand as this pertains to vehicles is that hp is not a direct determinate to accelerative ability. Horsepower is more a way of easily summarizing the abilities of a car, but not an exact or necessary thing. Horsepower is basically a way of stating torque with gearing already taken into account, which makes the pain of figuring out torque multiplication factors less needed for generalized performance figures. Here's the three most important factors in determining how fast a car can accelerate...
-effective torque at the wheels
-overall vehicle weight
-available traction
-total drag (constituted mainly of aero drag at speeds above 50mph)
Since we are just talking about differences in power and how it effects acceleration, we can basically toss out everything except torque since the others can be assumed to remain constant(please remember this is just a simple hypothetical). So now you need to understand what torque multiplication is, and here's an excerpt from an older post I made on the subject...
"What this all means comes into focus when you understand the concept of torque multiplication.
Torque is the only productive force that an engine creates, so when talking about acceleration
relative to gearing this is all that matters. Torque multiplication takes the torque output of the
engine at any specific RPM and multiplies it by the overall gear ratio (think of this as gear
reduction) to show us how much torque is actually being transmitted to the wheels at any given
speed and in any given gear. An example:
Engine A is making 150 ft/lbs of torque at 3000 RPM, and is in our earlier hypothetical 1st gear
which has a ratio of 3.42:1 and a final drive of 4.27:1.
Effective torque at the wheels @ 3000RPM = 4.27 x 3.42 x 150...
which equals 2,190 ft/lbs of torque to the wheels! Ever wonder why acceleration is always better
in lower gears than higher gears? That's why. The true accelerative ability of a car is defined by
these laws, and in the most pure sense torque at the wheels is all that matters (meaning HP is
not directly important or a determinate of potential speed). "
So knowing all this new stuff, you should be starting to see the big picture. Now you have the
definitions of horsepower, torque and torque multiplication, along with a basic understanding of
what they mean. All the concepts surrounding this haven't been covered here, so if anything isn't
clear or I forgot something important please just say so, and either I or someone else can fill in
the blanks. Hope this helps, peace