I used to think I understood the relationship between horsepower and torque, but lately I’m not so sure. I used to believe that almost anything you did to increase the horsepower of an engine would very likely raise the power peak at the expense of reducing the available power at other RPMs.
My questions:[list=1][li]what makes an engine “torquey” at low RPMs, compared to an engine with identical displacement but a “peakier” power curve?[/li]
[li]When tuning an engine (intake/exhaust headers, cams, etc.) does broadening the powerband result in less total efficiency?[/list=1][/li]
I’m not certain I even asked the questions I’m trying to find the answers to. Feel free to go on at length. I’m willing to learn.
Horsepower and torque aren’t directly related in a strict sense. Consider two engines of identical displacement. Slight differences in bore, stroke, type of cam and crank, et cetera will result in different power bands. The entire combination of these factors (and others) determines a breadth and overall yield of horsepower and torque. Certain modifications to an engine in an effort to increase horsepower may or may not result in and increase or decrease in engine efficiency. For example, adding a K&N filter will increase horsepower and engine efficiency because the air in the fuel and air mixture is cleaner. I know this answer is a bit vague, but so is the question. Can you ask something a bit more specific?
Lots of tuning methods are tuned to a specific engine speed which of course means they aren’t tuned as well outside of that narrow range. This is true of header and intake runner length, valve timing etc. Consider it a tradeoff of one property for another. There are some ways to try go get around this such as variable cam timing. It’s kind of exotic but I remember a bolt on cam gear that was available for VW rabbit/golf engines. It used a centrifugal mechanism much like a distributor but instead of advancing timing it retarded it as RMPs increased. I’m not sure how well it worked but I know from my own experience with a slightly peaky cam and a manually adjustable cam gear that the power band could be manipulated that way.
Efficiency is a nebulouos term. Do you mean power/displacement? power/fuel? power/dollar spent? power/engine life? Remember the two old hot rod shop sayings: There is no substitute for cubic inches and Speed costs money, how fast do you want to go?
Baloo, something else occured to me after reading Nen’s reply. Get a first year physics books and read the chapters that explain the definitions and relationships of force, power, energy and work, that will put things in a much more clear perspective. Torque is a measure of force. It doesn’t become power unless it has a displacement. Work is the result of power moving something.
Note that you want to look at my second post to that thread, not the first. Oh, you can look at the first too. And the third. But the second one has the most info.
