Let me enlighten some of you engine wizards about horsepower and torque. When you read magazines and listen to mechanics you start thinking that torque and horsepower are two different measures of an engines power. Well, thats not really so,,,torque and horsepower are related,,,once you draw the torque curve your horsepower curve is set also. Horsepower is time related,,,in other words it depends on the speed of the engine ,, torque is not,,its a set value the engine gives and the RPM is recorded so that horsepower can be calculated. In effect an engine with a lot of torgue has low end horsepower. The reason engineers dont talk much about torque is that you can get whatever torque you want depending on the gear ratio. Want a thousand foot pounds,,,, just gear it down,,,even a ten horsepower engine can give you 1000 foot pounds when its geared down. Engineers need a value that tells you what the engine is capable of doing and horsepower does that. Torque as an output,,,is meaningless unless accompanied by a speed,,thus horsepower. Horsepower = Torgue X RPM / 5252
Thus torque and horsepower are always the same at 5252 rpm. So be careful when you talk about an engine that is torquey,,,,its just an engine with more low end horsepower. Torque is important as an engine output ONLY at the dynamometer because after that we can get any torque we need by gears,,,ok ? Steve Ex -Ford Engineer
Using gears to get torque is bad because it brings down your top speed, and the car runs at higher RPM all the time. Forget Gears. Put a Blower on it, roots or a Keene Bell.
So explain to me how a car like the 5.0 can have 300lbs of tq and 225 horse. Yet the new ones have 305(?)lbs and 300 horse. Since the torque is the same, why is the hp different? The rotating speed? Does this make any sense...? lol
Don't let the formula intimidate you. HP is simply proportional to Torque X RPM, and therefore HP rises rapidly as RPM increases. Note this is why a "flat torque curve" still results in a rising HP curve. Note the 5252 is a constant based on James Watt's definition of "horsepower", a term he coined to help people relate to the power generated by the new fangled steam engine which was taking over the duties of plow animals. Also note that this 5252 constant results in HP always equaling Torque at 5252 RPM, which is why the dyno curves always cross at this point (this means HP is always LESS than Torque below
5252 RPM & always GREATER than above 5252 RPM.)
The multiplied result is how a high-rev'ing Ferrari or Lamborghini V12 can produce upwards of 500 hp and "just" 300 ft-lbs of Torque--that is
300 ft-lbs at 8750 RPM! While it's true gearing (and tire size) can determine the RPM the engine will spin at, it's not easily to build a mass-produced V8 or V6 that can rev that high without self-destructing. Also, it would be impractical to expect most drivers to shift 8, 10 or
15 gears (although big rigs have 10 and the new Lexus LS has an 8 speed auto!); therefore automobile engines are designed to produce reasonable "low-end torque", or good torque at low RPM, as well as torque at a reasonably high RPM, which results in high HP. A flat torque curve from
2000 to 5000 or 6000 RPM is considered a good thing for a passenger car.
The way I describe Torque and HP to my kid is...imagine 2 runners; one with strong legs but a long, slow stride and the other can pump his legs very fast. The 1st runner has lots of low-end Torque, but not a lot of HP due to the slow stride ("RPM"). He's like a tractor, he could push your car out of a ditch, but despite even stronger legs, cannot run as fast as the 2nd runner. The 2nd runner's fast stride (high RPM) enables him to have a very high top speed. In other words, his fast moving legs provide enough power to enable him to cover a great distance in a short period of time (distance =F7 time =3D velocity.)
Is that clear? Therefore a typical Mustang GT owner really wants POWER--high Torque at high RPM--not just gobs of Torque. Low end torque is great for initial acceleration off-the-line, or simply smoking your tires; however HP is what determines top speed, as well as how much distance can be covered in each gear. At 3200 RPM, both the 5.0 & 4.6 generate about 180 hp & 300 ft-lbs; at 4200 RPM, the 5.0 peaks at 225 hp (at a falling 281 ft-lbs torque), while the 4.6L still-climbing torque results in 260 hp. Beyond 5000 RPM, the stock 5.0L simply starts to "run out of steam," well before the much higher rev'ing stock 4.6L. In fact, though torque begins to drop off after 4500 RPM, the muliplied result allows HP to continue to climb (recall that its number becomes even higher than torque beyond 5252 rpm). Thus the 4.6L can produce 300 hp at 5750 RPM, despite making "only" 274 ft-lbs at this engine speed.
In other words, the 4.6L is a damn good engine...which is why it was named one of "Ward's 10 Best Engines" for 2006.
Gotcha. This was VERY imformative. I think we all learned something here.
So, one more question... ;)
We all know we can add heads and an intake, etc, say with a kit from any major manufacturer, and increase the 5.0s horsepower to, say, 300 horse. But, what did we really do when we made these changes? How do these parts change the horsepower on the engine, since the crank is still spinning the same, isn't it?
This is very cool. Thanks for sharing your knowledge.
Don't let the formula intimidate you. HP is simply proportional to Torque X RPM, and therefore HP rises rapidly as RPM increases. Note this is why a "flat torque curve" still results in a rising HP curve. Note the 5252 is a constant based on James Watt's definition of "horsepower", a term he coined to help people relate to the power generated by the new fangled steam engine which was taking over the duties of plow animals. Also note that this 5252 constant results in HP always equaling Torque at 5252 RPM, which is why the dyno curves always cross at this point (this means HP is always LESS than Torque below
5252 RPM & always GREATER than above 5252 RPM.)
The multiplied result is how a high-rev'ing Ferrari or Lamborghini V12 can produce upwards of 500 hp and "just" 300 ft-lbs of Torque--that is
300 ft-lbs at 8750 RPM! While it's true gearing (and tire size) can determine the RPM the engine will spin at, it's not easily to build a mass-produced V8 or V6 that can rev that high without self-destructing. Also, it would be impractical to expect most drivers to shift 8, 10 or
15 gears (although big rigs have 10 and the new Lexus LS has an 8 speed auto!); therefore automobile engines are designed to produce reasonable "low-end torque", or good torque at low RPM, as well as torque at a reasonably high RPM, which results in high HP. A flat torque curve from
2000 to 5000 or 6000 RPM is considered a good thing for a passenger car.
The way I describe Torque and HP to my kid is...imagine 2 runners; one with strong legs but a long, slow stride and the other can pump his legs very fast. The 1st runner has lots of low-end Torque, but not a lot of HP due to the slow stride ("RPM"). He's like a tractor, he could push your car out of a ditch, but despite even stronger legs, cannot run as fast as the 2nd runner. The 2nd runner's fast stride (high RPM) enables him to have a very high top speed. In other words, his fast moving legs provide enough power to enable him to cover a great distance in a short period of time (distance ÷ time = velocity.)
Is that clear? Therefore a typical Mustang GT owner really wants POWER--high Torque at high RPM--not just gobs of Torque. Low end torque is great for initial acceleration off-the-line, or simply smoking your tires; however HP is what determines top speed, as well as how much distance can be covered in each gear. At 3200 RPM, both the 5.0 & 4.6 generate about 180 hp & 300 ft-lbs; at 4200 RPM, the 5.0 peaks at 225 hp (at a falling 281 ft-lbs torque), while the 4.6L still-climbing torque results in 260 hp. Beyond 5000 RPM, the stock 5.0L simply starts to "run out of steam," well before the much higher rev'ing stock 4.6L. In fact, though torque begins to drop off after 4500 RPM, the muliplied result allows HP to continue to climb (recall that its number becomes even higher than torque beyond 5252 rpm). Thus the 4.6L can produce 300 hp at 5750 RPM, despite making "only" 274 ft-lbs at this engine speed.
In other words, the 4.6L is a damn good engine...which is why it was named one of "Ward's 10 Best Engines" for 2006.
An IC engine is an air pump. Whatever you do to pump more air through the engine will increase the resulting power (assuming you keep the optimal fuel:air ratio and don't blow the engine).
Superchargers and turbos increase the air pressure at the engine inlet and, therefore, increase the air flow, resulting in more power -- sometimes *lots* more power. Better heads reduce the resistance to air flow through the engine and, therefore, increase the air flow (mostly at higher RPM), resulting in higher max. RPM and more high-RPM power, but little impact on the low-end. Better exhaust systems decrease the back-pressure on the engine outlet and, therefore, increase the air flow; generally resulting in modest increases in power for a street car.
The MOD that makes the most increase of HP would be the Camshaft. The cam opens and closes the valves. So if you install a camshaft with higher lift and longer duration, you are allowing more air/fuel to enter the combustion chamber, thus more Torque/HP, and usually a higher redline. Heads & intake will help in boosting Torque & HP, but installing a larger cam will usually yield better results. Just remember, the more duration of the cam, the more lopey it will be.
If you intend to drag race, here's something to consider. Pick a combination that will start building torque around the RPM you intend to launch the car at. If you are going to launch at let's say 4000 rpm's, you don't want your torque to peak until after you have already launched. If you build allot of torque before your launch RPM, then your going to need slicks (M/T ET Drags or equivalent) so you don't spin off the line. Allot of people make the mistake of building torque down too low, then wonder why they can't get traction at the drag strip.
But to answer your question, what you've actually done was raise the upper RPM limit, thus more HP.
I'm not too sure new cams will make a significant difference with an '07 Mustang. Bob is absolutely correct in calling an internal combustion engine essentially an "air pump." The entire air path from intake to exhaust plays a role in the efficiency of this "air pump." The cam profile, albeit important, is just one piece of the puzzle. Since the '05+ 4.6L uses the valve head from the larger 5.4L Triton motor, air flow from the throttle body to the cylinders really isn't a problem. Furthermore the new S197's variable valve timing and sophisticated computer optimizes valve lift & timing to produce strong low-end torque as well a free-breathing for more HP at high rpm.
The new Mustang's exhaust is well-done as well, perhaps one of the finest stock exhausts in a mass production car. The stock cat-back plumbing is 2-1/2" mandrel-bent (smooth bends for better flow) with an H-pipe. The mufflers are a high-flow design and the cast header flows nicely as well. Aftermarket exhausts can change the sound of your Mustang, but don't expect any difference at the dyno, unless you remove the cats (worth about 15-20 hp).
It's been pretty well-documented that the weak link in the Mustang's "air pump" is the air filter & box. By far the best bang-for-the-buck mod on a S197 GT is a cone filter with a computer retune. The JLT intake with SCT2 tune (93 octane) netted me nearly 30 rwhp (292 rwhp vs. 265 stock)! After that gains are much more incremental due to the Mustang's well-designed stock motor and exhaust. Tweaks such as underdrive pulleys, "off-road" (no cat) X-pipe, headers, mufflers, etc. can nudge an S197 GT eventually to around 310-315 rwhp; but to leap significantly beyond that, you need to force-feed the motor via a blower, turbo, or nitrous.
W> > So what camshaft would you recommend for an 07 GT?
I'm not too sure new cams will make a significant difference with an '07 Mustang. Bob is absolutely correct in calling an internal combustion engine essentially an "air pump." The entire air path from intake to exhaust plays a role in the efficiency of this "air pump." The cam profile, albeit important, is just one piece of the puzzle. Since the '05+ 4.6L uses the valve head from the larger 5.4L Triton motor, air flow from the throttle body to the cylinders really isn't a problem. Furthermore the new S197's variable valve timing and sophisticated computer optimizes valve lift & timing to produce strong low-end torque as well a free-breathing for more HP at high rpm.
The new Mustang's exhaust is well-done as well, perhaps one of the finest stock exhausts in a mass production car. The stock cat-back plumbing is 2-1/2" mandrel-bent (smooth bends for better flow) with an H-pipe. The mufflers are a high-flow design and the cast header flows nicely as well. Aftermarket exhausts can change the sound of your Mustang, but don't expect any difference at the dyno, unless you remove the cats (worth about 15-20 hp).
It's been pretty well-documented that the weak link in the Mustang's "air pump" is the air filter & box. By far the best bang-for-the-buck mod on a S197 GT is a cone filter with a computer retune. The JLT intake with SCT2 tune (93 octane) netted me nearly 30 rwhp (292 rwhp vs. 265 stock)! After that gains are much more incremental due to the Mustang's well-designed stock motor and exhaust. Tweaks such as underdrive pulleys, "off-road" (no cat) X-pipe, headers, mufflers, etc. can nudge an S197 GT eventually to around 310-315 rwhp; but to leap significantly beyond that, you need to force-feed the motor via a blower, turbo, or nitrous.
W> > So what camshaft would you recommend for an 07 GT?
Well sure, just like a 5.0, if you expect cam/cams to make more than a little a difference you have to do something with the heads and the intake manifold.
Sorry for taking so long to reply. I've been extremely busy lately.
As for what camshafts I'd recommend, anything with more lift & duration than the stock cams. Think about it. What happens with more lift and duration in relation to air/fuel flow? Hmmm... The air/fuel has a longer chance of entering the combustion chamber. The trade off though is a lopey idle. A cam swap is much more cheaper than doing a head swap any day. If your looking to swap the cams, look at the specs for the cams. The main 2 things to look at is the operating range and the max rpms. If you are looking to mainly drag race your car, you definitely don't want a cam that starts working (read start making gobs of torque) way below the rpm you intend to launch the car at. An example would be you intend to launch the car between 3500 & 4000 rpms. I would look for a cam that starts working around 3000 rpms or a tad higher. This way you will have a better chance of getting the car to hook up. Now some will tell you that the best way to increase HP is to install a blower on it. Yea, that's true, if you have bottomless pockets and don't care where your throwing your money. If your looking for the best bang for your bucks, a cam swap is the best route.
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