Horsepower vs engine size


#1

I have a '97 Mustang convertible with a 3.8L engine, but the car is only rated at 150 HP. I’ve see several other cars with similar sized engines that have much higher horsepower, so I don’t quite understand the connection between engine size and horsepower.


#2

There are many things that go into extracting power from an engine. For example adding a turbo or super charger will usually give you more power, but at more expense.

It is also true that usable power is not the same as rated power. One car with 150HP may feel much more powerful than another car the same size with 150HP. Differences in gearing and tuning etc. can make a big difference. However remember that nothing is free. Increasing power might cause reduced reliability or mileage.


#3

There are MANY variables that determine horsepower, even among engines of similar displacement. The engineers who design engines must balance power, efficiency, and longevity when they decide how to build an engine.

The engine layout (inline, V, H, etc), the design of the pistons, crankshaft, camshaft(s), cylinder head, intake and exhaust systems, etc, all combine to determine the horsepower, torque, and fuel economy of a given engine.

Displacement is just one factor.


#4

Compare displacemenet/horsepower/RPM. The high horsepower is extracted from very high RPMs at the loss of low RPM torque due to camshaft grinds and porting.


#5

At one time the phrase “there is no replacement for displacement” was very true.

If I had to cite just one development that has made the previous statement untrue today,it would be the use of electronics.


#6

Ford chose to provide 150 HP in that engine. I have a 1998 Buick Regal with 195 HP/220 ft-lbs torque; it was also available with a supercharger at 240 HP/ 208 ft-lbs torque. Your car has 150 HP/215 ft-lbs torque, and Ford considered that adequate for your car. More recently, manufacturers have been successful at getting more horsepower out of their cars. Variable valve timing has helped a lot at providing a wider power band.


#7

Many recent 3.5-3.8l v6s get 250+ hp. They’re much more sophisticated than your 3.8, with DOHC and 4 valves per cylinder, along with 10 years of engine development. And, they probably cost more to make.


#8

To add to the confusion, your engine could be rated several different ways to come up with a wide range of ratings. Size has something to do with power but the type of valve train, fuel system and ignition timing have a lot to do with it. Two engines the same size can be totally different. If you read Engine Builders magazine, you will see what crazy things can be done to get more power out of old V-8 engines.


#9

I’ll also add to this the fact that horsepower isn’t really the best measurement of how powerful a car is. Horsepower was originally meant to describe the power of an engine in an industrial setting, not in a vehicle (can your 1HP go-kart outrun a horse?) and I suspect the reason why it has become the common measure of a car engine’s power has much more to do with the imagery the term evokes than it being the best unit for the job.

I personally think that the torque is more what you feel when you’re just toodling around town and I’ll bet that if you go through and compare the torque ratings of the various 3.8L engines you’ll find they’re all much closer together than their horsepower ratings.


#10

Good point - “people buy horsepower, but use torque.”


#11

I don’t care how much electronics gadgetry you slap on that 3.8L motor. You’ll still be sucking my big block exhaust fumes and admiring my diminishing rear bumper. :wink:


#12

But I doubt you’d walk away from a Nissan GT-R, with its 480 hp (some say much more) 3.8l twin tubo V6…there’s a good example of modern engine development.


#13

I guess you haven’t looked closely at my screen name then, eh?.

But let’s compare apples to apples. Naturally aspirated, all throttle, no bottle, no huffing or puffing, and displacement is still king.

BTW, even my naturally aspirated big blocks are more than 500 hp. Start bolting on the go fast goodies and I can double that. It’s no contest in a horsepower war.


#14

There is a saying that “Horsepower sells cars but torque wins races”.

When I talk to someone about their car, if they quote HP numbers then I ignore them. If someone talks about their car’s torque, I know that they know what they are talking about.

I have raced and beaten (on a dragstrip, mind you) many cars with more HP and less weight. I win because I have more torque. You’re probably not gonna be racing but I think you can see why you shouldn’t all of your faith in horsepower numbers.


#15

In my simple, pragmatic way of doing things, it appears that cutting edge technology is great for bigger egos with deeper pockets than mine. One hundred foot long 100,000 lb semis are pulled along at 75+ mph with 450hp engines. Those Cummins and Detroit and Paccar engines get better than 5mpg as they rumble along, often accumulating 1 million miles before an overhaul. How do high horse power toys compare to that? Does the 3,000 rice rocket go 33 times as far on a gallon of fuel?


#16

Good debate…IMO displacement is the ultimate torque determinant, everything else being equal. Throw in the latest IC advances though, and it’s obvious things aren’t equal from one motor to another; displacement just becomes one of the many factors.
Add the soon to be commonly used electric motor , and this ultimate drive motor will further confuse this debate.


#17

Piston speed is limited to about 1 mile/minute. Compression is limited by available octane. Exotic, high horsepower engines require short stroke design to allow high rpm operation. A 480 hp Nissan GT-R engine will be severly taxed trying to replace the 200hp 4.9L in my pick-up. It wouldn’t even come close to replacing a 450hp Cummins. How long would that Nissan last running at the 480hp RPM range? A world class track star might run at 20+mph, but can he run 20 miles in an hour? The high horse power rhetoric is for bragging rights based on momentary bursts of power, not sustained operation.


#18

I see your point. And, by the same token, how could a 4.9L replace the 480 hp in the Nissan ? Each as you seem to imply, is pretty performance specific. The IC is flexible enough to be engineered for varied demands. An amazing feat when you consider the strangle hold oil has on the transportation business.


#19

The horse power/displacement question which began this thread has been discussed, ad nauseum, for as long as I can remember. I sometimes enjoy throwing my $.02 in. I have found some success in repairing and maintaining and operating vehicles for commercial and private use. In my efforts, I have acquired a great appreciation for those vehicles and power trains which have proven to be reliable and economical while fullfilling their purposes and grand claims in advertising have often been the poorest basis for picking a vehicle. But no, my Ford’s 4.9L and the Nissan engine would not make a happy swap for either vehicle.


#20

Each as you seem to imply, is pretty performance specific

This is the key point. No single specification really means anything when it comes to an APPLICATION. The vehicle is a system of components designed for a specific task. Kinda the reason I poked fun at the HP debate in the first place.

The IC is flexible enough to be engineered for varied demands.

And the engine is but one component in the system. As just one example, the gearing chosen is just as important as the engine. They need to be matched to each other in order to get the best results.