I'm not a car expert, so please bear with me. I've always thought that engine size is a reflection of how much gasoline the car consumes. Horsepower is how much power it puts out. If that is so, why are there some cars with 1.8L engines that can put out 180HP (such as the upcoming Pontiac Vibe/Toyota Matrix), and others with ~4L engines that only put out 190HP (such as the Ford Mustang)? Is there a particular benefit to not 'maximizing' the amount of horsepower that an engine puts out? Does it lead to gasoline wastage? I don't think cost is a factor, because now there are high performance 4 cyllinder 1.8L turbocharged engines on cars like Volkswagens and Toyotas (not just BMWs and Audis).
Car Question: Relationship Between Engine Size and Horsepower
- Thread starter Shantanu
- Start date
engine displacement and horsepower are linked, but there are variables. a small displacement 4cyl(say 1.8L) may put out 100hp/L of displacement, but that's because it's more efficent than say, the 8L V10 of a viper, which(if memory serves me correctly) gets 50hp/l. if the engine has forced induction(eg. turbo charger) the hp/L ratio will rise. the compression ratio may be higher in the 4cyl, which will give it more hp as well. the 4cyl will also reach it's peak power at a much higher RPM than the V10. one of the factors(i think) is that a larger engine has more power wasted to friction, there are more cylinders that have to move, a longer crank shaft, more cam shafts etc. and for some reason my thought has ended, if i remember what i was going to put i'll edit this post 
There are all sorts of factors that have a direct relationship to increased horsepower: 4 valves/cylinder, turbo/supercharging, variable valve timing, etc... However, it is not always advantageous for every car company to always use these things. There are definite trade-offs. The rule of thumb for most add-ons is that they will increase horsepower, but reduce engine-life and cause increased wear. Some enhancements will also reduce gas mileage. The price of these improvements must also be factored in. If I'm creating an economy car, then high MPG, low operating costs, and low purchase cost are more important than increased horsepower. Also, most purchasers of cars like the Ford Mustang would rather have a simpler engine layout (that they might be able to work on themselves) as opposed to a packed-in, high-$$$ bleeding edge engine. Does any of this make sense?
ShizNitz - the SOHC/DOHC 289's are pretty fricking hard to work on. (At least when compared to the 302) The reason the 3.8 only puts out a measly 190 is to be an insurance beater.
Just remember NO MATTER what, there is NO REPLACEMENT FOR DISPLACEMENT.
You toss one of those Super dooper Supra motors in something like my truck it don't matter how much horse it has, it will not move my 5300lb beast for crap. The Viper doesn't get much HP per litre from the factory but there are guys I've seen go on the Dyno and their Torque Literally goes off the chart on small shop dyno's. it's a law of physics, Dodge is limited tho and connot just do that from the Factory,DOT won't allow it.
You toss one of those Super dooper Supra motors in something like my truck it don't matter how much horse it has, it will not move my 5300lb beast for crap. The Viper doesn't get much HP per litre from the factory but there are guys I've seen go on the Dyno and their Torque Literally goes off the chart on small shop dyno's. it's a law of physics, Dodge is limited tho and connot just do that from the Factory,DOT won't allow it.
That's some pretty good info here. I really like the 1.8L Turbocharged engines since they offer pretty good performance and don't eat up too much gasoline. Not that I'm a tree hugger...
Does torque affect acceleration?
Does torque affect acceleration?
Shantanu - yes. Torque is that "my nuts are being pressed against the seat" feeling you get when a car with torque (ie, not an import) launches from a stoplight.
Torque is vital to acceleration, it's the force that gives the car the ability to launch itself.
Viper GTS
Viper GTS
Then what does horsepower do? Is there some kind of mathematical calculus for torque + horsepower that tells me how fast a car will accelerate?
<<
Then what does acceleration do? >>Acceleration doesn't "do" anything. It is what it is, acceleration, the act of accelerating.
Zenmervolt
Elite member
- Oct 22, 2000
- 24,512
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All other things being equal, a larger engine will make more power (HP and Torque), however the key phrase is "all other things being equal". And the increase in power is not linear in size because with increased displacement comes increased internal friction and increased rotating mass. The big benefit to having a larger engine is that the power delivery tends to be more relaxed with more power available in the lower portions of the engine's RPM band, which places the power in the area where for most drivers the engine spends most of its time. A high output, low displacement engine will generally need to rev higher to achieve its power and thus it will more of a chore to drive than a more relaxed large displacement engine. Yes, Torque does affect acceleration to a large extent, and you will feel extra torque on acceleration far more than you will feel extra horsepower.
Zenmervolt
EDIT: If I recall correctly, HP is ft/lbs per second, so HP would be the ability to deliver torque at a sustained rate. (There is a mathematical formula from which you can get either torque or hp if you have the other, but I forget it right now and I have no desire to go looking through back issues of Road & Track to find it.)
Zenmervolt
EDIT: If I recall correctly, HP is ft/lbs per second, so HP would be the ability to deliver torque at a sustained rate. (There is a mathematical formula from which you can get either torque or hp if you have the other, but I forget it right now and I have no desire to go looking through back issues of Road & Track to find it.)
Just remember NO MATTER what, there is NO REPLACEMENT FOR DISPLACEMENT.
You toss one of those Super dooper Supra motors in something like my truck it don't matter how much horse it has, it will not move my 5300lb beast for crap. The Viper doesn't get much HP per litre from the factory but there are guys I've seen go on the Dyno and their Torque Literally goes off the chart on small shop dyno's. it's a law of physics, Dodge is limited tho and connot just do that from the Factory,DOT won't allow it.
My favorite examples are the first Dodge pickups with the Cummins Turbo Diesel engine. It only made 160 HP back then, but it had a solid 400 lb. ft. of forque.
At about the same time, Acura came out with the high performance motor for the Integra. It also had 160 HP if I remember correctly, but it only had 110 - 120 lb. ft. of torque.
Try swapping those engines.
You toss one of those Super dooper Supra motors in something like my truck it don't matter how much horse it has, it will not move my 5300lb beast for crap. The Viper doesn't get much HP per litre from the factory but there are guys I've seen go on the Dyno and their Torque Literally goes off the chart on small shop dyno's. it's a law of physics, Dodge is limited tho and connot just do that from the Factory,DOT won't allow it.
My favorite examples are the first Dodge pickups with the Cummins Turbo Diesel engine. It only made 160 HP back then, but it had a solid 400 lb. ft. of forque.
At about the same time, Acura came out with the high performance motor for the Integra. It also had 160 HP if I remember correctly, but it only had 110 - 120 lb. ft. of torque.
Try swapping those engines.
boost is a good replacement for displacement when you don't have much room to work with. remember the f1 cars used to run on 110+ octane fuel running about 50-70 psi of boost to make their 1.5 litre motors push 1500 horsepower. A big honkin turbo can make a little ole motor do wonders...
I run 20psi (daily driver) on mah vw, is quite fun.
I run 20psi (daily driver) on mah vw, is quite fun.
<<boost is a good replacement for displacement when you don't have much room to work with. >>
True, but boost (whether turbo or supercharging) is basically making the engine think it is larger than it actually is.
An engine is an air pump. The more you can pump through it, the more fuel you can add, therefore the more power you can make.
A small engine can only pump so much air naturally aspirated. But add forced induction and you force more air through than the engine can on its own, and you basically have a bigger engine in a small package. (as long as the internal parts can stand the added power).
Forced induction basically gives people what they really want: A bigger engine. They don't have the room for a V8, so bolt on a blower or turbo, and you have nearly the same thing.
All other things being equal, the larger engine will ALWAYS make more power, IF you have room for it in your car (and budget).
True, but boost (whether turbo or supercharging) is basically making the engine think it is larger than it actually is.
An engine is an air pump. The more you can pump through it, the more fuel you can add, therefore the more power you can make.
A small engine can only pump so much air naturally aspirated. But add forced induction and you force more air through than the engine can on its own, and you basically have a bigger engine in a small package. (as long as the internal parts can stand the added power).
Forced induction basically gives people what they really want: A bigger engine. They don't have the room for a V8, so bolt on a blower or turbo, and you have nearly the same thing.
All other things being equal, the larger engine will ALWAYS make more power, IF you have room for it in your car (and budget).
<< At about the same time, Acura came out with the high performance motor for the Integra. It also had 160 HP if I remember correctly, but it only had 110 - 120 lb. ft. of torque. >>
Still does. The Type-R has like 200 hp, only 130 lbs of torque I think. (Whereas the GS-R has 170 hp, 127 lbs of torque)
- Oct 28, 1999
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Another thing to keep in mind is that 4 cylinder engines have all four cylinders in line IE - inline 4 or I4. Some german cars(BMW), and some luxury Japanese cars(Lexus) have inline sixes vs. the typical V6 configuration. The advantage of having all cylinders in line is that you increase the efficiency of the engine. Someone hinted earlier at the rotations and masses that spinning inside of an engine. The V6 configuration "looses" power with it's inefficiency. All things being equal, a 3 liter I6 will put out better numbers than an equally speced out V6.
Also, to answer your question about HP. HP relates directly to the RPM's an engine can produce. Typically, the higher the redline of a car, the higher amount of HP you can squeeze out of it. It's because of it's ability to run up to 9k RPM's, that the Honda S2000 puts out as much HP as it does with an NA inline 4.
Also, to answer your question about HP. HP relates directly to the RPM's an engine can produce. Typically, the higher the redline of a car, the higher amount of HP you can squeeze out of it. It's because of it's ability to run up to 9k RPM's, that the Honda S2000 puts out as much HP as it does with an NA inline 4.
<<Typically, the higher the redline of a car, the higher amount of HP you can squeeze out of it.>>
This is true, but internal parts can only handle so much rpm. This is where larger engines come into play....they move more air with less rpm than do smaller engines with higher rpm. Everything is a trade off.
This is true, but internal parts can only handle so much rpm. This is where larger engines come into play....they move more air with less rpm than do smaller engines with higher rpm. Everything is a trade off.
So let me get this straight. On a car with high HP, but low torque, you'd have to "put the pedal to the metal" so to speak, to get peak performance (acceleration). On a car with higher torque, you can accelerate at full potential without putting as much strain on your car?
On that note, I've never actually put the pedal to the metal on any cars that I've driven. Sounds risky.
On that note, I've never actually put the pedal to the metal on any cars that I've driven. Sounds risky.
There's more than one way to get torque. The brute force way is with more displacement. Torque is always there and plenty of it. However, having a small displacement doesn't automatically mean you'll not have much torque. One can mate a small displacement but high reving engine with a tranny geared for high torque. To use much of that torque, though, you'll need to rev like a bastard.
<< boost is a good replacement for displacement when you don't have much room to work with. remember the f1 cars used to run on 110+ octane fuel running about 50-70 psi of boost to make their 1.5 litre motors push 1500 horsepower. A big honkin turbo can make a little ole motor do wonders...
I run 20psi (daily driver) on mah vw, is quite fun. >>
Yep My daily driver just hit 14.93 here which is a 13.93 at sealevel, not bad for a 4x4 Extended cab 5300lb truck
Mine has 8lbs of boost from a positive displacement SC
<<There's more than one way to get torque. The brute force way is with more displacement>>
<<Torque is always there and plenty of it. However, having a small displacement doesn't automatically mean you'll not have much torque.>>
Disagree. There is NOT always plenty of torque. Having small displacement DOES mean you'll not have as much torque as a larger engine.
The ONLY way to have more torque, is to have more horsepower. They are directly connected.
If, for example, you have 300 hp at 2000rpms, there's no way you can drop horsepower to 285 and not have less torque.
Generally speaking, the reason bigger engines have lower horsepower and more torque is because even though their HP peak may be lower than a smaller engine, the peak comes at a much lower rpm, therefore producing more torque.
That's why you can have a 400 HP big block 454 cid engine that has 550 lb/ft of torque, but a 400 HP 350 might have only 385 lb/ft of torque.
Reason? Because the 454's HP peak will be at a lower rpm than the 350, and therefore will be more useable....in other words, you can FEEL it better.
That's what I was talking about earlier regarding forced induction. That is a way of forcing more air into an engine, which has the effect of making the engine put out power like a larger engine. Supercharging, turbocharging, and nitrous all are types of forced induction. They force more air into the engine than is possible for the engine to suck in on its own, and basically make it a larger cubic inch engine.
<<Torque is always there and plenty of it. However, having a small displacement doesn't automatically mean you'll not have much torque.>>
Disagree. There is NOT always plenty of torque. Having small displacement DOES mean you'll not have as much torque as a larger engine.
The ONLY way to have more torque, is to have more horsepower. They are directly connected.
If, for example, you have 300 hp at 2000rpms, there's no way you can drop horsepower to 285 and not have less torque.
Generally speaking, the reason bigger engines have lower horsepower and more torque is because even though their HP peak may be lower than a smaller engine, the peak comes at a much lower rpm, therefore producing more torque.
That's why you can have a 400 HP big block 454 cid engine that has 550 lb/ft of torque, but a 400 HP 350 might have only 385 lb/ft of torque.
Reason? Because the 454's HP peak will be at a lower rpm than the 350, and therefore will be more useable....in other words, you can FEEL it better.
That's what I was talking about earlier regarding forced induction. That is a way of forcing more air into an engine, which has the effect of making the engine put out power like a larger engine. Supercharging, turbocharging, and nitrous all are types of forced induction. They force more air into the engine than is possible for the engine to suck in on its own, and basically make it a larger cubic inch engine.
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