Why do big engines make cars go faster, even though the only rev up to the speed of normal engines?

Question

I can see that they would have higher torque delivery, but why would a four-banger with a 5,500 redline not go just as fast as a v-8with the same redline? Links, opinions (supported by FACTS and examples are all highly appreciated.

Answer 1

common misconception = red lines are set where the engine cant go any faster, red lines are set for many reasons, some times for engine life, sometimes it is set so a customer cant feel an awefull vibration that occures in the next 1000 rpm, there are cases where a factory set a redline smack dab in the middle of a cars powerband, sometimes its set for fuel echonomy,

a 5 leater v8 means that car used 5 leaters of gas vapor to fire all 8 cylinders, where as your 2.5 leaer 4 uses you guessed it half the gas with half the cylinders, so the v8 is generating more power, because of the more power it used longer gearing

example = 4 m80s under a coffee can vs 8 m80s under a coffee can witch one is going to hit the ceeling first?

and there in lies the other big miscnception = engine equals speed, gearing has as much to do with speed as horse power, if you want to get technical its all about newtons and jules, a bigger engine has more power and torque so it can get through a longer gear, reaching second gear at a higher speed than the 4 cylinder, and every gear you add widdens the diffrence

example = no car on the market not the mclaren f1 not the ferrari enzo or even the bugatti veyron has as much power and displacement as even the smallest 18 wheeler semi but it doesnt gear for speed it gears for pulling power, another example is the dodge srt viper and the srt pick up, both use the same engine but the viper is geared for speed and only has enough weight to make it comfterable to drive, the truck is geared for pulling a load and is reinforced with enough steel that the truck can pull what the engine is capable of with out destroying the body

Answer 2

I could spend hours on this subject. The power you are capable of generating is dependant upon the amount of fuel you are capable of burning. The Four banger would probably have a capacity of around 2 litres the V8 is likely to have a capacity of 5 litres and over. If they are both doing the same amount of revs the V8 is probably burning more than twice the amount of fuel, and therefor releasing around twice as much chemical energy in the burning process.

http://science.howstuffworks.com/fpte5.htm

This will give you an idea about how the engine displacement effects the power characteristics.

Turbocharging of small motors is a method by which people try to get big horsepower from small motors. This again is an attempt to burn more fuel. The air is pressurised by the turbo the end result being that you have more air occupying the same volume. This means that you can then add more fuel to the mixture and burn larger amounts in the same sized cylinder.

Cars that rev a lot tend to have a very high power output ( KW or BHP) whereas cars with big displacement that don't rev a lot tend to have much bigger torque. A perfect example of this is in race cars. Formula 1 cars have somewhere in the region of 800 horsepower and around 450NM of torque( this differs with manufacturers) and rev out to 18,000 rpm. The NASCAR Motors this year have around 705NM (520 lb-ft) of torque with a red line of around 8200rpm.

The below links will give you an idea of the relationship between engine revs, torque, and powever delivery and also some information on large capacity performance motors
http://www.mustangsandmore.com/ubb/DanJonesTorqueVsHP.html
http://www.circletrack.com/techarticles/ctrp_0704_nascar_new_motor/

Answer 3

It's way more involved than that. Formula 1 has some of the smallest displacement engines in racing, but some of fastest cars on the planet. Bigger engines don't always mean a faster car, but with both engines at the same rpm, a V8 has twice as many cylinders making power, accelerating the car quicker. The biggest thing to watch is the power to weight ratio. A light car with a powerful engine is the goal.

Answer 4

They have more torque behind them and it makes more power to turn the wheels faster. A four banger takes a while to build up the torque to go fast where as the v-8 already has the power/torque on tap. You dont need wait for v8 power.

Answer 5

A 4 cylinder has smaller pistons which recieves less compression. They may be able to accelerate faster than a V8 because the engine is smaller and it takes less time to make a full revolution. On a V8 it has slower acceleration due to the size and extra weight but when it reaches higher RPM it has twice the power of a 4 cylinder thus giving it higher top end power and torque, giving it a higher top speed.

Answer 6

There are 2 ways to make more horsepower. Increase torque or increase work speed(rpm). V8's are large engines and make more torque so they dont need to run at extreme RPM's to make a lot of power. I4's are small and lack the ability to make a lot of torque but as we see on many Jap cars they can rev very high and make a lot of power for their size. High engine speeds mean more wear because its doing more work.

Many American's prefer the big engines because they make power at low engine speeds without having to downshift (less than 3k RPM) where small engines you need to be high RPM (over 4k RPM) which means you have to downshift 1 or 2 gears before you can go.

The old saying is there is no replacement for displacement (except FI but thats a whole different explaination).

Torque x RPM / 5,252 = HP.

Examples:
04 Honda S2000 - 240 hp @ 7,800 RPM & 161 lb-ft @ 6,500 RPM (fast but no low end power, you will need to downshift to go fast)
04 Ford Mustang - 260 hp @ 5250 RPM & 302 lb-ft @ 4,000 RPM (much better low end power, less need to downshift to go fast)
Both are about 5.5 sec 0-60 mph but the Mustang is heavier. If you put the Honda engine in the Ford it would be very slow and stuggle to move that much weight.

Answer 7

So your basically talking top speed I assume?

If the same car, weight and final gear ratio is used with a four-banger and with a V8 with the same red-line, and if the V8 is faster than the 4 banger is at top speed then it's simply because the V8 has enough power to overcome the wind resistance at high speed and still be able to reach it's red-line in high gear.

The 4-cyl. simply cant overcome the 'wind' at high speed and cant push the car faster to continue accelerating to its red-line in high gear.

It just comes down to Horsepower.
Yes, Theoretically, both car's should reach the same maximum speed by calculating the gear ratio and red-line RPM etc. to see how fast a car will mechanically "spin up to" maxed out. That's a simple fact of math.

Wind resistance increases the faster you go so it's not that the 4-banger car can't go as fast as the V8 car mechanically, it just doesn't have the horsepower to reach it's limit like the V8 does.

Answer 8

More powerful engine can turn a bigger gear. Two cars racing: Big engine car hits 60 mph in first at 6500 rpm while smaller engine cars hits 35mph at 6500 rpm at the same time. Who is winning? Get it?
Figure the same way in a boat. Big engine boat is running 70mph at 6000 rpm, smaller engine boat can't turn that big propeller to 6000 rpm so it is only going 45mph at 6000 rpm. If you put the big propeller on the small engine it would only be able to go 30mph at 4000 rpm because it can't get enough rpm to reach it's max power rpm.

Answer 9

RPM's have nothing to do with it. If you would like to do a search, (this sounds wierd, but trust me) type in drive now/talk later as a web search. You'll find a bumper sticker link where you can ask all kinds of mechanical questions and get a quick, thorough response.

Answer 10

Two guys, each 6 feet tall. One weighs 300 lbs.and the other weighs 150.Which one can lift more weight? Same principal.