Ain't no replacement for displacement?

[gangajas]

What do you prefer, that fat power curve of the Corvette or those final revs of the RS4?

[gucom]

not having driven any kind of high-powered car, i gotta say the advantages of torque do sound pretty good to me, although high-tech does as well... why not the AMG 6.3l V8, which has revs AND displacement?

[RC45]

Without seeing the Torque curves, the power curves do not show the entire picture.

Besides, what has any of this got to do with displacment?

Both engines are pretty much the same displacement

Gasoline has the same potential energy all over the world and in all cars - oxygen has the same combustion properties pretty much everywhere - and apart from a some minute differences in friction loss, it takes the same amount of fuel and air to make 1hp in Germany as it does the US (allowing for atmospheric variations).

So - having said that - it stands to reason and is obvious that there is NO replacement for displacment - the revs, cam, stroke vs bore simply dictate when and how the power is delivered - but the power all tkaes the same displacement to produce.

Lets see who can figure out how all enginesproducing similar power are all the same displacement

[gangajas]

Originally Posted by RC45 Besides, what has any of this got to do with displacment? Both engines are pretty much the same displacement

It's 4.2l vs 6l and it shows

[TNT]

a better comparision is a RX8 vs a 350z

[nthfinity]

Originally Posted by TNT a better comparision is a RX8 vs a 350z

While the wankle engine may technically only be 1.3 liters... the meathod of creating power is different... I read a good article comparing the wankel's to piston driven engines in racing a while back.

Still

The RX8 makes very little hp, and very little torque, the 350 is better in both aspects

[5vz-fe]

*EDIT* nevermind

[gucom]

Originally Posted by RC45 Without seeing the Torque curves, the power curves do not show the entire picture.

true

Both engines are pretty much the same displacement (...)Lets see who can figure out how all enginesproducing similar power are all the same displacement

as gangajas said, the 'vettes engine is 1.43 times as large as the audi's, so almost 1.5... yet they make nearly as much hp so somewhere there must be a difference. F1 engines are 2.4 litres, so by your reasoning a 'vettes engine should, purely based on size, make some 2250hp...

Gasoline has the same potential energy all over the world and in all cars - oxygen has the same combustion properties pretty much everywhere

exactly... potential energy, but not every bit of it is used (far from it), hence advanced injection techniques make such a difference, they make the burning process that much more efficient.
On the displacement / revs discussion, since im not a technician i looked it up on wikipedia here's a summary:

The amount of power generated by a four-stroke engine is proportional to its speed.(...)An engine where the bore dimension is larger than the stroke is commonly known as an oversquare engine; such engines have the ability to attain higher rotational speed since the pistons do not travel as far. Conversely, an engine with a bore that is smaller than its stroke is known as an undersquare engine; such engines cannot rotate as quickly, but are able to generate more torque at lower rotational speeds.

the formula for power (be it Kw, hp or whatever unit) is: Torque * 2Pi * rpm. As you can see both the torque developed by an engine and the revolutions per minute it makes are variables, meaning the same power can be generated by a theoretically infinite number of combinations of torque and rpm

[nthfinity]

actually... the being that the power is dependant on RPM, is not power also dependant on the volume of air over xx amount of time to come in? on a "bigger displacement" engine, that engine RPM is lower with a said volume of air, and in a smaller higher revving engine, it requires a higher rpm to combust a said volume of air in xx amount of time...

[gucom]

i calculated some VERY ROUGH torque figures from the graph and formula above, i interpreted the graph with a book as ruler and the naked eye to determine the exact hp figure, so the torque figure could easily be 10 or 20 ft.lbs higher or lower at some points - but at least it gives the general idea.

in my graph it peaks out at 427 ft.lbs

ps, as far as I can see an excellent explanation on torque and power, for those who want to know it for once and for all (like me, although i'll have to read it again when im not tired to completely understand it ):
http://vettenet.org/torquehp.html

[RC45]

Originally Posted by gucom Both engines are pretty much the same displacement (...)Lets see who can figure out how all engines producing similar power are all the same displacement as gangajas said, the 'vettes engine is 1.43 times as large as the audi's, so almost 1.5... yet they make nearly as much hp so somewhere there must be a difference. F1 engines are 2.4 litres, so by your reasoning a 'vettes engine should, purely based on size, make some 2250hp...

Come now.. think about it...

both those engines are pretty much the same displacement

Come now it is quite logical. A 6l engine will displace the same amount of fuel and air in a given time as a 4.2l engine - If the 4.2l engine spins faster



So - again - the only way an engine makes power, is by combusting a fuel and using the released energy int he combustion chamber to displace the piston which is attached to a con-rod which pivots around a crank.. this crank is turned or "cranked" around by these repeated explosions..

Since we know an Audi engine will not create energy, it can only assist int he converison process - and the amount of energy released by combusting gasoline is a fixed quantity per volume in this example.

So if it is a fixed quantity per volume, you need more volume if youwant more power.

Again - if we know gasoline mixed with air and ignited releases a fixed amount of energy per volume, either move the needed volume by having a big static volume, spinning a smaller volume more times in a given time period or forcing more into the smaller volume as it spins at a slower rate.

So - as much as you dont want to accept the fact, that 2.4l F1 engine yields no more energy from a given volume of the same octane gasoline as a 6.2l Corvette or a 4.2l Audi... it just spins far faster in the time period - thereby behaving like a larger capacity slow spinning engine and as result makes way more power.

So (if my math is correct) in a minute, that 19,000 rpm 2.4l F1 displaces 11,400l, while a 6500rpm 6.2l Vette displaces only 8500l... and surprise, the 4.2l 8000rpm Audi displaces about 8500l as well.

Lets spin the Vette to 7400rpm (if my math is correct ) and I am sure it will displace 11,400l as well - and probably make about the same power as the F1 motor...



Now the engineering tricks are to either spin an engine at an insane rpm level or make it so that at a smaller displacement it can get more air/fuel ina an out as fast as possible even at lower rpms and remain reliable etc.

But at the end of the day with allowances for differences in efficiancy and such like, if as an example 3 egines all produced 300bhp - they would essentially all consume the same amount of air/fuel in a given time period - one might be very small displacment, very high revving and be turbo charged to get the required volume of air/fuel through, the other one might be a large displacemnet brute spinning slowly and gulping a few times to move the given amount of air/fuel, and the third might be a medium displacment engine spinning faster than the big one but less than the tiny one.

But still, they would all need to move the same amount of air/fuel int he given time period to produce the power.

Now remember this power production still has been multiplied by a transmission and delivered to the road for "driving pleasure" - we are just discussing engine power production.

[RC45]

Originally Posted by phatbimmer BOOST!!!! 0X

Which simply forces more air/fuel inot the engine at each revolution - but in the end, you still move the SAME volume of fuel air over a given time to produce the same power in different engines.. meaning at the end of the day, similar power engines are there for similar displacement

[gucom]

RC what you're saying sounds logical, but could u give the calculations u used for the # of liters shifted per minute plz? cos i cant really recalculate them...

PS if we're talking about a large displacement engine we sure aint talking about a 1l motorcycle engine screaming at 10k revs...

[pagani]

Displacement and forced induction is the ulimate combo.
8)

[nthfinity]

Originally Posted by pagani Displacement and forced induction is the ulimate combo. 8)

Depends on what you want.... throttle responce is very important in circuit racing...

why did turbo cars start winning in F1? the power overcame the difficulties of lag... and the restrictions aided the turbo era...