How can an S2000 or similar car pull to 9000rpms and still idle?
04-26-2004, 07:59 AM
#41
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Volumetric efficiency is the most important determining factor in how fast the motor will spin under acceleration. Light weight components and shorter strokes help. The wrong setup can limit the rpm the motor. But lighter valvtrains and shorter strokes don't automatically add up to high revs.
Some exotic examples...
eg. Ferarri Enzo 6.0 litre V12 92mm bore x 72mm stroke 6600Bhp at 7800rpm.
eg. Lamborghini Murcielago V12 6.2 litre 87mm bore x 86.8 stroke 580Bhp at 7500rpm. ( this motor is almost square )
eg. 2003 BMW M3 CSL 3.2 Litre I6 87mm bore x 91mm stroke 360Bhp at 8000rpm. ( this motor is bottom heavy!!! )
None use forced induction either.
Of course the variable valve timing helps, but the main thing is how well you can get air/fuel in, burned, and out of the combustion chamber. The two cams per head also allow more flexibility with cam profile than having one cam alone. Add in the ability to change the advance/retard on the intake cam and now you can adjust for a sloppy idle. By ( if memory serves ) advancing the intake cam you build more low end power and create less overlap, less lope. And yes overhead cam engines have much more efficiency at higher rpm's due to the fact that they have two or three intake valves and two exhaust valves. Not to mention the much larger ports and less involved parts eg. no pushrods or rockers. Usually just cam "followers", hydraulic or solid. They are also typically a hemispherical combustion chamber which locates the spark plug in the center of the chamber allowing for quicker flame propagation upon ignition. Very even burn, very good efficiency. This is why the "hemi" engine has so much potential and is used in venues such as top fuel competition. And of course your aunt's Durango.
And even though I made an argument for overhead cams, I'll still take an LS1 any day of the week and twice on Sunday!!!
Some exotic examples...
eg. Ferarri Enzo 6.0 litre V12 92mm bore x 72mm stroke 6600Bhp at 7800rpm.
eg. Lamborghini Murcielago V12 6.2 litre 87mm bore x 86.8 stroke 580Bhp at 7500rpm. ( this motor is almost square )
eg. 2003 BMW M3 CSL 3.2 Litre I6 87mm bore x 91mm stroke 360Bhp at 8000rpm. ( this motor is bottom heavy!!! )
None use forced induction either.
Of course the variable valve timing helps, but the main thing is how well you can get air/fuel in, burned, and out of the combustion chamber. The two cams per head also allow more flexibility with cam profile than having one cam alone. Add in the ability to change the advance/retard on the intake cam and now you can adjust for a sloppy idle. By ( if memory serves ) advancing the intake cam you build more low end power and create less overlap, less lope. And yes overhead cam engines have much more efficiency at higher rpm's due to the fact that they have two or three intake valves and two exhaust valves. Not to mention the much larger ports and less involved parts eg. no pushrods or rockers. Usually just cam "followers", hydraulic or solid. They are also typically a hemispherical combustion chamber which locates the spark plug in the center of the chamber allowing for quicker flame propagation upon ignition. Very even burn, very good efficiency. This is why the "hemi" engine has so much potential and is used in venues such as top fuel competition. And of course your aunt's Durango.
And even though I made an argument for overhead cams, I'll still take an LS1 any day of the week and twice on Sunday!!!
04-26-2004, 08:20 AM
#42
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04-26-2004, 04:18 PM
#43
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i think theres something you guys are missing in terms of how many pistons. more pistons means smaller pistons for a given displacement. therefore you have less rotating mass per piston. if you had a 3 liter 4cyl and a 3 liter 10cyl right next to each other, the 10cyl would be able to rev much higher (with all else =) simply because there is less mass in each individual piston. so having more pistons for a given displacement theoretically allows a higher redline. you guys talking about how you couldnt rev a bike as high if it had more pistons seem to have this backwards and i'd just like to point out that if you had less pistons and the same displacement THEN you wouldn't be able to rev as high.
