SOCH vs DOCH
04-30-2006, 10:29 AM
#26
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2001 ML320 E, 2003 C230K Sport Sedan
But then, the 271 was 1/2 litre smaller engine......., nearly equal in performance, and smother running, it was a leap ahead in engine technology. New Seimens ECM control, etc.
Yes it was a long awaited upgrade, so was the new V6 & V8.
Yes it was a long awaited upgrade, so was the new V6 & V8.
Last edited by fasteddie; 04-30-2006 at 10:41 AM.
04-30-2006, 04:15 PM
#27
You can run as many valves as you want using SOHC or even OHV, the cam just gets very complicated. I believe Mitsubishi circulated photos of the cam it uses in its SOHC variable timing engine.
DOHC has a couple of advantages.
1. As someone else pointed out, you cannot independently vary intake and exhaust timing unless you're using a VTEC type system, where a separate cam load is used at higher RPM; most variable timing systems work by retarding or advancing the entire cam.
2. DOHC allows the angle between the valves to be greater, creating more of a pentroof chamber. Back in the 1980s Toyota had DOHC 2V engines for just this reason. You get a more spherical combustion chamber this way, yielding more power and efficiency.
DOHC has a couple of advantages.
1. As someone else pointed out, you cannot independently vary intake and exhaust timing unless you're using a VTEC type system, where a separate cam load is used at higher RPM; most variable timing systems work by retarding or advancing the entire cam.
2. DOHC allows the angle between the valves to be greater, creating more of a pentroof chamber. Back in the 1980s Toyota had DOHC 2V engines for just this reason. You get a more spherical combustion chamber this way, yielding more power and efficiency.
04-30-2006, 06:01 PM
#28
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2001 ML320 E, 2003 C230K Sport Sedan
Originally Posted by e1000
I believe F1 uses pneumatic valves due to the 18,000 to now 20,000 rpm they achieve.
F1 Got rid of the Valve springs about 5 or 6 years ago. They are using a pneumatic cylinder around the valve instead of the typical spring. The valves are still actuated by camshafts (by F1 rules), and closed by air pressure. The typical setup (today) is DOHC 32 Valve V8, 2.4 litre, about 850 HP (on European pump gasoline!!!!). RPM is up to 20,000 so far this year, probably 21,000 before the year is out.
Up until about 7 or 8 years ago, the hot F1 setup was probably the 5 Valve (3 intake). I believe it was to try to minimize the mass of the intake valves, and reduce the weight of the valve springs (trying to get the RPM up. more RPM = more HP). This was to avoid broken springs and Valves due to oscillations and shock waves traveling in the springs at the higher RPM.
Seems that big valves are hard to control above 13,000 RPM.
Check out the guy with no hearing:
http://video.google.com/videoplay?do...816484801539&q
ed
04-30-2006, 06:16 PM
#29
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a quarter mile at a time
Originally Posted by fasteddie
F1 Got rid of the Valve springs about 5 or 6 years ago. They are using a pneumatic cylinder around the valve instead of the typical spring. The valves are still actuated by camshafts (by F1 rules), and closed by air pressure. The typical setup (today) is DOHC 32 Valve V8, 2.4 litre, about 850 HP (on European pump gasoline!!!!). RPM is up to 20,000 so far this year, probably 21,000 before the year is out.
Up until about 7 or 8 years ago, the hot F1 setup was probably the 5 Valve (3 intake). I believe it was to try to minimize the mass of the intake valves, and reduce the weight of the valve springs (trying to get the RPM up. more RPM = more HP). This was to avoid broken springs and Valves due to oscillations and shock waves traveling in the springs at the higher RPM.
Seems that big valves are hard to control above 13,000 RPM.
Check out the guy with no hearing:
http://video.google.com/videoplay?do...816484801539&q
ed
Up until about 7 or 8 years ago, the hot F1 setup was probably the 5 Valve (3 intake). I believe it was to try to minimize the mass of the intake valves, and reduce the weight of the valve springs (trying to get the RPM up. more RPM = more HP). This was to avoid broken springs and Valves due to oscillations and shock waves traveling in the springs at the higher RPM.
Seems that big valves are hard to control above 13,000 RPM.
Check out the guy with no hearing:
http://video.google.com/videoplay?do...816484801539&q
ed
04-30-2006, 11:02 PM
#31
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2002 C230 Coupe(M111)
Originally Posted by fasteddie
But then, the 271 was 1/2 litre smaller engine......., nearly equal in performance, and smother running, it was a leap ahead in engine technology.
I'm not so sold on the performance end...the torque isn't there on the bottom end, and although its only 3HP less, that 189HP comes from double the boost the M111was running. An M111 with a pulley is still running less boost than the M271, and makes over 230HP. What I would have loved to see, is a 1.8 with a solid 200HP. Probably a lot to ask for...the M271 as it is is making in excess of 100HP per liter- good performance in anyones book.
