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Different but same Posted by ELaw [Email]  (#699)  [Profile/Gallery]
(more from ELaw) on Wed, 27 Feb 2013 10:01:04
In Reply to: What does variable valve timing..., Craig, Wed, 27 Feb 2013 09:14:10 Members do not see ads below this line. - Help Keep This Site Online - Signup |
VVT of course isn't exactly the same thing as variable compression, but it can have the same effect, and in some cases work even better.
If you look up a "Miller cycle" engine, you'll see what they do is keep the intake valve open during the early part of the compression stroke. This shortens the compression stroke, which effectively lowers the engine's compression ratio and thus reduces pumping losses during compression and the chance of detonation. However the engine's longer power stroke, which could also be termed an "expansion stroke" is retained, allowing it to extract more energy from the burned charge.
The downside of a classic Miller cycle engine is lower power due to less charge being drawn into the motor. But with a turbo engine and VVT, you could run it in a normal Otto-cycle mode off boost, then when it hits boost you could delay the closing of the intake valve to shift it into a Miller-cycle mode. The effect would be very similar to that of variable compression.
_______________________________________ Eric Law Current collection: '12 Audi A4 quattro (self-tuned) '14 Audi A6 quattro (also self-tuned) Gone but not forgotten: '72 99, '77 99 (became a turbo, twice) '80 900T 5-door, '81 900T, '86 900S (became a turbo), '86 900 SPG '86 9000, '97 9000 Aero A bunch of Audis, '69 Firebird, '64 Toyota Corona (first car, cost $35 and worth every penny) Be alert... America needs more lerts!
, Fri, 22 Feb 2013 06:18:09
, Fri, 22 Feb 2013 21:14:37
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, Fri, 22 Feb 2013 18:34:26, Fri, 22 Feb 2013 10:42:45, Wed, 27 Feb 2013 10:01:04 <-- Viewing This Message
, Fri, 1 Mar 2013 10:01:58, Fri, 22 Feb 2013 17:42:57
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