Variable Valve Timing in US
Guest
Posts: n/a
Variable Valve Timing in US
Does anybody find it strange that Subaru is one of the only manufacturers not offering variable valve timing in the United States? Even domestic manufacturers are beginning to offer VVT in their engines. Subaru could easily push some more power out of their current engines if they incorporated something similar to VTEC. It kind of makes our engines seem "dated" compared to other cars out there. Does anybody have insight on why we don't get Subaru's AVCS system like the JDM models do?
PS - I'm not sure exactly where to post something like this on the new board??? So I put it in General
PS - I'm not sure exactly where to post something like this on the new board??? So I put it in General
Registered User
iTrader: (9)
Joined: Nov 2002
Posts: 1,912
From: Bahay area, CA
Car Info: RIP: 2000 2.5RS Sedan, BRP Now: 08 WRB WRX Hatch
won't the STi come with AVCS when it comes out here? but then i heard that it may/may not come on the car because it would make the car too strong and fast 
i think it would help reduce emmisions
Daios (Day-ohhss)
i think it would help reduce emmisionsDaios (Day-ohhss)
VIP Member
iTrader: (2)
Joined: Nov 2002
Posts: 15,425
From: Under your bed, in your closet, and in your head
Car Info: Corvette Z51
I might be wrong, but doesn't a nice turbo pretty much negate the need for variable valve timing? I remember Honda first developed VTEC as some kinda turbo alternative or something, right? I'm not too sure on either count though, hehe, so someone please enlighten me.
Guest
Posts: n/a
...though I wouldn't hunt one down, I see more benefit in valve control than simply emission control. In lieu of a crank independent implementation ( electric solenoid actuators or some such ), it accurse to me controlling the intake and exhaust allows for better/finner control, i.e. manipulating lobe separation by controlling the centerline of both the intake and exhaust lobe centerlines with less retardation/advance. Because the amount of lift you have and the speed at which the valve moves dictates the torque your engine will produce, I see no detriment to being able to chase profiles, whether intake and exhaust or intake alone . Duration is pinnacle to what the engines basic RPM range will be. Short cams produce power in the lower RPM range, and larger duration cams pull at higher RPM, usually you sacrifice bottom end power to gain top end power as you extend the duration. Supposedly, for each ten degree change in the duration at .050”, the power band moves up or down in RPM range by approximately 500 RPM’s. This being the case ( my numbers with a grain of ~salt ), it seems a Motec and vvt is a great way to tune, particularly if your environment profile changes often; this isn't even getting into how much more beneficial this should be on a car with the high variable cylinder pressure of a turbo engine, as you could basically manipulate profiles to accommodate cranking pressure, or future displacement changes.
SLR-
SLR-
Cam phasing is there simply to reduce the compromises made in cam selection. But a wild cam for a phased system will have idle problems the same as it would on a standard type system. Cam phasing is all about being able to use wilder cams maximizing the power band and still idling well. On FI cars though, the difference is small because FI cars require less aggressive cams. On FI cars too much overlap equals boost lost out the exhaust valve. So the difference in the actual cam grind standard vs phased will not be much on an FI car. Pick your grind properly, and your set either way.
The Porsche system though, oohhha. Modifys lift and timing. That you could really justify.
k2
The Porsche system though, oohhha. Modifys lift and timing. That you could really justify.
k2
Last edited by DeliciouSpeed; Nov 22, 2002 at 10:57 PM.
Guest
Posts: n/a
Let's remember that variable valve timing like VTEC , VVT-i, AVCS doesn't get more power out of a motor.
Rather it keeps a more conservative cam profile in the lower rpm range for driveability and in the process gives less power at lower RPM. This also gives it better fuel efficiency and tends to pollute less.
Before those technology, cam profiles have always been a design compromise between two settings. The STi v4-5-6 cam profile are very aggressive and AVCS doesn't give it anything more.
A WRX AVCS cam profile at its most aggressive is almost identical to a STi v4/5 cam profile. The only thing the AVCS brings to the WRX STi JDM is a smoother idle and cruising, which I don't get on my STi motor, but then again I don't mind as much.
Rather it keeps a more conservative cam profile in the lower rpm range for driveability and in the process gives less power at lower RPM. This also gives it better fuel efficiency and tends to pollute less.
Before those technology, cam profiles have always been a design compromise between two settings. The STi v4-5-6 cam profile are very aggressive and AVCS doesn't give it anything more.
A WRX AVCS cam profile at its most aggressive is almost identical to a STi v4/5 cam profile. The only thing the AVCS brings to the WRX STi JDM is a smoother idle and cruising, which I don't get on my STi motor, but then again I don't mind as much.
