Quote:
Originally Posted by serialk11r
So since I was rather bored I went and looked up more specifics on valve control systems, and I realized something...Valvematic actually does not add much height over a VVTL-i engine because Toyota does away with VVTL-i on Valvematic engines for simplicity! So the locking pin and rollers are replaced with a secondary shaft and rollers/followers. So there isn't actually a packaging issue with Valvematic.
I realized there's one issue with Valvematic however. Because it only has one cam profile that is high lift, the duration at low rpm will need to be limited to reduce the lift. With VVTi, they can advance the intake significantly then cut duration so some of the bottom of the intake stroke is used to expand the charge, reducing the pressure and helping the fuel evaporate (for the record, there are minimal pumping losses associated with this since the piston travels back up and regains the energy in the compression stroke). However this comes at the cost of reducing the amount of charge pulled in. With VVTL-i (and i-VTEC for that matter), the low rpm torque is pretty well optimized because the cam is a full duration cam with a low lift profile. Of course with less charge pulled in we have less pressure blown out the exhaust, but I think when Valvematic engines hit American shores we will notice that they have a slightly upward sloping torque curve. Unless of course Toyota figured out a different way to promote fuel atomization.
On the side, I noticed that wikipedia says all the 1ZR and 2ZR engines (the only valvematic engines so far besides the 3ZR-FAE) are built in Tianjin, China, in FAW factories, which might be why we don't see much of them here in the US. I'm guessing they're waiting to retool their factories elsewhere for more A engines since it'd mean throwing out everything they use to make the VVTL-i system. But then the 2ZZ-GE is at the end of its lifespan, so they might be starting already  |
With less charge pulled in, we get less power. Boo...
Extended duration allows cars to make more power up top when the intake charge is traveling faster. The extended intake duration allows the high energy (air/fuel has inertia) charge to continue to enter the combustion chamber even as the piston starts up on the compression stroke.
Sounding like Valvematic is more of an efficiency oriented system.
PS have any Valvematic engines incorporated D4-S? This would help with the atomization.