Hi, Guest
06-26-2004, 03:39 PM
funny, i have been saying this for years!
also, VCT and Vtec are comepletely different.
vct uses a standard cam profile and adjusts timing on the entire cam.
vtec uses a 2 lobe cam and special rocker assembly
there are 2 seperate profiles on each cam, one for standard driving and a bigger profile for higher rpm driving. the bigger profile has a much higher lift, duration and overlap than the smaller profile which allows for better breathing at higher rpms in a NA application.
Vtec uses a computer controlled oil solenoid that energizes the rocker assembly to lock allowing the bigger profile to work the valves, this happens at a specified rpm(on most vtec honda/acuras @ around 5500rpm). the rocker assemble has 3 rockers per pair of valves, 2 of which are for the smaller lobes that directly activate the valves as a standard DOHC motor works, the thrid rocker is for the bigger lobe which sits directly inbetween the 2 smaller lobes for each cyl. normally the center rocker assembly for the bigger lobe is "floating" and the big lobe does nothing but move the "floating" rocker while the smaller lobes directly control the valves via their respective rockers. once the engine hits that magic rpm the solenoid locks the middle rocker assembly to the others via oil pressure and both valves per cyl are now being actuated by the bigger lobe as the smaller ones are no longer in contact with their rockers.
VCT is nothing like this.
VCT was originally designed by ford as a way of meeting the new(at the time) CARB requirements for new cars. the idea behind it was always for emmissions. a boost in power at varrious amounts out cam retard was just an added benifit.
although i'm sure rob will have something to say about that. :D
good post though
also, VCT and Vtec are comepletely different.
vct uses a standard cam profile and adjusts timing on the entire cam.
vtec uses a 2 lobe cam and special rocker assembly
there are 2 seperate profiles on each cam, one for standard driving and a bigger profile for higher rpm driving. the bigger profile has a much higher lift, duration and overlap than the smaller profile which allows for better breathing at higher rpms in a NA application.
Vtec uses a computer controlled oil solenoid that energizes the rocker assembly to lock allowing the bigger profile to work the valves, this happens at a specified rpm(on most vtec honda/acuras @ around 5500rpm). the rocker assemble has 3 rockers per pair of valves, 2 of which are for the smaller lobes that directly activate the valves as a standard DOHC motor works, the thrid rocker is for the bigger lobe which sits directly inbetween the 2 smaller lobes for each cyl. normally the center rocker assembly for the bigger lobe is "floating" and the big lobe does nothing but move the "floating" rocker while the smaller lobes directly control the valves via their respective rockers. once the engine hits that magic rpm the solenoid locks the middle rocker assembly to the others via oil pressure and both valves per cyl are now being actuated by the bigger lobe as the smaller ones are no longer in contact with their rockers.
VCT is nothing like this.
VCT was originally designed by ford as a way of meeting the new(at the time) CARB requirements for new cars. the idea behind it was always for emmissions. a boost in power at varrious amounts out cam retard was just an added benifit.
although i'm sure rob will have something to say about that. :D
good post though