MIVEC and cams?
Originally Posted by AWDrift07
Ok the record needs to be set straight. Mitsubishi's MIVEC and Subaru's AVCS are not like VTEC in any way. MIVEC and AVCS are the same generic variable valve timing mechanisms as Toyota's VVTi and BMW's VANOS and Double VANOS systems. In terms of Honda Engines, MIVEC and the like are the "i" in i-VTEC. The "i" stands for intelligent and is a reference to the variable valve timing control system that works inconjunction with the VTEC system. MIVEC is a variable valve timing system with fixed cam lobe profiles.
MIVEC only changes the relative alignment between the camshaft and its driving sprocket. This changes the relative timing between the intake and exhaust cams and thus their valve opening cycles or the intake and exhaust valve opening overlaps. No other valve timing parameters, including the amount of valve lift or valve opening duration are varied. The only thing that MIVEC varies is the valve opening overlaps. Also, MIVEC only varies the relative timing on the intake cam. AVCS, VVTi, and VANOS work the same way.
Think of it as a constantly adjusting, adjustable cam gear on the intake cam that retards timing based on engine RPM. The higher the RPM, the more valve closure timing is retarded. This allows the combustion chamber fill with more A/F, an obvious performance improvement. At low RPM, valve opening timing is retarded to improve combustion effieciency for low emissions and improved fuel consumption.
VTEC varies the amount of valve lift and valve opening duration using different, selectable cam lobe profiles on the same cam. The different profiles are selected and utilized hydraulically based on engine RPM. DOHC VTEC engines have variable intake and exhaust cam lobe profiles. SOHC VTEC engines have only varying intake lobe profiles.
Back on topic... it may be only a rumor but i have heard that HKS already has MIVEC cams in the works. They might really only have to redesign the intake cam. The exhaust cam should be very similar to the non-MIVEC cam considering the actual head and block specs have not been drastically changed in any way. The only internal change i have heard of is the new piston ring combo. Regardless, even if the development takes a while, i think it will be worth the wait!
MIVEC only changes the relative alignment between the camshaft and its driving sprocket. This changes the relative timing between the intake and exhaust cams and thus their valve opening cycles or the intake and exhaust valve opening overlaps. No other valve timing parameters, including the amount of valve lift or valve opening duration are varied. The only thing that MIVEC varies is the valve opening overlaps. Also, MIVEC only varies the relative timing on the intake cam. AVCS, VVTi, and VANOS work the same way.
Think of it as a constantly adjusting, adjustable cam gear on the intake cam that retards timing based on engine RPM. The higher the RPM, the more valve closure timing is retarded. This allows the combustion chamber fill with more A/F, an obvious performance improvement. At low RPM, valve opening timing is retarded to improve combustion effieciency for low emissions and improved fuel consumption.
VTEC varies the amount of valve lift and valve opening duration using different, selectable cam lobe profiles on the same cam. The different profiles are selected and utilized hydraulically based on engine RPM. DOHC VTEC engines have variable intake and exhaust cam lobe profiles. SOHC VTEC engines have only varying intake lobe profiles.
Back on topic... it may be only a rumor but i have heard that HKS already has MIVEC cams in the works. They might really only have to redesign the intake cam. The exhaust cam should be very similar to the non-MIVEC cam considering the actual head and block specs have not been drastically changed in any way. The only internal change i have heard of is the new piston ring combo. Regardless, even if the development takes a while, i think it will be worth the wait!
There was a thread here recently where Shiv was talking about tuning the MIVEC section of the ECU with good results and the multi-layer fuel maps of the 9's ECU... So I am confused as to why they would say that... Must be more to it than that... Maybe just on some high HP big turbo setups?
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Oct 17, 2006 05:12 AM
