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keith_d · 17-10-19, 08:30 AM

On bigger engines VVT is usually used to improve tractability at low revs while still maintaining gas flow at high RPM.

In a regular car engine the valve timing used to be designed(*) for smooth running at low RPM, which resulted in insufficient airflow at high RPM and therefore reduced power. At the other extreme, a race engine has valve timing is designed for maximum power at high RPM, but they are lumpy and un-driveable at low rpm.

My old Toyota had VVT using two different cam profiles. At low rpm the engine used an inlet cam with small openings of the valve to provide smooth power for regular driving. Around 5700 rpm the ECU activated a solenoid valve which used oil pressure to switch to a high lift cam. This provided improved gas flow and more power at high RPM.

VVT has also been used on some models to reduce emissions across the rev range, but that's no fun.

Just my thoughts,

Keith

(*) These days it's all about economy and emissions. Boring!!

17-10-19, 08:30 AM	#2
keith_d Member Mega Poster Join Date: Feb 2009 Location: Ruislip Posts: 1,131	Re: Yamaha MT125 VVT On bigger engines VVT is usually used to improve tractability at low revs while still maintaining gas flow at high RPM. In a regular car engine the valve timing used to be designed() for smooth running at low RPM, which resulted in insufficient airflow at high RPM and therefore reduced power. At the other extreme, a race engine has valve timing is designed for maximum power at high RPM, but they are lumpy and un-driveable at low rpm. My old Toyota had VVT using two different cam profiles. At low rpm the engine used an inlet cam with small openings of the valve to provide smooth power for regular driving. Around 5700 rpm the ECU activated a solenoid valve which used oil pressure to switch to a high lift cam. This provided improved gas flow and more power at high RPM. VVT has also been used on some models to reduce emissions across the rev range, but that's no fun. Just my thoughts, Keith () These days it's all about economy and emissions. Boring!! Last edited by keith_d; 17-10-19 at 08:33 AM.