View Single Post
Old 05-18-2022, 08:19 AM   #7 (permalink)
Master EcoModder
Join Date: May 2012
Location: Tampa, FL
Posts: 1,745

Volt, gas only - '12 Chevrolet Volt Premium
90 day: 38.02 mpg (US)

Volt, electric only - '12 Chevrolet Volt Premium
90 day: 132.26 mpg (US)

Yukon Denali Hybrid - '12 GMC Yukon Denali Hybrid
90 day: 21.48 mpg (US)
Thanks: 206
Thanked 420 Times in 302 Posts
Originally Posted by ERTW View Post
Diesels have "low vacuum" because they use turbos to fill the vacuum.
Diesels have low vacuum because they don't have a throttle, they control engine speed with fuel.

Originally Posted by ERTW View Post
if what you're saying were correct, then I should use a lopey cam and expect better mpg. the truth of the matter is engines need vacuum to run properly. If the intake valve opens too early you get lots of misfire. Vacuum creates the air speed that entrains, atomizes and emulsifies the air/fuel mixture, which creates a faster burn. A Toyota engineer gave me the Prius cam specs (which was at 40% BTE at the time). They phase the cam so that it closes at 100* ABDC, which means it opens the valve much later than typical...which means lots of vacuum. They give up a little pumping loss for better combustion and a much lower compression ratio (negative work).
I'm going to challenge you on that. The prius uses late intake valve closing which decreases vacuum because it pumps the intake gases back into the manifold, does not increase vacuum.

Hybrids do not need to have high vacuum for idle quality because... hybrids don't idle.

  Reply With Quote