# In theory can an engine have greater fuel efficiency at higher RPM?

**URL:** <https://community.cartalk.com/t/in-theory-can-an-engine-have-greater-fuel-efficiency-at-higher-rpm/100970>\
**Category:** General Discussion\
**Created:** [March 8, 2017, 10:39pm UTC](https://community.cartalk.com/t/in-theory-can-an-engine-have-greater-fuel-efficiency-at-higher-rpm/100970 "2017-03-08T22:39:39Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\
**Post date:** [March 10, 2017, 7:14pm UTC](https://community.cartalk.com/t/in-theory-can-an-engine-have-greater-fuel-efficiency-at-higher-rpm/100970/21 "2017-03-10T19:14:52Z")

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is it where Direct Injection comes into the picture?

> **[Gasoline direct injection](https://en.wikipedia.org/wiki/Gasoline_direct_injection)**
>
> Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct from manifold injection systems, which inject fuel into the intake manifold (inlet manifold).
> The use of GDI can help increase engine efficiency and specific power output as well as reduce exhaust emissions.
> The first GDI engine to reach production was int...

> there is no air throttle plate, which greatly improves efficiency, and reduces piston ‘pumping losses’

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**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\
**Post date:** [March 10, 2017, 7:32pm UTC](https://community.cartalk.com/t/in-theory-can-an-engine-have-greater-fuel-efficiency-at-higher-rpm/100970/22 "2017-03-10T19:32:33Z")

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I don’t think that ‘direct injection’ = ‘no throttle plate’. That’s a function of the valve actuation. The mixture has to be controlled somehow.

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**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\
**Post date:** [March 10, 2017, 11:37pm UTC](https://community.cartalk.com/t/in-theory-can-an-engine-have-greater-fuel-efficiency-at-higher-rpm/100970/23 "2017-03-10T23:37:55Z")

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If I’m getting it right, unlike “regular fuel injection”, it can go from stoichiometric into “ultra lean” under low load, so it does not need throttle at all, thus does not have it

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**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\
**Post date:** [March 11, 2017, 12:27am UTC](https://community.cartalk.com/t/in-theory-can-an-engine-have-greater-fuel-efficiency-at-higher-rpm/100970/24 "2017-03-11T00:27:21Z")

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The only gas engines without a throttle plate use variable intake valve lift to control air.

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