ArcticZ28

iTrader: (14)

General questions:
How is creating compression by using the force of the supercharger/turbo rather than the cylinder walls more efficient? Is it really 15% more efficient by running like this? What are the cons of this sort of setup?

More specific to us:
Has anyone thought about adapting an LSx engine to use this cycle? Does anyone use this currently? I assume it could easily be done with a custom cam.

DavidNJ

Miller cycle and Atkinson cycle use late closing intake valves to reduce compression. Typically, they will have a static compression in 16+:1 range, with normal or even slightly low DCRs. This allows greater efficiency at the expense of power.

Because the reverse flow is cripiling at low engine speeds, it is either coupled with an electric motor (the Prius) or a supercharger (Miller cycle).

Note Atkinson developed his cycle at the same time as Otto, during Gladstone's second term as Prime Minister (Chester Arthur was President, for as much as Chester Arthur was President) and Miller developed his cycle during Franklin Roosevelt's first term (before Old SStroker was around).

ArcticZ28

iTrader: (14)

I know they have late IVC's to bleed off SCR, but supposedly this helps it become more efficient in that the pistons have to do less work against the walls of the chamber and are rather pushing against the forced intake air from the super. I just don't understand how that is more efficient, unless it's just saying that it's more efficient because it takes less work for the pistons to press against the forced air to create compression rather than the chamber walls. If so, well duh.

ConnClark

In 1882 Sir Dugald Clerk discovered that thermal efficiency of an engine was based on compression ratio. He also discovered that if the expansion ratio exceeded the compression ratio thermal efficiency increased. By holding the intake valve open a little longer it in effect reduces the compression ratio with respect to the expansion ratio there by increasing thermal efficiency.

ArcticZ28

iTrader: (14)

So you're building an engine to 16:1 SCR and then bleeding off compression so it's down to 12:1. Yes, this means the pistons do less work but in turn results in less power. Isn't that like getting a large lift cam and then replacing your stock rockers with ones of lower ratio to achieve lower lift, and thus the springs do less work?

MadBill

The purpose of the Atkinson/Miller cycle is to improve efficiency, not power. The effectively longer expansion stroke captures more of the heat energy.