Type 4 mechanical compression ratio, Why is the factory compression so low? Options

[Beebo Kanelle]

OK, here's a fun one for the novice to ponder and you experts to answer:

Why is the factory mechanical CR so low?

and for reference, what is the highest mechanical CR that can be physically achieved? assume no octane limitations -

I'm just looking for the design limit for the highest CR that can be / has been in a Type 4 engine using available technology.

Thanks

[Beebo Kanelle]

guys! I didn't mean to start a firestorm over this... I was just curious as to what the mechanical limitations of the type 4 engine was

no secrets here.

as for the concept, its a variation of the Atkinson / Miller cycle.

On circular intake ports it seems to be possible to minimize the pumping losses while taking advantage of a much greater expansion cycle. for example, instead of 1-2 pts, utilize 5-7 pts, allowing for a cooler exhaust and broadening the torque curve.

Years ago I took my Audi 5000 turbo and increased to CR to 11:8 +- while altering the cam timing events so the actual CR was 8:1 - that is my reference point - variations on this theme have been done to jaguar engines and a domestic v8 - all liquid cooled

I bought a 914 when I started having more time, and have become intrigued with the Type 4 engine.

as far as the modeling, right now its computer - and I'll see where that leads me.

[jd74914]

guys! I didn't mean to start a firestorm over this... I was just curious as to what the mechanical limitations of the type 4 engine was

no secrets here.

as for the concept, its a variation of the Atkinson / Miller cycle.

On circular intake ports it seems to be possible to minimize the pumping losses while taking advantage of a much greater expansion cycle. for example, instead of 1-2 pts, utilize 5-7 pts, allowing for a cooler exhaust and broadening the torque curve.

Years ago I took my Audi 5000 turbo and increased to CR to 11:8 +- while altering the cam timing events so the actual CR was 8:1 - that is my reference point - variations on this theme have been done to jaguar engines and a domestic v8 - all liquid cooled

I bought a 914 when I started having more time, and have become intrigued with the Type 4 engine.

as far as the modeling, right now its computer - and I'll see where that leads me.

Tough crowd. (IMG:style_emoticons/default/laugh.gif)

What software are you using? Commercial or homebrew? I saw your post looking for cam-to-lifter geometry so I assume you're at the connecting measured cam profile to actual lift stage.

It's be interesting to see what kind of efficiency gains you can see from increasing the expansion ratio. I do wonder what the trade off in terms of power will be with leaving the intake valve open so long. Either of these cycles offer relatively good efficiency gains (though a Miller might be tough just due to mechanical strength of the head attachment), but may fall down too much in the overall WOT power part since we don't have the variable valve timing knob to tune.