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]

Thank you all for all your input. I knew that the collective intellect could be relied upon for valuable insight and experience

To answer a few comments/observations made, I am trying trying to maximize the thermodynamic efficiency of the design, not just max HP numbers...

Whatever the numbers end up being, it has to be drivable, have sufficient torque throughout the range and without going to endless amounts revs - I always try to minimize frictional losses.

this is not to be a track / race engine; just a daily driver

So to sum up, the enemy that needs to be addressed is heat management, and combustion chamber limitations, correct?

and yes, this sort of stuff always costs... its just a fun project - for an old guy.

I always welcome any and all comments / observations / experiences so keep 'em coming.

and to R Towle, do you have the camshaft specifications from your 13:1, 200 hp engine? I am specifically interested in your valve timing events

thanks again.

[stugray]

So to sum up, the enemy that needs to be addressed is heat management, and combustion chamber limitations, correct?

There has been some discussion about a water cooled head, air cooled cylinders but I dont think anyone has ever done it.

I seem to recall pictures of it done on a type I engine long ago (what WASNT done to a type I in the 80s-90s ? )

If you want 100hp/liter in a 4cyl NA boxer, just get a FA20 from a BRZ (which happens to be 86mmX86mm with 12.5/1 CR)