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.

[Bulldog9]

Eh, I'm not buying it.

Driveable? Porsche sold thousands of these cars making less than 100HP and were/are completely driveable and enjoyable. That's subjective anyhow.

All you've talked about is HP/liter and ridiculous compression ratios. Now you are looking to maximize thermodynamic efficiency?

You also seem to be ignoring the 'collective intellect'

I just finished a 2056 build (you can look at the #770 Update thread). I havent put on a dyno yet, but even in a 911 body, the car is responsive, has great driveability, power and loves to rev to redline. I'm guessing will be at the 125-130 HP range.

There are dozens of build threads all over the 914 world, aircooled.net, and if you've spent 5 minutes searching, you have found all the Raby stuff out there.

I'd like to see an example of one of these engines you've built.... or even what year your 914 is..... I think your talking in circles.... But hey, I'm just a grumpy guy. But I'm thinking TROLL ALERT here. Gonna be fun. (IMG:style_emoticons/default/popcorn[1].gif)

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.