On-Off Supercharging, Compression Problem

[Clu Osborne]

A few weeks back, I posted some messages about how to build a functioning

on-off supercharging system.

One of the biggest problems is the compression ratio. Supercharged engines require

low compression to run properly and to prevent engine damage. Non-supercharged engines

are the opposite, requiring higher compression. Even with modern electronic controls, when

the supercharger was turned off, performance would suffer or may not even run.

Well, since the compression was in the cylinder heads, if there was a way to vary the volume

of the chambers, it may be possible to vary the compression ratio. This would mean creating

heads that can vary the position of their valve train, valves, and chambers.

No such heads exist, but I have a few ideas on what would be needed.

First, the heads would have overhead cams, since the valvetrain will move toward or away from

the engine block. Devising a variable belt tension system would keep everything running.

Second, the movement itself would be accomplished by hydraulics, controlled electronically.

The pressure to the hydraulics itself would be maintained by an electric pump, which can be

easily powered by the car's electrical system, or supplemented by a second battery.

The biggest problem here is that since the heads don't exist, they would have to be designed,

cast, and tested, which is expensive but doable.

Of course, the other problem is devising a system to engage and disengage the supercharger

that is more efficient than the setup used by Phase IV Machine.

[nomoneynocar]

In Reply to: On-Off Supercharging, Compression Problem posted by Clu Osborne on January 21, 2000 at 14:39:25:


If you want more power, just engage the supercharger.

Therefore it doesn't matter that the engine will

be lackluster with the supercharger off, because

that is the whole point of an on/off supercharger,

On=power, off=economy.

Engageing and disengageing is done using a magnetic

clutch, as used by the mercedes CLK kompressor, who's

supercharger disengages below 2000rpm

[Clu Osborne]

In Reply to: But... posted by nomoneynocar on January 22, 2000 at 04:02:17:


But if the compression ratio is too low, the engine may not run at all, or run very poorly.

[nomoneynocar]

In Reply to: Re: But... posted by Clu Osborne on January 22, 2000 at 11:03:42:


There must be a good compromise. You probably wouldn't

need to go any lower than 7.0:1 for the supercharger

to be able to run big boost safely, and many naturally

aspirated cars with large capacities run that sort

of compression with no problems. They still run

fine, just not making huge power.