Compression question

[bluebombersfan]

I know the basic rule about compression No lower then 100psi and each cylinder pressure within 15% of each other.
But my question is how low of a compression can a engine run on?

 

[Wicked_Sludge]

the bare minimum? probably around 20 PSI...maybe a bit lower.

an engine with that little compression will have no power, stall alot, get terrible mileage,...but itd run.

why?

 

[bluebombersfan]

wow, really 20 psi, just wondered cause my dads snowblower that we barely use runs exellent but only had 60psi so I didn't know what to think. I thought it shouldn't even be running but yet it runs so well I wouldn't even think about rebuilding it nor would I know how.

 

[Wicked_Sludge]

your comparing apples to oranges. small engines like those used in snow blowers, lawn mowers, and the like are built with a fraction of the quality and precision of an automotive engine. compression on those engines escapes past the rings, out the valves (both from poor seat quality and from less-than-optimal cam timing), etc etc. 60 psi from an engine like that is probably very good.

 

[bluebombersfan]

surprisingly then I got 150psi on our weedtrimmer

 

[shadetree]

Wicked is right. It depends on the engine. Small block chevys will run just fine with 50psi and less. Engines with low compression are sometimes a little harder to start, and of course are low on power as compression adds greatly to torque.shady

 

[RangerFabWorks]

Wicked is right. It depends on the engine. Small block chevys will run just fine with 50psi and less. Engines with low compression are sometimes a little harder to start, and of course are low on power as compression adds greatly to torque.shady

ford guys always making fun of us chevy guys.

 

[RangerFabWorks]

btw im just playing

 

[4b316]

Your weedwacker is a 2 stroke and thats going to have a high CR.I had a ford 8N tractor that would run on 25lbs of CR but had to start it on ether