[Vwdiesel] 1.6L Diesel Compression

James Hansen jhsg at sasktel.net
Fri Nov 23 20:24:42 PST 2007

MikeyBigFish at wmconnect.com wrote:
> Folks,
>            When tracking down specifications for the VW1.6L diesel n/a.
> I stumbled upon compression ratio (23:1).
> See page#16 on this Audi/VW link below:
> <A HREF="http://www.audivwcrewpr.com/servicemanual/Mk2/10.pdf">vwdiesel1.6Lna&td</A> 
> I know VW is very accurate w/ their specs and 23:1 is their standard.  
> How is compression measured? 

Hold the phone.

Compression ratio and compression are two different things.

Compression ratio is a ratio of the swept volume of the cylinder, versus 
the volume of the space left above the piston when it's at TDC.  All 
diesels are over 18:1  They start better at 23:1, and run better with 
boost at lower compression ratios (boost pressure raises the "effective" 
compression by cramming more air in (increasing the volumetric 
efficiency)  Somewhere inbetween is where most diesels are- going over 
23:1 takes away your safety margins and increases your chance of lifting 
the head off the block- leaking past the head gasket.

Compression as a thing you measure is referring to screwing a test gauge 
into the combustion space, and turning the motor over.  The max pressure 
you get on the gauge is the "compression" as obtained by the 
"compression test".


I always have to look this one up and my books are in the shop.
read: my memory for numbers sucks.

> Anyone know what cylinder compression should read on fresh 1.6L diesels?
> Also, what is the unacceptable level?

When it starts poor and everything else is in good shape- valve adjust, 
injectors, timing, glow plugs, air filter, timing, fuel pump, timing....


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