According to ford spec's @ 8.1 cr (as per manual) conpression tests read as nornmal @8.5 bar @8:1Comp ratio
The following are my results-

1-130.5 psi
2-130.5psi
3-130.5psi
4-130.5ps



I believe my Cr is 7.6:1 but the head has been skimed, is there a linear progression? ie -

7.2:1(ratio) =110PSI (Compression)
7.4:1=120Psi(compression)
7.6:1=130Psi(compression)
7.8:1=140PSI(COMP)

And so on and so forth..............

Thanks for you time.y



My Best , Tim.



it makes sense that

 

They're closer to 9:1

1 bar is 14.7 psi, call it 15 cos it's simple.

130 divide by 15 is 8.6, plus a little for the missing 0.3 and it's between 8.7 and 8.9

 

Compression and compression ratio are two different aspects.

There will be a trend/correlation providing you only ever changed the ratio aspect. get a bit more complicated when you bring in valve timming.....which has massive affect on compression.

 

As does boost and charge temp in cylinder increase. But these are statics. As quoted in manuals and as tested with a spark plug replacement pressure gauge. 99% of passionford won't know their dynamic cr, 25% probably won't know what one is

 

Did you measure the bore/stroke volume and the volume of the combustion chamber at tdc as that's the best way to get a true compression ratio

 

^^^ true this, main reason why a lot have issues

 

I'm willing to bet he doesn't have a 12 inch pin mag block, or a calibrated burette, any cc fluid or a cc plate.

 

To a lot of people you just spoke foreign, when you test measure yours do you use a dti gauge to get true tdc as the piston floats over or just go with the notch marks

 

Glad someone understands :-D

True TDC with the dti. Rechecked for each piston ( don't assume firing pairs are equal) grease around the top inch of the cylinder to seal the rings on the way up, scrape excess grease from the piston/bore clearance with a scrap feeler blade and away you go

 

Snap. My dti is probily the most used engineering tool I own I think, other than feelers and a vernier