Compression Ratio

[SHOgoFast]

So I have spent some time seaching over on the old forums about compression ratios on the 3L swaps. I believe these to be simple questions without conclusive answers...

CR with Hybrid, svt heads = ??

CR with 3L Swap, 3L heads = ??

Is this overly simplified with just the difference in heads?

I will be completely satisfied with links as well if I happened to miss something.

Another question...does anyone know the stock deck height and gasket thickness?

[Big Jim]

The stock 3.0 has 10:1 compression.

I'm sure that someone that has done it will chime in and let you know about SVT heads on a 3.0, but I think I remember that it is about 11.25:1 although it can be brought down to a more managable 10.5:1 or 10.75:1 by porting, especially unshrouding the valves.

[DemonSVT]

From this really cool website and a page that has been online for over 3 years.

Compression Ratios by Chamber Size



2.5L Engine
44.5cc = 9.70 to 1
50cc = 8.91 to 1

44.5cc 98-99 SVT = 10.02 to 1
44.5cc 00 SVT = 10.31 to 1

50cc 98-99 SVT = 9.28 to 1
50cc 00 SVT = 9.49 to 1

3L Engine
44.5cc Hybrid = 11.24 to 1
44.5cc 89mm bore Hybrid = 10.85 to 1
44.5cc 90mm bore Hybrid = 11 to 1

48.2cc - 01+ Oval Port = 10.07 to 1
48.2cc 90mm bore = 10.24 to 1

50cc = 9.78 to 1
52cc = 9.47 to 1

You'll lose about 0.125cc chamber volume for each 0.001in of material that you remove during surfacing.
Taking off, say .003" will only raise your compression ratio by about 0.06 point.
Maximum safe limit is .006”

50cc is the maximum you can enlarge the 2.5L head chamber to without completely ruining the heart shaped hemispherical chamber. (i.e. being stupid!) The 3L head can go up to ~52cc in this same fashion. I would stop at 48cc and 50cc respectively.

The Hybrid overbore is taking into account opening up the chamber to match the larger bore size. The actual chamber CC would not be the stock 44.5cc 2.5L head. I used this nomenclature to state it was stock 2.5L head. This is highly recommended to ensure proper swirl and air flow. If this was not done the CR would raise to ~11.4 and ~11.55 respectively. However you would lose much more in efficiency then the small CR jump would gain back.