Compression ratio check
Turbo Mini Forums

Hi, I’m about to start building my new engine. I am taking the block for machining this week, I was wondering if anyone could cast their eye over my compression ratio calcs?

1380 bore
18cc pistons
0.8cc ring lads
3.8cc bk450 head gasket
25cc chamber volume
? cc deck height

The pistons are forged accralite, I understand that these sit aprox 40 thou down the bore on a standard heck height. The block I have has almost certainly been skimmed on the deck previous. I will have to build the block up once it has been overbored and measure the deck height properly.

With a deck height of 0 I make the compression ratio 8.25
10 thou – 8.1
20 thou - 7.96
30 thou – 7.82
40 – 7.7

I will measure the actual height on a dry build when I get the block back and get the block faced to suit.

Do these calculations look about right? cheers, dan

yep thats about right,

I'm on a 1380 with 18cc psitons, and a 24cc head and mine is about 8.3 ish

cheers joe. what deck height are you running? cheers, dan

about 5 thou

great. im hoping to run at around 8.0 - 8.1, but will have to wait and see what the current deck height is. cheers, dan

did you machine the 1380 pistons to 18cc yourself?

no these are forged accralites. that how they came. i believe that omega will still make them but only in batches of 3-4 sets minimum. cheers, dan