The Triumph Dolomite Club - Discussion Forum

Had a message from chap doing my head and the combustion chamber volume I would like following the finish skim. Any ideas as to what I should be aiming for. I cannot for the life of me find the 'book' figure for the Sprint engine.

Looking to achieve the STD CR of around 9.5:1, nothing crazy.

http://performancetrends.com/Compressio ... r_V2.3.htm

Quite a few dimensions to consider.

Know your bore and you know the cilinder cc's. The compressed headgasket of a sprint is about 1,2mm thick and must be added to the combustion chamber. With this data you know how much cc's you need in the head.

There's a lot off difference in the chambers per head so make them equal. Otherwise your cilinders have all different ratios. Also measure the piston height. Most decks are not straight with the crank bore. That can cause also different ratios from front to rear.

Raising compression ratios and end up with uneven ratios can cause one cilinder slightly pinking without noticing but causing damage.

Jeroen

I know my block was machined to first oversize which has resulted in 90.8mm pistons I believe. Then the stroke is normal, 78mm but then I add the 1.2mm for the gasket which makes 79.2mm. My swept area is therefore 512.85cc I think.

Beyond this I'm a bit lost!

I'm on a holiday in Italy atm and in a state better not to make calculations for you but the headgasket cc's are combustion chamber cc's and not cilinder cc's.

Jeroen