3 replies to this topic

[chrisn89]

Hi Everyone,

im building a 1293cc A series at the moment and just looking to make it a fast road spec,
just wondering for a fast road, reliable engine that will be a daily driver, should the compression ratio be kept the same or raised slightly?

Cheers
chris

[Cooper-202S]

If its your daily drive then running cost is a consideration.
If you want to run it on ordinary unleaded stick to 9.75-1.
If you can afford to run it on super then you can go to 10.5-1.

Please bear in mind they are static ratios and you may end up with lower compression running due to the engine breathing poorly. That how people run 11+to 1 without det problems

In the 1st instance you would be better to sort out the head, manifold and Carb set up as well as the exhaust before raising the compression.

If all that is sorted the you can either skim the head or deck the block.
As you haven't gone directly to 1380 then i wouldn't deck the pistons flush with the top of the block as pistons vary and next time you rebore it they may end up proud, better to keep a little metal in hand.

Strick a balance between head and block you can always open out the chambers later if you need to drop the C/R next time you rebore.

[Sherlock]

Good advice from Cooper-202s, with modern rubbish fuels it's no good for road use to go above 10:1 compression, on normal unleaded, in the old days of the famous 5-star petrol, 11.5:1 was quite possible for everyday use, but sadly those days are gone.

[chrisn89]

hi guys

okay thanks a lot for the help and advice, all of it is taken into account and has helped a lot,

cheers
chris