m20b27

[gromgsxr]

if you had a later m20b25 8.8-1 compression engine and fitted a eta crank and 130mm rods with the 325i pistons and head roughly what compression ratio would you have if the block wasn't decked?

[maggspower]

it would be well under 8-1 so not really ideal at all, unless you are going eyeballs out turbo.

With this set up you will lose the squish band, which effects the way the mixture burns withing the cylinders. Really you want to be tightening it up not making it wider.

You should be able to get the block deck hight skimmed for a reasonable figure.

[gromgsxr]

ok some math to do then i really want to keep it to 8.8-1 so just need to work out how much to remove, how do you work out the compression ration with regards to to domed pistons/ head comb?

[HairyScreech]

why would you want to keep the compression so low?

[gromgsxr]

to have to ability to run boost if required

[gromgsxr]

if low comp m20b25 engine deck height is 206.7mm with the 81mm eta crank and 130mm rods would make a new deck height of 204.7mm so if exactly 2mm was removed from the top of the block the piston would effectivly be in the same height as it would be on a standard settup? is that correct?

[maggspower]

to have to ability to run boost if required

"If required"? Just build the engine as you have designed it, not an N/A build which you might turbo, build it for the application. A good turbo build would make a bad N/A and vice versa.

if low comp m20b25 engine deck height is 206.7mm with the 81mm eta crank and 130mm rods would make a new deck height of 204.7mm so if exactly 2mm was removed from the top of the block the piston would effectivly be in the same height as it would be on a standard settup? is that correct?

In theory yes, but it is best to dry build the engine with the head you plan on using, to check all the clearances , and be sure.

[gromgsxr]

yeah n/a was what i was gunna stick with, iv got a spare low comp bottom end and a eta crank kicking about and most of the bits to build it up so was thinking its something i can throw together for a relitivly low cost to play with, so if the block was skimmed would put me in the static compression range of 9.42-1 or so i think

[reggid]

if you had a later m20b25 8.8-1 compression engine and fitted a eta crank and 130mm rods with the 325i pistons and head roughly what compression ratio would you have if the block wasn't decked?

7.97:1 nominally if pistons are 2mm down the bore, if you deck it correctly it gives 9.42:1 which is a decent setup and along way ahead of the dead weight junk that most 2.7 combos are.

[gromgsxr]

So that's all the numbers I got to so my maths is correct, few more questions then, con rod bolts are not reuseable I would assume? The little end bushes how robust are they do they usually wear out and need replacing on a re build? Would the combo work with a standard cam? And apart. From an adjustable cam gear would there be anything else that would really need to be taken in to consideration.