Dropping CR without changing pistons?

[Thuppu]

So, what would be the best option to drop CR without changing the pistons? Machine the pistons, put a thicker head gasket, open up the combustion chambers..? How about the squish area, what I have understand it should be about 0,8mm? How does it effect timing if it rises to 1,5mm for example?

[EspenW]

Isn't E85 pretty widely available in Finland?

Edit: only 14 stations as far as I could see. That is worse than here.

[Error404]

I'd have thought easiest way is skim the pistons

[Jamo]

Compression dropping gasket or ghetto twin head gasket, methods are available on the forum in older posts, drop to about 8.5 cr IIRC

[Rocco]

Or thicker head gasket... the cheapest and easiest way I think if you don't want to strip the block

[UrS4boy]

Compression dropping gasket or ghetto twin head gasket, methods are available on the forum in older posts, drop to about 8.5 cr IIRC

[Thuppu]

Ok, I know it's possible to drop the compression with a thicker head gasket, but it rises the squish area that isn't good. But is the benefit of lower CR greater than the loss of the worse squish area?

Espen, I have 100km to the nearest E85 station.

[Jamo]

So does skimming the pistons, you can't have your cake and eat it in this case without buying the correct new pistons, both methods work well though

BTW this has been covered before http://www.s2forum.com/forum/showthread.php?t=4270 good read if you haven't seen it before

[driftin jo]

Have the piston machined properly, don't just skim the top of them, have them dished out properly. Then you will have the same result as new lower comp pitons at a fraction of the cost.

[UrS4boy]

So, what would be the best option to drop CR without changing the pistons?

Interms of cost effectiveness, this:

http://www.034motorsport.com/engine-components-audi-i5-head-gasket-compression-dropping-multi-layer-steel-audi-cyl-p-114.html

[Thuppu]

So does skimming the pistons, you can't have your cake and eat it in this case without buying the correct new pistons, both methods work well though

BTW this has been covered before http://www.s2forum.com/forum/showthread.php?t=4270 good read if you haven't seen it before

Ok, that was a good read, but I didn't find a direct answer for my question. Many good opinions though. Which is more inportant to reduce knock as much as possible, optimal squish or lower CR?

[prj]

Dropping the CR using a gasket or skimmed pistons will be less effective than getting the same CR by doing it properly.
You will have more fuel consumption, and less knock resistance than on an engine where it is done properly.

Of course, it will still be more resistant to detonation than a car without any lowered compression at all.

[4WheelDrifter]

7A pistons are flat topped, so that was good enough to convince me that skimmed pistons are ok.
Plus it's cheap, and you can always further drop the CR later with a thicker gasket.

[quattro84]

The squish area has a non-neglectable influence on combustion, i would not remove it at all.
A better solution would be to redo the bowl shape if the material thickness allows it.
Easiest way (if available) would be to use shorter conrods...

[Error404]

/\ could you use an eccentric small end bush to effectively shorten the rod?