CR with stock pistons (2.0)

[yeahmag]

I'll be running one of Jakes cams on my rebuild which needs 9.0:1 CR. What's the hightest CR you can get out of stock pistons 2.0 (with US spec 'dished' pistons) ?

I guess in reality all you can do is remove the 'cylinder head gasket' and the base shim... Anyone know approximately where that puts you? Assume stock, unmolested 2.0 heads (I have yet to cc them).

-Aaron

[Acox914]

i thought stock usa pstons wre 7.6:1 ?

[yeahmag]

I assumed that was with the head gasket and stock cylinder spacer in place. I could be wrong though.

-Aaron

[Acox914]

i bet you are right....

euros were 8.0:1

[jackmech]

Aaron's correct. Stock compression on factory built US 914 2.0 engines was 7.6:1. To raise compression you can remove the head gasket, cylinder base shim, and you can also flycut the heads and weld up the combustion chambers. So really, you can have any compression ratio. Stock pistons in stock chambers depend on how many times the heads have been cut. There really are too many unknown variables to accurately give an estimation. If you measure the actual volume of your combustion chambers, then we might be able to figure something out.

[yeahmag]

Care to take a guess what they'd be without the spacer and gasket? You are probably aware of how thrifty I have to be with this rebuild from the 914club.com board... But if it's the wrong thind to do I'll just have to wait and save up for the KB's or something.

-Aaron

[Acox914]

i was told there was no way to get to 9:1 with stock pistons...(removing head gasket and base shims...)

youd have to shorten the barrels or something....

[yeahmag]

Sure. I'm planning on cc'ing the chambers. I guess I was looking for someone in the know (or some numbers, stock or otherwise that I could plug in - deck height, 'typicall non-molested' 2.0L head cc, etc...).

Aaron, Did they tell you what it would be with those items removed? Am I even in the ball park?

-Aaron

[Acox914]

no idea....
i was told i could pick up at most a half point....

[yeahmag]

oof... OK. I'll talk to John Edwards about the KB's. The cost creep on this project is unbelievable...

Thanks.

-Aaron

[Dave at Pelican Parts]

The only way to know is to mock it all up and measure.

You want deck heights in the 0.040" range. Stock 2.0 combustion chamber volume is in the 65cc range, unless I'm doubling the first digit. Dish volume is in the 5cc range I think.

You can grinc the numbers to give you a very very rough idea, but you may still wind up hosed if you don't measure your actual parts!

--DD

[yeahmag]

Thanks. I was basically looking for info on whether it was a possiblity. Seeing as I need to run 9.0-9.5:1 for the cam my choices seemed to be clean up the old p/c and try and run them or get the KB's and bore for 96mm. Being on a non-existent budget is what's dictating all of this.

Seems like from Aaron's finding I need new pistons... Of course I would mock it up and measure before the final build!!!

Thanks!

-Aaron

[jackmech]

65 cc? My recollection (is the 914Club still down) is that most chambers end up in the 55-59 cc range. :unsure: