Are facts about CR in 'building a 2.7' right?

Post Sat Nov 11, 2017 6:51 pm

Hi

I was wondering if those CR values are right mentioned in a stroker building guide.

-"Again, depending on which gasket is used and whether the head has been skimmed, using a 325i head on a later 10.2:1 Eta short engine will give a CR of 9.4:1 which is plenty. If you can even find an early 11:1 Eta engine, the CR would be 10:1 which is even better. Because you are using a 325i head, just bolt a 325i inlet manifold straight on." -:roll:

But i've seen posts where they have calculated the CR to be about ~8.0:1 which is not even close to the numbers given in this guide.
And with my knowledge it would be still best to use i pistons with 885 head, and with a little mill to the block you can really achieve a desent CR.

Post Mon Nov 13, 2017 6:53 am

there is an eta version with 9:1 (in addition to the 10.1:1 and 11:1) so add a head with 4cc more and the CR gets down into the 8's. thats how it is in the USA and down under but probably different for the UK probably read it on a US forum

Post Mon Nov 13, 2017 8:09 pm

Can't understand why there should be different engines in uk comparaed to for example germany. As much engine wikis tell, earlyer etas are about 9.0:1(cant remember the exact number) and late aka seta's are about 8.5:1. Im just wondering where have they got this info about so high compression eta engines.
And what makes it 11:1? the piston? what does it look like and whats the product code? Or were the etas different in e30 and e28 chassis?

Post Wed Nov 15, 2017 4:38 am

ETA engines in e30 are lower compression compared to eta in 5 series which are higher or something like that

Post Thu Nov 16, 2017 5:36 am

High comp etas are BS. Officialy there is only earlier 9.0:1 and late 8.5:1. Doesnt matter if its 5/3series.
I dont know where have they got so big numbers from. Maybe WITH 731 head and some skimming. But with 200 head- not possible.

Post Thu Nov 16, 2017 10:39 am

Lol they are real, I know someone who build one. You can tell based on the dome shape vs dish etc

found some old data that says from the 525e

Post Thu Nov 16, 2017 8:45 pm

lol, why should the 5 series have higher comp? is there any reason? Bmw built 2 seperate engines for 5/3series? Why should an eta engine, with very low power even need such a CR, sounds like ///M engine.
Even if you are telling me that I(me) am wrong then i would like to see that sheet with not just a cr number but with exact measures(that means piston, chamber, deck height and so on to calculate that magical 11:1)
And building a 11:1 is something else. What i"m meaning is a cr from factory.

Post Fri Nov 17, 2017 11:02 pm

koerake1 wrote:lol, why should the 5 series have higher comp? is there any reason? Bmw built 2 seperate engines for 5/3series? Why should an eta engine, with very low power even need such a CR, sounds like ///M engine.
Even if you are telling me that I(me) am wrong then i would like to see that sheet with not just a cr number but with exact measures(that means piston, chamber, deck height and so on to calculate that magical 11:1)
And building a 11:1 is something else. What i"m meaning is a cr from factory.

it was an earlier engine rather model specific, later models are same by my understanding.

this is commonly refereed to, use it at ones own risk. i do have on old spread sheet that confirms it

anyway its not the proper way to build a 2.7L starting with eta

Post Sat Nov 18, 2017 6:47 am

No information in bentley about 10.2 and 11. And why does this sheet show that 8.5 and 9.0 is usa? Euro. engines are also 8.5 and 9.0 which is more realistic.

You can take the eta but will need b25 pistons and adjust compression ratio with skimming a block. This requires an adjustable cam gear + highly recommended would be performance cam. Its all expensive and owning a hobby car is not cheap. Just eta and 885 swap will actually work fine, get yourself a proper remap and its allready better than b25- and thats a lot cheaper.

Post Tue Dec 25, 2018 8:53 pm

koerake1 wrote: ↑
Thu Nov 16, 2017 5:36 am
High comp etas are BS. Officialy there is only earlier 9.0:1 and late 8.5:1. Doesnt matter if its 5/3series.
I dont know where have they got so big numbers from. Maybe WITH 731 head and some skimming. But with 200 head- not possible.

https://en.wikipedia.org/wiki/BMW_M20#M20B27

"A compression ratio of 9.0:1 was used on the US 528e, and 11:1 on Euro 525e and 325e cars - this was reduced to 10.3:1 in 1985"

Personally, id buy a cheap block and mate it with a 325i head. Rebuild the bottom end (bearings and seals) and get some Schrick cams + chip/tune and be happy.

Those ETA blocks are going for €500 to €2,000 (low milage or rebuilt ones). Or one can source crank and pistons elsewhere and tear everything down....