difference between early and late eta blocks?

Post Sun Jul 06, 2008 10:02 am

Just curios really

They say if you build a 2.7 with the early eta block it gives higher compresion - i am guessing there are slightly diffeent pistons that make the difference and not crank or bore differences between the early or late blocks.

The reason i ask is that my current 2.7 (early eta bottom end and 2.0 head) is pnking again very mildly after taking out the 41.1 diff, it used to pink quite badly with the 3.46 diff and now only mldy with the 3.64 diff.
i also notice that the 082 AFM i have seems to make it pink a tad more than the 083 AFM ( i was just swapping them over for experiment really)

I will be getting it mapped at some stage and i want to make sure its worth my while getting it mapped the way it is - i like the ide of as high compresssion ratio as possible as it will never see boost but don't want it in such a way that we have to strangle the engine to avoid the pinking. I have a 325i head available i could throw on which i think would going by Andyboys numbers will yield 10:1. I prefer torque not all out power so i might pull ut the 268/268 cam i have in it too.

Any thoughts?

Post Sun Jul 06, 2008 10:09 am

does anyone know if the oversize BMW HEadgasket for skimmed heads might be suitable in this instance?
How much CR will they drop?

Post Sun Jul 06, 2008 12:54 pm

about 0.2-0.3 points, pulling the 268 will probably make it worse.

Post Sun Jul 06, 2008 5:05 pm

Cheers Reg.

I havent a clue if that would be enough to bring me into a good/suitable CR.

Post Sun Jul 06, 2008 6:29 pm

If you are using an early pre 84/85 eta block you have an 11:1 compression ratio. These cars can have pinking problems anyway so changing the cylinder in your case has made it worse. What car is the 084 and the 083 AFM from?

A remap might be in order and would probably sort your problems out. I have been warned by A-Tech that a 2.7 build without a remap would be abit rough above 3000 rpm. BMW lowered the compression ratio of the eta to 10.2:1 for a very good reason. I think pinking was part of that reasoning. Get it remaped it might sort it out. Besides if the ignition timing and fuel to air mixture are off causing the pinking problems then your engine is not performing to it maximium potential anyway.

Post Sun Jul 06, 2008 6:39 pm

maybe i'll just put the 2.5 head on
itsalways been an option but for some reaon i liked the idea of running the 2.0 head with really high CR- i thought if mapped it could fully solve the pinking and due to the high CR yield good torque figure.
msybe i shouldnt have linked high cr=good power/torque!!

Post Sun Jul 13, 2008 3:23 pm

Just a thought,have you tried it on super unleaded? I know that the ECU has no knock sensors but a higher octane fuel may just do the trick for you...I tried it when I first installed my 2.7,but carefull checking revealed that the tiny gain in mpg was more than offset by the extra cost,with no poor running on ordinary fuel I now use that all the time.