eta i head compression.

[TopOfTheLine89]

I have a 87 eta, I know people say you can't put the i head on because you loose alot of compression with the regular eta pistons. Does anyone know what my compresion would be with the i head? Cause if i turbo it the low compresion would be a good thing so im wondering how low the compresion would be.

[BigD]

You know what... an old timer BMW mechanic in Vancouver told me that the whole loss of power with i head swap is bogus. Yeah the compression is lower but the cam is still bigger and hotter, and the valves are larger. There is still a very nice power gain. Again this is 2nd hand info but I do know that this guy has done it, along with 1000 other weird things with BMWs. Just saying that before you go believing gut feelings, find someone who has tried it.

[Jordan]

Compression will be around 8:1.

Assuming you swap an entire I top end on, and convert to Motronic 1.3 you will see some modest gains. Really nothing worth the effort though IMO.

[TopOfTheLine89]

Thanks guys, that is exactly what i wanted to know. Cause 8:1 compression would be great for a turbo setup.

Is motronic 1.3 just the ecu? what all would need to be changed? injectors?

[nando]

you'd want pretty much everything - engine harness, injectors, sensors, etc. basically everything above the block. you also need the front crank sensor and harmonic balancer/toothed wheel.

[TopOfTheLine89]

damn, maybe ill just stick to my plans of swapping in the i cam,valvesprings and intake manifold then call it a day. Would be way safer to turbo though with the 8:1 compression.

what would happen if i swapped nothing?lol. high reving ETA performance?

[BigD]

You mean just turbo an eta? Nothing spectacular... well from a performance standpoint. The cam is still too lame so it's not gonna rev very high or perform well while there but you'd float a valve.

By the way, a little off topic, why do people obsess over having a forged crankshaft? Do these really ever break? I've seen broken pistons and rods but crankshafts???

[MR 325]

what would happen if i swapped nothing?lol. high reving ETA performance?

You won't be high revving without the i Motronic setup.

[M20Curtis]

You won't lose power, I run an '84 e with i upper end, cone filter, and free flow exhaust, on stock chip I put down 138rwhp and 151lbft of torque. Don't listen to anyone saying it doesn't work, I can pull harder than any stock 325i I know.

[ZeroCool]

You won't lose power, I run an '84 e with i upper end, cone filter, and free flow exhaust, on stock chip I put down 138rwhp and 151lbft of torque. Don't listen to anyone saying it doesn't work, I can pull harder than any stock 325i I know.

Any more details on how you did this?

Is it really just as simple as the i upper end and the computer?

Is the eta's bottom end capable of reving up to like 6k?

I'd love to do this to my eta as it should be pretty easy to get the parts cheaply over time.

[NomadE30]

Any more details on how you did this?

Is it really just as simple as the i upper end and the computer?

Is the eta's bottom end capable of reving up to like 6k?

I'd love to do this to my eta as it should be pretty easy to get the parts cheaply over time.

Yes the eta bottom end is able to run that high, only problem limiting eta is the single valve springs and 4 oil journals instead of 7. And the only thing limiting from there is Rocker arms and harmonic balancer alogn with you don't make any power past 7k

[MR 325]

You won't lose power, I run an '84 e with i upper end, cone filter, and free flow exhaust, on stock chip I put down 138rwhp and 151lbft of torque. Don't listen to anyone saying it doesn't work, I can pull harder than any stock 325i I know.

That's not that great of numbers.

[M20Curtis]

Yes its that simple of a bolt on and I know that isnt that great of numbers but for a 100k+ bottom end, nothing rebuilt, and $250 invested, it sure kicks a stock e cars ass.

[TopOfTheLine89]

You won't lose power, I run an '84 e with i upper end, cone filter, and free flow exhaust, on stock chip I put down 138rwhp and 151lbft of torque. Don't listen to anyone saying it doesn't work, I can pull harder than any stock 325i I know.

What electronics did you swap? How hard was it?

[M20Curtis]

I got a harness with my 325i head I bought and it replaces the stock harness. It really wasnt that hard, everything is plug and play. You just need to also replace the front harmonic balancer and use the new crank sensor and it should fire right up.