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      12-29-2010, 04:37 AM   #130
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Quote:
Originally Posted by maxnix View Post
Well, geometric compression ratio is not as important as Mean Effective Pressure, which in turn is a function on many other engine operating parameters including rpm.

But in any case, it is usually the case that a lower CR will require a higher flow (more pressure) to reach the same MEP as the same engine with a higher CR will achieve the same MEP with less flow, and thus requires less pressure.

It is interesting BMW chose and open deck design for a turbo engine. Presuming the OEM pistons are forged?

Yes, OEM pistons are forged, and made by Mahle

Quote:
Originally Posted by mycoupe View Post
Just some thoughts here on what you stated...


2. Are you assuming he wants more compression? Because I am pretty sure he stated that he was switching to a lower compression like the Alpina so that he can run more boost and therefore make more reliable and safe power.

Exactly the reason why I'm going to a 9.5:1 compression ratio - more reliable at the same given boost level. I'm not looking to max out the boost pressures - I've been running 15/16psi for a long time now, and still want to run the same but at a lower compression ratio.

Quote:
Originally Posted by NTTY View Post
Amazing post, thank you for sharing!
Who did the modification of your software gearbox? What are the possible modifications?
Thank you!

The gearbox software was rewritten by ZF themselves and an engine tuner in Germany. Unfortunately it's not a commercially available software revision as it was done as a one-off as part of an exchange of services

Quote:
Originally Posted by scheherazade View Post
Was the cylinder sleeve scored all around evenly?
Or was it scored mostly on the side opposite of the conrod/crank joint during down-stroke?

I expect a little bit of scoring, as things aren't perfect.
Every startup when oil pressure is low should contribute a little bit, and build up over time.
Was the crank scoring simply visible (as in still flat, but texture changed so light reflects differently), or was the scoring deep (grooved)?

-scheherazade
Sleeve was scored all around fairly evenly. Was fairly grooved too

Quote:
Originally Posted by SLEEPYDUB View Post
I was directed to this thread by Terry because im having idle problems and smoking problems whenever i decelerate. I also am consuming about a quart of oil every 1000 miles or so.

Tony, do you think that my problem could be similar to yours? A clogged up PCV system, or bad carbon build up on the valves? Im trying to pin point the problem and fix it, but BMW isnt helping me at all.
The smoke when you decelerate is definitely something I suffered from - I suspected it was oil being drawn past the piston rings. The excessive oil consumption should also suggest this as well. A blocked PCV wouldn't explain the excessive oil consumption, although it might explain the lumpy idle.

BMW's stance is difficult - they won't look at the problem because they don't want to commit to such a large labour bill only to discover there's nothing wrong with the engine. I would suggest you approach your dealer and ask them to investigate - you'll probably have to agree to pay the labour, or a fixed portion of the labour, in the event that they discover there is nothing wrong with the engine. If there is something wrong, then BMW will cover the cost under the warranty.

At the very least you need to have a full inspection of the head to see the state of it
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