Need help with what happens after my build

thomsenski

New Member
Mar 16, 2018
5
3
0
Ride
2009 335i when its not broken
Hi I have a 09 335i that has down pipes, charge pipes, intercooler, aftermarket blowoff valve and several other add ons,

so long story short owned car for short time and spun bearing, building new motor for it and changing pistions to JE forged pistions, The ones I'm finding if I'm correct are going to lower the compression ration .7 10.2 to1 and after will be 9.5 to 1
so with the way the car is now how is this going to effect it? what do I need to do about tunning for this? I know lower compression allows more boost? but I know everything has a cause and effect.

any advise? or should I try and stay with the 10.2 to 1 compression
 

doublespaces

General of the Army
Oct 18, 2016
8,939
4,144
0
AZ
Ride
2009 E93 335i
With direct injection, seems like I've heard a lot of people just staying stock compression.
 

Ninja_Spartan

New Member
May 7, 2018
1
1
0
Ride
335i DCT 2009
Did the bearing spin due to low oil pressure or just a bad bearing?
Iv'e had the same issue with mine. Spun a bearing and currently in the process of a rebuild. I'm also looking at lower compression pistons either JE or Carrillo 9.5:1.

i'm planning for 600whp on pump gas which is the main reason i'm looking at a lower compression.

Did you stay with stock compression or go lower to 9.5?
 
  • Like
Reactions: doublespaces

langsbr

Captain
Apr 5, 2017
1,176
673
0
Ride
07 335i 6MT e90
If you're going to run an ethanol blend you'd probably be fine with stock compression, but reducing it will only make it more resistant to knock. If I were building a motor, I'd drop it at least to 9.5, maybe a full point.
 

boostE92d

Corporal
Jan 9, 2018
147
86
0
Houston TX
Ride
12 335is
Lowering the compression ratio is going to make the car sluggish when you are off boost. It was a trade off made in the past. Reduce compression to ward off knock, so you could run higher boost. You can definitely have high compression and high boost safely with these motors and the tuning that is available. You absolutely can do what you want, it's your car. Just know that there is no reason to lower compression when building a direct injection motor. You can easily avoid knock at high boost through tuning and not give up transient response, especially if you have access to 93 or e85.