Thread: Turbo Boost PSI
View Single Post
      03-09-2012, 12:02 AM   #37
Major General

Drives: 340i M-sport AT
Join Date: Mar 2006
Location: Chicago

iTrader: (1)

Originally Posted by BMW Gator View Post
I have been reading alot and have not seen any discussion regarding boost pressure? What is the stock psi?
Looking at the dyno charts of tuned 1m's there is no reference to boost psi at specific rpm's? I assume a "tune" also remaps the turbo psi at specific rpm's? - Is the boost psi electronically controlled in the N54?
Thanks - just trying to get educated before I take delivery of my 1m in a couple of months!
Here's some info to get you going.

Stock boost is .8 bar, which is 14.7 x .8 = 11.6psi normal boost.
Overboost is rated at 1 bar or 14.7 psi.

Stock pressure on the non M N54 is 8.7psi.
The JB+ at "max" setting gives the N54 up to +4.75psi.
At the "max" setting boost should be about 13.45psi.

On an 09 135i, we had a JB+ set to near "max".
Using a 'hijack' program, we hijacked the fuel gauge to be a turbo boost gauge. The setting was near max, not all the way, and we were seeing a bit over 12psi at full boost. This is not overboost, it was "normal" with that setting.

Burger tuning claims that with the JB+ set to "max", real RWHP gains
BT claims that at a +2.75 setting, RWHP is +40hp and +50lb ft.
My guess is that non wheel power is about 340hp and 350lb ft, which is close to the 1M's stock power output.
Max setting is capable of up to +60hp at the wheels.

I think that's a bit optimistic but I can tell you that at near max setting the power difference is substantial, not just noticeable, but substantial.
Driveability was very OEM like, which was very surprising for such a simple piggyback device.

Realistically, I think the setting we used gave us about about +3.75, which accounts for the boost reading showing something like 12.5psi.
I can't be accurate on that because when you hijack the gas gauge you only have 4 hash marks by which to judge, so some estimation has to happen.

N54 compression ratio is 10.2:1, which is quite high for a turbo enigne, but that's what we can have thanks to direct injection and it's cooling effect on the combustion chamber.

The 1M's N54 compression ratio is also 10.2:1 same as the non M engine.
Increased power for the 1M is coming from tuning, not from added compression, just for data point.

The turbo's used in both versions of N54 are Mitsubishi TD03, very small little buggers. They can be modded with a different compressor wheel that will allow a greater air flow and the turbines can be clipped helping reduce back pressure and giving a bit better flow at higher rpm.

Back to the TD03 turbo's, the 1M N54 also uses the same manifold and turbo's as the non M N54.
Part numbers:

N54 135i: 11657593015 & 11657593017
N54 1M: 11657593015 & 11657593017

These little turbo's spool quickly and they are ideal for a power curve that has big torque at low rpm. But, they run out of flow capacity as engine speed and turbine speed increase. That's why our engines just don't pull very hard at higher rpm. Clipping would help that a bit.
A larger turbo would help that quite a bit, but lag would markedly increase.

Some of the 1M engine internals were beefed up to have good long life while under a 50K mile warranty. That's also a bonus for 1M drivers who want a tune as the 1M engine has the advantage of beefier internals, and bodes well for using larger turbo's.

Last edited by RPM90; 03-09-2012 at 10:03 PM.