How much additional HP can I squeeze out?

[HondaGoneRogue]

Originally Posted by raceman

With pleasure.

I myself drive one of such tuned cars (well with better spec, due to catless exhaust manifold, better breathing exhaust system and adjusted ECU to Injen SRI intake).
300-310 HP 125i is reality and car is not left much behind by 135i in real street situation. On the contrary, I like this engine much better than stock twin turbo, although it lacks a bit of torque on lower revs, but works like butter on upper.
Now US, tuners do something to help guys overseas. It's not rocket science.

A real street situation will have the 135i tuned as well (400hp)
But I am happy to see the 128's getting some love!

[SJ]

Originally Posted by raceman

With pleasure.

I myself drive one of such tuned cars (well with better spec, due to catless exhaust manifold, better breathing exhaust system and adjusted ECU to Injen SRI intake).
300-310 HP 125i is reality and car is not left much behind by 135i in real street situation. On the contrary, I like this engine much better than stock twin turbo, although it lacks a bit of torque on lower revs, but works like butter on upper.
Now US, tuners do something to help guys overseas. It's not rocket science.

How about the stock 128i transmission. Let's assume automatic . (I'm an automatic guy with drinking coffee and talking on cell phone - not very German, I know.)

It seems the auto-tran in the 128i is less robust than the one in 135i. Someone said it was provided to BMW by GM, but the one in the 135i is from someone else. Can the stock auto-tran, drive train, cooling systems handle the engine tuned to ~280-300 horses?

[raceman]

Originally Posted by SJ

Can the stock auto-tran, drive train, cooling systems handle the engine tuned to ~280-300 horses?

Good question.
I assume that anyone with 125i/128i WILL NOT use car for extreme racing on the road or track. This car was not designed for that, no matter which engine.
135i is better suited for such purposes, although it is ALSO NOT a car with real racing spirit and core.
M3, Alpina or re-worked Schnitzer cars are about that.
125i/128i with 280-300 HP is practically 130i with some chip tuning power increase over stock engine. So,technically everything on 125i/128i is same or close to 130i that is proven car already.
Additional power doesn't mean that 125i is converted to 135i, it simply means that in situations when driver needs higher acceleration car will deliver it.
During day it may happen one or couple of times or not, so having additional 30-40% horse power under the hood brings some peace of mind and of course joy.
To think that gearbox will meltdown or take apart due to such increase is exaggerating, given that car will not be used for what it wasn't designed.
I would be more concerned about brakes and suspension in case that constant high speed style of driving would be my target.

[Eddie_440i]

Raceman, have you done the 280ps ECU tune on your 125i ? Price ? Happy ? Was it worth it ?

[raceman]

Originally Posted by Eddie_125i

Raceman, have you done the 280ps ECU tune on your 125i ? Price ? Happy ? Was it worth it ?

I did 270 HP first. Car ran quicker 0 to 100 or 200 km/h than 130i in straight comparison (around 6.2 s with AT). Subjectivelly it is not tremendous increase, but adds lot of confidence when driving fast.
After catalytic converter exhaust manifold replaced with catless + no mid silencer and Bastuck sport quad end ECU required once again re-tuning to new situation (short ram intake was installed, but I don't know if that gave any improvement). All in all, further optimization did a god job (it felt like more gain than initial 50+ HP increase).
Car is pure joy to drive without any turbo lags, revs to 7000 with nice character in upper revs. On the road it's very close to stock 135i to extent that no more power is actually needed, except for some extreme acceleration.
I think we squeezed out the last drop of power from N52 engine.
Two stages ECU tuning was around 1600 Eur, full exhaust replacement further 2000 Eur.
ECU tuning is definitelly worth, as it doesn't change anything out of BMW's stock setup for N52 with 272 HP.
Exhaust and ECU optimization for higher flow with de-cat is matter of taste.
It costs more and give less HP (in total about 30-35), but subjectivelly engine revs differently (way more responsive in mid and specially higher revs). I would do it again and again, but still it's very subjective opinion (car is louder in very nice manner, reminding 'real race car sonics'.)
Except for massive torgue in 1500-3500 rpms, I prefer this engine over stock N54 in mid and high revs and overall feel.