[Quicksilver_M235]

I'm simply curious? This is already a fairly stout ride, but I've been digging around trying to find out where that 'fine line' is between just enough and too much.

Whereby too much means its time to beef up the internals.

Guestimates?

[amw896]

Originally Posted by Erebus

I'm simply curious? This is already a fairly stout ride, but I've been digging around trying to find out where that 'fine line' is between just enough and too much.

Whereby too much means its time to beef up the internals.

Guestimates?

probably 550ish whp. The m235i already has some beefed up internals.

[aschmitty6]

Originally Posted by amw896

probably 550ish whp. The m235i already has some beefed up internals.

I've only read that the crank is forged, not so sure about pistons. The N55 is pretty stout, seems the transmission is the weak point. There are a few P2 235s out there running 500whp, 450 wtq safely.

[mike@x-ph.com]

I would not go over 450 whp on auto cars ... Manual with upgrade clutch can probably go over 600 whp with the right fueling

[XutvJet]

Originally Posted by Erebus

I'm simply curious? This is already a fairly stout ride, but I've been digging around trying to find out where that 'fine line' is between just enough and too much.

Whereby too much means its time to beef up the internals.

Guestimates?

It's all guesstimates as BMW never intended the N55 to make the power of something like the S55 in the M3/M4. If they could have made the N55 a monster, they would have used it in the M3/4. Think about that for a moment.

IMO, you're walking on egg shells once you exceed 400whp/400wtq on the N55. The short block of the M235 is fairly stout with its forged crank (same one as the M2, the other N55s have a cast crank), the same rods and bearings as used in the M2 and the S55 in the M3/M4. Even though it's a open deck (just like the N54), you rarely hear of N55s or N54s have block issues. The M235 comes stock with a robust oil cooler and it also has oil squirters in the bores (unlike the more basic N55s). The head is fine and you never hear much about issues with it beyond maybe a VANOS issue which is generally easy to remedy.

The issue though is once you really start pushing a motor past about 20% of it's intended power levels, whether it's an N55 or something else, you start venturing into dangerous territory. You can be one tuning hiccup from getting a spun rod bearing due to super knock at heavy boost onset. And yes, N55s have been known to spin rod bearings, both stock and modified. The turbo's life will be greatly reduced if you run it hard.

Are there people that push these motors into the 500whp+ range without issues? Sure, but that doesn't mean it can necessarily live a long and happy life with that power. When running that much power, the tuning must be perfect or else one split-second hiccup could mean a $10K+ short block replacement and/or $2,500+ turbo replacement or both.

If you have the financial means, go for it, otherwise be happy with the basic mods and make sub 400whp/wtq or buy a used M3/M4 and make 400-420whp/wtq out of the box and reliably make nearly 500whp/wtq with basic mods.

[ceedawg]

Originally Posted by XutvJet

It's all guesstimates as BMW never intended the N55 to make the power of something like the S55 in the M3/M4. If they could have made the N55 a monster, they would have used it in the M3/4. Think about that for a moment.

IMO, you're walking on egg shells once you exceed 400whp/400wtq on the N55. The short block of the M235 is fairly stout with its forged crank (same one as the M2, the other N55s have a cast crank), the same rods and bearings as used in the M2 and the S55 in the M3/M4. Even though it's a open deck (just like the N54), you rarely hear of N55s or N54s have block issues. The M235 comes stock with a robust oil cooler and it also has oil squirters in the bores (unlike the more basic N55s). The head is fine and you never hear much about issues with it beyond maybe a VANOS issue which is generally easy to remedy.

The issue though is once you really start pushing a motor past about 20% of it's intended power levels, whether it's an N55 or something else, you start venturing into dangerous territory. You can be one tuning hiccup from getting a spun rod bearing due to super knock at heavy boost onset. And yes, N55s have been known to spin rod bearings, both stock and modified. The turbo's life will be greatly reduced if you run it hard.

Are there people that push these motors into the 500whp+ range without issues? Sure, but that doesn't mean it can necessarily live a long and happy life with that power. When running that much power, the tuning must be perfect or else one split-second hiccup could mean a $10K+ short block replacement and/or $2,500+ turbo replacement or both.

If you have the financial means, go for it, otherwise be happy with the basic mods and make sub 400whp/wtq or buy a used M3/M4 and make 400-420whp/wtq out of the box and reliably make nearly 500whp/wtq with basic mods.

I think it is still inconclusive how much power the N55 motor can handle, and the stock turbo ,exh manifold and fuel system will definitely keep one from finding out. One group says 500whp one group says 600whp in the N55 and with the S55 we are seeing cars exceed 700whp which is more than 50 % of what it was made to do.

I hate to make claims lest I have seen someone personally post their personal
experience with the limits.
There is always a risk when adding more power. I tend to feel stock is underpowered. We have seen this. However we see the N54 has surprised us all and I would not be surprised if when the fuel limit issue is figured out along with installing a big turbo the N55 will surprise as well.

[Dynamic_m235]

Originally Posted by mike@x-ph.com

I would not go over 450 whp on auto cars ... Manual with upgrade clutch can probably go over 600 whp with the right fueling

How come

[mike@x-ph.com]

Originally Posted by Dynamic_m235

How come

the auto transmission will struggle with over 450 torque

[Dynamic_m235]

Originally Posted by mike@x-ph.com

the auto transmission will struggle with over 450 torque

I've seen plenty run over 450wtq do you have any examples so I can check them out?

[mike@x-ph.com]

Originally Posted by Dynamic_m235

I've seen plenty run over 450wtq do you have any examples so I can check them out?

I ran 500 wtq on my N54 auto with no issues, that being said i always recommend my customer not to cross the 450 wtq mark.
Its never recommended to push your daily driver to the limit.

[Texan2er]

Originally Posted by mike@x-ph.com

I ran 500 wtq on my N54 auto with no issues, that being said i always recommend my customer not to cross the 450 wtq mark.
Its never recommended to push your daily driver to the limit.

Do you mean to 450 wtq or are you talking crank? Just wanting to check since I know the ZF 8HP45 in these cars is only rated for 450NM, and 450 wtq will be approaching 700NM at the crank.

Never tuned an auto car before, and wanting to have really well defined thresholds.

[XutvJet]

Originally Posted by Texan2er

Do you mean to 450 wtq or are you talking crank? Just wanting to check since I know the ZF 8HP45 in these cars is only rated for 450NM, and 450 wtq will be approaching 700NM at the crank.

Never tuned an auto car before, and wanting to have really well defined thresholds.

If you want a lot of power in any turbo BMW, the 6MT is the only way to go. The ZF in the F series is robust, but it is not designed to handle a lot more torque than stock. A stock M235 RWD auto makes around 320wtq stock on a Dynojet. That's around 390tq at the flywheel. It's very easy to increase the wtq by another 40-100wtq (120tq flywheel) by a piggyback or tune and DP. This is significant and torque (and heat) is what breaks things, not HP. HP is a number derived from torque.

A conservative tune and DP is as far as I'd ever push any N55, especially one with an automatic. That ZF is a VERY pricey piece to buy used and frightening if bought new (~$11K).

The main limiting factor in the 6MT is the clutch which can easily upgraded and the 1-2 syncro if shifted hard often or when the tranny isn't fully warmed up. I'm sure you could break it too with a lot of torque and hard launches. But used 6MTs are plentiful and even a new 6MT is somewhat reasonable at $3,500.

[Estoril6rod]

On-topic question: what about the OEM turbo? Does anyone know the estimated efficiency range of these turbos?

Heading towards the BM3 stage 2 route (91 oct) so I think its important, if not critical, info to have... thanks!!

[Amack]

Most people with a ps2 are hitting between 450-500 hp and I haven't read anything bad about it. Bigboost kits are pushing 550ish and stories seem good.

Maybe we only hear the positives and not the negatives. Who knows

[bryan_G01]

engine can take 600+ easily.

Auto tranny will throw up right around there, manual will hold a little more.
keep it under 25 psi.

[ChristosD]

can the stock turbo hold 18psi comfortably through out the rev range
( i assume the max the turbo can manage is 21psi so don't want to max it out tuners have told me 80% of its max is where they would push the turbo to safely?)

[bryan_G01]

Originally Posted by ChristosD

can the stock turbo hold 18psi comfortably through out the rev range
( i assume the max the turbo can manage is 21psi so don't want to max it out tuners have told me 80% of its max is where they would push the turbo to safely?)

up to 22, than your on your own...

[ChristosD]

can stock lpfp and hpfp keep up with the stock turbo at 22psi? i only have 91 octane available where i am.