I would have thought it's the same(ish?) unit and the 125 can be fettled with to give similar output as the 130.

Sure someone with correct knowledge will be along shortly to advise.

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They are both 3 litre motors. Basically the same engine, but BMW restricted the power of the 125i so that it did not threaten sales of the 135i. Consequently, the 125i can be remapped to produce about 265bhp - the same as the 130i.

The 125i has smaller brakes than the 130i. This too, is a relatively cheaply addressed by swapping parts.

 

125i standard is much slower, mapped is still a bit slower and less urgent at least compared to my early 130i which is a bit peppier than the later cars anyway.

 

As Toed64 says, the engines are identical 3.0 N52's apart from the electronic map. The 125i has slightly longer gearing though, so even when the same (higher power DISA) 130i map is uploaded, the 125i will have negligibly slower acceleration.

The 125i is a wonderful car, I'd happily have one today. Having been electronically neutered from birth means it can't have been thrashed.

 

...
Having been electronically neutered from birth means it can't have been thrashed.

That's a good point - I hadn't thought of that!

 

Unless it's already been mapped of course

 

Good info, I didn't know they were the same engines

 

125i standard is much slower, mapped is still a bit slower and less urgent at least compared to my early 130i which is a bit peppier than the later cars anyway.

125i 0-60 6.2s (0-62 6.4) :

https://www.parkers.co.uk/bmw/1-series/coupe-2007/125i-m-sport-2d/specs/

130i 0-60 5.9s (0-62 6.1) :

https://www.parkers.co.uk/bmw/1-series/hatchback-2004/130i-m-sport-5d/specs/

That's no where near "much slower". The 125i is geared slightly lower (mostly in the lower gears), it's the only way with a 50hp deficit it can get even close to the 0-60 time of the 130i. With the same output power as a 130i it'll be quicker and more responsive to rev regardless of what a butt dyno might make you think.

Marco polo above says its geared longer or is that just in the later gears ? The three standard cars I have driven were a lot slower than my pre facelift 130i .

 

Need to check the Differential ratios.

 

I think the 125i might have a lower final drive ratio too (3.23 vs 3.46 I think?) which would make all gears longer.

I've got a 3.15 diff from an M3 on my 130i and it makes all the gears noticeably taller.

 

...
Having been electronically neutered from birth means it can't have been thrashed.

That's a good point - I hadn't thought of that!

Excuse my ignorance both but surely 7k rpm is 7k rpm no matter what state of tune the engine is. Or is it something more technical?

 

...
Having been electronically neutered from birth means it can't have been thrashed.

That's a good point - I hadn't thought of that!

Excuse my ignorance both but surely 7k rpm is 7k rpm no matter what state of tune the engine is. Or is it something more technical?

Essentially, engines burn fuel and air to make torque. The burn is an explosion which creates pressure in the cylinder to push the piston down which turns the crank and makes torque.

So... Torque = cylinder pressure

Remap an engine to make more torque means it burns more air and fuel, creating higher cylinder pressure.

Higher cylinder pressure means more stress on all moving components in the engine.

So 7k is 7k, but higher cylinder pressure at 7k means more wear.

 

Excuse my ignorance both but surely 7k rpm is 7k rpm no matter what state of tune the engine is. Or is it something more technical?

Lower cylinder temps, lower piston pressure. Everything will have experienced less torque; crank/clutch/gearbox/diff/etc.

130i has a bit more power/torque above 4,500 rev/min.

 

They are both 3 litre motors. Basically the same engine, but BMW restricted the power of the 125i so that it did not threaten sales of the 135i. Consequently, the 125i can be remapped to produce about 265bhp - the same as the 130i.

The 125i has smaller brakes than the 130i. This too, is a relatively cheaply addressed by swapping parts.

The 125's have smaller brake discs yes, but the calipers are the same size so stopping power isn't improved, just less fade on heavy prolonged braking.

 

Excuse my ignorance both but surely 7k rpm is 7k rpm no matter what state of tune the engine is. Or is it something more technical?

Lower cylinder temps, lower piston pressure. Everything will have experienced less torque; crank/clutch/gearbox/diff/etc.

130i has a bit more power/torque above 4,500 rev/min.

Thanks marco and Sam. It was indeed a bit technical but I live and learn

 

Glad I started this post, some good info here, many thanks.

 

They are both 3 litre motors. Basically the same engine, but BMW restricted the power of the 125i so that it did not threaten sales of the 135i. Consequently, the 125i can be remapped to produce about 265bhp - the same as the 130i.

The 125i has smaller brakes than the 130i. This too, is a relatively cheaply addressed by swapping parts.

The 125's have smaller brake discs yes, but the calipers are the same size so stopping power isn't improved, just less fade on heavy prolonged braking.

Not convinced that's entirely true. Yes same caliper/pads will mean the same braking force/pressure on the caliper, but on the 130 it's being applied approx 10% further from the hub/wheel centre so creating greater braking torque surely? If it were the case that rotor radius/diameter made no difference to brake force no manufacturers would ever fit larger diameter rotors. They'd just make them thicker (more massive) to deal with the extra heat.

I think what Twenny was saying is that the 130I doesn't have bigger brakes per se, it just has bigger discs. I know for sure that he has put the 130I discs on his so now has the same brakes as a 130i and it is a relatively easy swap so no need to worry about mapping a 125i and having insufficient braking as a disc swap is not that difficult.

 

Think he now has the M135i Brembos on the front another fairly cheap upgrade these days

 

Think he now has the M135i Brembos on the front another fairly cheap upgrade these days

Yeah I didn't want to confuse things mate but you're right he now has a lovely set of Brembo's on

 

They are both 3 litre motors. Basically the same engine, but BMW restricted the power of the 125i so that it did not threaten sales of the 135i. Consequently, the 125i can be remapped to produce about 265bhp - the same as the 130i.

The 125i has smaller brakes than the 130i. This too, is a relatively cheaply addressed by swapping parts.

The 125's have smaller brake discs yes, but the calipers are the same size so stopping power isn't improved, just less fade on heavy prolonged braking.

Not convinced that's entirely true. Yes same caliper/pads will mean the same braking force/pressure on the caliper, but on the 130 it's being applied approx 10% further from the hub/wheel centre so creating greater braking torque surely? If it were the case that rotor radius/diameter made no difference to brake force no manufacturers would ever fit larger diameter rotors. They'd just make them thicker (more massive) to deal with the extra heat.

Hey I'm just quoting from people bigger and better than myself -

https://www.babybmw.net/forum/viewtopic.php?t=63521&start=45

Around half way there's a deep discussion about brakes/discs/heat etc etc

 

Think he now has the M135i Brembos on the front another fairly cheap upgrade these days

Think he now has the M135i Brembos on the front another fairly cheap upgrade these days

Yeah I didn't want to confuse things mate but you're right he now has a lovely set of Brembo's on

Oh I do I do I do I do - (in a Lion from the wizard of Oz voice)

 

Hey I'm just quoting from people bigger and better than myself -

https://www.babybmw.net/forum/viewtopic.php?t=63521&start=45

Around half way there's a deep discussion about brakes/discs/heat etc etc

Ironic thing about that discussion is that everyone was correct:

Tyres are the actual limiting factor in just how much actual deceleration is possible for the majority of road cars. Nearly all road cars can overcome the grip of the tyres with their standard brake set up, no surprise there as that's what the manufacturer designs them for.

Larger brake discs and/or caliper pressure/brake pad area will generate higher maximum braking torque on the wheel, so assuming you don't change the master cylinder to compensate you'll need less brake pressure to achieve the same braking torque at the rotors. So the brakes feel more powerful, because they are.

Larger brake disks are (usually) more massive (read heavier) and so can absorb more heat energy for the same rise in temperature and so fade less/later under extreme use.

If you were to fit a the largest full race set up from a company like AP Racing on a car with skinny 205 all weather tyres you'd have so much braking force the car would be almost impossible to drive at urban speeds without locking up all the time. Assuming the wheel size was large enough to fit the 410mm brake disks of course.

Read headed section "disc diameter":

https://www.apracing.com/Info.aspx?InfoID=34&ProductID=1967

Few people know more or have more experience about brakes than AP Racing.

Hmm interesting.

Like I said, bigger and better than myself, so I'm happy to acknowledge you could be right but not too loudly.

The 130i brakes did feel better than my OEM Set up although they still faded badly at Bedford after a few heavy braking laps.

 

Oh I do I do I do I do - (in a Lion from the wizard of Oz voice)

Oh ! I thought you were quoting ABBA

 

Oh I do I do I do I do - (in a Lion from the wizard of Oz voice)

Oh ! I thought you were quoting ABBA

Nah Knowing me knowing you.

 

Hmm interesting.

Like I said, bigger and better than myself, so I'm happy to acknowledge you could be right but not too loudly.

The 130i brakes did feel better than my OEM Set up although they still faded badly at Bedford after a few heavy braking laps.

You need these:

https://www.apracing.com/product_de...ig_brake_kits/bmw/z4_applications/z4m_coupe_front-6_piston_kit_cp5575-1010.aspx

Only $5k

http://www.modbargains.com/AP-Racing-Formula-Big-Brake-Kit-E85-Z4.htm

Money money money

(That was ABBA lol)