Facelift 2.5i v 2.5si, how to tell the difference?

[corsair]

Hi all, first post !

I'm still learning but as I understand it there are three 2.5 litre N52 engine specs available in the later cars:

- 2.5i - 174bhp, 197g/km
- 2.5si (2006) - 214bhp, 202g/km
- 2.5si (2007-2008) - 214bhp, 199g/km

The badges on the wings seem to state the difference between 2.5i and 2.5si, however sometimes these aren't present or have been altered. An online tax check gives the rated CO2 output so this can help, but might not necessarily be correct and also could be a pain to check on the fly when viewing a car.

Does anyone know of any other visual differences between the 2.5i and and 2.5si that can be checked when viewing to confirm what spec engine is fitted?

This was all kicked off by this ebay listing, which states the car's an Si with 214bhp, however the badging is indeterminate and a vehicle check states 197g/km which would suggest it's the lower output 2.5i engine..

Thanks

 

[JamesClements]

Hi OP easiest way to tell is the 2.5i doesn't have a sport button the 2.5si does same as the 3.0si

The 2.5si also has a 3 stage inlet manifold with a second disa valve, the 2.5 only has 1 DISA. If you look behind the manifold I think you can see the second DISA

 

[corsair]

Thanks - that's great info; presuably the sport button is only relevant to Sport models (or do some SEs have them as well?).

I'll take a look at some pictures of listed cars to try and get a better idea of how to spot these differences!

 

[jamie_z4]

funny ernough i spotted that car this morning and straight away knew it wasnt an Si due to the lack of sport button!

FWIW ive had 18 z4 E85/86's now and the difference between the 2.5i N52 177 and 2.5si 216 is quite noticable. They feel a bit flat for sure.

 

[jamie_z4]

presuably the sport button is only relevant to Sport models (or do some SEs have them as well?).

No, the sport button should be present on any Si model N52 regardless of trim level.

 

[corsair]

Cheers!

Yes, thanks to JamesClements' post I've since revisited that listing and clocked the lack of Sport button (d/side of the transmission tunnel in front of the gear lever, correct..?). Tried to report it to ebay but unsurprisingly they don't seem to care about / offer the option to report stuff for inaccurate descriptions.

It appears that the post-2007 2.5Si is the one to go for as it just squeaks into the lower tax bracket of the 2.5i, has a lot more poke and same fuel economy on paper (whether this plays out in the real world is open to debate I guess).

 

[JamesClements]

Cheers!

Yes, thanks to JamesClements' post I've since revisited that listing and clocked the lack of Sport button (d/side of the transmission tunnel in front of the gear lever, correct..?). Tried to report it to ebay but unsurprisingly they don't seem to care about / offer the option to report stuff for inaccurate descriptions.

It appears that the post-2007 2.5Si is the one to go for as it just squeaks into the lower tax bracket of the 2.5i, has a lot more poke and same fuel economy on paper (whether this plays out in the real world is open to debate I guess).

Yes that's correct fuel economy will be similar I imagine - I have a 2.5i non si and a 3.0si and the fuel economy is similar. Around 38-40mpg on a run on the motorway, average mpg (mostly hooning ) is around 24. 2.5i with a map will be close in terms of performance so don't be too put off if you can find a well specified 2.5i, which is what I did

 

[jamie_z4]

Cheers!

Yes, thanks to JamesClements' post I've since revisited that listing and clocked the lack of Sport button (d/side of the transmission tunnel in front of the gear lever, correct..?). Tried to report it to ebay but unsurprisingly they don't seem to care about / offer the option to report stuff for inaccurate descriptions.

It appears that the post-2007 2.5Si is the one to go for as it just squeaks into the lower tax bracket of the 2.5i, has a lot more poke and same fuel economy on paper (whether this plays out in the real world is open to debate I guess).

It might be more helpful educating the seller rather than reporting to ebay, however it is still a reasonable price for a facelift sport even with the puny power output

 

[corsair]

Yes that's correct fuel economy will be similar I imagine - I have a 2.5i non si and a 3.0si and the fuel economy is similar. Around 38-40mpg on a run on the motorway, average mpg (mostly hooning ) is around 24. 2.5i with a map will be close in terms of performance so don't be too put off if you can find a well specified 2.5i, which is what I did

Thanks - the 2.5i is an N52 as opposed to the earler M54? I still can't get my head around how little these engines seem to vary in fuel economy despite their differing sizes / outputs. I hear the valvetronic's supposed to reduce pumping losses (although can't quite see why) so maybe this is responsible.

The plan currently is either a later 2.5si (for the lower tax) or a 3.0si.. but that's probably a way down the road as I need to sort other life stuff first.

Ta for the thought about the map - however I've done the modding / fiddling thing before and tbh I'm at a point in life where I just want a decent, standard example of something

It might be more helpful educating the seller rather than reporting to ebay, however it is still a reasonable price for a facelift sport even with the puny power output

Cheers - I did try to drop them a message but (presumably) being a listing for a car ebay want a load of personal info I'm not prepared / bothered to enter just to try and educate someone who'll 50/50 get snotty with me poking my nose in. Would like to make it right for others like me who might swallow the misinformation, but not if it's going to be a pain to do so.

 

[Zedebee]

Thanks - the 2.5i is an N52 as opposed to the earler M54?

Pre-facelift Z4s had the M54 in 2.2i, 2.5i and 3.0i. The 2.5i was good for 193bhp. There was no Si. The N52 2.5i essentially replaced the M54 2.2i
Post-facelift Z4s had the N52 with the silver top in 2.5i, 2.5Si and 3.0Si, which were then replaced in 2007 by the N52K black-top engine with the same designations and same bhp, but incorporated several modifications.
The Sport button was fitted to all Post-facelift Si cars regardless of SE/Sport spec.

 

[corsair]

Pre-facelift Z4s had the M54 in 2.2i, 2.5i and 3.0i. The 2.5i was good for 193bhp. There was no Si. The N52 2.5i essentially replaced the M54 2.2i
Post-facelift Z4s had the N52 with the silver top in 2.5i, 2.5Si and 3.0Si, which were then replaced in 2007 by the N52K black-top engine with the same designations and same bhp, but incorporated several modifications.
The Sport button was fitted to all Post-facelift Si cars regardless of SE/Sport spec.

Thanks - I was wondering if the 2.5i was the M54 as these appear less efficient than the later N52, so might explain similar fuel economy figures between the 2.5 and 3.0 if you were comparing an M54 with N52..

I didn't know that about the N52K (was aware of changes and lower emissions but not about the labelling) - by "block top" I assume you mean the engine cover; differing from the earlier silver items on the pre-2007 N52. That should be an easy thing to spot if viewing

 

[JamesClements]

Pre-facelift Z4s had the M54 in 2.2i, 2.5i and 3.0i. The 2.5i was good for 193bhp. There was no Si. The N52 2.5i essentially replaced the M54 2.2i
Post-facelift Z4s had the N52 with the silver top in 2.5i, 2.5Si and 3.0Si, which were then replaced in 2007 by the N52K black-top engine with the same designations and same bhp, but incorporated several modifications.
The Sport button was fitted to all Post-facelift Si cars regardless of SE/Sport spec.

Thanks - I was wondering if the 2.5i was the M54 as these appear less efficient than the later N52, so might explain similar fuel economy figures between the 2.5 and 3.0 if you were comparing an M54 with N52..

I didn't know that about the N52K (was aware of changes and lower emissions but not about the labelling) - by "block top" I assume you mean the engine cover; differing from the earlier silver items on the pre-2007 N52. That should be an easy thing to spot if viewing

In general i don't think capacity makes much difference to real world fuel economy on the N52. Although don't daily mine though so never really bothered about MPG. I think the black top engine is less prone to CCV related problems

Both engines M54 and N52 are very reliable. Main things to look out for on the N52 are the waterpump, expansion tank, oil filter and rocker cover gaskets I have replaced all of these on both my cars mileage on both is around 85k. Other than that pretty bullet proof with regular servicing/maintenance

 

[corsair]

Pre-facelift Z4s had the M54 in 2.2i, 2.5i and 3.0i. The 2.5i was good for 193bhp. There was no Si. The N52 2.5i essentially replaced the M54 2.2i
Post-facelift Z4s had the N52 with the silver top in 2.5i, 2.5Si and 3.0Si, which were then replaced in 2007 by the N52K black-top engine with the same designations and same bhp, but incorporated several modifications.
The Sport button was fitted to all Post-facelift Si cars regardless of SE/Sport spec.

Thanks - I was wondering if the 2.5i was the M54 as these appear less efficient than the later N52, so might explain similar fuel economy figures between the 2.5 and 3.0 if you were comparing an M54 with N52..

I didn't know that about the N52K (was aware of changes and lower emissions but not about the labelling) - by "block top" I assume you mean the engine cover; differing from the earlier silver items on the pre-2007 N52. That should be an easy thing to spot if viewing

In general i don't think capacity makes much difference to real world fuel economy on the N52. Although don't daily mine though so never really bothered about MPG. I think the black top engine is less prone to CCV related problems

Both engines M54 and N52 are very reliable. Main things to look out for on the N52 are the waterpump, expansion tank, oil filter and rocker cover gaskets I have replaced all of these on both my cars mileage on both is around 85k. Other than that pretty bullet proof with regular servicing/maintenance

Thanks - certainly seems that way about the capacity, but I'm intrigued to know more. Usually bigger = more part-throttle pumping losses and lower efficiency under normal conditions.

Ta for the heads-up about the issues; was just watching similar about the later engines being potentially a bit more problematic around the CCV.. typical. As you suggest though it seems like they're pretty relaible on the whole with no really worrying / potentially catastrophic faults (like the Boxter IMS bearing for example!)

 

[Smartbear]

Thanks - I was wondering if the 2.5i was the M54 as these appear less efficient than the later N52, so might explain similar fuel economy figures between the 2.5 and 3.0 if you were comparing an M54 with N52..

I didn't know that about the N52K (was aware of changes and lower emissions but not about the labelling) - by "block top" I assume you mean the engine cover; differing from the earlier silver items on the pre-2007 N52. That should be an easy thing to spot if viewing

In general i don't think capacity makes much difference to real world fuel economy on the N52. Although don't daily mine though so never really bothered about MPG. I think the black top engine is less prone to CCV related problems

Both engines M54 and N52 are very reliable. Main things to look out for on the N52 are the waterpump, expansion tank, oil filter and rocker cover gaskets I have replaced all of these on both my cars mileage on both is around 85k. Other than that pretty bullet proof with regular servicing/maintenance

Thanks - certainly seems that way about the capacity, but I'm intrigued to know more. Usually bigger = more part-throttle pumping losses and lower efficiency under normal conditions.

Ta for the heads-up about the issues; was just watching similar about the later engines being potentially a bit more problematic around the CCV.. typical. As you suggest though it seems like they're pretty relaible on the whole with no really worrying / potentially catastrophic faults (like the Boxter IMS bearing for example!)

The efficiency improvement is largely down to the valvetronic system altering valve lift to act as a throttle.
I understand the throttle body is usually the main source of inefficiency, with the n52 the throttle body gets used as a fail safe.
Rob

 

[Mike6]

There is a bewildering array of engine specs. My 2005 2.5 SE has a sports button and also has around 194 bhp but the facelift version of 2006 only has around 174 bhp but I believe it has a sixth gear instead of my five speed. Dont know whether or not it has a sports button. My car was also supposed to have been manufactured in America but according to its engine plate etc it was manufactured in Germany. My MOT inspector was intriqued so looked it all up and said definetly made in Germany.
There are threads on this site where someone took the time to set it all down chapter and verse. Might be worth trying to find it.

 

[corsair]

In general i don't think capacity makes much difference to real world fuel economy on the N52. Although don't daily mine though so never really bothered about MPG. I think the black top engine is less prone to CCV related problems

Both engines M54 and N52 are very reliable. Main things to look out for on the N52 are the waterpump, expansion tank, oil filter and rocker cover gaskets I have replaced all of these on both my cars mileage on both is around 85k. Other than that pretty bullet proof with regular servicing/maintenance

Thanks - certainly seems that way about the capacity, but I'm intrigued to know more. Usually bigger = more part-throttle pumping losses and lower efficiency under normal conditions.

Ta for the heads-up about the issues; was just watching similar about the later engines being potentially a bit more problematic around the CCV.. typical. As you suggest though it seems like they're pretty relaible on the whole with no really worrying / potentially catastrophic faults (like the Boxter IMS bearing for example!)

The efficiency improvement is largely down to the valvetronic system altering valve lift to act as a throttle.
I understand the throttle body is usually the main source of inefficiency, with the n52 the throttle body gets used as a fail safe.
Rob

Thanks - I've looked into this and it's an ingenious system. Sources claim that it reduces pumpling losses at part throttle, however I can't quite get my head around this. Pumping losses at part throttle result from the pistons drawing against a vacuum on the induction stroke; in a "normal" engine this is the result of flow being restricted to all cylinders by the throttle on the other end of the plenum / inlet manifold. With valvetronic the restriction is moved from the throttle to the inlet valve..

To maintain a steady vehicle speed at part throttle you need a set amount of power, so a set amount of fuel and air; so surely the mean force acting on the piston to resist motion and cause losses is the same regardless of how that restriction is being achieved..? I can see an argument for valvetronic giving better combustion efficiency at part throttle due to higher air / fuel mix velocities entering the cylinders through the restrictive valves; so maybe that's actually where the efficiency gain comes from.

Would love it if someone more educated / clever than me could break it down

There is a bewildering array of engine specs. My 2005 2.5 SE has a sports button and also has around 194 bhp but the facelift version of 2006 only has around 174 bhp but I believe it has a sixth gear instead of my five speed. Dont know whether or not it has a sports button. My car was also supposed to have been manufactured in America but according to its engine plate etc it was manufactured in Germany. My MOT inspector was intriqued so looked it all up and said definetly made in Germany.
There are threads on this site where someone took the time to set it all down chapter and verse. Might be worth trying to find it.

Indeed; Zedebee has broken it down well up-thread. Basically 2.2, 2.5 and 3.0 M52 engines pre-2006; with only the 3.0 getting the 6sp gearbag. Post-2006 it's all N-series engines; the 2.0 four pot along with 2.5 and 3.0 six pots. All of the six pots (and maybe the four) now have the 6sp box, with the 2.5 being offered in lower output "2.5i" form or higher output "2.5si" formats.

As a low-commitment entry to the marque I quite fancied an early 2.2i, however the tax is the same as the 3.0i, fuel economy barely any better than the 3.0i and insurance pretty much irrelevant thanks to my advancing years..

 

[Mr Tidy]

As a low-commitment entry to the marque I quite fancied an early 2.2i, however the tax is the same as the 3.0i, fuel economy barely any better than the 3.0i and insurance pretty much irrelevant thanks to my advancing years..

I think the running costs for any of the pre-facelift M54 sixes are the same, but you'd probably pay less for a 2.2i than a 2.5i or 3.0i which would be a lower commitment! But you might find yourself wishing you had bought a bigger engine. But for me a straight 6 is one of the Z4s unique features.

Aside from the engines the biggest bonus of the facelifts is that Sport models have the highly sought-after M-Sport seats which were an option on pre-facelifts that hardly anyone chose!

 

[Zedebee]

My car was also supposed to have been manufactured in America but according to its engine plate etc it was manufactured in Germany. My MOT inspector was intriqued so looked it all up and said definetly made in Germany.

Nope, all E85/E86 (and Z3s before them) were made in Spartanburg, South Carolina. The engine itself may have been made in the motherland, but the car was assembled in USA.

 

[corsair]

As a low-commitment entry to the marque I quite fancied an early 2.2i, however the tax is the same as the 3.0i, fuel economy barely any better than the 3.0i and insurance pretty much irrelevant thanks to my advancing years..

I think the running costs for any of the pre-facelift M54 sixes are the same, but you'd probably pay less for a 2.2i than a 2.5i or 3.0i which would be a lower commitment! But you might find yourself wishing you had bought a bigger engine. But for me a straight 6 is one of the Z4s unique features.

Aside from the engines the biggest bonus of the facelifts is that Sport models have the highly sought-after M-Sport seats which were an option on pre-facelifts that hardly anyone chose!

Thanks - I agree largely; I like the idea of the 2.2 as a "toe in the water" option, however if the running costs are similar and the capital's there for a larger-displacement model (which, given the apparent fact that these are right at the bottom of their depreciation curve could be recovered on resale) it seems there's not a lot to going for the smaller one.

The M-sport seats of the later models do look really nice, plus there's the fact that the whole range got the six-speed box, which personally really appeals.. although as above the gem of the range appears to be the 3.0 which has always had that extra set of cogs.

I'm currently saving for a flat and commuting in a Mk7 Civic (which has been great for the money tbh) but I'm hoping that once the housing market's sorted itself out I'll be able to move, commute by bike and indulge in a more fun vehicle as I'll be doing minimal mileage - in which case the 3.0 seems like the only choice

 

[Mr Tidy]

The other advantage is that BMW were a bit miserly with the standard equipment on Z4s, and the bigger engined models tend to have more options like heated seats, cruise control, Bi-Xenons, etc.

I hope things work out with the flat and ultimately Z4 purchase.