F30 320i vs 328i engines - Part number comparison

BMW has just announced a new entry level F30 3 series, the 320i. The 320i shares the same N20; TwinPower single turbo, twin scroll, 2.0 liter inline 4 cylinder engine as the 328i. The 320i is factory rated at 180 hp at 5,000 RPMs and 200 lb-ft of torque from 1,250 RPMs. Stacked next to the 328i with 240hp at 5000 RPMs and 255 lb-ft of torque from 1250 RPMs and the obvious question is what is the difference in the two engines.

The first obvious answer is there is something in BMW's DME control software that limits the power, most likely by limiting boost pressure, on the 320i. That appears to be true as both the 320 and the 328 use the same DME hardware (PN - 12148604210) and the same engine control system MEVD 17.2.9. With a software tweak the likely difference between the 320i and the 328i we go in search of other changes that might limit the 320is ability to make the same power the 328i N20 puts down.

Read more about the 2013 BMW 320i entry level 3 series

The next easy target is the intake, exhaust manifold and turbo. Surprisingly they turned out to be the same part number. In fact the 320i and the 328i share the exact same part numbers for a majority of the engine components.

Shared engine components between F30 320i and 328i

• Cylinder head - PN 11127624778
• Connecting rods - PN 11247624616
• Crankshaft - PN 11212212762
• Intake manifold - PN 11617588126
• Air box - PN 13717597589
• Air filter - PN 13718507320
• Intercooler - PN 17517618809
• Radiator - PN 17117600520
• Throttle body - PN 13547588625
• HPFP - PN 13517584461
• MAF - PN 13627602038
• DME/ECU - PN 12148604210
• Exhaust manifold/turbo - PN 11657642469

See what is missing in the above list? The difference in the 320i and the 328i is the pistons. While both have a 10:1 compression ratio the 320i has a different part numbers for the pistons then the 328i. What that exactly means in terms of the ability to boost the turbo pressure and get 328 horsepower from your 320 is not yet known.

Stay tuned as we continue to sift through BMW's technical documents searching for an answer.

WOW! So there's some serious potential to turn things back up in this car then!

If you could get to 210-220hp with a similar boost in torque with a Stage 1 upgrade, this car just got a whole lot more interesting to me.

Originally Posted by tim330i

See what is missing in the above list? The difference in the 320i and the 328i is the pistons. While both have a 10:1 compression ratio the 320i has a different part numbers for the pistons then the 328i. What that exactly means in terms of the ability to boost the turbo pressure and get 328 horsepower from your 320 is not yet known.

Stay tuned as we continue to sift through BMW's technical documents searching for an answer.

This effectively says that the 328i is a $2-3k engine tune over 320i from the factory. Is N20 just for US spec 320i or for Euro/Canadian 320i as well? I wonder if non-US folks have already figured out how to boost the 320i.

What's the bore & stroke between the engines?

From your list there are lots of areas for lost power & response from these:

-smaller diameter throttle body
-smaller or non straight intake manifold runners
-smaller diameter airbox
-lower flow CFM air filter
-smaller intercooler
-non dished pistons
-crankshaft with a lower stroke
-smaller exhaust manifold/turbo
-non polished or ported cylinder head

Seems like they are limiting power via less air & a controlled less powerful combustion. Plus the turbo recovery and cooling are more crippled.

Are we sure it's 10:1. Here's the difference in the short block description

328i
Short Engine N20B20A 1 11002297079
only in conjunction with

320i
For vehicles with
Low compression engine
S858A=Yes <== what is this?
01 Short Engine N20B20A 1 11002297079

isn't starting w/a lower compression engine better for swapping in a big honk'n turbo?

(of course that would only be coupled with greatly increasing for the airflow both in and out ; just wanted to frame it with that)

Originally Posted by m8o

isn't starting w/a lower compression engine better for swapping in a big honk'n turbo?

Unfortunately, I'm not sure how much turbo swapping is going to happen. The turbo and exhaust manifold are a single component. The engineers have their reasons (hot-side performance), but from a mod perspective it sucks. It's not like the traditional way where it's just a matter of matching the housings to the flanges.

Basically we'll have to rely on a vendor to engineer an exhaust manifold and plumbing, or swap in from another engine/year like they do on the Audi's A4's, which have a similar setup. I checked the 745Li (IIRC), which is a turbo'd v8, but the header flanges are different and it may not even be an "upgrade". Intra-make part upgrade/swapping is not a new concept, but in the case of turbo's it requires knowing the subtle differences between the parts.

Back on-topic, I think the OP was incorrect, but I'm open to be proven wrong. I hope I'm right though cuz I'll be pretty pissed if it's just a tune

So I'm really curious about the pistons. That could either be no big deal or big freaking deal when it comes to turning the power up. Why swap them? The biggest reason I can think of is cost-savings OR greater rotating mass efficiency through a different crown design or ring pack design. But it's not like the regular n20 is some inefficient beast - so neither of those really makes sense to me except perhaps cost-savings achievable by using a lower quality piston because you are running so much less dynamic compression against them with the detuned engine.

If I'm totally off base then the 320i is going to be the entry-euro-tuner's delight. No forced "lines", cheaper, and an engine ready to play in the ~260whp range on pump gas.

There is defnitely a difference in compression ratio. The 328 is 10:1 and the 320 is 11:1. Thus, the higher compression 320 will knock a lot sooner than the 328, so less tunable. I've also heard that the 320 has thinner drive shafts.

Originally Posted by vitchie

There is defnitely a difference in compression ratio. The 328 is 10:1 and the 320 is 11:1. Thus, the higher compression 320 will knock a lot sooner than the 328, so less tunable. I've also heard that the 320 has thinner drive shafts.

Where did you get your info on the compression ratio? BMWUSA.com (i know, not the best source of info) lists it as 10:1 -

http://www.bmwusa.com/Standard/Conte...fications.aspx

The 320i gets different part numbers for the rear half shafts, but it doesn't look like the 328 shares half shafts with the 335i either. So you could say the 328i shafts are thinner then the 335i. I have no idea if that is true or not, but you see my point.

Tim

Originally Posted by av98

What's the bore & stroke between the engines?

From your list there are lots of areas for lost power & response from these:

-smaller diameter throttle body
-smaller or non straight intake manifold runners
-smaller diameter airbox
-lower flow CFM air filter
-smaller intercooler
-non dished pistons
-crankshaft with a lower stroke
-smaller exhaust manifold/turbo
-non polished or ported cylinder head

Seems like they are limiting power via less air & a controlled less powerful combustion. Plus the turbo recovery and cooling are more crippled.

I think you misread my post. All the things you listed besides the pistons are the same. They share the same BMW part number for the 328 and 320.

Tim

Originally Posted by Ronin951

Are we sure it's 10:1. Here's the difference in the short block description

328i
Short Engine N20B20A 1 11002297079
only in conjunction with

320i
For vehicles with
Low compression engine
S858A=Yes <== what is this?
01 Short Engine N20B20A 1 11002297079

Originally Posted by vitchie

There is defnitely a difference in compression ratio. The 328 is 10:1 and the 320 is 11:1. Thus, the higher compression 320 will knock a lot sooner than the 328, so less tunable. I've also heard that the 320 has thinner drive shafts.

These seem to be in direct contradiction to each other. I seem to remember reading about the 320 in Europe having a 11:1 compression ration but the description of the short block above seems to say otherwise.

Tim

Check post #6 here: No official quote from BMW, but rather a BMW tuning company in SA.

http://www.bmwfanatics.co.za/showthread.php?tid=39504

Makes sense I guess. That means that you'd need a thicker head gasket or something to decrease the compression ratio to really be able to turn up the boost. Not the end of the world but not as simple as a software flash.

Tim

According to RealOEM the 328i N20 piston (11257618811) is no longer manufactured http://www.realoem.com/bmw/showparts...70&hg=11&fg=20

The bmwusa configurator says the 320i base weight is 3295lb, so with the same N20 engine as 328i(3410lb, 8AT), where is the weight reduction coming from? Also, detuned N26 is not available on 320i, which is odd since N26 should benefit BMWNA on the PZEV footprint. This may mean N26 is either too expensive, or, N26 cannot be tuned(disappointing!).

Originally Posted by tim330i

I think you misread my post. All the things you listed besides the pistons are the same. They share the same BMW part number for the 328 and 320.

Tim

Yep I did your statement wasn't very clear. Which still makes the important specs on the engine valid- bore, stroke, compression- what are they?

Originally Posted by namelessman

The bmwusa configurator says the 320i base weight is 3295lb, so with the same N20 engine as 328i(3410lb, 8AT), where is the weight reduction coming from? Also, detuned N26 is not available on 320i, which is odd since N26 should benefit BMWNA on the PZEV footprint. This may mean N26 is either too expensive, or, N26 cannot be tuned(disappointing!).

Wow that's a huge savings, great to know. If a BMS software tune gets the 320i to 215 whp/trq you have yourself a 328i equivalent.

Originally Posted by av98

Yep I did your statement wasn't very clear. Which still makes the important specs on the engine valid- bore, stroke, compression- what are they?

Data from bmwusa configurator shows that bore, stroke, compression are the same on both cars.

328i:
Engine
Type/cylinders/valves per cylinder
TwinPower Turbo/Inline 4/4
Displacement
1997 cc
Bore/stroke
3.3/3.5 inch
Nominal output hp/rpm
240/5000-6000
Max. torque lb-ft/rpm
255/1250-4800
Compression ratio
10 :1


320i:
Engine
Type/cylinders/valves per cylinder
TwinPower Turbo/Inline 4/4
Displacement
1997 cc
Bore/stroke
3.3/3.5 inch
Nominal output hp/rpm
181/5000
Max. torque lb-ft/rpm
184(250) / 1250-4500
Compression ratio
10 :1

I have feeling the data on BMWUSA.com is wrong.

Originally Posted by namelessman

Data from bmwusa configurator shows that bore, stroke, compression are the same on both cars.

328i:
Engine
Type/cylinders/valves per cylinder
TwinPower Turbo/Inline 4/4
Displacement
1997 cc
Bore/stroke
3.3/3.5 inch
Nominal output hp/rpm
181/5000
Max. torque lb-ft/rpm
184(250) / 1250-4500
Compression ratio
10 :1

320i:
Engine
Type/cylinders/valves per cylinder
TwinPower Turbo/Inline 4/4
Displacement
1997 cc
Bore/stroke
3.3/3.5 inch
Nominal output hp/rpm
181/5000
Max. torque lb-ft/rpm
184(250) / 1250-4500
Compression ratio
10 :1

I'm not sure if the source data from BMW was messed up, or if you accidentally did a copy-paste error, but the 328i certainly doesn't have only 181 hp...

Originally Posted by elistan

I'm not sure if the source data from BMW was messed up, or if you accidentally did a copy-paste error, but the 328i certainly doesn't have only 181 hp...

Fixed copy-paste error in previous post, thxs. Bore/stroke/compression ratio still the same on both data sheets.

The datasheet also says 320i 8AT has 250 lb-ft, which is almost the same as the 328i. So it seems the only difference is really 60+HP.

Footnote
Figures in ( ) apply to vehicles with 8-speed automatic transmission.

Nominal output hp/rpm
181/5000
Max. torque lb-ft/rpm
184(250) / 1250-4500

Unfortunately, here's what I *think* happened. I have an email out to BMW to comment.

2012 MY 328's have 10:1 N20's tuned low

2013 MY 320's have 11:1 N20's boosted low
~2013 MY 328's have 11:1 N20's boosted high (see my post about piston being discontinued)

This would mean that BMW would put the same engine with the same CR in both 320 and 328. Makes sense for simplicity sake. The bad thing (for 328 owners) is they will already be tuned high (most likely more boost from factory). So, from BMW's perspective 328 owners can no longer piggy back to ~335i power, but 320 owners can piggy back to 328 power. This is oversimplified, but hopefully you get the idea.

If a "legacy" 328 needs a new piston all 4 will be replaced with the 11:1 CR ones and a software update. This whole setup means that BMW has to only maintain 1 set of pistons and two tunes. Not 2 sets of pistons and two tunes. One way to confirm without digging into the engine is to check new vs old 328 boost pressures, which is probably where they would make the adjustment (like a piggyback).

This is all speculation, but might be worth looking into deeper.

EDIT: This jives with namelessman's post. Power increase from boost would primarily be seen in the HP range.

Is HP = torque x rpm? Since the torque specs on both are similar(at least for 8AT), so maybe the difference is to taper the engine rev on 320i N20 at 5000rpm to throttle at 181hp, but allows 328i N20 to keep pushing to 6000rpm and 240hp. I guess we would see dyno charts soon enough on this. For now, 328i does appear to be a $2k-3k(expensive) factory tune versus 320i.

As tim330i noted, the bmwusa data can be incorrect too, or else it would really be odd that 320i N20 MT only get 184 lb-ft@1250-4500rpm ....