Increasing bore and stroke

[Thirdkelley]

Been researching a lot about potentially stroking out the n54 engine, taking us from a 3.0 L to a 3.2L.

Firstly, here are the specs of the n54 engine:
Compression ratio 10:2:1
Displacement: 2979 cc
181.8 cu in
Stock Measurements:
Bore: 84mm or 3.30709 in
Stroke: 89.6mm or 3.527559 in
Rod Length: 145mm
-At 7000 rpms pistons go 34.37 m/s

I've found forged pistons for our engine that will take the bore to 86mm. If we can find a way to increase stroke by 2mm, we would get the numbers of a 3.2L engine. I have attached an image of the end calculations from these increases.

The displacement would go from 2979 cc to 3190.7 cc which is a considerable amount!

Just trying I brain storm here.

I also found schrik cams on a euro site for around 480 euros.

[fboutlaw]

You'd need a crankshaft designed for the extra displacement. Is there clearance to carry the extra size in the block? Likely, but you lose margin and would have to measure your block to make sure it fits.

Fuel/Air: Once you change the cylinder size, you start stretching what you can do with fuel and air delivery. The car should be ok as it's conservatively boosted and has a super high pressure fuel system, but you'll likely wear down the components faster in the fuel system.

ECU... I'm not sure ours would automatically compensate for the extra size, and it very likely would not run effectively. You'd need a complete re-map of your ecu on a dyno before doing any real driving or an aftermarket ecu that's made for complete custom applications like this.

Cooling: with the extra cylinder size, you'll also have to find a way to amp up engine cooling. Larger radiator? High flow water pump? Not quite sure how to accomplish this one.

Usually in cars with an iron block they do make slightly oversize pistons OEM to be able to rebuild the engine, but I haven't seen BMW do this, and that makes me wonder if going oversize is something they've tried and deemed not worth doing with the aluminum block.

[darkrom]

Wouldn't it be cheaper/safer/easier to run bigger turbos?

[DietTab]

displacement wont do anything, you're limited by the air the turbos push.

[135Pats]

This isn't the motor to do that to...native bore to stroke is already aggressive.

Find yourself more fuel and more airflow, the power will follow.

[flinchy]

boring the motor by 2mm will just make it weaker unless you sleeve it, which would probably let you bore it even further

better off keeping the cylinder walls thicker for strength and run more boost.

[Nugget]

Not sure you want to be boring out a boosted open deck block.
I'm with everyone else here, just add more (or more efficient) boost.

[amsnow440]

Originally Posted by Nugget

Not sure you want to be boring out a boosted open deck block.
I'm with everyone else here, just add more (or more efficient) boost.

Also the block comes sleeved from the factory. This tells me that BMW engineers felt that the open deck cylinder walls were not strong enough for a boosted application. I don't know if I'd feel comfortable reducing the size of the cast iron reinforcements they implemented, via boring or re-sleeving.

[Taskmaster]

headwork and cams - and it won't cost you nearly as much.

[Spoolin Montego]

It would make a lot more sense to just invest that money into upgraded turbos. I'm willing to bore and stroke the engine would cost a fair amount more than the aforementioned.

[BeGood69]

I reached 3204cc
my stroke is +3mm and piston/sleeves 85.5mm
And shaved 200+g from piston/rod/wrist pin/rings and rods and pistons never bigger.

;-)
Oh and price wise I am still way below a build cost even with st3 head and ferrea valve kit.

[drogods]

Originally Posted by BeGood69

I reached 3204cc
my stroke is +3mm and piston/sleeves 85.5mm
And shaved 200+g from piston/rod/wrist pin/rings and rods and pistons never bigger.

;-)
Oh and price wise I am still way below a build cost even with st3 head and ferrea valve kit.

How did this affect the performance of the engine?