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Replacing M52 exhaust manifolds with S52

18K views 18 replies 6 participants last post by  Mark_F 
#1 · (Edited)
I've posted a couple of times about this and I've done a lot of searching. Most of the posts seem to quote from the same article that makes removing the old manifolds sound very easy. I thought I'd post how I got on and what problems i'm facing for anyone else that wants to try this.

My car is a 1998 323i coupe with aircon - there is no secondary air pump etc attached to the manifolds on this model. I've already removed the backbox and center section which was fairly straight forward so I'll skip this part.

Today I removed the M52 manifolds. Cracking the nuts off was the easy part, soaked them in penetrant and set about them with an 11mm flat edge socket. I worked from above and removed the front bank nuts first. All of the studs came out with the nuts. For what its worth, I was able to do this without the use of flexy joints etc, only straight sockets were used, despite having the flexy's available, I found them more of a hinderance than a help.

Once the nuts were off however, I was unable to withdraw the manifold due to space within the bay - the connecting arm to the steering rack being the main culprit. I then removed the rear bank nuts, again, 11 of the 12 studs came with the nuts, the rear manifold was easy to remove once freed from the cylinder head.

Then came the most frustrating part of the day, all the nuts were off, both manifolds were separated from the head, but I found it VERY difficult to remove the longer front bank from its bavarian prison. In the end, I removed the o2 sensor with the manifold in position and withdrew the manifold from the topside by squeezing it past the aircon pipes.

Here you can see the old manifolds on the right and the M3 evo manifolds on the left.



Now, my questions are as follows..

How in the name of all the is holy are these going to fit back in? They appear longer and wider than the standard manifolds that were a tight squeeze in the engine bay.

Will I have to remove the connecting arm from the steering rack? Doing so should give me a lot more room to manouvre. - It looks like it is secured with 13mm nuts with knuckles at both the steering wheel end and the rack end? Simple as that?











With regards to the exhaust itself, the M3 exhaust is considerably heavier duty in every respect than the standard m52 system. I will weigh them for comparison, but the backbox alone must weigh double that of the 323 box.

Thoughts please.
 
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#4 ·
I'm not sure. You should be able to reach all 12 nuts from the top with the other manifold still in place, but I don't know if you will have the space to remove it from the bay with the front bank still in place.

I'd say probably, but can't be 100% on this.
 
#5 ·
The weight comparison is as follows.

Manifolds x2

M52: 5kg
S52: 6.9kg

Center section

M52: 13.5kg
S52: 19.6kg

Backbox

323i single pipe: 13.6kg
Evo Staggered twin: 22kg

Total weights
323i system 32.1kg
Evo system 48.5kg


I've also added more pictures to my first post of the rack position etc in relation to the cylinder head. It looks as though the rear bank will snake around the rack, but I have no doubt the rack connecting arm must come out for the mani to go in.
 
#8 ·
Interesting write up. Having looked into this myself I discovered that not only was the M3 system much heavier there was no power gain to be had and there is a thread on another forum showing a dyno print before and after with a power loss. Hats off to you to what you're doing but you may want to change it back. See how it goes though.
 
#9 ·
If there was no performance difference, and possibly a power loss don't you think BMW would just have slapped some 323i manifolds on the M3 and saved a lot of money.
M3 manifolds are equal lengths on the pipework which is important for making more power, the hashed together standard 323i pipes will never be as good as the M3 manifolds.
The difference when fitted to your 323i may not be noticable when done but with other mods like a M50 inlet manifold a big bore throttle body, cams and a chip it would make a big difference.
Good luck with it :thumbsup
 
#11 ·
Interesting posts. I'm very open minded about all of this and I like hearing your views.

Before the engine even runs the evo system is at a disadvantage in being an extra 16kg. I reckon that's roughly the weight of the spare wheel.

I think ideally you would mate the manifolds to a custom s/s mid section, for sub 250hp I don't see the need for the mid section to be twin pipe.. or the size bore that the m3 uses. Quite a bit of weight could be dropped off that.

The backbox can be gutted of all the sound deadening which would reduce the weight by quite a bit, this is something I am considering but I'd be worried about the resale value / the neighbors filing an antisocial behaviour order.

Having read up on the M3 manifold removal and refit, the rack link does need to come off which would have saved a lot of time in the first place if I'd started by doing that.
 
#14 ·
I ended up removing the aircon pipes, you can still see one cable tied out the way in the pic above. I'll likely just remove the full system, pump, radiator etc to try and recoup some of the 16kg the M system added.

Ok, so..

I removed the rack link which was a bit of an arse to do as I was trying to remove it from the rack first. The correct way to do it is, loosen both 13mm bolts and remove the screws from both ends. Drive a flat head screw driver into the knuckles to widen them and slide the rack end knuckle all the way down the shaft towards the rack. You should then be able to slide the steering wheel end knuckle off the shaft and then slide the rack end back up and off.

I also removed the lower brace to make locating the new manifolds easier as they have quite a long tail on them. Two 16mm bolts on either side, I removed the driver's side completely and loosened the passenger's side allowing me to spin the brace round and out of the way.

Before rack link is removed;



Rack link off, more room to work.



Here you can see both shaft ends, circled.






Here we have £75 of nuts and gaskets. :eek I got genuine 323 studs, nuts. M3 downpipe gaskets but the exhaust gaskets are not bmw.



I cleaned up the head flanges and installed the front bank studs first and trial fitted the front bank. It wouldn't have been possible to get the rear bank in with the front bank located. So I installed the rear studs too, then placed the front bank loose in the bay and manouvered the rear bank in to position. With both manifolds in the bay, you can then locate them onto the studs. - DON'T FORGET THE GASKETS!!! :shifty:



With both manifolds in position, it became very difficult to take any useful pictures from below and you can't see a lot from above apart from the manifolds themselves.







All I can say, is WHAT AN ARSE OF A JOB. I thought the hard part was getting the old manifolds off. It isn't. Getting nuts on all 24 studs and tightening them is the hardest part of this job. The front bank is fairly easy to get at, the inner most runner of the front bank being the hardest to get at. Before I ran out of time today I managed to tighten 10/12 of the front bank and just 4/12 of the rear. Even getting the nuts onto the studs is a challenge let alone getting a socket in there..

Will update more tomorrow on how I get on.
 
#16 ·
Just to confirm, the exhaust is now fully fitted. The rear bank was pretty tedious. The majority of the nuts are accessed from above and I used a combination of spanners and 3/8 drive sockets.



I've still to refit the rack link and I'll need to get a mid section support bracket as the M3 one is different from the 323 one. - Even though my 323 one was rusted off, which explains a knocking I've been getting.

Hasn't been run yet either so can't comment otherwise. I've completely removed the aircon now too as I can't remember the last time it was gassed. Will weigh up what I've removed and see how much I've saved.
 
#17 ·
I`ve successfully fitted a new rear manifold today in 3 hours, on ramps. No need to remove aircon pipes, brace under the car or the front manifold.

Manifold came out from below no problem as I`d unbolted the exhaust in both places. Now that i`ve done it I reckon I could do it again in half the time.

11mm socket, various length extensions and a small driver. Simples. Runs like a dream. Next job is to sort my front suspension. Fresh everything including Bilstein B8`s I think.
 
#19 ·
Ha! Just when I thought I was finished..

The backbox is only sitting in position in the photo above. When I went to mate it to the center section, I found that both pipes on the backbox are female type. The center section has one male one female. I've had a look at all the m3 exhaust parts for sale on ebay and had a look on real OEM and can't confirm if this is normal?
 
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