Newbie Exhaust Questions (M20)

[e30rik]

So I’ve been going through my 325is trying to track down a couple issues I’m having. The main thing is it doesn’t run as smooth as you’d expect from an inline 6. It makes good power and everything it just doesn’t have that smooth feeling, it’s hard to explain. There’s also some ticking that doesn’t seem like usual valve noise. Anyways, after going through the car I found that one of my exhaust manifolds is leaking as well as the flex pipe piece before the o2. So before I go taking the exhaust apart I just had a couple of questions as I really haven’t done much exhaust work.

First of all, is there any decent cheap header options? My stock manifolds aren’t in the best shape and replacements seem expensive from what I’ve seen. I found a cheap bolt on option which appeals to me because I don’t weld.

https://flasharkracing.com/products/exhaust-header-for-1988-1993-bmw-e30-320i-323i-325i-325ix?currency=USD&variant=44892485583146&stkn=268151fca02a&utm_campaign=&utm_source=google&utm_medium=cpc&utm_campaign=512-PMAX-Exhaust-header-Old&gad_source=1&gclid=EAIaIQobChMIgZ7EpvTrgQMV9M3CBB0Rzw69EAQYASABEgIC-_D_BwE

Any experience with these?

While I have it apart I plan on getting all new studs and nuts. Might be a stupid question but do you just thread them in by hand and then tighten the nut against the headers? Also what’s the best way to remove the old ones without snapping them?

Finally, is there any way to confirm my cat is good? I originally suspected it might be bad just due to the “not smooth” running issue but I don’t want to mess with it if unless I’m sure it’s faulty.

I would appreciate any advice you guys have, thanks

[82eye]

that header looks like suspicious cheese to me. even good aftermarket headers can have fitment issues. crappy ones are a distinct nightmare. i went with a well-known IE long tube and it isn't an easy fit either. decent brand headers for e30 seem perpetually out of stock right now.

the only way you're going to find out is take a chance. remember you'll still need to solve for the mid, and add an appropriate solution to mount an 02 sensor. which means you are back to cutting and welding no matter what. there are shorty headers that you can buy that will mate direct to the stock mid, the one you have pictured will require custom work.

if your cat is original it will need replaced by now.

the exhaust studs are typically removed and replaced using a double-nut, two nuts backed on to each other. some studs have a square head which can be used for install and removal, the originals are threaded both ends only. good luck with removal.

edit : i see that header has a mid included that may work. it deletes the cat, which is an issue if you have to smog the car.

[McGyver]

The ticking could just be the normal valve noise, which could be helped with a valve adjustment.

For the exhaust, I've never seen a manifold crack. Depending on where you have a leak, it might just need a new gasket.

If the flex pipe is leaking, you could get a bolt-on catalytic converter section:

https://www.bimmerworld.com/Exhaust/Catalytic-Converters/Magnaflow-Direct-Fit-Converter-BMW-86-91.html

https://www.ecstuning.com/BMW-E30-325i-M20_2.5L/Exhaust/Emissions/Catalytic_Converter/

[e30rik]

What do you mean by fitment issues exactly? The ones I linked look like standard ebay type stuff, they all have the same shape and then the cat delete pipe. I’d rather keep the cat but at the same time there’s no emissions testing and it would make life really easy if this was a truly bolt on solution. As for the studs I feel like an idiot now, that explains why all the gasket/stud sets have 2 nuts per stud but I’m glad I asked.

The ticking could just be the normal valve noise, which could be helped with a valve adjustment.

For the exhaust, I've never seen a manifold crack. Depending on where you have a leak, it might just need a new gasket.

If the flex pipe is leaking, you could get a bolt-on catalytic converter section:

https://www.bimmerworld.com/Exhaust/Catalytic-Converters/Magnaflow-Direct-Fit-Converter-BMW-86-91.html

https://www.ecstuning.com/BMW-E30-32...tic_Converter/

Valve adjustment has less than 10k miles on it and the noise is more noticeable when the engine is hot at 2.5-3k rpm.

The manifold leak is definitely at the gasket, I just heard warping can be an issue.

I thought about getting the cat you linked, was just hoping I wouldn’t have to mess with the manifolds but this seems like the best route unless someone can confirm the ebay headers are a good fit.

[Panici]

What do you mean by fitment issues exactly?

Bolt holes not lining up to the block studs. Pipes bent/welded at the wrong angle causing contact to subframe/body. Flanges not actually flat (warped from welding). Et cetera.

[McGyver]

What do you mean by fitment issues exactly? The ones I linked look like standard ebay type stuff, they all have the same shape and then the cat delete pipe. I’d rather keep the cat but at the same time there’s no emissions testing and it would make life really easy if this was a truly bolt on solution. As for the studs I feel like an idiot now, that explains why all the gasket/stud sets have 2 nuts per stud but I’m glad I asked.

Valve adjustment has less than 10k miles on it and the noise is more noticeable when the engine is hot at 2.5-3k rpm.

The manifold leak is definitely at the gasket, I just heard warping can be an issue.

I thought about getting the cat you linked, was just hoping I wouldn’t have to mess with the manifolds but this seems like the best route unless someone can confirm the ebay headers are a good fit.

The cheap exhaust manifolds will be cheaply made. Poor quality welds that may crack with time, flanges that aren't flat, bolt holes don't line up, etc. It's all about how much attention the lowest paid welder had for your part that day. It could bolt right up, or it could need some modifications.

Removing and replacing all exhaust studs and nuts is a good idea, but also risky. You will probably snap a few. Make sure you soak all the nuts for at least a day with a penetrant oil (bp blaster) and apply it several times. It is also a good idea to hit the nuts with a torch (blue or yellow butane bottle for copper pipe soldering). Heating up the nut will expand it, hopefully making it easier to remove without shearing the stud. Buy a broken stud remover in case you snap one. I have an ARES 70016 and never snapped a stud after buying it.

You will only need 1 nut per stud. You can jam two nuts together to give you something to leverage to install the stud. Then a wrench on each nut will separate them so you can remove both to install the manifold. This is the same technique to remove the studs.


If you snap a stud at the head, you're going to have to either drill and use a bolt extractor, weld a nut to the stud, or do some other work that may require removing the head. So be careful, use a penetrant, and use heat from a torch.

Finally, if the flex pipe isn't leaking (and I've never seen one leak on my cars), get new gaskets for the downpipes to the manifold and manifold to head. I've never seen these cast manifolds warp enough to not seal or develop a crack.

[McGyver]

Oh, and it's unlikely that an exhaust leak is the cause of a rough running issue. It could affect the oxygen sensor reading, but I doubt it.

[e30rik]

Okay, you guys convinced me. I'll pass on the headers. I'm going to order new gaskets, studs and nuts as well as that removal tool and I'm going to go with the Magnaflow cat. I'm pretty sure mine is original and the flex pipe is for sure leaking. I checked for leaks using the exhaust side of a shop-vac and soapy water.

As far as the work goes, I'm definitely gonna soak everything down with PB and I do have a torch. I'm hoping some of the studs come out with the nuts but if they don't come relatively easy I'll just leave some of the old ones in if I have to.

Oh, and it's unlikely that an exhaust leak is the cause of a rough running issue. It could affect the oxygen sensor reading, but I doubt it.

I'm not sure I would even say it runs rough. It's hard to explain exactly what I'm feeling. I don't think the leaks are the main issue but as you said they might be effecting the o2 and wouldn't that mess with the cat? The cat was my next suspect since I've gone through all the obvious stuff.

[McGyver]

I don't mean to talk you out of getting headers, they'll sound and look awesome. It's just another level of work to make it happen.

The magnaflow cats don't seem to last very long (3-5 years) compared to a factory cat (30+ years). So another option would be for you to pull the cat section and take it to a local muffler shop to weld in a new flex pipe. That should be really cheap ($100 or less) and will give you a chance to replace the two gaskets I mentioned.

[e30rik]

I don't mean to talk you out of getting headers, they'll sound and look awesome. It's just another level of work to make it happen.

The magnaflow cats don't seem to last very long (3-5 years) compared to a factory cat (30+ years). So another option would be for you to pull the cat section and take it to a local muffler shop to weld in a new flex pipe. That should be really cheap ($100 or less) and will give you a chance to replace the two gaskets I mentioned.

3-5 years isn't too bad considering the price difference from the OEM cat which doesn't seem to be available anyway. I have a hard time letting other hands work on my stuff, though sometimes it would be nice. Mainly just comes down to not having anyone I know I can trust (professionally). Not saying they're not out there...

Anyways, one more question before I start ordering stuff... Looks like there might be two options for studs?

RealOEM lists:

https://www.fcpeuro.com/products/bmw-stud-bolt-m10x40-11621716870

BW has those and also lists these:

https://www.bimmerworld.com/Genuine-BMW-Stud-Bolt-07129908134-E30-E34.html

15 bucks a piece kinda hurts, I'm hoping the second ones are good or if you guys have another P/N.

[e30rik]

Actually I misread the diagram, I guess the first ones are for the manifold to downpipe connection, but since I'm here I might as well ask if the second link is the best option for the manifold studs.