M30 swap - bunch of questions [warning: long]

[cernymuz]

Hey everyone, my first post on here

I bought an E30 with M30B35 swap inside couple months ago. The swap seems to be successful for the most part, however there are some issues remaining.

- badly made exhaust: see the pics, it is priority no. one to fix. I am wondering how many of my issues below can be pinned on it and the O2 sensor placement.

the headers are dual 5cm (2") tubes that enter the former X section with O2 sensor, now known as a clusterfuck, welded to a 7cm (2.75") tube connecting it to a "resonator", which is in fact only a ~10cm (4") thick. Behind it, there is another 7cm tube connecting the end "sport" muffler (not in picture, but not restrictive)





- maaaybe little less power than expected, torque noticeably fading around 5000k. I suspect it to be direct result of the exhaust design

- very poor MPG: I noticed the high fuel consumption immediately, but it took me a while to actually measure it. I did kinda inaccurate measurement, but it suggests that I'm getting around whopping 10-12MPG (mostly city). Can it be because of the exhaust design? Contributing factor is definitely 4.27 differential (to be swapped for 3.64 now)

- idling high: The engine idles rather high, at around 1000rpm. I almost certainly pinned it to leaking air intake hose. I mention it in case it might have some relevance to the other issues



SO NOW, to fix the exhaust

I was told by couple of experienced BMW guys that the NA engines need some resistance. straight piping them only hurts them apparently, right?

So I am looking into getting some middle part with O2 sensor mount and have it welded into the routing instead of that "X" monstrosity.
something like the following:

http://aukro.cz/show_item.php?item=2438324536

that one is ETA (325e) cat. I am trying to get the guy to measure the diameters, but he is not a fast one. does anyone know them? Is it a good choice?

What would be other alternatives to use that would be using mostly stock parts? I am sort of on a budget and in the Czech republic, where getting some aftermarket parts is a nightmare (for the wallet and logistically)



Do you think sorting out the exhaust will fix the power and MPG issues? What might be other areas to look into?

Thank you guys in advance!

[shiboujin]

restriction is always an enemy. Having back pressure makes sense for header design. Anything behind the header, you want as free flowing as you can get.

Your problem mostly stems from vacuum leaks post MAF. You need to fix all those air leaks first and foremost. When your idle is normal and there's no more leaks and the exhaust is good, you should be fine.

Also. Hi from reddit.

[The Humjet]

Fucken hell that exhaust is a disgrace, I've never seen such bad workmanship in my life.
I'd just cut that whole x section out and run a y-piece at the end of the headers into a 2.5" pipe going through a muffler and resonator. That should help open it up.
I don't what to say about the fuel consumption. My friends m30b35 swapped e30 is also a pig on fuel we tried going for a longer ratio diff from a 4.10 to a 3.45 that has helped a bit. But it still loves a drink. I think next I might give him my Miller Maf and W.A.R chip I have lying around and see if an economy tune could help it out. These engines are very big with a lot of cubes its just how it is with these kind of engines.

[cernymuz]

Thanks guys.

Are there any tricks how to identify the leak around MAF? Like spraying detergent on it if it were leaking out, not into the tube. Or even an easy way to seal it?

Getting the hoses here will be a true bitch, the major car parts dealers don't seem to carry them.

[shiboujin]

I spray around with something flammable like starting fluid. if the idle changes when you spray a spot, you haz leak.

[cernymuz]

seems that there is no leak past the MAF, I didn't spray upstream from it, not to cause any problems.
How would I check the MAF is working? unplug and plug back in and see the difference of performance?
What about O2 sensor?

[shiboujin]

MAF sensors have a resistance setting. You need to look up the proper measurement. Unplugging it is a horrible way to check it. I guess it could be an O2.