Worth swapping to OBD-II exhaust manifolds?

[LTDScott]

I need to drop the exhaust on my M50NV (OBD 1) swapped race car for some trans work so I figured I may take the opportunity to upgrade from the stock cast manifolds to something better. I have no idea where the downpipes are from (previous owner did it) but they clear everything, so I don't want to mess with them. I also don't have the means or desire have exhaust work done at a shop at the moment, so I want something that's a bolt in and relatively cheap. That means cheapo eBay shorty headers or stock OBD 2 manifolds.

OBD 2 manifolds are popular, but what's the advantage? I know they are stainless which means some weight savings, but do they make any more power? Are they direct bolt-in replacements for the OBD 1 manifolds? I know I'd have to weld or otherwise block off the EGR and O2 sensor ports, but are the flanges in the same location?

[Varinn]

I can't answer the worthiness of it, but I can say that I am using OBD2 manifolds on my full OBD2 S52 swap. They are not a direct install for an e30, the front header will need to be cut and reshaped to give the downpipes room to clear the front subframe.

Post modification, tons of space. Pre modification put the flange <10mm from the subframe on e28 m5 mounts.

[LTDScott]

Hmm. The angles look suspiciously close, but just a small difference could wreak havoc.

[LTDScott]

Nobody?

[dynoclimb]

I did this a couple of months ago, unbolted everything, pulled out the cast OBD I's and threw in the OBD II's and bolted everything back up. No issues.
They are much lighter, and probably flow better. I haven't really noticed a performance difference, but it does sound different.

[pandaboo911]

They are tubular and much lighter. The ports on the obd2 manifold are actually smaller but since the obd2 midpipe flows much better they are an upgrade.

[Wanganstyle]

Nobody?

our e30 lemons has been been running OBD2 exhaust manifolds since the 24v engine install.

our headers are 100% unmodified m52b28 besides welding up the air injection ports;

a little weight savings is the main difference; no idea about flow; we didn't have any M50 cast iron headers to compare with.

[LTDScott]

Thanks for the responses. The impression I'm getting is that they should be a direct replacement for the cast iron manifolds minus the plugging of the air pump and O2 sensor ports.

Part of my motivation to use the later manifolds is weight saving, but I hoped there may be a performance improvement. That said, even if there isn't the fact that they used them on the M3 is a good sign. I'll start looking for a cheap set.

[LTDScott]

Well I bought some OBD2 manifolds, got the secondary air injection holes welded, bolted them on the car, and found the angle of the bottom flange on the front manifold that meets the downpipe is wrong. After a lot of cursing and research, I discovered that the previous owner of the engine (it has been in 3 other cars before mine) used E34 manifolds, not E36 :(



I would have just said screw it and re-installed the original manifolds, but I don't have gaskets for it. So now I have to decide what to do. The easiest thing is to just reuse the old ones, but I could install the new ones and have the flange on the downpipe modified to E36-style by a muffler shop. Or I could just abandon all of it and get some eBay longtubes, but that will require a trip to the muffler shop too. That wouldn't be so bad except the car isn't street legal and needs to be towed :(

[marek|steezkal]

So the E34 manifolds fit in a 24V E30?

[Nick_S]

I ran into this issue with E34 manifolds. The front header is at a slightly different angle than an E36. The rear is the same.

[marek|steezkal]

Bummer, I was hoping to keep the cast manifolds because I cannot stand the raspy tinny sound of tubed manifolds. At least the ebay tubed manifolds sound awful.

If adding a small spacer under the mounts doesn't help enough, I'll be looking for some OBDII mani's.

[LTDScott]

Bummer, I was hoping to keep the cast manifolds because I cannot stand the raspy tinny sound of tubed manifolds. At least the ebay tubed manifolds sound awful.

If adding a small spacer under the mounts doesn't help enough, I'll be looking for some OBDII mani's.

I'm not sure what you're trying to get at, but yes, the E34 M50/M52 manifolds will bolt onto an E36 M50/M52 engine, except that the flange for the down pipe is different between the E34 and E36. Seems like you have cast manifolds from an E34? If so, you could just have a muffler shop modify the flange on the down pipe (if it was sourced from an E36). That's what I'm electing to do.

FWIW I have three flat washers under my engine mounts to raise up the engine slightly.

[marek|steezkal]

Yes, E34 cast manifolds. I'm planning on making my own 3-hole down pipe flanges out of 3/8" or 5/16" steel plates and welding them to my down pipes that I will modify.

I was just worried that one or both of the manifolds wouldn't clear the subframe, sway bar, and/or the control arm bushing.


Edit: Did your front E34 manifold come REALLY close to contacting the E36 engine mount arm? Mine is maybe 1 mm away from the heat shield that goes over the mount arm. I'm hoping that won't be too much of an issue with heat.

[King Mufasa]

sorry to go off topic

Make them 6-2-1 Maserati does that on their v12's for a reason..

this is VW's I always wondered what it would yield on a str6 BMW