How do you guys close/weld up the holes on OBD2 manifolds?

[static]

just like subject asks

so i am guessing the holes/slots have to be welded then machined? to get smooth surface?
What are you doing about the gaskets? using the obd1 ones? (i imagine the obd2 gaskets would have holes for the obd2 crap)

Thanks
Alex

[FredK]

There are many ways to go about doing this. If you choose to get the air pump gaskets and pattern a blockoff plate from them, you must use the OBD-II gaskets.

The OBD-II gaskets don't have any extra holes in them. However, they are 3 ports wide (so you need 2 gaskets for an engine), unlike the OBD-I gaskets, which are 2 ports wide (so you need 3).

If you weld the ports shut, you just need to put a big blob of weld metal at the edges of the injection channels. However, this method requires a pretty good welder because the flange is very thick and you must get good fusion with the weld.

After welding you can use a belt sander to bring the level of the weld back down.

Here's a pic of someone else's manifold:

[static]

thanks

i also found some info here

http://forums.bimmerforums.com/forum/showthread.php?t=491245&highlight=obd2+manifolds

so is it 100% that all the dimensions of the obd1 and obd2 manis are the same? I really want to make sure it'll bolt up to my custom downpipes before i take everything off, and wouldn't be hitting anything.

edit: while on topic, how hard is it to replace the exhaust mani studs? mine are all rusted to crap - is that a potential problem? (i.e can that weaken them to the point of snapping?)

Thanks
Alex

[FredK]

I'm not absolutely sure the dimensions are exactly the same, but a lot of E36 people have bolted up OBD-II midsections to OBD-I cars with no problems. This isn't the same thing, of course, but at the very least they're going to be close if not exact.

I've seen people snap exhaust manifold studs before, but it seems fairly rare. I have a 147k M50 on my hands and though the studs looked terrible, none of them really gave me much trouble upon removal. On 22 out of 24 studs, they just came out with the copper locknut when I removed them.

I think the key is to give it a pure torque and not to twist or put weird angles on the studs when removing them, and you should be pretty safe. Hopefully. :mrgreen:

[static]

Thanks again Fred

So providing i'll plug the holes the same way as on your pic, what gaskets do you recommend i use? (i'd rather use obd2 2-piece, of course, but i don't want to have any troubles with cutouts, leaks, etc)

Alex

[FredK]

I'd just go with the OBD-II gaskets. There are no extra holes or cutouts in them. As long as the welds are good and flat with respect to the rest of the sealing surface, there shouldn't be any problems with leaks.

I started to weld the flanges myself, but I'm just driving myself batty with other projects!

[bdi_fc]

I left all the air pump connectors on my exhaust manifold up to the rubber hose that connects to the airpump.

Edit: see attached picture. I have the parts within the red circle still attached to the manifold.

Should I close this off? Does it affect anything?

[So Live]

Static, post up if/when you get yours intalled and if theyre the same or not.

[Mike B.]

The dimensions are the same where they mate up to the exhaust ports, but the location of the collectors/secondaries is different. You have more room for the mid-pipe with OBD-I vs. OBD-II headers.

[Jason89i]

obd2 headers have (2) o2 ports that are not used. i found that an oil drain plug (cant remember which car) fit almost perfectly flush with the inside. i THINK the plug was an m18x1.5......but dont quote me. jason

[static]

The dimensions are the same where they mate up to the exhaust ports, but the location of the collectors/secondaries is different. You have more room for the mid-pipe with OBD-I vs. OBD-II headers.

CRAP! now you guys tell me when i have he manifolds in my hand ready to bolt them right in.
well, better than finding this out when the manis are off and the car is undrivable. (it's my daily car during summer months btw)

Edit: wow, it seems i have been seriously mislead thinking they will bolt right up. Apparently, changes to the downpipe is necessary :( and you guys seem to think that obd2 manifolds will clear the e30 body worse than the obd1 cast ones.
Hmm, maybe i should just use a turbo manifold? 8-) they seem to be quite compact

[Bmjpv]

Those obd2s are stainless. I cut a pie shape out of the rear/inner pipe and subleted the welding (my wire feed is not setup for stainless)because I wanted a really good and clean job. I cut aprox 3/4-1" of pie out (don't cut all the way threw and you won't loose indexing) to kick it back and away from the crossmember. Note, make the cut next to the flange,it"ll give you that stronger weld.

[BigD]

The dimensions are the same where they mate up to the exhaust ports, but the location of the collectors/secondaries is different. You have more room for the mid-pipe with OBD-I vs. OBD-II headers.

Do you know this for a fact? IE you bolted up OBDII manifolds, tried to bolt up OBDI pipes and failed? Cause that's what I'm planning on doing because everywhere else I read that the I and II manifolds are the same as far as fitment goes..... I guess I'll try to fit the OBDI pipes up to my motor tonight.

[Bmjpv]

Ya ,I know the for a fact! To do a really nice job (that you can modify and reweld) you need the obd2s. The obd1a are cast iron ,can't be modified and I understand they don't flow as good, I too beleave this to be true. Find and mod those 2ers good luck joe

[BigD]

Well thanks for making me haul the downpipes out of the basement, but here, once and for all OBDI pipes on OBDII manifolds FIT (don't mind the bung on the downpipes, the PO put it in for a wideband sensor):