Homemade exhaust help

[Grrrmachine]

I'm pricing up bits to fit a six-branch to my M20, which means changing lots of other bits since I'll be deleting my cat. I need to get the middle silencer, but I also need to make up the downpipes including an X-pipe, to go between the six-branch and the middle silencer.

That's where I need help. It seems the six-branch has an internal diameter of 40mm, which seems too small, and I don't know what diameter the middle silencer inlet pipes are.

And then what size X-pipe do I get? Smallest I can find is 45mm, which seems too big to fit to the 40mm manifold pipes.

Confused

[e301988325i]

BTB run a single 2.5" dia pipe to the rear, I don't have a vernier here to measure the others. There's pics of mine of the whole system in the old BTB group buy thread about page 10 IIRC.

[Grrrmachine]

I tried a homebrew method, and measured the circumference of the existing pipes with string. It seems the manifold ends with 50mm outlets, and 45mm pipes slot into that. Does that sound right?

If so, I presume I need a 50mm X-pipe, and use 45mm pipe to make up the rest of the downpipe between the six-branch and the middle box.

[e301988325i]

http://www.e30zone.net/modules.php?name ... &start=350

You can see here that BTB swell the pipes so that two pipes of the same size can overlap.

Looking at the pics, I'd say the 6 headers @ 40mm dia, the 2 collectors at 45-50mm and the single a known (2.5") 63mm dia.

[Grrrmachine]

I should say, I have the six-branch here already (hartge). And it has two existing pipes fitted to get to the middle box; they're just rusted to f*ck and don't have an X-pipe fitted. But seeing it compared to the BTB system is handy.

But this will be a twin-pipe system throughout, so that I can keep my rear silencer which is only a year old anyway.

[steve_k]

For any pipe's you need the try jetex as they do all shapes & sizes of pipe for you to make up your own system (they even do middle & back boxes) including X-pipe's & Y-pipes.

so they could be a good place to try.

[Grrrmachine]

Bit far away from me, but thanks for the tip ;)

[steve_k]

Any updates?

[Grrrmachine]

Still keeping my eye out, but it's dependent on finding a centre box for a reasonable price. They start at 100 quid here, and there are NO second hand parts, so it's a bit of a gamble on something that may not fit.

Once I get a middle box, I'll buy the bends and X-pipe and make my own downpipes. Looks like the X-pipe should be 50mm, accepting 45mm pipes from the six-branch and 45mm to the middle silencer.

Even an X-pipe is 25 quid to ship it to Poland

[Grrrmachine]

Hmmm. The consensus on the Polish E30 forums for deleting the cat is to replace the middle section with the centre box of a 323i. The part is obviously the right shape for the floor pan, but does anyone know if the bore of the pipes would be much of a restriction?

Seems daft to fit a six-branch and then throttle it straight away.

[Grrrmachine]

seems like the 323i piping is 45mm, same as the rear silencer and the manifold, so no breathing issues there. Now I just need to finda 45mm X-pipe - the only seller on eBay wants 25 quid just to ship to Poland

[jmc330i]

Could you get one made locally? My brother made up an X pipe from 2 Y pipes we had laying around.

[Grrrmachine]

I can get an X-pipe here for 50 quid. Just seems daft the UK selling them for half price, but then charging the same amount again for postage

[jmc330i]

Just done a quick online quote and it seems about £20-25 postage to you. I would of offered to buy one and send it over to you, but it seems it won't save you any

[Grrrmachine]

Right, X-pipe selected, 323i mid-section ordered, it's going to be a 45mm twin-pipe system all the way through.

My next head-scratcher is the joints. The end of the mid-section is straight pipes, usually joined with a sleeve, whereas the end section has flares and flanges. I'm guessing I need to get the mid section flared somewhere (with flanges fitted), but what about "sealing rings"? I can see these on RealOEM, but there's both metal and "non-asbestos" rings and I'm a bit confused. Do I need both?

[jmc330i]

On my 2 piece 325i exhaust, there is 1 'non asbestos' ring and 1 thinner metal ring.
The thicker non asbestos ring slides over one pipe which slides into the rear section and is then clamped by the flanges, while the thinner metal ring is clamped between the 'flares' of the other pipe.

I've got to get under the car tomorrow, I'll get a pic if you want?

[Grrrmachine]

Yeah, that would help a lot. I've got the thin metal rings from taking my own 2-piece apart, but no sign of the non-asbestos thing.

[jmc330i]

Only got a pic of the thicker non asbestos ring....



You can see it on the lower pipe in the pic, between the loosened clamps. The lower pipe is straight (and about 30-40mm longer than the other pipe) and slots into the pipe of the rear section. The non asbestos gasket slides over the pipe and is clamped between the flare on the rear section and the clamp on the mid section. It's squashed when the clamps are tightened and so creates a tight seal around the pipe.
The upper pipe has flares on both ends, the thinner metal ring sits inside the flares and the clamps hold it all together.


Sorry the pic isn't better, but its raining here again and under the car wasn't the nicest place to be!

[Grrrmachine]

I really appreciate that, it's cleared up a lot of things for me. Cheers muchly!

[Rtaylor2208]

On my 2 piece 325i exhaust, there is 1 'non asbestos' ring and 1 thinner metal ring.
The thicker non asbestos ring slides over one pipe which slides into the rear section and is then clamped by the flanges, while the thinner metal ring is clamped between the 'flares' of the other pipe.

Mine is the same, I had to buy one of each ring from the dealers when I replaced the rear section last year as they were pretty crushed.

I found that I couldn't get a perfect seal even with it al tightly clamped up so seperated the joints used a little Holts Gum Gum where they meet and clamped it all back together. Its been good as gold since.

[Grrrmachine]

Right, here's some photos; partly for the sake of the archive, partly for opinions.

I got all my exhaust bits out of the basement and mock-fitted them to see what a full system looks like. So this is a standard two-piece system from a facelift 320i with a catalyzer. Not shown are the twin 3-to-1 manifolds:



Now this is my proposed solution. An original Hartge manifold (H26, I think), running to a 323i mid section with the same rear section as before:



As you can see from this pic, the Hartge pipes have been flared and sized exactly to fit into the 323i centre box. This isn't my doing, so I'm guessing the previous owner used the same method. Really grateful to jmc330i for showing me how the gasket rings work here:



And this is my minor dilemma. I don't want to cut the rear section, since I have a funny feeling the MOT man will want to see my catalyzer once a year. But I don't want the ballache of owning two full exhausts, so I'm thinking of cutting the rear pipes off the 323i centre box and using the same flared connections as before:



It's a pretty tight fit though! I COULD buy a cheapie 323i rear box too for fifty quid and save myself the hassle of customising the centre box, but I need to offer the whole lot up to the car first to see just how much I would need to remove from the centre box in order to flare-and-flange it.

[Grrrmachine]

Time for an update:

I got the manifold and the backbox mounted to the car, and then offered up the centre box for trimming.



It lined up with the back box perfectly...



but with the manifold bolted tightly in place, the front pipes are nowhere near where they should be



This isn't my fault; it's the atrocious angle of the pipes entering the centre box, as well as the old home-made straight pipes coming out of the sixfold. So I got those lengths off (they were held on with clamps) to assess whether new versions could be knocked up with better angles to the centre box. This is what I have knocking around:



Yes, that's an X-pipe, taken off an E34. Roughly measuring, that X-pipe will just on the straight section from the manifold to the centre, and then I can cut up the angles and weld them in place to make everything work.

So the options are; make a new centre length with an X-pipe, or make one without the X-pipe, or refit the lengths and cut the centre box with better angles.

Opinions?