I am moving along on my 914/6 conversion. I basically have a 2.7l engine. I have new MSDS headers and a M&K Muffler (MKM26). I installed the headers without difficulty. I did torque them before installing the muffler. I then went to install the muffler and the distance between the exhaust flanges is 3cm narrower than the flanges on the headers. The distance between the muffler flanges is 58cm (center to center). The distance between the header flanges is 61cm.

What is going on?

Here are my three theories.
1. I shouldn't have torqued the header bolts before installing the muffler. I may be able to rotate the headers inward a bit.

2. Wrong muffler? Doubtful

3. Headers are bent or something like that- extremely doubtful.

Any ideas?

I'm no expert on /6s but there's a stub pipe on each side of mine that's meant to be adjusted based on whatever muffler you choose.

You new the answer. #1 Get headers and muffler on and together first, then tighten it all up.

Similar thing here. I didn't measure it, but it probably wasn't as much as 3cm.
I have msds header and stock muffler. Next time I will try not tightening the
head nuts until muffler is on, but this time I ended up using a strap clamp to
pull the ends where I needed them to be. It is too much force to try to hold
things manually while installing the bolts and nuts.

I've experienced the same thing and it seems pretty common to have to move things around, either by loosening the parts up for significant adjustments or just pushing-and-pulling if you're close.

I have a different problem with the headers on my six conversion.
I have brand new Bursch headers and a new Bursch 914/6 muffler.
The collector outlet on the headers is 2 inches in diameter but the inlet diameters on the muffler are only 1 1/2 inches in diameter.
They line up okay but there is a 1/8th inch step around the circumference of the muffler inlets that I'm sure will hurt flow and performance.
Why would Bursch manufacture them like this?
My car currently has some weird shorty headers on it with custom bent pipes and tube muffler, so I can't compare the headers to stock heat exchangers.
Do stock 914/6 heat exchangers only have 1 1/2 inch diameter outlets on them?
What would be a better muffler to use that has 2 inch inlets?

my 1-5/8 headers have 1-7/8 ID collector out & line up and match both stock 911 sport muffler & my 911 Bursch (1-3/4 ID Inlets) just fine w/o monkeying around with "adjustments"

there were 2 Bursch models - one for 911 & 1 for 914-6 - maybe that's a clue

- also - i have seen some "914-6 headers" that have goofy angles & bends & would definitely not fit an essentially "stock" setup - some are shorter and use an adapter pipe that is sometimes bent to get from the collector to the muffler

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My MSDS headers didn't line up either when I tightened them before bolting them to the muffler. But I loosened them and bolted the muffler and it worked great! Though a small exhaust leak exists that I can't seem to fix...

Exhaust leaks drive me nuts.

Have you tried any exhaust paste as a sealant?

If you think about it, the headers, whether they be Bursch or MSDS are very long. There is a couple of feet between the engine exhaust flanges and the muffler flange. A very small movement at the exhaust ports of the motor is magnified tremendously by the length of the headers. So, rotating the headers just couple of degrees at the engine will increase or decrease the distance between the muffler flanges by inches.

So, as noted earlier, put the headers onto the car, but do not tighten the exhaust port nuts. With the headers hanging "loosely" under the engine, raise the muffler into place and move the headers to match up with the muffler inlet ports. Carefully align the muffler flanges with the header outlet flanges to assure that they are installed aligned with one another. Once you have that matchup done and the gaskets in place, tighten the header to muffler bolts, and then go ahead and tighten the engine exhaust port nuts. There is enough slop in the holes on the headers to allow for this process to work well.