M&K street muffler on LWB car w/ stock bumpers?

The issue I’m having is that the muffler extends too far back on my car ('70 with a 2.7) near the lower corners of the license plate panel, so I can’t get the panel back on properly. It’s almost like the heat exchangers need to move forward by 1/2" to make a bit more room, but I'm guessing there isn't that much adjustment in the heat exchanger mounting points. I've already been talking with Brian@rarlyl8 about the fitment, and he has mentioned that the fit can be pretty tight on early cars but that it should fit.

I’ve seen pictures of the 911R version fitted to cars with fiberglass bumpers (most with a cutout in each lower corner for the outlets) but haven’t found much about getting the muffler with the "sport" or "GT3-style" outlets to work with the stock bumper.

If anyone has experience getting this muffler to fit, I'd really appreciate the help. Thanks!

You should never have to remove the back panel to get the muffler on. Something is drastically off. Hopefully M&K can respond and help. Otherwise look for a nice used Leistritz...they are hands down the best for early 911's.

Are your heat exchangers stock or after market?

I've had both the 911 R version with the outlets under the bumperettes and the early sport version with the narrower spacing. There was a great deal of room around both of them when installed, since the "can" is so much smaller than a Leistritz or Dansk. Neither came close to touching the license plate panel.

The front of the "can" should be hard up against the motor mount where the two flanges and the two strap mounting "hooks" are. If the muffler "can" is not hard up against that, with the inlet flanges bolted to the heat exchangers, than the inlet pipes are either miss located or too long. Reading between the lines (since you say it looks like the heat exchangers need to move forward), it sounds like that is the case. In other words, if the flanges on the muffler are bolted to the flanges on the heat exchangers and there remains a gap between the muffler can and the motor mount, than the inlet pipes on the muffler are the problem.

Thanks, Doug and Jeff!

I didn't realize that the muffler should be able to drop out the bottom completely without removing the license plate panel but that makes sense. The car has SSI heat exchangers.

Thanks for the fitment reference points, Jeff. My existing muffler bracket appears to not be original/correct, so I don't think it was helping things, but even with it removed for a test fit, it doesn't fully allow the license plate panel to install flush with the bumper edges.

I'm guessing there isn't tons of adjustment where the SSIs mount to the exhaust studs, so I'm a bit unclear about where another 1/2" or so of clearance could come from though. I'll try this again once I have a new muffler bracket in hand and can assess the mounting gaps to see if it might be the inlet pipes or SSIs. Thanks again!

There is no adjustment whatsoever in the location of the SSI heat exchangers. Their flanges that mount up against the exhaust port have round holes with no slop or play around the exhaust studs. The location of the muffler mounting flanges on the SSI heat exchangers will be precisely where they are on the original stock heat exchangers. They are most likely not the issue here.

I'm a little confused about your muffler bracket. The stock one serves as the rear engine mount, to which the engine cross bar is attached. It will never interfere with the license panel. Here is a diagram and a couple of photos that should help. In the diagram, part #1 is the stock engine mount and muffler bracket. The photos show an engine with this mount installed, both with and without a muffler attached. Is you're different?

Thanks, Jeff. I think some pictures might help clarify my less-than-perfect explanations!

The first picture shows that the bumper corner and license panel don't quite sit flush with the muffler installed. It can fit a little bit better with a little pressure, but it's not going to get all the way to flush without trimming *something*. And it sounds like in your case, the muffler wasn't anywhere near the license plate panel.

The second picture shows how the muffler currently fits with the inside of the mounting bracket (and you can see where I previously trimmed part of the bracket).

The final picture shows the bracket that was installed using the bottom two studs on the engine mount. The bracket itself doesn't interfere with the license plate panel, but it appears to have been pushing the muffler body "back" a little, causing it to interfere more with the license plate panel. I've seen pictures of the correct bracket (901-111-151-04), which seems to use the upper mounting studs on the engine mount. The muffler fits closer to the engine with the bracket removed (while the correct bracket is on its way!), and the flanges for the muffler align well with the SSI flanges.

If the SSIs really don't have much/any adjustment available, it seems like the only option might be to shift the bumper rearward. What do you think? Thanks again for your help!
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O.k., I think we are narrowing it down. The mounting bracket you show does not appear to be stock. Here is a photo of a stock mounting bracket. The ears with the holes go up and pick up two motor mount studs. The ears that hang down have two flanges, meant to hold the flange on a stock muffler. That part of the mount is bent forward at about a (guesstimated) 15 to 20 degree angle. If it is not bent forward like that, it will hold the muffler too far aft. Yours looks like it has an offset, but it's hard to tell which way and how much.

Thanks, Jeff. The picture you included of the correct bracket is exactly what I've ordered. I think you're absolutely right that the old bracket was causing the muffler to sit farther back than it should.

But the problem is that even with no muffler bracket at all--the muffler is just attached to the SSI flanges since the non-stock bracket is removed--the muffler doesn't quite fit. I would think that the way it's currently installed should maximize the amount of clearance available behind the muffler. I'll look into how much I can adjust the bumper as a next step.

Hmm... You are exactly right. Without any mounting bracket on the motor mount, and the location of the mounting flanges to the SSI heat exchangers controlling fore and aft location, your muffler should fit up behind the license plate panel with plenty of room to spare. Both of my M&K mufflers had more than enough room, and both bolted up to the SSI flanges while being properly located to the stock muffler mounting bracket. Weird. It is sounding more and more like the muffler inlets are misplaced or too long. The good news is that it is a pretty easy fix. All you have to do is cut the flanges off the inlets, then hang the muffler on the correct (stock) mount where it needs to be. Then bolt the now loose flanges to the flanges on the SSI heat exchangers and re-weld to the inlets. Any muffler shop should be able to do that in less time than it took me to type this... ;)