New M&K pre-muffler intereferes with shock on a M491

[burzel2]

I'm hoping a few other people have installed the M&K pre-muffler on a M491. When I dry fit the muffler there is barely any clearance to the shock. I believe it will make contact when driving and there's no way it will clear when jacking up the car. I've been in contact with Brian (RarlyL8), but he has not seen this issue. My car is a 1984 Coupe with a ride height slightly lower than stock.

I'm worried the larger rear trailing arms from the 930 are taking up the clearance. The picture below shows the clearance with the car on the ground.



And this one shows the contact after jacking up the car only about one inch.



Does anyone else have a M&K pre-muffler installed in a M491 or a 911 with turbo trailing arms and a normally aspirated engine?

[997Sbeebe]

wow, it must be the rear trailing arm depth that causes the issue. i guess this is something they [M&K] simply have not run across before. probably not going to be cost-effective for them to design a pre-muffler (the initial pipes) for the M491 alone, but they still might be willing to. maybe you can send it to them for individual customization.

[john walker's workshop]

nothing a claw hammer massage won't fix. i've seen a lot of cat bypass pipes flattened out in that area.

[NY65912]

Just as a point of info, no issue on my M491 with a Dansk pre-muff. I sure would like to hear how the M&K sounds.

[TheSt|G]

Originally Posted by john walker's workshop

nothing a claw hammer massage won't fix. i've seen a lot of cat bypass pipes flattened out in that area.

Yup. Many OE applications have similar dents for the same reason.

Regardless, those are some good looking welds.

[burzel2]

I would have to put a serious dent in that sweet pre-muffler to get the shock to pass by without touching. Check out this comparison with the cat. It's flattened out near the shock.



I guess I don't have too many feasible options. Modify the M&K or buy a different pre-muffler. Pulling the shock bolt out to jack up the car is kind of ridiculous. Skinnier shocks? I think I'm out of of options.

[RarlyL8]

We've done a few M491 G50 cars and I looked up my notes this evening. The bolt was ground a bit at the closest spot. The PM was installed while the bolt was out of the shock. The wheel was jacked up while the car was in the air so it didn't hang down past the normal shock travel. I do not recall and there is no mention of having to message the pipe but I only do that as a last resort.

[burzel2]

Just to close out this thread I ended up denting the muffler with a little heat and a ball-peen hammer. It definitely added some restriction on the one side but hopefully not too bad. Maybe one day I'll cut out the dent and weld in a flat piece that isn't concave.

[rfloz]

Interesting. I got my M&K pre-muffler (track use only, of course) a few years ago from Ben when he was making them. It had to be dimpled just a bit less than yours. There is no more than 1/4" clearance now and it's never been an issue.

[redridge]

interesting the wide body has this issue but not the narrow body....

[burzel2]

The wide body has the issue because the rear trailing arms (banana arms) are bigger. The shock mount is closer to the engine.