[pram133]

Hi everyone, I have a M240 Xi convertible and I am trying to put a custom exhaust. This brace ( marked) is very tight to allow a 3 inch mid pipe. Can I loosen this and add washers to increase the gap? Could someone explain whats that brace is for and will it affect driving or car height etc if I make any adjustments? I don’t remember seeing in Coupes🤔. Thank You.

[Ajowhan]

That is because these are convertible only braces. They are there because convertible are less rigid due to having no structural support of the roof that coupe has. That said, the braces are mainly for rigidity of the car.

Without diving deep in the engineering of it, I personally don't think adding a washer or two to increase the gap slightly will present anything noticeable to average user. I however probably would not risk it for an exhaust for myself.

[NewWorldOrder]

Originally Posted by pram133

Hi everyone, I have a M240 Xi convertible and I am trying to put a custom exhaust. This brace ( marked) is very tight to allow a 3 inch mid pipe. Can I loosen this and add washers to increase the gap? Could someone explain whats that brace is for and will it affect driving or car height etc if I make any adjustments? I don’t remember seeing in Coupes🤔. Thank You.

Why don't you just delete the resonators? The pipe is already over 3 inches, and you'd save money for essentially the same amount of sound.

[pram133]

Originally Posted by Ajowhan

That is because these are convertible only braces. They are there because convertible are less rigid due to having no structural support of the roof that coupe has. That said, the braces are mainly for rigidity of the car.

Without diving deep in the engineering of it, I personally don't think adding a washer or two to increase the gap slightly will present anything noticeable to average user. I however probably would not risk it for an exhaust for myself.

Thank you. Yes thats what I understood so far. Will test it out.

[pram133]

Originally Posted by NewWorldOrder

Why don't you just delete the resonators? The pipe is already over 3 inches, and you'd save money for essentially the same amount of sound.

I am doing a full custom dual exhaust from CAT back. I don’t know how much I can accomplish perfectly in that narrow space. Will update

[cooolone2]

Use OVAL pipe... Or crush it where needed. For a few inches, it won't matter much. Doesn't change the OD and won't really effect the fow either. If you're worried about what it looks like, then cut a bunch of pieces that you'll crush concentrically and have someone lobster weld them all so it "looks" good! Lmao!

Custom? Stainless?

And oh, by the way, adding washers and lifting the brace away from the surface it supports will add stress to the bolts holding it in place. I would make sure they're grade 8 or higher ... You want as many threads seated as is present when there's no washers. By using washers you can lessen the number of threads engaged and therefore allow for problems. So... If you're going to raise the bar by using washer to space, say 1/4” I would recommend getting the same thread pitch bolt, grade 8+ but with the additional length that you're adding so it seats as many threads as before!

Good luck!

[Resoelg]

Are you exchanging for cat back aftermarket exhaust or total custom design?

[pram133]

Originally Posted by cooolone2

Use OVAL pipe... Or crush it where needed. For a few inches, it won't matter much. Doesn't change the OD and won't really effect the fow either. If you're worried about what it looks like, then cut a bunch of pieces that you'll crush concentrically and have someone lobster weld them all so it "looks" good! Lmao!

Custom? Stainless?

And oh, by the way, adding washers and lifting the brace away from the surface it supports will add stress to the bolts holding it in place. I would make sure they're grade 8 or higher ... You want as many threads seated as is present when there's no washers. By using washers you can lessen the number of threads engaged and therefore allow for problems. So... If you're going to raise the bar by using washer to space, say 1/4” I would recommend getting the same thread pitch bolt, grade 8+ but with the additional length that you're adding so it seats as many threads as before!

Good luck!

Thank You. Yes I will keep that in mind. I got a longer Bolt like 1/2 inch more but I will check for Grade. Which grade is better on bolts.. Grade 6 or 8.. sorry not familiar with this.

[pram133]

Originally Posted by Resoelg

Are you exchanging for cat back aftermarket exhaust or total custom design?

Actually I got this idea of race CAT back from M2 and run dual pipes all the way from CAT pipe.
So far we are stuck around differentials.

[aerobod]

Originally Posted by pram133

Thank You. Yes I will keep that in mind. I got a longer Bolt like 1/2 inch more but I will check for Grade. Which grade is better on bolts.. Grade 6 or 8.. sorry not familiar with this.

Metric bolts have a different grade system than imperial bolts. The minimum recommended grade for automotive use is 8.8, higher tensile bolts that are commonly available are 10.9 and 12.9.

BMW also use one-use stretch bolts, they may be used on the bracing bars, so just substituting a longer bolt without knowing it’s grade may not allow it to be tightened properly without the risk of it breaking.

Here is a typical primer on bolt head markings: https://henrysautowarehouse.com/bolt...h-identifiers/

[pram133]

Originally Posted by aerobod

Metric bolts have a different grade system than imperial bolts. The minimum recommended grade for automotive use is 8.8, higher tensile bolts that are commonly available are 10.9 and 12.9.

BMW also use one-use stretch bolts, they may be used on the bracing bars, so just substituting a longer bolt without knowing it’s grade may not allow it to be tightened properly without the risk of it breaking.

Here is a typical primer on bolt head markings: https://henrysautowarehouse.com/bolt...h-identifiers/

Thanks for the detailed information.
After searching in 5 different hardware and Autoparts store, I found the M12 -1.50 is the right fastner which threaded perfectly. I forgot to pay attention to the tensile strength. I will make sure its 8 or above if I ended up needing it. My buddy and me working on the driveway without a full lift, may take 1 more weekend before we fully assemble and test it.