Repacking the muffler

[Bob_Spidell]

Steve, how you gonna seal the seams? In my experience, all it takes is a pinhole leak to cause that annoying 'popping on deceleration' (yeah, a little is cool but too much is embarrassing). If you do decide to spring for a MIG, you'll want a spool gun to do aluminum.

 

[steveg]

Steve, how you gonna seal the seams? In my experience, all it takes is a pinhole leak to cause that annoying 'popping on deceleration' (yeah, a little is cool but too much is embarrassing). If you do decide to spring for a MIG, you'll want a spool gun to do aluminum.

I can seal the seams with muffler sealant - like the guy did in the original Lotus posting.

Welding's another project entirely. This one can be done with screws. I want to be able to re-pack it in a few years if it gets loud again. From a little basic research, I'd say Randy's correct - the melting point of aluminum is too low for this application.

 

[John Turney]

... I'd say Randy's correct - the melting point of aluminum is too low for this application.

1,200 F is too low? They coat steel exhaust tubing with aluminum.

 

[steveg]

1,200 F is too low? They coat steel exhaust tubing with aluminum.

Seems like since I already built it, it's worth trying out the aluminum.

 

[steveg]

Racers discussing EGT in the 1300 - 1450 bracket at WOT:
https://www.britishcarforum.com/bcf/showthread.php?75939-Max-safe-EGT&highlight=exhaust

Red57 can chime in, but I believe they're measuring at the manifold.
Sounds like I have a reasonable chance of this working.
If I do another muffler, would get a little more latitude by building the detachable end cap at the rear of the muffler rather than the front as above.

 

[healeyblue]

I sure hope you don't see those kind of temps at the outlet of the muffler.:rolleye: I think you will be fine temp wise but the heat and cooling of the aluminum to steel may cause accelerated corrosion and loosening of the screws, but is definitely worth a try.

 

[Randy Forbes]

Indeed, the strip of aluminum isn't going to melt, but I expect it will get annealed to the point of the screws losing their bite. That was the intended point of my previous post.

 

[steveg]

I sure hope you don't see those kind of temps at the outlet of the muffler.:rolleye: I think you will be fine temp wise but the heat and cooling of the aluminum to steel may cause accelerated corrosion and loosening of the screws, but is definitely worth a try.

One of the things I find charming about LBCs is the nearly limitless opportunities for what my friends and I call "science projects". If I'd bought a 356 instead of the Healey I'd have missed out on 15+ years of science projects!

 

[steveg]

Indeed, the strip of aluminum isn't going to melt, but I expect it will get annealed to the point of the screws losing their bite. That was the intended point of my previous post.

Understood. Will verify that and report back. Have sheet SS now and info on drilling and cutting it, but want to prove out the work I've already done before moving on to the SS. Maybe I need to find Grade 8 #10 lockwashers if such things exist. The Grade 8 LWs on my manifold studs have retained their temper.

 

[steveg]

Got lazy and decided to replace the aluminum inner sleeve with SS. Will have an update pic tomorrow or so.

You can cut it with a hacksaw and water. Drilling - am using a cobalt bit at slow speed/high pressure with water. Threading is normal. Everything takes longer.

IMO if you cut the rear of the muffler off instead of the front, the aluminum would be more likely to hold up as it would be farther downstream and not as hot.

 

[Michael Oritt]

I have a twin EGT gauge on the Courier (MGA 1588) and the probes are located about two inches from the exhaust manifold flange in the tubes from cylinders 1 and 4, before they merge with 2 and 3 . When things are right I normally see WOT temps of 1200-1300. The headers are ceramic coated and there is no muffler downstream.

 

[steveg]

Redid the insert in .033" laser-cutable stainless sheet (it's what was available as a scrap from the metal house):

Thread strength seems plenty strong. Will use star lockwashers for final assembly with muffler cement. Still waiting for the Acousta-Fil.
SS was easier to bend than the AL, but drilling was harder with the necessity for slow speed and water.

 

[4tecdog]

I need to suppress the noise on my AH spares S/S side exhaust fitted to a BJ8 been going through a few options like modifying to exit from rear but this will probably mean fitting an extra resonator box then I will lose the extra ground clearance I really need on our excessive speed ramps. The idea of extra wadding in the exhaust sounds good, but I don’t know how the exhausts are constructed and if the best way to fill the twin exhausts would be to cut the ends off fill with Acousta-Fill and weld back or make two holes fill with Acousta-Fill loose packing and weld a patch over this way the internal pipes would not be cut. I believe this packing expands with heat. Any suggestions would be very welcome.

 

[steveg]

I need to suppress the noise on my AH spares S/S side exhaust fitted to a BJ8 been going through a few options like modifying to exit from rear but this will probably mean fitting an extra resonator box then I will lose the extra ground clearance I really need on our excessive speed ramps. The idea of extra wadding in the exhaust sounds good, but I don’t know how the exhausts are constructed and if the best way to fill the twin exhausts would be to cut the ends off fill with Acousta-Fill and weld back or make two holes fill with Acousta-Fill loose packing and weld a patch over this way the internal pipes would not be cut. I believe this packing expands with heat. Any suggestions would be very welcome.

Acousta-fil is a sheet you wrap around the internal tube. Since you have welding, you'd get a better job by cutting the end off.

MGAguru tried drilling holes in his muffler and repacking with lack of longevity:

https://mgaguru.com/mgtech/carbs/ex103.htm

 

[4tecdog]

You can also get Acousta fill in a bead form from Demon Tweeks just thought that might be another way of filling the area around the pipe without actually cutting the pipe. The patch would be fairly small.

 

[steveg]

I only see Acousta-fil in the mat and "boa" form (continuous string like a feather boa). The boa looks easier to insert than the mat.

 

[4tecdog]

Yes if I can insert this boa form though a rectangular slot in the top of the exhaust it might work, I can then weld up. difficult to know how much to stuff in Demon tweeks sell it in 400g packs and they say that is enough for a 400x100 exhaust so if I can get it fairly evenly distributed it should work.

 

[twas_brillig]

We've got a supertrapp clone our VW 1600 cc engined dune buggy, and I like it: noise level not bad, and it sounds more like a British 4 cylinder sports car than a VW. Dunno how the back pressure is compared to other options.
I've also got an old Buell motorcycle with a Vance & Hines exhaust that the previous owner had gutted (took the packing out; then ripped everything else out too). I tried the steel wool etc. approaches but couldn't make them work; finally was able to source an after-after market packing material (a blanket material rather than mesh or popcorn or whatever) and it's now pretty civilized. Doug

 

[steveg]

Repacked the muffler today. Only needed one pkg of 350mm x 1m Acousta-Fil.
I made the two 28" tubes out of poster board. They made it easier (ift not easy) to slide the packing into the 27" long skinny muffler.
Will have a DB reading in a couple of weeks when I get my car back on the road.

 

[steveg]

Followup: exhaust repacked almost as loud as before. Next step to dismount and check the filling. Maybe I packed it too tight.

Somewhat quieter >3000 rpm, but that isn't much help as most of my freeway driving is less than that.

Am also going to change out the Monza 1.75" pipes for some stock 1.25 inchers and see how that goes.