Aluminium Exhaust

madjak · Postby **madjak** » Thu Sep 25, 2014 2:37 pm

Has anyone here tried an aluminum exhaust? I'm making a custom exhaust for my road / race car so I'm going to try it and see how it works out. Not much online about it but generally here are the pros and cons of Ali vs SS.

Pros

Weight: Nice and light... way lighter than stock. Lighter than SS especially the mufflers

Sound: Aluminum is more malleable, so it deadens the sound better. It will also have a thicker wall (ie 2mm). SS can sound raspy so you have to run additional resonators / mufflers. I think with an aluminum exhaust, you can get away with less muffling for the same dB output. The timbre of the exhaust note is also nicer... more mellow with way less rasp.

Easier for DiY: Much simpler to fabricate, and easier to find someone who can weld aluminum than SS (easier for me anyway)

Look: It will be a unique look. A light coloured ali tube poking out the back.

Cons

Heat: Generally heat isn't a major issue for the exhaust once it's past the Cat. The aluminum can get heat cycled and become brittle however I've spoken to several people who have run them for years and race cars running the aluminum from the headers back. Following on this point, you probably need to run more hangers to hold the exhaust in place, and potentially a flex joint to stop the harsh vibrations coming from the headers.

Damage: The biggest negative is damage due to going off the track, rocks flicking up and speed bumps. In a MX5 the front section is pretty well protected inside the tunnel but once you get to the diff, you either have to go over or under the drive shafts and then the muffler will be exposed at the back. I think a protective shield of some sort may be required as well as making sure everything is up out of speed bump range.

Cost: I'm not sure this is a negative as I think aluminum is cheaper than SS. All up I've ordered around $300 worth of bits for muffler, pipe, hangers, mandrel bent "u", with another $100 in luxuries like v-band clamps and a flex joint etc. We'll see the total when it's all done.

Rick

pezchops · Postby **pezchops** » Thu Sep 25, 2014 2:52 pm

ally is prone to fatigue very easily and even more when you throw heat into the mix.
so you may develop cracks here and there quicker that mild or ss
but you never know until you try.

hks_kansei · Postby **hks_kansei** » Thu Sep 25, 2014 3:39 pm

With the muffler part, while alu may reduce rasp (I seem to recall way back in the day people sometimes made copper/brass pipes for the same reason) are you sure that the rasp = volume?

either way, the main issue I think will be fatigue, and possibly keeping the cat-pipe flange tight.
Alu and steel expand/contract differently under heat, so you may find the bolts at the join backing off.

You'll probably need to use some form of locking nuts (nylocs will just melt out), either lockwire, or maybe even double-nut it.

madjak · Postby **madjak** » Thu Sep 25, 2014 4:04 pm

I think the copper exhausts were for alcohol and rocket fuels as they react to stainless / metal. I think the rasp sound is from the thinner wall tube used in stainless. Typically why mild steel exhausts are less raspy as they have thicker walls.

My plan is to use a V-band clamp where the metal changes. This means there will be a stainless flange and an aluminium flange as the transition point. Should work ok there.

I think the cracking may be an issue, but this car isn't a daily driver so hopefully it will last long enough. There are cars on the honda forums that have been using aluminium exhausts for around 5-6 years now. Not a lot of information but from a few posts I read, they are still going strong. I know of one race car that ran the same aluminium exhaust for 15 years.

The other issue I forgot to list was the heat transfer properties of ali as it cools around 20x faster than steel. This means the exhaust air will slow more as it travels down the pipe and cools. This may or may not cause backpressure and effect scavenging. I think the generally, as long as the exhaust flows well enough this won't be an issue.

lizard · Postby **lizard** » Thu Sep 25, 2014 4:12 pm

madjak wrote:I think the copper exhausts were for alcohol and rocket fuels as they react to stainless / metal. I think the rasp sound is from the thinner wall tube used in stainless. Typically why mild steel exhausts are less raspy as they have thicker walls.

My plan is to use a V-band clamp where the metal changes. This means there will be a stainless flange and an aluminium flange as the transition point. Should work ok there.

I think the cracking may be an issue, but this car isn't a daily driver so hopefully it will last long enough. There are cars on the honda forums that have been using aluminium exhausts for around 5-6 years now. Not a lot of information but from a few posts I read, they are still going strong. I know of one race car that ran the same aluminium exhaust for 15 years.

The other issue I forgot to list was the heat transfer properties of ali as it cools around 20x faster than steel. This means the exhaust air will slow more as it travels down the pipe and cools. This may or may not cause backpressure and effect scavenging. I think the generally, as long as the exhaust flows well enough this won't be an issue.

The other issue I forgot to list was the heat transfer properties of ali as it cools around 20x faster than steel. This means the exhaust air will slow more as it travels down the pipe and cools. This may or may not cause backpressure and effect scavenging. I think the generally, as long as the exhaust flows well enough this won't be an issue.

mate its a xm5 not some exotic V16 20000RPM quadcam aero motor :roll:

madjak · Postby **madjak** » Thu Sep 25, 2014 4:38 pm

mate its a xm5 not some exotic V16 20000RPM quadcam aero motor

If I had an exotic V16 20,000RPM screamer, it would be using inconel exhaust not aluminium. But yes I get your point. For me an ali exhaust is easier and cheaper than stainless. Plus its a good deal lighter. So why not?

project.r.racing · Postby **project.r.racing** » Fri Sep 26, 2014 9:00 pm

unless you are chasing wieght savings. then mild steel is the best product to use.

ben wilson · Postby **ben wilson** » Sat Sep 27, 2014 12:29 am

pezchops wrote:ally is prone to fatigue very easily and even more when you throw heat into the mix.

You could say exactly the same thing about stainless.

madjak · Postby **madjak** » Mon Nov 10, 2014 2:19 pm

Well my exhaust survived the weekend! It is a little loud, but sounds great on the track. The sound is really nice, with no raspiness or harshness.

One good thing about the aluminium exhaust is that it's cool to touch after around 5 mins of track work, which makes working under the car much safer!

No cracks in the welds, no melts... so we'll see how it lasts now.

speed · Postby **speed** » Mon Nov 10, 2014 5:21 pm

Thanks for the feed back. How thick is the wall?

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madjak · Postby **madjak** » Mon Nov 10, 2014 6:59 pm

2.5mm... It's thicker than I wanted but my aluminum supplier had it there in stock. 2mm or 1.6mm would be fine, but I figure 2.5 is probably a bit more resistant to rock hits etc.

It's still very light, especially with the aluminium muffler.

madjak · Postby **madjak** » Mon Nov 17, 2014 12:36 pm

I blew all the stuffing out of the muffler on the weekend. I suspect the rear weld failed where the exterior plate of the muffler joins the perforated tube. Nothing to do with the welds I had done so the aluminium muffler from Summit might not be the best quality. I'm surprised a non-turbo engine can blow the packing out of a straight through muffler, there must be a lot more force in the exhaust than I thought!

I had plans to replace it with a larger muffler anyway and had already ordered one prior to this failure. Whilst the car sounds great at a racetrack, I also run it at club events and may need to drive it on the street to and from events.

speed · Postby **speed** » Mon Nov 17, 2014 5:27 pm

Fibre glass stuffing? Was going to suggest stainless steel packing but then you'd have to braise to alloy. Um is that even the right term. Totally out of my depth here!

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Hellmun · Postby **Hellmun** » Mon Nov 17, 2014 7:03 pm

I blew the packing out of an Xforce Stainless muffler in 1 day at phillip island.... 90 aspirated kilowatts! When I cut it apart all I found were cloudy beads and lots of open space.

madjak · Postby **madjak** » Mon Nov 17, 2014 7:57 pm

The glass packing just blew out as I was reving the car to take off from the line. Not even at high revs! It wasn't melted or anything, just no-longer in the muffler! You can see some strands left hanging out at the tail end of the muffler.

It's a shame it didn't work as that muffler was only 900grams... not quite enough muffling though unless you only run at circuits. I'll see if I can get a refund as muffler shouldn't blow apart like that.

here is the item I purchased, maybe best to avoid. http://www.summitracing.com/int/parts/vpe-12900/overview/