Aluminum exhaust vs. stainless exhaust

[snowborder714]

With the new turbo system planning in the works, I'll eventually need to get/make a new exhaust. I am wondering if anyone has any knowledge around using an aluminum exhaust for an autox/road race application. This would most likely not but a 100% full aluminum exhaust, but would have a partial downpipe out of stainless steel because of the heat (unless someone has proof otherwise). It will have a few v-band clamps to make install/removal/possible rerouting easy.


Pros of aluminum:
-lighter weight
-cheaper

Cons of aluminum:
-much easier to dent/destroy
-doesn't retain heat nearly as well as SS (will heat up floor boards/surrounding area)
-might be possible for exhaust temps to reach high enough to cause issues with metal (softening/melting)
-becomes brittle over time because of heat?


To deal with the cons:
-it'll be tucked up as far as possible to hopefully not make it the lowest point that would scrape first (think prep for under chassis aero....in the very distant future )
-could line under carriage with heat reflective tape in trouble areas
-definitely will consider coating or wrapping part/all of exhaust if it would help with heat and not add too much weight
-can't really do too much about metal temps
-can't really do too much about brittleness
-will make sure it's securely and solidly supported by hangers to help prevent it bending/flexing too much to deform/break



Interesting/helpful links about aluminum/aluminum exhausts:
aluminum exhaust systems - Technical Forum
stainless exhaust vs. aluminum exhaust - K20A.org .:. The K Series Source . Honda / Acura K20a k24a Engine Forum
Project Miatabusa Part 12: Why You Can't Make Aluminum Exhausts, And Why I Did It Anyway (interesting comparison of Burns vs. Vibrant v-bands on pages 3 & 6)
Yield Strength



Any opinions or real world experience (for an actual autox/road race car) would be helpful! I'd be open to hearing about issues with metal properties, but I don't want this to turn into a bunch of "on paper..." talk.

[Dyesuperman]

Interested in what people have to say about this as I had been considering doing this as well

[YES]

Most people would probably say go with stainless steel but if it was me I would do the aluminum just to explore and see what the outcome is.

[silicosys4]

The cons outweight the pros waaay too much for this to make sense to me.

[WES_393]

I wouldn't wrap the aluminum since it will keep the exhaust hotter. It's the same reason I would never paint a head or transmission. You want that heat to get out, not stay in.

[ec17pse]

Would it not be better to get 0.6-0.8mm walled stainless instead of aluminum? Its going to be light possibly either as light or just a bit lighter! And yes if you wrap it then your going to help make it soften faster!

If anything you should think about cooling it, so either add cooling fins to help or once you have placed the system cover it with some sheet metal to make the underside flat and incorperate a duct so air can flow through it and cool the system as you drive! I think that would be more benificial as so many cars these days come with coolers under the car so it would work to a point ( i hope) lol

[Hal]

I went aluminum from the down pipe back last year.

No issues, but then I don't drive it a lot.

No noticeable heating from the under side even w/o the oem heat shields.

But at less than 20 lbs including the muffler (no cat), it's hard to beat the weight savings.

3" (thin wall no less) and a Hooker muffler.

Quiet at idle and good for 750+ to the wheels.

Hal Landry's Photos | Facebook

Hal

[ec17pse]

Oh and i forgot to add why not loose the v-bands and just use the proper way that race cars use and just slip the pipe over pipe and use springs to hold it in place! That what we would do if building a track car. It saves some weight and is still very easy to take off if needed, only problem is you cant run any sensors just incase of a small leak unless you make it super tight fitment

[Hal]

Slip joints leak.

You'd have to weld tabs on for the springs and do it so they can with stand the constant tension.

I made my own hangers and v-band flanges then used Vibrant clamps.

[ec17pse]

Originally Posted by Hal

Slip joints leak.

You'd have to weld tabs on for the springs and do it so they can with stand the constant tension.

I made my own hangers and v-band flanges then used Vibrant clamps.

I did say they leak and that why you cant use sensors after the joint! But this is the best way to save extra weight. This is what we normaly do on touring cars and formula 3 cars, rally cars are bolted for strength and use thicker pipe aswell. And just on a side note they dont all leak as you can just add some exhaust rtv to the joint! Ive built many like this for fast road cars and none have ever leaked! Its cheaper and if not just as easier to remove

[snowborder714]

Thanks for the input so far, especially Hal.

How many miles (on average) do you drive your car in a year? I don't drive mine that much either, so this part doesn't worry me too much.

That's a very nice weight, as well. Do you remember what wall thickness you went with?

[nastynine]

the aluminum exhaust will save you a lot of weight but will eventually start to oxidize.

[snowborder714]

I can prevent the outside from oxidizing by painting/coating it. Would I need to worry about the inside oxidizing, or would it even with the hot exhaust gasses flowing through it?

[nastynine]

Yea I would coat the outside with a high temp paint or something, I'm sure home depot carries something in that field. As for the inside i wouldn't worry about that oxidizing at all, the carbon build up will take care of that.

[954TalonTsi]

Kind of expensive, but anodizing would help dissapate heat, protect against corrosion, and help metal integrity under repeated heating. But like I said expensive process...

[EagleT2000]

I'd go with stainless, unless your going for max weight savings or on a tight budget for it.

[snowborder714]

I'm building a race car, so obviously this is for weight savings.


Anodizing would be a great option, but I'm not sure I'd want to see what it'd cost!! But it may be interesting to look into.

[jakelandry]

I have a quick question... Whats the disadvantage of an open downpipe? Less weight no?

[snowborder714]

Most racing sanctions/locations have noise restrictions, and I'm not sure an open downpipe would meet those.

[TSi Kid]

Hows an aluminum exhaust sound in comparison?

[snowborder714]

Hal, would you be able/willing to grab a clip of your exhaust at idle and with some rev? I can't say I've ever heard an Eclipse with an aluminum exhaust.

But you can search and find video clips for other vehicles.

[outlawdsm]

I have run an aluminum cat-back exhaust on my car for about 20k miles. It has been daily driven, drag raced, and road raced. Only issue I ran into was how I made the hangers at first (out of alum. bad idea) I have since changed the hangers and have no issues.

[EagleT2000]

Anodized aluminum hmm, wonder how much that would cost.

[954TalonTsi]

Well you figure e.t.s charges 100 for an intercooler- thats maybe half the total surface area of your typical exhaust, depending on exhaust size. It may be hard to find a shop with an anodizing vat that'll fit sections of pipe that big. If you can afford 100_200 it'll definetly be benifical and one off.

[TSi Kid]

Hal, would you be able/willing to grab a clip of your exhaust at idle and with some rev? I can't say I've ever heard an Eclipse with an aluminum exhaust.

But you can search and find video clips for other vehicles.

Yeah I couldn't find any dsms with it

I would love to get my car to have that nice high revving "scream" if I could

[Dylan0123]

Found this pic of a 1g w/ aluminum pipe after a stainless downpipe


I like the idea, less weight and less materials cost

[outlawdsm]

An aluminum exhaust will not sound any different than any other material, the muffler and resonators affect the sound, not the material of the tubing.

Also I wouldnt worry about anodizing the exhaust, there are tons of non-anodized aluminum parts on many cars on the road today with no issues.

[TSi Kid]

An aluminum exhaust will not sound any different than any other material, the muffler and resonators affect the sound, not the material of the tubing.

The thinner material wouldn't have a different sound at all?

[outlawdsm]

Originally Posted by TSi Kid

The thinner material wouldn't have a different sound at all?

Typically the SS would be thinner than the aluminum. I have no exact proof that it wouldnt sound different, I only have my experience on my car and there was no audible difference.

[TSi Kid]

Typically the SS would be thinner than the aluminum. I have no exact proof that it wouldnt sound different, I only have my experience on my car and there was no audible difference.

Hmm, I would've thought aluminum to vibrate more and give off a different sound due to the density differences. I'll have to try it out..