New 4" Aluminum Exhaust
 

Just thought I'd share some pictures of the new 4" aluminum exhaust I had fabricated for me by Big 3 Racing. I'm hoping this will do the trick to get me to the 500whp mark on the BNR's. The car still has a 3" SS down pipe, but that tapers out to 4" and then it is a V-band connection to the aluminum exhaust. It will also come in handy when I decide to go to the Borg Warner S475 I have sitting on my shelf.

Why aluminum? It's a gamble because of the rotary heat, but after reaching out to other members (mainly the 13B Chevy Nova guy who also did this) and metallurgist's; I decided to go with it. It weighs a fraction of a 4" stainless exhaust and is cheaper then stainless. Also, Vibrant makes 4" all aluminum mufflers, which the car is running two.

Before this I had a 3" resonated MP and 3" N1 exhaust. It's quieter at idle and somewhat louder for everything else. It's bearable, but I would need ear plugs if I were to go for a 2+ hour drive. I plan to take her to the track this weekend so I'll hopefully get some video to show how she sounds.

Enjoy the pics!

Attachment 756154

Attachment 756155

Attachment 756156

That's beautiful, really like the exit design as well. Did you have to add mounting points to distribute the load on the aluminum?

Nice! I'm interested to see how it does long term. Also interested to HEAR how it sounds!

Any idea on the final weight?

Dale

What gauge did you use?

Lighter than srainless and a hell of a lot cheaper than titanium.

very cool, did you think about getting the apexi gt spec exhaust? it is a 4" also.

Looks great.

Thank you everyone for all the compliments!

The sound is a lot deeper and gets rid of any raspyness that you would usually hear from a 3" N1.

We used the factory hangars and just made sure to give it plenty of wiggle room for when the aluminum expands under heat.

The fabricator forgot to put it on the scale, but he described it as about 1/3 of the weight of the old exhaust (the aluminum mufflers only weigh 2.4lbs!)

We had to order the aluminum from a different supplier, Vibrant only sells 1.5mm aluminum piping. We used 2mm thick piping.

The GT spec is 3.75" from what I remember, is still stainless, costs around $675, and you still need a custom 3.75" mid pipe. My whole setup cost me $900 parts, labor, and tax included.

Nice, very interested to hear how it sounds as well.

did you use a flex pipe at the mid section? i would recommend it if you didn't.

The shop that did this has built numerous aluminum exhausts for both race and street cars and they said it wouldn't be necessary. Of course I'm the first rotary, which the extra heat has me concerned, but the shop offered to fix it if it does fail due to flexing.

This looks great, and the fabrication is top notch, but I really question the wisdom in this choice of materials...

If anyone remembers reading the USCC from SCC magazine long ago, one of the cars invovled had an aluminum exhaust and it melted down and burned the car up! There maybe a reason no one offers an aluminum exhaust.

At the local circle track here, where they run 240SX in a "pure stock" class, a few geniuses have attempted aluminum exhaust with similar results.

From Racing Beat's website:

The melting point of pure aluminum is 1221°F and common 6601 T6 aluminum is 1090-1202°F. Not sure what alloy they are using, but I doubt that it is much different.

With that said, perhaps the EGTs are low enough at the exit of the downpipe that it is well below the melting point of aluminum. Most motorcycle exhaust are similar to your setup, start stainless and terminate with aluminum muffler. Some investigation with a pyrometer would easily prove/disprove this.

Not trying to be a jerk, rain on anybody's parade, or pretend to be a know it all. I just hope we do not end up seeing pictures of another FD fire!

Vince

Exactly my thoughts! I've pondered this in the past but read few horror stories of melt downs which immediately switch me off. OP I hope the best for your setup and recommend EGT sensors.

in for the sound clips

Nice .. also interested to see how it holds up
If you wanna test your ear plug theory...come on down hour to, hour back :)

I read the same information when making this decision and the only condition I could find where people had catastrophic failures is during road/track racing and drifting. Basically where the exhaust will see high heat for a extended amount of time.

I use my car primarily as a street car and occasionally for drag racing. I don't plan on putting the car through a condition where the exhaust might be compromised.

the exhaust may see those temperatures early in the exhaust stream but by the midway point it should have cooled off considerably.

if it went all the way to the turbo then i could foresee it not lasting even a few days.

Very clean build and installation. It will be interesting to see your long-term results.

As a machine shop manager who works with a lot of aluminum, my biggest curiosity is in regards to the thermal expansion properties and how those will effect your welds and overall construction. A ~ 1000 degree temperature change is going to cause several hundred thousandths of growing/shrinking during the heat cycles.

All in all, beautiful work and shows you're not afraid to try new frontiers.

Thank you for the compliments, I do unconventional things such as this for the same reason I got into rotary engines in the first place. To do something on a platform that others say can't be done and to prove them wrong. I already set the record for stock frame turbos and I want to be the first to join the 500whp club on stock frame turbo's.

The thermal expansion is absolutely hilarious and it expands more then we accounted for. At ambient temperature the tip is flush with the bumper, after 30min of driving the tip sticks out a good 2.5"'s past the bumper. It's like the exhaust gets a erection when you drive it and is currently putting excess stress on the rear exhaust hanger. This project was intended to have some trial and error involved, but I'm so far very satisfied with the results.

Unfortunately the weather in Cleveland was brutal this weekend and I didn't have a chance to run it down the strip. I'll try to get sound uploaded as soon as possible.

I just read your post that the exhaust grows about 2.5 inches when its warmed up. I was wondering if you also experience any exhaust leaks from the V-band connection with it expanding/contracting?

The exhaust looks great, I have a complete 4 inch exhaust from the turbo back out of stainless steel and its a heavy mother you know what. I can only imagine how easy it is to move yours around.

Great job.

I'm reminded of those GM cars, GTO's I think they were, in the late sixties that had cast aluminum headers on the V8s (I think 455 cubic inch V8's) and they left drips of molten aluminum on the drag strip when the owners took them to the race track.

Nice idea, I'm interested to see the system 6 months down the track from now. It would definitely be light weight.

Any updates or changes made after a couple months of driving?

Interested to know long term data too!

Water injection to the exhaust? jk :) Like the idea. would love to hear it!

+1 for updates!!!!

Sent from my DROID RAZR using RX7Club

Well, I live in Cleveland so the car got put away for the winter in the beginning of November. I put about 1,500 miles on the car after getting the exhaust on and ran it down the drag strip a few times, tried to get audio but the V8's would start their burnouts about 2 seconds after I would launch; so you could really only hear the car for about 1.5 seconds.

The only causality that happened about 80 miles into driving it was that the rear exhaust hanger broke due to a bad weld where the hangar met the pipe. Since the exhaust grows about 3-4 inches longer when fully warmed up it was putting excess stress on that hanger and combined with the bad weld it failed. The same shop re-welded and reinforced the hanger as well as added a skid plate of 4mm thick aluminum at its lowest point (for free). The exhaust only got a minor scrape, but for long term driving I thought it would be a good idea (turns out it's hard to fit a 4" pipe all the way to the back of the car, so there's a low spot). Other then the rear hanger the exhaust has been rock solid and has been heat cycled, seen rain, and been launched on without any failure. At this point I'm more then confident in using aluminum as a downpipe back solution for exhausts.

As for driving, at idle it's quieter/deeper then my old 3", but definitely louder and deeper at all other points. The sound is amazing and I have received many compliments from V8 guys saying that it's the best sounding 2-rotor they've ever heard. The only downside is highway cruising for long periods of time, it's manageable when you're moving around the rev range but when you're just sitting around 3K you start to think there is a bug eating your brain and you want it to DIE! So yeah, that part is annoying.

As for power, as I said earlier; it leaned out my entire map a full point! I had to add more fuel and it definitely picked up power as well as spool-up.