Race exhaust
 

Just picked up a Jackson S/C Miata to run SSM autocross. I need a good guess on the exhaust system requirements. It's a pretty stock internal 1.6 with an M45 supercharger which will be tuned on E85 to maybe 180 rwhp.

The exhaust needs to keep the sound to 93dB at 50'. Not going to buy something all chromy and fancy. I need to get kinda close before I go to the tuner because if I need to make changes to the exhaust, I'll have to redo the tune. I'm thinking in terms of DynoMax bullet mufflers, Ultra-Flo's etc.

So for any supercharged racers out there...what's the minimum exhaust I need to keep this from being an ear-bleeder? Starting with race headers and no cat. Trailer queen -- No street use at all.

Hard to say with the blower. The blower car is going to be louder than an N/A car or a turbo car. With my turbo using both lengths of dynomax bullets in 3" diameter and the 3" borla xs pro my car is in the lower to mid 80's for db. But I've got the turbo making it quieter too.

The pretty standard setup that passes nationals sound at your level of power (aka CSP power) is a 2.5" exhaust and a flower master hushpower II mid mounted with an under car dump and super trap plates in case to run events where it needs to be under 90db.

Research what makes the most power where you need it in the power band for autocross and add as many larger resonators/mufflers as you can.

I'd put on a magnaflow resonator and the largest magnaflow muffler. I remember Brain had some specs on the size that fits. I'd imagine someone will chime in.

That largest magnaflow also weighs a ton.

I'm thinkin' Dynomax Ultraflow 17222. If there's room for it.

Was recommended by their tech support guy who supports tracks with sound control. I have a pair on a built V8 that worked out well.

To be at 93db you are going to have to have a lot larger and heavier muffler than you want. When we went from a turbo to a twin screw, the increase in exhaust db was almost unbelievable. In addition to the tube style muffler we were running that dumped just behind the seats, we've now added a mini cooper sized 2 chamber muffler in the stock location with full tailpiping.

You're also making real power.

Good input, thanx.

I'm running an HKS Hi-Power that came on a turbo parts car I bought that is straight through but surprisingly quiet. Just throwing it out there.

Back when I had the m45 on my car at about 190 hp it passed sound at Laguna Seca with stock headers, cat, and Racing Beat Exhaust. That was a normal sound day which was 93 db if I remember right. Every other time I have been there it has been a high db day so dont know what my current setup is. Figure this info will at least give some sort of idea.

You could always add a Supertrapp at the end for tracks with lower DB levels.

Supertrapps are known for significant back pressure -- at least if you run few enough discs to have much effect on noise. I would worry that it wouldn't work well with up my tune.

My first fall-back is to run an extra 90 elbow at the end which I can aim left or right. Wherever the sound meter isn't. Good for -3dB. But I don't like to be that close, so I'd then add another muffler or resonator and re-tune.

I have the full borla spec miata kit on my 130hp n/a 1.8 car. Without the add-on muffler, it's super loud and sounds just like a spec miata inside and outside the car. With the muffler, it barely sounds any different inside the car but my friends say they can barely even hear the car when I'm on track. I haven't ever had it at an event with a sound meter. I only bought the rear section for late Sunday nights after a track weekend when I don't want to piss off the neighbors while unloading the trailer, but it's light enough that I've just been leaving it on the car.

It was more than I wanted to spend at the time, but it ended up being super easy button and I don't regret spending the money. Also note that it has a built-in cat delete.

Specs are very loud and not attractive sounding.

Build an aluminum exhaust and use 3 vbands to allow you to drop in another muffler if you need it.

aluminum exhaust will be under 10lbs with 3 mufflers.

Yes completely accurate. The aluminum exhaust I made that weighed 12 pounds with all 3 mufflers was about 80db. The mid pipe muffler also failed from heat twice on an N/A car running e85. Its still really friggin quiet with both rear mufflers installed. So much Burns packing is in those two rear mufflers, it has like the muffler volume of 6 Burns mufflers, lol.

Any details on your aluminum exhaust, and maybe pics of the failure? I am building one for my race build.

you can PM if that works better.

I posted most of them in the fab thread I think. Not the failur pics not sure if I took any. But basically it failed because we used 3000 series stainless to make the perf core because it only costs like $60 for a 4x4 sheet rather than $300 for 6061. One fail type it looks like the welds were literally melted off, the other time it failed was because the rivets that hold the 2 halves of the muffler together (so it can be re-packed) failed and pounded the core into the end cap until it broke in half, but that was a design failure. It wasnt able to take the loading from the g forces since the end cap was just sheet metal, the rivets tore out. Made a billet end cap instead and used screws, it didnt fail like that again, the further back mufflers are still running the sheet metal end caps with no problems.

Alright, so not the mid pipe, your diy muffler in the midpipe. lol.
awesome.

I looked for your aluminum exhaust info in your SSM build thread but didn't find it. Did I miss it, or do you have another thread?

Its in the fab thread not my build thread since its not on my car.

went through fab thread and this is all there was.















no exhaust pics, just mufflers. do you know the lengths/diameter of the mufflers you made?

Oh I didnt put in the "finished" pics. Heres the only under car shot.

https://www.miataturbo.net/attachmen...ine=1389121929

https://www.miataturbo.net/attachmen...ine=1389121929

Note that 2nd shot is in no way how it goes together. Its got a couple different configurations and I ran out of spare v-bands so its kind of just stuck together randomly so I could weld the vbands without warping them. The most difficult part of this is getting the header flange in 6061, you got to make it yourself I used a cnc, it could be done with a hand drill and hack saw though.

I wonder how you're getting away with aluminum perf when Emilio says he's burning out 304 stainless? I thought stainless had a way higher melting point. AutoX vs track I guess?

And also e85. And the midpipe muffler was definitely having heat problems. Though the two times it melted were the two times it was on the dyno.

the aluminum mufflers I have seen (online) being built have used stainless perforated tube with aluminum end caps, weld stubs and case.

Maybe that would have been a better idea. Then at least I could have gotten the perf cores pre-made rather than having to roll my own.

Just got off the phone with tech support at FlowMaster. Was looking for design info on the Hushpower and learned some interesting stuff.

The HP-2 has been redesigned and is now available in a more compact case with the same internal size. The case ears are now gone. And a longer one is available so you can get 12" and 18" case lengths in 2.5". Don't know about the larger pipes you guys use.

The HP is not a chambered muffler. It has two perf cones which meet in the center of the can at the cone bottoms. So the flow goes in the cone, passes into the can, and back into the second cone. They claim no pressure loss compared to open pipe on a flow bench.

And they have a larger version of the same technology available called a DBX. His suggestion was to run a DBX or an 18" HP in the rear location and then after trying it, add a 12" or 18" HP mid-pipe if more silencing is required. Quoting him, with this technology you could make up an entire exhaust system with HP's connected end to end over the entire length of the car and it would still flow like an open pipe. He said it, not me.

Part No's: 12512409, 12518409, 12514310

I thought that using the same mufflers back to back wouldn't help with sound anymore than with just one. Mainly because they have the same tone or something along those lines. But hey, I could be wrong and/or that's not what you meant..

Kind of, when dealing with an absorptive muffler, IE a glass pack, having the same muffler back to back doesnt do much more than just the single muffler. Thats why my racecar has both available lengths of the dynomaxx bullets in 3" mounted end to end in my midpipe.

Makes sense, never saw the dynomaxx before.. Seem pretty affordable.. I guess you like them?

They're ok. Lightish and cheap and cut down the noise. 409 stainless is the downside so they will rust.

You know, I questioned him about the two muffler thing too. He said what we're talking about is true of tuned cavity-style mufflers but not linear mufflers. As an example, you wouldn't expect a 20" glasspack to be no better than a 10" glasspack. Longer is better, and building length in "modules" is okay.

Previous HP's could be had in 409 or 304SS for a few bucks more. Don't know if that's still true. But the website says all stainless steel has a lifetime warranty.

My bigger concern would be not knowing if a muffler that free-flowing is up to silencing a supercharged engine. I've got a supposedly pretty good street/race muffler on a supercharged rally Rabbit and it's a serious ear-bleeder.

Muffler packing volume is the real secret to reducing noise. You see those mufflers I made that are super quiet? They've got more volume than the monster magnaflow and the whole system weighs less than it. If its too loud just keep jamming more and more mufflers with more and more packing volume under the car until its quiet enough. Most of the weight of the muffler is in the case.

I believe that. I've never seen a micro muffler with serious capability.

I wonder why no one produces anything similar to yours? You'd think there would be at least a small enthusiast's market. Maybe that's your ticket to joining the 1%.

Ha, those things take like 4-5 hours a piece to make, would take an hour less if I could find pre-made perf cores. If I wanted to make real money they'd be on the burns stainless cost level. Though on noise attenuation/weight ratio they kill Burns.

Dragging this one back up because the thread is on point for my question. What did you DIY muffler guys use for packing? The muffler specific stuff is stupid expensive and I can only find it for dirt bike mufflers. Any concerns with using mineral wool insulation cut to size? Maybe break it up and pack the muffler that way? Just looking for packing material that won't cost more than a premade muffler.

A good material I have used is Ceramic Wool (kaewool?). My exhaust has been using it for a couple of years without losing the packing (I added a semi-fine stainless mesh outside the perforated core to ensure it wont just peel and escape).
Its not too expensive, no heat issues ever (you wont be able to melt it with a TIG torch even). As for weight, id say its just as heavy as rock wool.
As usual with fibers, its quite nasty, even nastier than fiberglass. Breathing protection mandatory, tight suit and gloves recommended.

spec-31

I got started on my aluminum muffler build, but just barely. Leafy you weren't a kidding those perforated cores are a pain in the arse, although now I can make them in 15 min.

Little roller rig I built.
https://cimg3.ibsrv.net/gimg/www.mia...65e72bbd70.jpg
https://cimg7.ibsrv.net/gimg/www.mia...a911de3d6c.jpg

Finished product:
https://cimg8.ibsrv.net/gimg/www.mia...df57aeac60.jpg
https://cimg9.ibsrv.net/gimg/www.mia...ee75319370.jpg


This core is 24" long, which is huge for a muffler, might end up getting cut down a bit depending on how the clearancing effort goes.

More to come.

I stopped using aluminum core even on aluminum ones with aluminum pipes. I just use purchased stainless cores and on the aluminum ones I just float the core on both ends. The aluminum cores just break even if they're floated, I think they just get too hot locally and blow out, even on an auto-x car on e85.

Well shit.......guess I can replace them quickly now. What thickness did you use if you don't mind me asking?

Like .065 I think.

Ahh, ok, this is .125" so maybe it'll last 2 laps instead of only 1.

So against my better judgement I went ahead with the all aluminum muffler build. I added a center gusset that'll get tack welded to the case after it's put together.
https://cimg2.ibsrv.net/gimg/www.mia...f5600e1b57.jpg

I decided to give mineral wool insulation a try.....50$ buys enough for 25 mufflers . It's rated not to melt at 2000 deg.
https://cimg0.ibsrv.net/gimg/www.mia...ce55854b12.jpg

Stuff it in a box and welder up.
https://cimg1.ibsrv.net/gimg/www.mia...de959ce68d.jpg

Money shot......
https://cimg5.ibsrv.net/gimg/www.mia...9fefaf44f8.jpg

8.8 lb's for 4x12x20 muffler, The comparable magnaflow 14578 at 5x11x22 weights in at 23 lb's from what I'm seeing online (haven't weighed one myself). I'll take a 15 lb. weight savings any day.

Oh, non-reackable? yeah that aluminum core should hold up fine. I always make them so you can repack them because they get less effective after a few seasons, at least with the spec 31 or the burns packing.

This is my first time seeing this thread, but perfect timing. I've been thinking of making my own muffler lately. Thanks everyone for posting pics and info. Makes me wanna go build one now.

Yeah, this packing may not hold up in which case me and an angle grinder will will be spending a lot of time together. I could have cut the weight in half with thinner materials and a much smaller case. End plates are .125", perf. tube is .125 and the skin is .065". I think the beefiness is a good trade off for the weight.

I ran a full aluminium exhaust with vibrant muffler for 3 or so events. The problem with my motor is the overlap on the cams causing massive pressure waves at around 4000rpm which tore apart the perforations in the muffler and all the packing blew out. The whole exhaust was super light though so it's definitely something I'll try again when level up my ally welding skillz.

I like the idea of sleeving the inside with perforated SS but keep the rest of the exhaust and muffler as aluminium.

Well done Bronson!

I created a two muffler system to deal with sound. I used a stainless packed 17" long 4.5" diameter tucked up beside the PPF near the header. This takes the brunt of the heat and a good chunk of noise. I then added a fiberglass packed 15" long 4.5" diameter just before the diff with exit pointing down. This grabs the higher frequency sounds and is further back thus more protected from temp. Both are re-packable if need be. This design leaves the door open for flat panel undertray.

You caught me 😀, that's in the long term hopper.

I have been wanting to build an aluminum muffler for a while now. This site sells 7" OD 16 gauge aluminum tube which was my plan for the body: Aluminum Intake Tubing 7" OD

I'm curious to see what you do with the hangers.

Double post

Finally wrangled enough time to finish this up. I had to add 18" worth of stainless tube and a flex joint to my down pipe. This section will get a shell of a cat to pass visual inspection. That added 5lbs to what ended up being a very light setup at 14.5 lbs.
https://cimg2.ibsrv.net/gimg/www.mia...8df5ce8289.jpg
https://cimg3.ibsrv.net/gimg/www.mia...41611962b5.jpg
https://cimg4.ibsrv.net/gimg/www.mia...b451b71b30.jpg
https://cimg6.ibsrv.net/gimg/www.mia...e4be4a6f78.jpg
we'll see if those screws pull out of the case over time.

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Yeah yeah, booger welds...... :asshole:

Where's vlad to make fun of your cheater bends?

https://cimg7.ibsrv.net/gimg/www.mia...f34d4b687a.jpg
Believe it or not those are mandrel bends, just cut what little bend I needed from the 90's and used the strait leg since I was short on strait pieces.

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