so how are these compared to lets say a cherry bomb cause they look similar internally except for the fact cherry bombs are packed with fiberglass ?

 

Not a bad design, keep up the good work. I'm glad to see people taking the time and effort to do some real world testing on designs and materials. Did you ever get dyno figures with your completed setup? Would be interesting with and without the tip silencer.

 

No dyno figures yet, I had to battle fuel for a while and also water pump failure, and now rear end failure, fuel and water pump have been fixed, rear end I'm still waiting on all my new bearings to come in to finish the rebuild. I had to get 2 diff to make one decent one thanks to stuck spider gears. I'm going to do another one with a torsen diff . After that I need to install my new shocks and coil overs along with camber plates, then uts moving on to alignment and corner weight balancing and after all that I can finally dyno lol. Busy schedual I lead somtimes.

 

Brilliant!

 

Where did you get the long strand ceramic wool? What brand / specs?

 

I'm not sure what the exact brand of the stuff that I have is, but I was going to get the Kaowool stuff as seen here:

http://www.anvilfire.com/sales/pages/kaowool_index.htm

But the guy that carries them (about an hour drive from here) didn't have that brand in stock and just gave me another brand. What I did is actually call up my closest Thermal Ceramic dealer, and asked who was the closest to me that they sold that stuff too. Once I had that contact I just called them up and setup a time to go pick some up. Here's the main dealers list:

http://www.thermalceramics.com/site....id=2&pageid=20

 

I just bought some Kaowool to repack two 4" round magnaflows with. I'll wrap the perforated core with 316 Stainless Steel coarse wool first. Since stainless retains heat it will burn off oil residue. And be a protective layer so the Kaowool won't get sucked out the pipe.

http://www.mcmaster.com/#stainless-steel-wool/=7dzvgc part # 7364T83 Rustless Metal Wool 316 Stainless Steel, Coarse, 1 lb Reel In stock at $42.84

Then Kaowool on top of the stainless.

 

Out of curiosity and interest I think I am thinking about making my own muffler with that ceramic stuff inside. Question though, which would be better for sound reduction and retraining performance? A straight through design or baffled?

 

pretty cool stuff

 

straight through is better for performance

 

How much louder is straight through? How big should the body be? Thinking a 3 inch with an oval tip. Should I just do a tube or make it as wide as you made your dual tip?

 

The Dual tip is purely cosmetic and a single 2.5" is more than enough to outflow the back for most NA cars. If you go bigger out there than anything on the inner diameter piping, the muffler isn't going to be your restriction.

How loud it will be will depend on alot of things, perforated tubing choice for one, packing material, how tight the material is ... Its too hard to judge without much trial and error really. But generally speaking the bigger the holes in the perforated tubing the quieter it should be as it would allow more sound to go through the material, but would also slow down the flow a bit, now in the back end you can probably get away with bigger holes as its the furthest from the stream and its already slowed down the flow of air.

It will also depend on if you want to do just one muffler or two mufflers throughout the whole system, if the first one does a really good job, which is the way it should be, then the second one should be there to take care of the lower pitches. This is all from my own understanding.

 

Thought this might be of interest in this thread. This is an HKS cat replacement pre-silencer that comes on their S4 TII exhaust system. I had this on my 87 NA for about 8 years. It was used when I installed it. The odd thing about the failure is there's no rust present, it was caused by metal fatigue due to heat cycling. It failed on the top side, bottom is in great shape. Note that the outer casing is 2 layers of aluminized or stainless steel.

The second pic shows how it was constructed. The steel wool is very coarse, coarser than the copper Brillo pads you find in the stores for pot scrubbing. The steel wool is not packed very tightly but isn't loose either. The outer layer is some kind of ceramic wool that was about an 1 to 1-1/2" thick. Body is 11-1/2 X 9 X 4-1/2" Piping is 2-1/4" diameter with 1/8" punched holes that cover approximately 35-40% of the surface area of the tubing. Tubing is smooth.

This pre-silencer worked very well for quieting down the exhaust and gave a good tone to the exhaust. Bought it off eBay for 14 bucks cause no one knew what it was. The complete HKS TII exhaust system new ran $1400 FOB Japan.

I must say, when this blew out, I might as well have been running straight headers it was so loud. On top of that, being directly under the passenger seat, it caused major frequency vibrations throughout the entire car. Anything that was loose in the car rattled. It was so bad I had to empty out the console of anything loose and wear ear plugs on the highway.

 

looks like a rats nest... so how old was it before it finally died? you said about 8 years but how old was it when you got it? thats pretty impressive

 

Have no idea as to how 'used' it was when I got it. I hacked up/re-welded an RB pre-silencer as a replacement. It was too long to fit in the space. It sounds good til 2500 rpm, then gets too loud and raspy, much louder than the HKS. I was impressed with the HKS unit. The RB unit has no ceramic wool. Oval units quiet much more effectively than the round ones. I have a round Magnaflow on the widebody and it doesn't do as well as I had hoped.

 

i gotta get some pics of my exhaust. i have a turbo but its 3.5 in straight through all the way back. got a borla oval under the car and magnaflow out back all stainless steel. sounds freaking awesome and not annoying loud at all until my wastegate opens then its LOUD! think im going to route the WG back into the exhaust soon. i know it would probably be much louder with no turbo and also it cant be that large in a non turbo app for proper flow

 

The outer shell of my RB universal 3" presilencer pulsates pretty violently when used in an NA exhaust system. They were designed to be used with a turbo. I'm going to test a way to keep it from fatiguing itself to death like your HKS did. It involves wrapping with a second layer of steel, like the HKS. Heck maybe three layers.

 

I never did answer this question yet so maybe I should .

The link to dyno pull difference can be found here:

https://www.rx7club.com/showthread.p...highlight=dyno

this is only a before and after kinda deal, not with and without the silencers, but the silencer will definitely hurt power especially in the top end.

 

I know this is an old thread, but I'm currently in the process of making my own mufflers. No packing, or sound absorbing material.
I'm also not concerned about noise, just flow, and tuneability.
Will post pics and results if I have time.

 

my friend had an Re amemyia dolphin tail, and it came apart like the HKS above, i guess it was really thin sheet metal.

actually we tore a stock FD muffler apart too, and the end caps are like cast, but the outer case is like sheet metal. hit it with a hammer, and it just cracked and came apart in chunks. the FD muffler is WEIRD inside

 

Here's a small update. I removed the RB 3" presilencer and set it aside. I then installed a Rotary Engineering glasspack so I could test a couple of engines in the car. So far I've used a 6 port 12A exhaust manifold. These don't have an expansion chamber like US-spec exhaust manifolds. The 6 port manifold is almost like a a mini cast header. As such it doesn't offer any muffling like the US-spec do with their joining of the two ports right away (think of a dual woofer box with one connected out of phase = no bass).

The car has a lot of bass at idle and you hear a lot of it leaking through the mini megaphone made from 16 gauge aluminized (expands from 2" to 3") and out of the 16 gauge shell of the Magnaflow mid muffler. This muffler has a 4" shell with a 3" core. This means only 1/2" thick of muffler. Yikes!

I decided not to wrap the RB universal and instead I'll try a turbo. Think that'll prevent the shell from acting so much like a speaker cone?

Hey Mike, remember when we were discussing how once you jump up to 3" how this gets into the realm of "audio" and is the reason why it drones compared to 2.5" and smaller? I wonder how much muffling the turbo will actually do. Maybe some of the bass will be reduced.

 

yep! the turbo works really well. the NA engine goes BRAP BRAP and the turbo chops that up into little pieces, so its much more like a steady flow.

plus the turbo removes a bunch of heat, sometimes, so the exhaust turbo back is cooler