How do you guys make presilencers?
 

You need a shell, some end caps, a perforated core and some muffling material. Pretty basic.

But the magic is in the details. How/what materials. What diameter core? What percentage of holes? What density of muffling material? What length? And so on.

From my own research and observations, I believe this list of parts to be an adequate starting point for anyone adventerous enough to build their own.

Outer shell:
4" round 14 gauge tubing in mild steel or SS

Core:
2" or 2.5" diameter perforated steel tube with around 50% holes

sound absorbing material:
pop scrubbers?

End caps can be 1/4" or 3/8"

A popular maker of presilencers for rotaries uses 7/16" end caps which double as flanges. However if you're welding them in place in a custom application, as thin as 1/4" will likely suffice.

Did I skip anything? Oh yes. The expansion chamber. Opinions on its usefulness? Is it necessary? The popular maker included an expansion chamber on their 2" and 2.5" classic presilencers but dropped it on their 2.5" and 3" universal presilencers.

Something to ponder for a bit. :)

Next I'll compile a list of the parts I'll use to assemble a rotary ready presilencer. Got some parts already. Will need to order the rest in a few days.

My parts list:
 

The goal is to build a long primary for the GLC. With limited space comes limited options... unless you build your own. I have 14" of room so here is what I came up with.

Shell:
Amazon.com: 4" 304/304L Welded Stainless Steel Tube .083" Wall 2' Length: Automotive

Core:
2" Stainless Steel Tube Perforated Pipe Exhaust 0 5M Long Straight 50 8mm OD | eBay

Sound absorbing material:
•post scrubbers found at the dollar store
•Stainless Steel 434 Wool Roll 1 lb Reel Coarse | eBay

End caps:
Speedy Metals - 1/4" {A} x 4-1/2" {B} Cold Finished 1018
or
Speedy Metals - 3/8" {A} x 4-1/2" {B} Cold Finished 1018

The core tubing comes from the UK. It takes a while to get here, but it's worth it compared with local sources wanting up to 4 times as much money.
https://i.ebayimg.com/t/2-Stainless-...DehQ~~60_1.JPG
They sell it in half meter lengths, which for us means 19.5 inches. That's pretty good whether you're going for a full length presilencer with minimal waste or two of the mini style like I'm doing. Mine will have a 10" core (actually two at 9.75") and a 4" expansion chamber = 14" total length. Should fit the car fine. And yes a 4" expansion chamber is what is recommended to absorb the supersonic exhaust pulse. I'll get more into the specifics later.

The shell comes in lengths by the foot. It has to be 14 gauge (.083") for adequate noise leakage prevention. Any thicker and it's too heavy. Any thinner and you're in Noise City. I chose the 2' foot length and will chop it in half for two 12" lengths. Then add on two inches of additional 15 gauge tubing I have here (.074"). Not as pretty but it beats buying three feet and having lots of waste. Sure I could come up with something but I already have 15 inches of mild aluminized 15 gauge tube. I can't mix 304SS with mild in parallel and expect them to expand at the same rate, but if I just add a little length to the expansion chambers of both, it will work. I did something similar already and it works fine.
http://ecx.images-amazon.com/images/...PL._SX342_.jpg

The pot scrubbers can be found at a dollar store but they need to be the right kind. Not the interwoven kind but the type that will expand and slip over the core tube like a sock. I think one scrubber = 1 inch. So a 16" core would require 16 pot scrubbers.
http://www.foodservicedirect.com/pro.../OT378913L.jpg

Then wrap it all with coarse stainless steel wool. One 1 pound roll is enough for two 16" cores. I'll have some left over for another set of oversized 20" core presilencers I'll do next. :)
http://www.lustersheen-online.com/xc...ainless434.png

And cap it off with your steel end caps! Sorry no pics as they need to be custom made.

Or if you prefer to have them made to order, they just need to be about 3 7/8" OD with a 2" ID hole in the center. The OD depends on the ID of the 4" shell tubing.

In order to make my own end caps, I got a 4" hole saw and a 2" hole saw. It's hard to find an actual 4" saw as most are larger for running conduit through a 4" ID hole. So look for a genuine 4", not 4 1/16" or whatever. The end cap has to fit INSIDE a 4" OD tube which is .083" wall thickness.

Nice thread! Archive this when its done.

here is the drawing for the end cap, so simple even i can get the drawing to work!

Well now THAT is handy to know, one question Jeff, would you say this is a viable way to re-core/pack a presilencer can that you already have that has "burned out", or is that just a silly idea.

http://www.ebay.com/itm/DB-dB-KILLER-REMOVABLE-BAFFLE-END-CAN-EXHAUST-MOTORCYCLE-ROAD-LEGAL-BS-Approved-/181132889023?pt=UK_Motorcycle_Parts&hash=item2a2c5c8bbf#ht_2524wt_736

Use one of these. Then wrap it with glass. They come in multiple shapes and sizes and lengths too.

^That would be good for building a final muffler too.

Sent using RX7Club for Android.

Yeah, for a street bike that's a great idea. lol you try one of these on a rotary and tell us how it went.

It'll blow it out?

I use a cherry bomb glass pack as a pre-silencer, but its offel loud. I've got an RB exhaust on the way for my N/A RX7 so it'll only be loud for a month or so.

RB is the way to go. Anything glass will blow out quickly.

My 13B powered GLC for example has a Magnaflow 5x8 oval in the usual presilencer location, and I estimate it'll last only maybe 6 months. Even though it's a Magnaflow, which is a half decent muffler brand, it won't last long this close to the engine. So my only solution is to fab a set of presilencers for a long primary and swap them in. More power and probably the same noise level. :) Hence the reason for this thread. Pics and more info will be posted as parts are ordered and work begins.

Had to do this in two pics so you could see how close the presilencer location is to the engine.
https://www.rx7club.com/attachments/...h-img_1171-jpg
https://www.rx7club.com/attachments/...h-img_1172-jpg

The pre-silencer on the widebody project was a prototype that ended up performing very well. The build was similar but two things someone may want to consider.

First, if flanges are designed for the ends with bolt together joints the entire unit can be pulled apart and re-packed later. Second, for packing materials you should look into "silica rope" or a "silica sleeve". Silica is good up to 2300 degrees. The rope can be purchased in 1" size that fully fills the gap remaining between the tubes. The sleeve is 1/8" wall thickness and slides over the 2" inner tube. Either can be held in place with safety wire.

Silica rope. McMaster-Carr part number 8828K75
Silica sleeve. McMaster-Carr part number 88155K71

I'd like to have a presilencer stretch from header collector to axle. Long primaries made in the manner of your presilencer would be heaven to the ears.

I hadn't heard of a silica rope/sleeve. Be sure to try it and post a video or something!

I've finalized the dimensions I'm going to use. 18" total length, 14" core with 4" expansion chamber. :)

So I'll order 3 feet of 14 gauge tubing and two perforated cores. 3 feet is 36 inches so chopping in half gives us 18 inches each. I'll have to flatten the expansion chamber a bit to fit under the floor. It should still function as an expansion chamber, at slightly reduced capacity. I'm sure it'll be fine.

The perforated tubes have been ordered. Up next, gotta get some steel to do the end caps.

I did it on the widebody build. I don't have vids of it but maybe Dave can post some up.

The silica will last forever at the temp rating and quieted the car substantially.

-billy

Super cool thread, will have to do this once the RB one wears out behind the turbo!

Be sure to add a slip-fit feature. Otherwise the core will buckle like this. https://www.rx7club.com/1st-generati...8/#post9932392

The perforated tubes arrived from the UK. Only took 15 days to get here. The qaulity is outstanding. :D

The steel plate for the end caps was ordered, as was a roll of coarse SS wool.

The steel plate and coarse SS wool arrived. Just need a length of 14 gauge 4" tubing.

The plate was machined and yeilded 4 discs to use as end caps.

The expansion chamber of an RB presilencer was measuered. Here are the results.

Here is my build for a resonator/presilencer on my 12a FB build hope this helps anyone looking to make one. I recycled a blown out one off a chevy impala and rebuilt it but the concept will be the same on a scratch build...

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over all leigth was like 26 inchs, O.D. was 4 inchs and I.D. pipe was 2.5 inchs
I hope this helps out for anyone wanting to try a hand at making a resonator/ presilencer. Also upon looking into the one made by racingbeat I found that they make theres almost like this with an expantion chamber inthe middle and 2.5" pipe inside a 4" pipe mine is a bit longer but i was working with an already made perferated pipe from another car.

Nice job. A couple issues I see popping up. RB doesn't have an expansion chamber in the middle. Theirs is in the front. You used what looks like regular fine steel wool, not coarse stainless steel wool. The stainless won't burn. :) My first repacking of a presilencer didn't go too well and you can imagine why. But give yours a try.

Haha once the steel wool burnt up it got very quiet. I fact before I put this section in my exhaust it was very loud at idle.. Well in fact all the time loud. But after about 3 days of breaking the resonator in I can't tell it's running anymore from inside a building. I could before. So I would guess that once the wool burnt up it got a lot quieter and I am happy with that. I still have sound passing through the header pipes but that is a new header build with thicker weld els'

Jeff, if you don't mind my asking do you know an approximate cost for all of your raw materials so far? I'm contemplating building a muffler for myself right now instead of buying the Power Pulse muffler from RB. I'm trying to see how much $$$ it would save and if it is worth the extra effort to build my own. I like the idea of it being rebuildable for sure. And it's always fun to make your own stuff exactly the way you want it.