Muffler Tech

[Unclejake]

Coby is a brand and was owned by a guy I raced cars with. He may still own the business but I have lost touch with him.

The Coby brand includes products such as reducers, doughnuts,  mufflers and resonators. 

A resonator is a free flow style design slightly similar to a motorcyle baffle system. A resonator will reduce nasty exhaust noise but leave a fair bit of burble in your exhaust tone. 

They can sound great, but can also sound shit if the exhaust diameter is too large for engine displacement 

[cletus]

something with a bit of a 'maze'inside ie not straight through.

 

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[cletus]

you would probably get away with a straight thru muffler if the engine had a turbo , but an NA engine will need something better.

 

go hang out at a boat ramp and when a tractor with a coby sticking up launches a boat, thats a good indication of what a non turbo 2L diesel would sound like

[bathcollector]

34 minutes ago, Unclejake said:

Coby is a brand and was owned by a guy I raced cars with. He may still own the business but I have lost touch with him.

The Coby brand includes products such as reducers, doughnuts,  mufflers and resonators. 

A resonator is a free flow style design slightly similar to a motorcyle baffle system. A resonator will reduce nasty exhaust noise but leave a fair bit of burble in your exhaust tone. 

They can sound great, but can also sound shit if the exhaust diameter is too large for engine displacement 

Bill sold Coby a while back now. He is a good bugger and can wrestle a race car round a track with the best of them. I think he still has the Nova but doesn't drive it anymore due to health reasons. I miss his monthly visits at work.

[Unclejake]

Thanks for the update. He had such terrible arthritis it was a wonder he could even think through the pain. His cars were always immaculate and he was a gentleman to race beside. 

There's not many blokes I'd touch wing mirrors with entering the Pukehoke hairpin at 160kmph on drum bakes,  but Bill (and a drain layer from Te Awamutu) were amongst them. 

 

Edit: IMHO business should be like racing with those chaps. Go hard, go into it to win... but give your opponent racing room on the track and help him out off the track. Shake hands, share a beer in the evening, bit in the morning go out to try to beat him again without ever trying to make him lose

[ul9601]

is harris pipe any good?

[Bling]

Depends how much bigger you are talking. Pretty sure my exhaust was smaller diameter pipe and slipped inside my muffler so was an easy job. I grabbed it locally though so I knew it would all work. Been a while, they may have even flared me a bit of pipe to make it a closer fit.

[locost_bryan]

iirc the Coby I fitted back in the 80s had the inlet end slotted so it could be clamped onto a slightly smaller pipe, always got a WOF from Marshlands Garage like that.

[Dudley]

If you put a supertrapp on the back you’ll be able to fine tune the exhaust noise to whatever you desire 

[Truenotch]

3 hours ago, Kerry-TGI said:

Exhaust is 44mm which I think is 1 3/4", can get one 2.25" which is 57mm

I think you should call a muffler shop. Realistically, it won't really matter what you fit, but you'll want something close to 44mm to avoid using a reducer. 

[yoeddynz]

On 30/01/2014 at 21:18, kpr said:

I use normal fiberglass chop strand.  This is after going to a muffler shop and ordering some muffler packing, then getting handed what looked to be a bag of fiberglass, they brought from a boat shop down the road. but 5 times the price.

It does burn out after awhile. but lasts good enough for what i need.   tear it up and pack it in fairly tight.

 

sure to be alot better products out there!  but chop strand is easy to get and cheap.

Old thread dredge happening. 

Chop strand. I think I know what this is. I'll ask my friendly itchy fiberglass boat/kayak building fella who down in the village and nab some from him to try. 

@GregT this is the thread I was referring to. 

[GregT]

Chop strand is unpleasant to use. The bike/kart repacking mat is much nicer.

[kpr]

I use this stuff now.  is a whole lot cheaper than buying from motorbike shop etc..

https://nzfg.co.nz/product/muffler-packing/

sometimes use a bit of chop as well

[HumberSS]

Thread dredge has helped thinking about next moves on the camper 3.4l 4V V8, guessing circa 250hp. Want to start collecting bits for exhaust build. Don't have adrenalinR money. Original thoughts were 2" all the way, 18" resos after collector and a largeish 2into1 muffler up in the guts above the diff then 2.5" pipe to back. I don't want loud, but also don't want to choke the thing, max HP's and mid range torque, so wondering if this is the right approach. Happy to entertain twins all the way, 3"(obviously) and multiple resos (are the m&h from STA any good, as they are aweful cheap). Chir

[Kiwibirdman]

59 minutes ago, HumberSS said:

Thread dredge has helped thinking about next moves on the camper 3.4l 4V V8, guessing circa 250hp. Want to start collecting bits for exhaust build. Don't have adrenalinR money. Original thoughts were 2" all the way, 18" resos after collector and a largeish 2into1 muffler up in the guts above the diff then 2.5" pipe to back. I don't want loud, but also don't want to choke the thing, max HP's and mid range torque, so wondering if this is the right approach. Happy to entertain twins all the way, 3"(obviously) and multiple resos (are the m&h from STA any good, as they are aweful cheap). Chir

Your plan should be OK. I wouldn't bother with the resonators, straight pipe through to your 2 into 1 muffler. The length of the tail pipe can make a huge difference. Also the number of bends.

My Silverado has a side exit exhaust with a 140 degree bend out of both mufflers to get the side pipes in the right place. This is quieter than the previous tail exit with bends of no more than 90 degrees with the same front pipes and mufflers.

[HumberSS]

9 hours ago, Kiwibirdman said:

Your plan should be OK. I wouldn't bother with the resonators, straight pipe through to your 2 into 1 muffler. The length of the tail pipe can make a huge difference. Also the number of bends.

My Silverado has a side exit exhaust with a 140 degree bend out of both mufflers to get the side pipes in the right place. This is quieter than the previous tail exit with bends of no more than 90 degrees with the same front pipes and mufflers.

Thanks man, I do want it fairly quiet though - a bit of a sleeper. Don't want it droning in the back with my kids having to yell over it. I also want to be heard when I yell at them.

[kpr]

reso's /glass packs  after headers can actually help power wise, and smooth things out.  esp in bottom end.   

[HumberSS]

15 hours ago, kpr said:

reso's /glass packs  after headers can actually help power wise, and smooth things out.  esp in bottom end.   

Would you recommend one or two different reso's per bank (and are the M&H ok)? And what about pipe size? My collector is 63mm, should I step down to 2" or 2.25" through the resos and stick with that all the way, or go up to 2.5" through the muffler? Remembering this thing is likely around 125hp per bank at a guess.. And do I need a balance pipe before muffler or would that be sufficient for the balancing aspect (will be above diff). Im open to sticking with a twin system right the way through but am trying to keep it packaged pretty tightly hence the 2 into 1. I also dont have heaps of room for a tail pipe so might side exit behind the wheel. Thanks man

[shizzl]

Back in the day there was an old gulls in Whangarei that made his own mufflers. 
 

he did the exhaust on my fxgt one night, started at 5.. the deal was that I bought him dinner and $250 cash. 
 

it sounded amazing when I drove away.

 

basically a folded up box, 2” in, 2-1/4” out, the was a 90 angle on its end on both ends to direct flow left and right, and a 50x50 box in the middle, he called them “race box mufflers “.  He did 2.5” from the floor pan to the rear muffler which was glass packed.

 

it blew the glass out after a year or so of 7200rpm abuse. 
 

my mate had the same set up on his mk5 cortina, shit that thing was quick with that exhaust and twin throat. 
 

the shop is no longer there, was opposite where pak n save is in town. 
 

id like a better muffler on the hunter, those stainless dummy’s don’t do squat

[RUNAMUCK]

Dumpys/fart cannons are fucking terrible. They often sound terrible because theyre too big for the engine displacement. Yeah bro, my 2K/2FE corolla goes hunnits with this 5" pipe.......

/im not even sorry the law doesnt allow loud pipes any more.