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Let's talk about muff. 


This thread is basically aimed at KPR as he's been playing around with mufflers a lot lately, but I'm keen for everyone's input. 


I'm about to fit a new muffler to the race car and am looking for something that will sound good - unlike the flowmaster copy that is on there currently. At the moment is sounds cackly/raspy and I'd like to to have a more pure 4cyl tone. My aim isn't quietness, but flow and tone is important. 


The Flowmaster copy is something like this: 



So far the only option I've looked at in person is a Coby stainless straight through, fibre packed muffler (full muffler, not just a resonator) that measures 320L x 265W x 140H with an offset inlet and centre exit. It's a similar style to this: 



Or possibly more like this: 



Now there are a few key factors that will effect the outcomes: 

Muffler placement

Pipe Size

Muffler size? 

Muffler/baffle style

Fluted pipes

Resonance chambers

Material (steel/stainless/aluminium) 



My current setup has the muffler in the belly of the car - just in front of the diff - with a ~1m stainless pipe out to the back. It'll be 3" inlet and outlet with no other mufflers or resonators. 


What have people found when using different mufflers in different locations? How does the pipe length before and after the muffler change the sound or effectiveness of the muffler? What type of muffler saps the most horsepower? 


I've also considered going to a side pipe, but it'll be a challenge to fit a decent muffler if I do. Funnily enough, I've always preferred the sound of the car with no muffler at all (there have been 3 occasions... One was open headers after bellying a ripple strip and losing the whole system on the last lap of a race  :-D ). 


I realise there aren't any definitive answers to this question, so share the results you've found with different cars and arrangements. Any input appreciated and other people's questions are also welcome here. 



Share away. 

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My aim isn't quietness,


too easy.   just run some straight through glass packs.  will take the rasp out.   bit of pipe after last muffler generally makes them work, doesn't have to be a huge amount. but  keep it the same size as rest of exhaust and a good 200mm long should work fine.   imo mild steel is the best material to use. sounds better and will take a hiding without cracking.  ali if you want to drop weight but only rear section as i found out the hard way.


stay away from anything that isn't straight through since noise isn't a huge issue. anything else will kill the flow unless you oversize it alot.   only reason i run a tripple pass on mine is to cut down the noise. they are useless at taking the rasp out also. i run 2 glass packs in front of it to kill the rasp.


oh and for size,  tune your collector length/ diameter on your extractors, then run anything bigger than that afterwards.



/ make it super quite and listen to the dort.

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Sounds easy. So anything bigger than the 2.5" collector + straight through should be big enough, or are you talking header volume vs muffler volume? And do you think it's best to have the last muffler near the rear of the car (like you say ~200mm or so) as opposed to the middle of the car like I have now?  

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i'd go with 3"    

my trueno, i run a  5" glass pack barrel thats been squashed into oval for ground clearance, up front.   then a fairly long  6" glass pack at the rear.  its super quiet with the turbo,  i would think it would sound pretty sweet na.  had a similar setup on the starlet when i first built it also, sounded sweet, but too loud for street.


that 1m long stainless section at the rear, probably isn't helping the cause.   but can't say ive tried a setup like that before.  but in saying that, sounds like your main issue with current setup, is lack of reso's / glass packs

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I reckon the material does make quite a difference to overall sound,  harder materials (stainless and titanium) tend to be louder when compared to similar spec mild steel exhausts. ali is a cool idea for weight saving, but pretty hard to prevent cracking from vibration?


My evo just runs a tiny reso up front and a straight through rear muffler and it's fairly sedate in 3''.


The original setup on the starlet was a 2 1/2 system and it was super stealth (not loud enough for me) once again single reso up front and a reasonable sized rear muffler..  /  offtopic turbo talk...


Mazda will probably just get a 2 1/2 mild steel system due to packaging constraints and lowish power target... 


maybe something like this?



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Mind If I aska few questions here too?


Im running 2" mandrel bends to a triple chamber muffler and I have a cat in the middle. Nice and quiet but sounds like a honda when revved up.


This is what I have,


This is what I want.


Im guessing I need to add resonators to take out the nang? Autobend do a muffler like mine but with an internal reso, could that be the go?

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if its a race car id put a donut in it..

allthough its not a stockcar, but i use a donut the same size as the front pipe.

it gives it a little back pressure.


i wouldnt use stainless if you dont want the crackle or twangy sound.


i put stainless on the cortina and quickly threw it away for mild steel shiz


years ago there was a old guy up in whangarei who made his own mufflers, he called them a race box.

had all sorts of different shaped inside and was glass packed.

he could get the exact sound you wanted while he built it..was an awesome muffler, although it ended up being quite heavy,it did gain extra hp..


he said he designed it to give a little back pressure in the first set of baffles,then the last couple of sets would suck the gasses out..

it was amazing watching it

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Fouled plugs means tuning is off.


Seriously look at something like a NA drag car, open headers makes the most power on the dyno, any exhaust you fit looses power everywhere, smaller the zaust more power lost. Heaps of proof out there of 2L NA cars going  3" and beyond and still picking up power.

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Spencer is on the money, the need for back pressure is a myth, probably brought about by people ripping off the exhaust manifold and wondering why the motor runs like shit.


Ideally you don't want any restriction, as any restriction will increase pumping losses and decrease overlap scavanging efficiency. However, this doesn't mean run no headers, the pipe is crucial to the efficient operation of IC engines - much more than backpressure which is why the above happens!


The only reason to run a small diameter pipe back from the last collector is if you are using it as a tuned length and want to keep the exhaust velocity & temperature high, otherwise go as big as possible.

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listen to these dudes!  ^        just to add to the above, an exhaust too small will cause revision, not so much issue with small cams,  but it will kill a big cam setup.  i gained massive  amounts of mid range going to a big exhaust.  15-20kw at wheels on a 4age.    strangely enough the peak power stayed the same.

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Reversion is simply the exhaust gases momentarily flowing backwards during the overlap phase of the camshaft at low cycling rates. During the overlap phase the engine is on the exhaust stroke and the piston is pushing out the last of the exhaust gases. Prior to reaching top dead center the intake valve begins to open. At low cycling rates the intake charge and the exiting exhaust pulse have yet created any momentum. Thus the piston pushes some spent exhaust gas into the intake manifold. This is why engines with big camshafts idle and sound radical. The exhaust pulses shoot up into intake manifold causing a major disturbance. The cylinders receive an uneven mixture of air, fuel and spent exhaust gas. The piston then reaches top dead center and begins the intake stroke. At this point both valves are open, in fact the exhaust valve in some cases may not shut for another 50 degrees of crank rotation. During this 50 degrees of crank rotation the piston literally draws from both the intake and exhaust valves causing the exhaust gases will momentarily reverse. At high cycling rates the inertia of the incoming intake charge and the out going exhaust pulse keep the gases flowing in the proper direction. Not a problem until you add water into the exhaust stream. Concerning headers, reversion can be severe enough to add water to oil (milky oil), rust valve seats, even stall the engine. This effect only happens at idle, but engines encounter their greatest reversion pulse at shut down.

For this reason Lightning Performance Marine has developed guide lines to help you decide what options to add when considering an exhaust system.

Our guide lines are based on a 454 C.I. engine with a standard Mercury header and 8" long collector. The camshaft should be no larger than 240 deg. duration @ .050 lift. Lobe separation angle 112 degrees. Valve lift is not that much of a factor. These figures are just guide lines. Cubic inch displacement, valve size, connecting rod length, valve timing, etc. all have an effect on reversion.


Lightning Performance Marine makes many options to reduce or totally eliminate reversion.


  1. Header selection The tip to header selection is to choose a design that will introduce water into the exhaust stream as late as possible. For example our 40340 header is actually made to replace a Mercury manifold with a 3" riser block. This header is 4" taller than a standard Mercury header plus it rocks forward 2" thus were able to add a 2" longer collector. If the height is not a concern you just added 6" of dry length to the header.

  2. Collector selection If you have room to add dry collector length do it. Collectors are available in a variety of lengths.

  3. Cubic inch displacement The tip here is simple, the bigger they are the harder they suck back. Either reduce the duration of the cam or start add some anti reversion options.

  4. Camshaft selection With regards to headers the only thing your concerned about is how much piston movement in volume takes place while the exhaust valve is open on the intake stroke. A wide lobe separation angle actually advances the exhaust valve timing event which will close the exhaust valve sooner, but the down side is it also moves the horsepower and torque curve up the RPM range. Rhoades style bleed down lifters will deduce the cam duration by as much as 20 degrees. Available only in standard hydraulic these lifters are a great choice.

  5. Connecting rods Marine engine builders rarely think of connecting rod ratios effecting reversion, but it does. A longer than stock connecting rod will make the piston dwell at the top during the overlap cycle thus less piston movement with regards to crank rotation


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