designing muffler for formula cars......

[Nishant_iitd09]

hi frnds,
we are trying to design our own muffler....but still we haven't got any proper theory and concepts , how to design mufflers??
if there is anyone who can help us in this regard....please. help us

we its really hard to design mufflers, but we are fully determined to prepare this year.


Nishant Jaiswal
Team Axlr8r.. IIT delhi, INDIA

[Chris Allbee]

Start by researching acoustic attenuators (or filters). Get familiar with the 3 main types band-pass, high-pass, and low-pass. And just because I know someone will bitch about it: Helmholtz.

Once the math makes sense to you then you should be able to figure out the rest. Fair warning, the math is complex (and sometimes imaginary ) and may take some serious study if you haven't progressed that far in your schoolwork.

[Jimmy01]

I've looked at the theory a few times and realised that I didn't care enough about acoustics to waste my life learning how to get realistic numbers for a system which you probably have not modelled correctly anyway.

My muffler design technique usually involves pulling something out of my a**, last year didn't quite work so we welded an extension on at comp and passed noise. I've found the engine noise (as apposed to exhaust noise) is quite a large contributor to sound level for fsae cars. Muffler design won't help with this, so it's a good idea to have your exhaust outlet as far away from the engine (given packaging and exhaust length).

Get yourself (or borrow) a reasonable sound level meter, make a simple muffler which you think might work, test it. If it fails you could just buy one (from a wrecker if money is an issue) or make one with more restriction. More restriction generally equalls quieter, but you will maybe lose power. But I'd rather have a week of my life to make the car better/ more reliable than wasting it designing an ideal muffler.

[BWill_Inc]

stock mufflers are really lightweight and it might be hard getting use from doing a custom muffler

[Bazanaius]

If you're on a budget, or worrying about noise, generally the stock silencer from the 'full fat' version of your engine (so R6, rather than fazer) is a good bet. A bit heavy for sure, but the restriction really isn't a problem given that you've only got 20mm in front of everything.

[RenM]

most stock mufflers have a very high backpressure and thus reduce your engine performance significantly

[Chris Allbee]

Originally posted by RenM:
most stock mufflers have a very high backpressure and thus reduce your engine performance significantly

"Significantly"? More than a 20mm restrictor? Considering the stock muffler from a modern sportbike is good enough for close to 100hp, I fail to see the logic of your statement.

[RenM]

Mufflers using reflection have a high back pressure because they divert the gas flow.

The air u suck through the restrictor is cold, the one you blow out of your exhaust is hot, thus having a much higher volume. And having 2 flow restrictions does not improve your performance.

[Chris Allbee]

Still calling it a lie. Sorry, but the stock muffler can flow enough air at high RPMs to produce 100hp will be able to flow enough air not to be the main restriction in a FSAE engine. In fact...that's why I think they put the restrictor on the intake side...

Now to put a little more of some mud in the air. Your hot exhaust also has a larger orifice to exit from as in greater than 20mm even on a super-duper restrictive stock muffler (that makes 100hp).

RenM, I'm sorry, but if you are having a hard time making reasonable power exhaust with a 20mm intake restrictor, I can guarantee the problem isn't the muffler.

[RenM]

The thing is, that just because u have a restriction in your intake that is more influential does NOT mean that any other restrictions dont matter at all. It is not as influential as the air restrictor but it does have an effect:

A Muffler that increases your back pressure WILL result in a lower power output for 2 reasons: First of all with a high back pressure level you will find it more difficult to fill your cylinder with fresh gas and secondly your charge-cycle work will increase resulting in higher pumping losses.
That is a matter of fact and has nothing to do with my ability to build mufflers. Actually its the reason why i built my muffler myself with very good results.

It is the same for bends in your manifold or to low pipe diameters. They will increase your backpressure with the same results.