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Cat Converters - Need Advice For Bigish Power

The Mafia

By The Mafia,
in Engines & Forced Induction

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The Mafia Grand Master

The Mafia

Posted
Posted (edited)

Hi Guys

At the moment I'm looking at upgrading my cat because the car is a bit loud. Drones like a bitch between 80kmph and 100kmph.

Currently Producing 300rwkw and looking at the 3.0l bottom end in the near future.

Anyway, the current exhaust is 3inch off the Turbine, and another 1.5 - 2inch from the waste gate plumbing back in just before the lower bend in the front pipe. The Cat that is there has 3 inch flanges and is one of those "extreme flow through non restrictive" ones.

Anyway, I've searched and seen a few threads about a few Different cats:

Catco

Metalcat

SMB

Xforce

Does anyone have any recomendations for me? I want to retain power and get rid of this drone, and quiet the exhaust a little.

Thanks guys

Edited by The Mafia
Devils_Advocate21 Mentor

Devils_Advocate21

Posted
Posted

i think you forgot a few things, what is it from cat back? as well as what it made of mild, stainless, titanium? these might help as well. the Cat itself doesnt really hinder on noise control as far as i know, its other factors usually from the cat back, IE: Resonators, inner mufflers and the likes, as well as mild steel does drone. aswell as what size is it from the Cat back.

Ive got same issues, but running the highflow metalcat heaps of drone, but running 3.5 to resonator to then 4" through from there to a cannon, its expected with that esp when in mild steel. Gotta love the drone... inner mufflers may help but may hinder on overall power through restriction tho changing from mild steel to stainless or titanium cat back usually will help as well.

Correct me if im wrong

Cheers

A

shnaped_second Mentor

shnaped_second

Posted
Posted

Changing from twin high flow cats to twin metalcats on our supercharged xr8 made a huge difference in noise (alot louder) so if noise restriction is what you are after id stay away from them, but 300kw is a fair bit for a street car so im guessing you do track work? maybe a straight through pipe as thats what i have on my 34 and it doesnt drone and isnt too loud...

discopotato03 Grand Master

discopotato03

Posted
Posted

Hi Mafia , one thing I've never gotten around to proving is the worth of putting "soft spots" along an exhaust system to beat that low frequency vibration or drone .

The story I get is that everything has a set or natrural frequency point where it will ring like a bloody bell and transmit vibration into everything around it . It seems to me that large exhaust systemys are quite rigid and capable of acting like a great long engine steady - transmitting lots of vibration to our speaker box like cabin area .

David Vizard used to say that exhaust systems should be hung not mounted to isolate unwanted noise .

I tend to think that if soft spots like those stainless mesh covered concertina things are placed along the exhaust in a few places the tailpipe loses much of its rigidity and can have its vibratioin isolated by well thought out flexible hanging mounts . I remember on occasions being in Goulburn where they have an Olden dealership and Commodes backed up on ramps , they seem to have quite a few soft points down the back and I doubt its to do with stopping the pipes cracking when the engine moves about .

By any chance would the drone occur at low revs in high gears and mysteriously correspond to 60/80/100 km/h ?

Any how I'm interested in what other peoples thoughts are , cheers A .

Devils_Advocate21 Mentor

Devils_Advocate21

Posted
Posted

Could we assosiate this drone to resonance frequency? I could well associate mafia's problem to similar background to mine, as i have got the "Drone" syndrome with mine. mainly around the 80-85 it would start, and reach around full drone around 100-110 around that area, where it is quite loud. this would be assosiated with 5th gear, so around that rev range it does it, 4th gear would be similar to around the 60 mark, but no where near as loud as 5th at the above speeds.

On the theory of the flexible hanging mounts. Im not too sure if they would be greatly assisting the problem no matter how many you put in or have, as the metal itself would still have its natural RF properties, and would still occur. Changing the characteristics of the metal will help, Stainless vs Mild, Stainless having that tinny sound while Mild having the drone. The only way I can see to minimize the drone, is to either change restriction value of the system, ie: mufflers, resonators etc. and change to a better steel compound mild to stainless/titanium.

Cheeers

The Mafia Grand Master

The Mafia

Posted
  • Author
Posted

hey guys sorry I haven't posted yet.

Its a Stainles 3inch+1.5inchWG system to the cat, then from there 3.5inch mild steel to a 4inch cannon and a 5inch tip..haha. Its very big.

I was talking to cubes and he said the cat will need a pipe put through it, as this one is just "super high flowed" lol.

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