High flow cats ? Sizes? Make a sound difference?? I need advice.

[bradizle]

Hi guys well im going back to my exhaust shop to finish getting my extractors and cats installed.


However the cats alone are a big price at 300 EACH. they are a 3 inlet outlet... and a big 5inch body. Ballastic racing cats they are.

thing is I could save $400 just by buying some cats off ebay that are the same 100CPI , 3" outlets but however the body is 4".


What the hell is the difference ? there is only 1 inch difference between the 4" and 5" and they still flow the same but however they are just some chinese stainless...

The whole ideal of getting my exhaust was for the note. I want the deepest I could get and im extremely happy. but now is to deepeen the note.

Let me give an example. If I had straight pipes instead of cats. Would it sound deeper than having 100cpi cats?.... does the low CPI determine how much deeper it sounds aswell as more flow obviously. I do not want any cackle and popping on decline. But even using a 100cpi cat would give me some popping wouldnt it? or is that determined by the mufflers used in the catback system (mufflers etc).

Why spend so much money on 100cpi cats when you could just run a straight pipe instead? I heard there is a fine or something? but 100 cell cats are still illegal. I dont get the point??? Why justify the money???


To put my whole question simply....
If the cats will make it deeper than running no cats I will do it.... But if having no cats will make it even MORE deeper it sounds like a better option? Someone told me running no cats will give me a 10K FINE? but 100cell is illegal anyway, ill still get the fine. I can't find any infomation on this given subject.

MY friend is selling some magnaflow mufflers but the insides are pretty much melted and stuffed and missing.. all they are is a 3" outlet. 4" body. 100cell.
Its going to save me so much money just buying them off him.

I just can't see the benefit of forking out $600 for some cats that are 5" body and are huge 100cell. If they will make my note deeper Ill definatley go for it.

Some have told me no cats will make it sound super deep. and some say it will sound TINNY. Tinny on 4cyl turbos... but we are talking a v8 here.

Sorry if ive repeated myself in this but ive had a few to drink and my mind is all over the place about learning about cat converters and how they work.. :rofl2::rofl2:

 

[ducker85]

What the hell is the difference ? there is only 1 inch difference between the 4" and 5" and they still flow the same but however they are just some chinese stainless...

5" body will convert more gasses compared to a 4". 100 cell per inch cats are illegal as they do not trap enough harmfully gasses or 5" will be better.

The rumors for a 10k fine for no cat is a fine for 'tampering with a motor Vehcial' were as 100cpi cats is just a defect IF you fail an omission test otherwise it's impossible to tell without removing the cat.

Had full exhaust on a L67 and when I changed to 100cpi cats (only thing changed) it got very loud!!!! Can't comment on depth on note as it was only a 6 and didn't sound too great I've 2,500rpm

 

[Not_An_Abba_Fan]

To get it straight, cats don't "trap" anything, they convert. The catalyst inside heats up and due to the precious metals, it "burns" the exhaust gas again and converts harmful oxides of nitrogen and sulphur into CO2 and water vapour.

100 cell cats are illegal in Australia due to the fact that they can't convert at the right levels to meet emissions standards. I mean, they state they are for off road use only, but why even fit a 100 cell cat if you're not going to use the car on the road? Just leave the cats off. For on road use, the highest flowing legal cat is a 200 cell.

As to the size question, basically, the larger the body, the deeper the sound. So a 5" body cat will produce a deeper note than a 4" body cat.

 

[Michael-08-VE]

To get it straight, cats don't "trap" anything, they convert. The catalyst inside heats up and due to the precious metals, it "burns" the exhaust gas again and converts harmful oxides of nitrogen and sulphur into CO2 and water vapour.

100 cell cats are illegal in Australia due to the fact that they can't convert at the right levels to meet emissions standards. I mean, they state they are for off road use only, but why even fit a 100 cell cat if you're not going to use the car on the road? Just leave the cats off. For on road use, the highest flowing legal cat is a 200 cell.

As to the size question, basically, the larger the body, the deeper the sound. So a 5" body cat will produce a deeper note than a 4" body cat.

Hey abba, is there a generic size for cats on a sv6 alloytech? Or is it more like fab it to fit? Get the cats and add some pipe if needed?

 

[bradizle]

To get it straight, cats don't "trap" anything, they convert. The catalyst inside heats up and due to the precious metals, it "burns" the exhaust gas again and converts harmful oxides of nitrogen and sulphur into CO2 and water vapour.

100 cell cats are illegal in Australia due to the fact that they can't convert at the right levels to meet emissions standards. I mean, they state they are for off road use only, but why even fit a 100 cell cat if you're not going to use the car on the road? Just leave the cats off. For on road use, the highest flowing legal cat is a 200 cell.


As to the size question, basically, the larger the body, the deeper the sound. So a 5" body cat will produce a deeper note than a 4" body cat.

very interesting... say if you ran no cats and a straight 3" pipe straight through what would that sound like? as deep as it can get? or does the body of the cat hollow sound or something to make it deeper??????????

 

[Michael-08-VE]

It would sound terrible, in my opinion. Look at all the ricers, they have huge cannons on the back and they are only little 4's they're deep at idle but sound like **** everywhere else. I'm guessing the bigger area helps drop the note to a lower frequency but you'd have to balance out the volume, as you add room in the exhaust it'll get quieter. Just a guess.

 

[PIR4TE]

very interesting... say if you ran no cats and a straight 3" pipe straight through what would that sound like? as deep as it can get? or does the body of the cat hollow sound or something to make it deeper??????????

No straight pipe is not as deep as putting in the cats, cats not as deep as having some sort of pseudo expansion chamber.

You can have deeper using long throw in the primaries, calculated merge and expansion before it reaches the face of the cat biscuit (cellular substrate inside the cat). The nature and dimension of a collector / diffuser device in this section determines how the engine energy pulse and sound pressure is converted into performance and sound. So there's the most important first step... making the right sound for the right reasons in the first place.

Then the limited space in that header / pre-cat region in our car informs options for optimising both. What I did recently was calculate the best dimensions to promote the expanding gas and diffuse sound pressure at this point with twin 3.5" megaphone diffusers and incorporate the design of the compulsory barrel cat to best effect. Result is a tuned expansion chamber that looks a little like this:

Mang!

Apart from the rear silencers, the next important performance / sound modifier occurs at the second harmonic, typically behind the cross member at rear but the exact point is a correlation to where the engine develops max brake torque / rpm. Allow the pressure wave a clear run with straight pipe to this point and install a proper x-pipe for full cycle boom and noise reduction. In other words I suggest delete the numbnut off-the-shelf aftermarket token kiss, x-merge or factory H balancer and the mid muffler / resonators.

Then choice of rear silencers matters because do most of the work, like they are supposed to.

Here's my exhaust with bi-modals open at idle, note unless your speakers / subs are hifi it will sound really quiet as it is all happens less than 90hz:

[video=youtube_share;cVx6ibTc2Ps]http://youtu.be/cVx6ibTc2Ps[/video]

 

[Benboy]

Whatever you decide to do to modify the exhaust (for on-road use) away from standard will be illegal making your vehicle un-roadworthy. Furthermore, removal of the Catalytic Converters is also illegal and heavy fines are imposed for breaches of the Pollution Control on said vehicle.

 

[Not_An_Abba_Fan]

The reason a cat is the size that it is, is for one reason only, to expose as much surface area of the catalyst to the exhaust gas, thus making the conversion process as complete as possible. There is no set size rule, just make sure the cat meets the correct emissions standards for your year vehicle and the pipe size matches your system, only for ease of fitment.

Fitting a straight 3" pipe in place of the cat, IE: an expansion chamber of sorts, will not make it deeper, just louder, because you are removing a baffling device.

The bigger the exhaust diameter, the deeper the note. It's that simple. But, also, the bigger the exhaust diameter, the slower it will flow.

To get the deepest possible sound out of a V6, fit the system with an X pipe and a front muffler, but you will need to fit large body straight through glass packed rear mufflers. As much as they are "rice", cannons actually work best in this scenario. The reason they sound like they do on a 4 cylinder, is that there are only 4 cylinders and a 4 cylinder engine is a "180 degree" engine. IE: the crank shaft is flat plane. It gives the exhaust a note that is unique to 4 cylinders. (Oh, and F1 cars, because they are 180 V8's). A V6 will not sound like a 4 cylinder with cannons and an X pipe exhaust, because there are essentially 6 pulses in each cannon due to the X pipe, instead of 3.

 

[Michael-08-VE]

F1 cars are 1.6L turbo 90 degree v6's.