Knocking out HoneyComb

[R32Big_boy]

My arse it doesnt make more power. I had my car dynoed and it made 126 at the wheels. There was a massive power drop in the power band originally, thought it might have been timing or something. Guttered the cat and went back a few days later and my car is now making 140rwkw. I've got two dyno charts to prove it does work. No scanner though. its an r32 gtst by the way.

[Cubes]

Your cat was probably stuffed to start with causing the drop in power.

[Duncan]

if gutting the cat makes no difference, then why do people claim to 'fell the difference' when they go to a 'high flow' cat which (from what i have interpreted) is just a normal cat flanges but with a greater volume inside?

it ain't any bigger in diameter it must be less restrictive..!

conclusion drawn by me: if high-flow cats make a difference then so does gutting the cat.  

bring on the disagreements!

I'd suggest that people want to feel an improvement when they have spent some cash

I'm willing to bet if you did a blind test between cat and no cat no-one could pick the difference. Even if there is a kw or 2 on the dyno it makes bugger all difference in real life

/Disagreement

[Jimbo2000]

i bought my car with a gutted cat (didnt know)

went to replace it with a new catco 3" highflow and discovered it was gutted.

felt NO difference before/after, could tell a slight noise diff

very slight whistling/sucking sound sort of a thing instead of raw grunt noise, definately not worth the fine.

[RBVS]

with mesh in the cat i could run a minium boost setting of 12psi, with out mesh no less than 14psi. it flows a s##t load more with the mesh knocked out. I could tell if my cat was in or not without a dout. Also cars that run anti lag can not have cats as they will just blow out and get very hot. Race car's will not have a cat because they restrict flow, FACT.

[Cubes]

RBVS,

Race cars also don't use a hollow cyclinder (knocked out cat) in the middle of their exhaust, they use a straight through pipe as they know the hollow cyclinder increases back pressure.

What boost setup have you got to be able to run a minimum of 14psi?

Obviously a 14psi wastegate? or a stocker RB20 type wastegate with a gated bleeder?

There is no doubt there is power to be had if the cat is replaced with a straight through pipe.

Providing the cat you are using supports the kind of exhaust flow levels you are after then a cat is not going to restrict power hardly over a cat converter that has had its guts knocked out. Thats providing the cat is in good working order to begin with. A typical symptom of a stuffed cat is the lack of boost.

[knore]

If your going to do it, do it right, get a pipe made up to go where the cat was, then get the housing of the cat and put around the pipe so it atleast looks like a cat

[SmoothLine]

i heard of a guy who gutted his cat at the car now shoots 5 foot long flames...

'he' said 'he' cant notice any difference other than a louder exhaust noise and a large orange glow when changing gears off the rev limiter...

'he' is also an absolute champion of a bloke lol

[knore]

haha fair enough

any restriction at all in an exhaust system especially for turbo vehicles reduces power

If i had it my way the dump would come off the turbo turn right and come out the front of the sideskirt :headspin: but u cant have everything i guess

[PTR33]

haha fair enough ............ but u cant have everything i guess

Yeah, if you did have everything, where the hell would you keep it?

[T0nyGTSt]

Well I think we're amateurs compared to the rotor guys.

It seems almost every early RX7 I come across with those hilarious 15 x 8" fatz seems to shoot big arse flames.

T.

[Cubes]

I've seen one shooting huge flames.

He was dumping extra fuel in via the Microtec hand controller.

[whatsisname]

A cat with the guts smacked out of it doesn't go meow any more... oh hang on, sorry, wrong type of cat.

A hollowed out cat is worse for performance than a new decent quality high flow one. A straight through pipe, in the same size diameter as the rest if the system, WILL out perform a high flow cat. The honeycomb is a restriction and regardless of how high flow it is it will still rob power. The rwkw difference between a straight through 3” pipe vs. a 3” high flow cat is more than 1 or 2kw. The difference between a 3” straight through pipe vs. a 2.5” cat is bloody massive!

[jnr32r]

Ok But getting back to Legalities though,

If you ever get pulled over and the cop is what most are (a c#%t). And he decides to defect you left, right and centre.

Hes not going to get under the car and undo your cat to see if its hollow or not.

Dont you get a defective notice where you've got like x number of hours to get it all clear.

And if that includes getting an emissions check, you would still have time to go to your local exhaust place and buy a new cat, fitting it and avoiding the $10000 fine???

[Cubes]

Matt,

Exhaust Technology now have 3.5" cats that are supposed to flow in words "Anything you throw at it".

They are pricey but.. Some where up around the $400 mark.

I've got it written down some where.

[knore]

Yeah, if you did have everything, where the hell would you keep it?

Anywhere and everywhere you want... you have everything remember

[Kaido_RR]

but it shoots flames..

so does my stock cat :wassup:

[whatsisname]

Matt,

 

Exhaust Technology now have 3.5" cats that are supposed to flow in words "Anything you throw at it".

 

They are pricey but.. Some where up around the $400 mark.

 

I've got it written down some where.

I'll bet a $40 3.5" pipe still flows more than a $400 3.5" cat. But yes a 3.5" cat would be the go for everyday use and maximum horsepower potential.

[Cubes]

I'll bet a $40 3.5" pipe still flows more than a $400 3.5" cat. But yes a 3.5" cat would be the go for everyday use and maximum horsepower potential.

Oh yer no doubt it does BUT its probably the highest flowing cat we have available in AUS, they have only just become available.

As I've said all along, Cats do rob power but so do hollow cats. Its only the straight through pipes that don't.

For track days etc slap in one of those cheap JMS cat replacement straight through pipes. Not sure how it would affect the powerfc's tuning, Microtec would have no issues as you could have another map setup for it.

[Roy]

...Race car's will not have a cat because they restrict flow, FACT.

Funy how cetain race categories in Europe actually have to run them... and have for a good number of years now.

My car is getting dynod next week with 2 x mufflers and cat, then with centre muffler and cat removed, see if it makes more power or brings on boost quicker, if it does then ill drop it for Sprints etc