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How bad is a cat for performance?

eznfrank - 3/3/11 at 09:48 AM

I know we all have this tendency to fit a cat just for the IVA and then bin it afterwards, but does anyone have any data on just how restrictive they actually are?

I'm in the market for a can at the moment and ideally would prefer something I can fit for the IVA that will be noise and emissions friendly that can stay on afterwards without making too much of a dent in the power.

Apologies in advance if there's a flurry of dumb ass questions from me over the next few days, I'm just about to go on a bit of a spending spree for the Indy and need to get my head round a few issues.

Ez

jimgiblett - 3/3/11 at 10:14 AM

Modern high flow cats arent too bad. One of the upsides is that they reduce noise as well as emissions.

- Jim

Davey D - 3/3/11 at 10:18 AM

you can get different types of cats. Some are more restrictive than others. if you got a high flow sports cat, then it shouldnt dent performace too much.

when i had my 200sx i would fit the cat for mot time, and you could really notice a big difference in performance when it was fitted. it would feel more sluggish like it was holding back when you planted the throttle

probablyleon - 3/3/11 at 10:29 AM

I've heard there's a possibility of them melting with bike engines. I reckon that would have a fairly serious impact on performance, ultimately blocking the flow completely and destroying the engine. I too would be happy to sacrifice a little bit of performance to leave one permanently installed (and not have to go through the installation / de-installation rigmarole every MOT). I'd also be interested to hear about people's experiences and how much of a danger this really is.

vyperstrype - 3/3/11 at 10:49 AM

U2U sent.

coyoteboy - 3/3/11 at 10:59 AM

quote:
I've heard there's a possibility of them melting with bike engines.

How? The only way I can think of is if you're really badly tuned (they don't like running at extremes of AFR, rich is what overheats them), this is why most early cat based cars ran at stoic for 90% of the drive styles which really dents performance.

[Edited on 3/3/11 by coyoteboy]

Tris - 3/3/11 at 11:08 AM

The story ive been told from one of the RGB guys is that as the bike engines don't use closed loop fuel control (lamba), the cats that they were all forced to use (as part of the regs) only lasted a couple of events before collapsing and melting.

I have been looking into the same thing myself - ive even just brought a motorsport 200 cell density cat off ebay to use only at IVA time. If you compare this cat to the cat which is within the stock bike (ZX12 in my case) manifold, the bike cat is a lot lower cell density and a fraction of the size.

turnipfarmer - 3/3/11 at 12:51 PM

I researched this issue myself. What I found (and I hope I'm right as I've now bought one!) is this...

They come in 100, 200 & 400 cell densities. The higher the number, the more they restrict performance.

100 is only really suitable for the track. Not road legal as far as I know, so probably wouldn't get through IVA.
400 is a performance strangler.
200 high-flow is the one to go for. You can leave it on permanently, as it doesn't have too much adverse effect on performance.

The core can either be ceramic or metal. Of the two, the metal core has the greater longevity.

GBS sell them for about Ł100. Have a look at their kitspares website.

HTH