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Cats and turbos

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Cats and turbos

Post by kevhaywire on Sat Mar 28, 2009 2:07 pm

So how much of a restriction do they present to a turbo in moderate boost applications (up to 15psi)?

I've had a 3" ceramic cat laying around for a while and I'm tempted to fit it. Anyone know of any before and after plots? If they sap 50hp or more, then I won't bother, but 15 - 20hp I can live with.

Anyone got any firm data / ideas?

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Re: Cats and turbos

Post by JNLRacing on Sun Mar 29, 2009 4:21 am

I'm running a 3" sport cat on mine and it's so small it may aswell not be in there. Really can't see it making a lrge hp difference at all.

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Re: Cats and turbos

Post by kevhaywire on Fri Apr 03, 2009 3:25 am

Spoke to someone today who has done a back to back dyno comparison of cat versus non-cat. It was a small 3" 100 cell sport cat and it made 367hp without the cat, and 345hp with.

Not a huge difference in outright power, but he did say the spool up is where you notice the cat's prescence the most. It's noticably slower to spool, so much so the timing needed adjusting to prevent det.

I think I'll leave the cat off then Very Happy

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Re: Cats and turbos

Post by dirtytorque on Fri Apr 03, 2009 5:49 am

kevhaywire wrote: so much so the timing needed adjusting to prevent det.


How come?
Was the onset of boost less progressive??
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Re: Cats and turbos

Post by junkie on Fri Apr 03, 2009 1:44 pm

22bhp for £600ish at a guess on price is brill to be honest.
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Re: Cats and turbos

Post by mrbeige on Fri Apr 03, 2009 2:19 pm

junkie wrote:22bhp for £600ish at a guess on price is brill to be honest.
It's a 22hp loss dude Laughing

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Re: Cats and turbos

Post by junkie on Fri Apr 03, 2009 2:56 pm

hahaha totally read that wrong oh the shame.

Well does this also mean it can be looked at from another angle though, what was the power run with the standard cat on, im sure the sports cats are more for the people who want to run a better flowing exhaust whilst still passing an MOT without the need to be changing back and forth every year.

So ultimately a no cat system will flow better of course and a sports cat will always flow worse due to there still been a restriction there which affects spool but will be better than a standard restrictive cat due to less cells.
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Re: Cats and turbos

Post by boost panda on Sat Apr 04, 2009 2:21 am

kevhaywire wrote:
Not a huge difference in outright power, but he did say the spool up is where you notice the cat's prescence the most. It's noticably slower to spool, so much so the timing needed adjusting to prevent det.

I think I'll leave the cat off then Very Happy

That must be a fair restriction then, to be robbing the engine of 6% of its peak power.
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Re: Cats and turbos

Post by kevhaywire on Mon Apr 06, 2009 1:59 am

Yeah, the chap said 6% is the average loss he sees with "Sport" cats on the Rover Tomcat engines he maps. I hate to think how restrictive OE cats are then! Shocked

The reduction in timing I suspect is to combat the backpressure raising EGTs. Standard 1.8T maps have zero degrees timing on boost at certain loads and rpms, so it's obviously an issue VW have encountered too.

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Re: Cats and turbos

Post by dirtytorque on Mon Apr 06, 2009 2:38 am

kevhaywire wrote:Yeah, the chap said 6% is the average loss he sees with "Sport" cats on the Rover Tomcat engines he maps. I hate to think how restrictive OE cats are then! Shocked

The reduction in timing I suspect is to combat the backpressure raising EGTs. Standard 1.8T maps have zero degrees timing on boost at certain loads and rpms, so it's obviously an issue VW have encountered too.


ahhh...

thnks.
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