Pre Cat Gutting!

[Turbo Joe]

Is it really beneficial to gutt the pre cats? I've seen folks do this out of tradition but haven't seen any figures or hardcore proof that it is actually beneficial. If there are any benefits, are they marginal or greatly noticed differences. Its said that the turbos spool up quicker but my mate had his pre cats gutted and I noticed little to no difference in the performance between both of our cars. For this reason I've given it a miss not really seeing any noticable benefits.

[GrahamS4]

I don't think it's beneficial, perhaps ever so marginaly, but the cost and effort involved, not worth it at all IMO.

[Turbo Joe]

I definetly agree with you on the hassle involved. Just doesn't seem worth the trouble to me.

[Harper--D]

I think it only really makes a big difference when you put beter/bigger turbos on there as they really restrict the flow IMO!
Dave.

[MarkB]

I don't think it's beneficial, perhaps ever so marginaly, but the cost and effort involved, not worth it at all IMO.

Graham, why do you think that? You've seen improvements in your MAF and FATS since making your recent changes

[GrahamS4]

I don't think it's beneficial, perhaps ever so marginaly, but the cost and effort involved, not worth it at all IMO.

Graham, why do you think that? You've seen improvements in your MAF and FATS since making your recent changes

Yes, I have had what I would describe as marginal increase. I was interested in having the work done as so many do and so many also just upgrade the cat back.

I was intrigued what upgrading the whole exhaust turbo back would do. Being honest, now I know the outcome, I dont think I would bother. Having said that, I can justify it as I am happy I have upgraded the whole exhaust. It has to be better and I have not upgraded one section leaving an obvious restriction. If nothing else it it has much more potential should the turbos ever be changed.

Now what I should really have said above is I don't think it is beneficial on stock S4 downpipes. My reasoning being if my RS4 pipe exercise saw a marginal increase, the same on stock S4 pipes must give an even lesser gain?

It may have had some benefit, but nothing drastic enough that the map could be altered to reap any further gain past the hardware change itself. It does feel good to drive, but it did before and you cant measure that so my instinct is not to trust it's beter just because I spent money on it. Maybe Saturday (dyno) will somehow show different, but I doubt it. I will be looking at boost and torque curves closely though.

Perosnally I think a cat back is a not a performance upgrade. It's just noise. You could argue gutted stock cats and a cat back is a peformance upgrade, but the labour to remove and replace the same stock downpipe seems excessive when you don't otherwise need to remove the downpipes to fit a cat back.

Gutting RS4 downpipes instead of fitting aftermarket downpipes makes sense as there is a massive cost difference for the parts and the labour to remove and refit although sizeable is still the same. Only makes sense if you feel your car is in a state of tune the down pipes are a restriction though.

I really could not justify to someone removing and refitting stock S4 downpipes makes sense.

[s4woody]

well my car was showing 522NM on the dyno with a map that was done through the post and my pre-cats and main cats gutted..
measurable gains or not the pre-cats are simply there for emissions..they hold up the flow of exhaust gasses..ever tried breathing through a breeze block..well thats what the none pre-catted turbos have to do..if it wasnt worth it im sure it wouldnt be done..MRC invest alot of time in doing this and im sure if it didnt work doug wouldnt get his habds burnt as often as he does..

[GrahamS4]

I am in no doubt it makes a difference, but a worthwhile or noticeable one I think has to be decided by the individual.

measurable gains or not the pre-cats are simply there for emissions..they hold up the flow of exhaust gasses....

This is why I am happy I have upgraded the whole exhaust, mostly liking the idea of the 200CPI cats I have now.

One thing I did not include in my thoughts there was EGT temps. I dont have a measuring block on my '98 car so cant tell, but I read EGTs are lower and so that alone is good I understand.

To be clear, this was something I read up on and went into with my eyes open and requested to be done, I was not sold this solution or anything like that.

[Turbo Joe]

The problem is that everyone is doing from word of mouth and no hard evidence has been presented in its favour. If the turbos were having that much difficulty breathing we would see a noticable performance difference between per gutted and non pre gutted.

[GrahamS4]

The problem is that everyone is doing from word of mouth and no hard evidence has been presented in its favour. If the turbos were having that much difficulty breathing we would see a noticable performance difference between per gutted and non pre gutted.

This is the thing. Having seen them, I cant argue removing the precats seems like a good plan. Just on MAF and FATS alone, there is no massive change.

The car feels good, but I have no trust in that. As I say, it did before. If on Saturday peak power is only marginally more (or indeed the same) but I can see boost coming on earlier, an even meaner torque curve and my peak power not tailing so rapidly, I'll openly admit I will change my tune. Maybe I should have more faith in my senses, but they have failed me before so I am wary.

[Turbo Joe]

Keep us posted on the results. It will be an interesting investigation.

[s4woody]

i understand your feelings but thats almost like saying i wont have something done by this or that tuner cos nobody really knows if its any good..
i would have thought that its all about word of mouth..i have something done and tell people then someone else tries it..isnt that making progress..??

The problem is that everyone is doing from word of mouth and no hard evidence has been presented in its favour

the turbos will have little or no restriction so that must be better for ther working life..
why do people fit 710N's instead of 710A's or 710C's or
whooshy DV's..cos we all know there crap..but have they been tested on a dyno..i think not..so word of mouth tells us to use 710N's..
i think its all trial and error..but word of mouth is worth its weight in gold..

[S4TAN]

i think its all trial and error..but word of mouth is worth its weight in gold..

Yep - it's called "received wisdom" ...

[shineydave]

or more likely "perceived wisdom" depending on your outlook

[hardhitter]

On a totally otherwise stock motor it's probably not worth doing for the gain like is being discussed. The only reason you might want to do it is reduce the possible heat build up in the turbine housing. It's interesting to know how the throttle response changes though.

Say if you fitted a cat back system, gutted the pre-cats, it will certainly be a good base say for a custom remap. You could probably get it mapped a bit further than your totally stock car.

But it seems well worth doing when going up to the KO4's (as folks have said) as the RS4 much bigger diameter DP's to match.

Surely someone has done back to back rolling road tests with stock vs gutted pre cats before ?