Pre Cat Gutting!

[s4woody]

ifme MRC or any other garage/tuner offered to do this pre-cat gutting for nothing there would be a que of cars outside a mile long..its all down to the money...is it really worth a few hundred quid for this..well i reckon yes it is..and im sure if a poll was done the results would speak for themselves..

Seems to be undecided, some for and some against

[GrahamS4]

We'll have to get MRC to slightly de-tune your S4 for a few days and see if you notice the difference.

I noticed the remap (phew!), I noticed the H&R ARBs, I noticed the Goodyear F1's instead of the P6000s, I notice the Porsche brakes dont fade like the stock ones, I am just not entirely sure I can tell a 4% increase in torque. Sure it's a good thing and if you want to spend some money on making he car the next nth better, it has to be on list. Is it on the list of noteable improvements to the car, hmm, not really in my book. Not sure anyway.

It's a bit harsh to say I wouldn't do it again. Maybe I would. Maybe some stats would convince me and maybe driving two cars back to back I would feel the difference. Driving in in one state and out in another, it's very hard to keep an unbiased view.

[Turbo Joe]

so are you saying that every company that sell DP's with no pre-cat are just ripping people off due to word of mouth..
do you use 95 unleaded cos you dont believe that 97 or 99ron is going to make your car any better..
i understand the paying top money for something that mite show a little gain but i really dont understand your reasoning..

Seems to be undecided, some for and some against. Still unless figures and proof are brought forward, so called benefits are just speculation and not confirmed. I think the "breathing through the breezeblock" analogy is an extrapolation beyond realistic reasoning. Whether this knowledge passed down is actually "passed down wisdom" remains a theory until evidence is brought forward to support it. I'm not saying that it is not beneficial to gutt the pre cats but its seems alot of trouble to go to just on passed on words and no proof.

I going by experience sir. My mate's car performs more or less the same as mine, his pre cats gutted, mine not gutted. For 10bhp/20nm/03 secs, its seems alot of trouble to go to just for these minor increases. A K&N filter was once bragged to give you better benefits than the normal filter but even that is under question thesedays. As I stated before I do not argue that there may be benefits, but I just don't think it is worth the trouble. As fot the gutted pre cats keeping the turbos cooler, I don't disagree, but by how much, 1,2,5,8,10 degrees, who knows? How can this actually be tested?

[Turbo Joe]

ifme MRC or any other garage/tuner offered to do this pre-cat gutting for nothing there would be a que of cars outside a mile long..its all down to the money...is it really worth a few hundred quid for this..well i reckon yes it is..and im sure if a poll was done the results would speak for themselves..

Seems to be undecided, some for and some against

I think it just boils down to personal preference. A poll in favour of pre cat gutting is a far cry from proof and hard figures. Some say it is worth it and benefits can be noticed but others including myself have serious doubts based on experience and live comparison as apposed to word of mouth.

[Harper--D]

Was your mates car tweeked so the map was better for the gutted dp's?

[quattronutter]

i think its worth doing if your upgrading turbos downpipes etc.. at the same time,any restriction in the exhaust will improve performance if its removed,the gains will be more beneficial if your running more bhp/torque,less so if its near standard

[Turbo Joe]

Its an MRC map he has so I'd say yes as this is a common practice with MRC.

[saf]

I am running less boost that you bro. I believe your SKN map holds 1.3 bar. That may well make a difference. Im running 1.25 and have 130,000 mile son the clock.

I think just for the easier breathing its worht doing. under hard boost the heat really builds up at the exhaust side. Might be a reason why your turbo's went pop at 78,000K. I guess we can have a check when you get the old turbos back see what kind of damage on there.

Removing the precats are a cheaper way of having newer downpipes. Well its the next best thing. I didnt hear of this until MRC started doing this, so it does seem like a new trend.

Harper-D , thinkign back, my car was mapped with the precats gutted.

[S4TAN]

I just couldn't feel a 4% variation.

Bet you'd notice a 4% variation in your pay packet Graham ....

Bottom line is this: getting rid of the pre-cats is a good thing. How much of a good thing depends on your point of view and, as I said previously, how you stack up the cost/benefit trade-off.

For some the trade-off is positive ... for others it's negative. Neither party is wrong per se simply because it can't be viewed in absolute terms such as "right" or "wrong". It comes down to personal choice and what each individual perceives as value for money....

... or something.

[s4woody]

ok so you dont think the gain outweighs the cost/trouble..why have you got a milltek cat back..?
Audi devolope this car with an exhaust that they feel gives optimom performence..now its been debated that a milltek cat back alone dont give the gains that people say..IE 10-15bhp over the standard system..its also been said that with the pre-cats removed you are more likely to see a gain..see where im going...now im sure your car sounds awesome but im also sure that you've read alot about the milltek and even been told there worth it..kinda like word of mouth i'd say...
this thread could drag on for ages and to be honest i know what works on these cars and what dont..if you really dont wanna do summit then dont let anybody or posts on here force you into it..enjoy your car..but dont complain when you get your arse spanked by an MRC remapped S4 with no pre-cats and a milltek..TTFN

[S4TAN]

but dont complain when you get your arse spanked by an MRC remapped S4 with no pre-cats and a milltek..TTFN

Righteous my man!

[Harper--D]

PMSL!

[GrahamS4]

I just couldn't feel a 4% variation.

Bet you'd notice a 4% variation in your pay packet Graham ....

Mate, it if went down I'd notice a 0.004% variation!!

Anyway, todays the day, I reckon we must be able to conclude something from todays dyno fun.

[s4woody]

well i saw the gain for myself and it aint word of mouth..its for real..come on graham spill the beans..

[GrahamS4]

well i saw the gain for myself and it aint word of mouth..its for real..come on graham spill the beans..

Ok, here it comes. Unfortunatelly the plots from yesterday are on totally different scales to to my previous plots, so on first glance it was not easy to digest everything. Due to time they were also unable to measure boost. But from BHP and torque plots we can see some changes.

Peak Power measured at the wheels was only a tenth of a BHP different from two differnt dynodynamics dynos over a year apart. Testament to dynodynamics consistancy I'd say and hopefully means we are comparing eggs with eggs.


Before (Stock S4 exhaust):

Torque curve flat lining at: 3200rpm
Peak Torque: 360FtLb @ 4000rpm
Torque at 6200rpm (where torque is tailing): 240ftlb
Peak BHP (249 @the wheels) reached at: 5120rpm
BHP @ 5900rpm: ~235BHP (tailed ~14BHP)


After (RS4 exhaust gutted precats):

Torque curve flat lining at: 2880rpm (320rpm earlier)
Peak Torque: 380FtLb @ 4000rpm (+20 ftlb or 27nm)

In fact from the point the torque starts to level off at the rpm above, the torque is consistantly always at least 20ftlb more than before.

Torque at 6200rpm (where torque is tailing): 270ftlb (+30ftlb or 40nm)
Peak BHP (249 @the wheels) reached at: 4800rpm
BHP @ 5900rpm: 249BHP (held power)

So the facts show it has made a difference, slighly earlier torque, slightly earlier peak power, good increase in torque accross the range and peak power holds well where as it peaked and started to dive before.

Should have trusted my senses more. No need to be so cautious, that freer top end does exist!