Pre Cat Gutting!

[S4TAN]

or more likely "perceived wisdom" depending on your outlook

Reducing back-pressure and heat soak on the turbos by removing the restrictive pre-cats must surely equate to something a little more substantial than merely "perceived wisdom" don't you think?

It's all relative: retaining the stock exhaust and simply gutting the pre-cats on stock d/p's with K03's won't elicit the same gains as fitting 3" totally cat-less d/p's with a Milltek dual 2.25" cat-back and K04's for example ...

But I guess the point is it will deliver some benefit - no matter how small - just depends how far you want to go with it ... and how you personally stack up the cost/benefit analysis ...

... or something.

[UKS4APR1]

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..

That's just a reliability issue, not a performance gain - 710N's are the same as 710A's in performance, but are more robust and less prone to failure. 710A's are very prone to failure.

[UKS4APR1]

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

Thanks GrahamS4 for your unbiased and informed conclusion

[saf]

I believe that gutting the precats is worth doing on any car, and definitely the K03's if not for the power but just the fact that it reduces the heat build up on the turbo hot side.

Those precats are awfully close to the turbos. Like Woody says "ever tried breathing through a breeze block".

Id say, if youre having exhaust put on the car, or having the downpipes off for whatever reason it would be a good idea to have the precats done as youre half way there already.

At present Blower I believe is having some BHP under construction which = change of turbo's etc. As the downpipes are off I would recomend gutting them, firstly you would have less heat build up, and secondly as a result, less restriction. Even a few extra bhp squeezed will make a difference. Its the pennies that make the pound!

Reducing that back pressure as Julian has said was my main goal, and I believe that in doing so my whining K03's have lasted the miles that they have.

When downpipes are off at the garage , you could Just take them away and drill away at them for a few hours till job is done.

I think looking at the pics below (courtesy of another thread) it becomes apparant as to how restrictive the precats are.

I wouldnt say its necessary to do them, but if youre running high boost as in the usual stage 3 upgrade or high boost on weak K03's just for safty reasons its a good mod to make just for prolonging the life of the turbos. Any power gains made are a bonus.

[Andiroo]

or more likely "perceived wisdom" depending on your outlook

Reducing back-pressure and heat soak on the turbos by removing the restrictive pre-cats must surely equate to something a little more substantial than merely "perceived wisdom" don't you think?

But I guess the point is it will deliver some benefit - no matter how small - just depends how far you want to go with it ... and how you personally stack up the cost/benefit analysis ...

I agree with S4TAN and saf on this, and I think the benefit IMHO will be reaching your peak torque earlier down the rev range and higher peak torque overall (especially with a remap), not so much bhp. We found this with the Miltek modified dp's against oem, ok an RS4 but the logic is still sound Sometimes torque is the answer not bhp

Cheers,

Andiroo

[s4woody]

my point was that word of mouth allowed people to find out they are more reliable..i never had 710N's fitted as i was told to get viper DV's from AMD..

That's just a reliability issue, not a performance gain - 710N's are the same as 710A's in performance, but are more robust and less prone to failure. 710A's are very prone to failure.

[Turbo Joe]

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.

[okkim]

I have some facts about gutting the pre cats. The car (A6 biturbo, tiptronic) has a chip and cat back exhaust, and it was dynoed before and after the gutting. Nothing else was changed.

The difference was +10 HP and +20 Nm, on the 2500-5500 rpm range. And the maximum power and torque came 500 rpm's earlier. On the 1/4 mile the car was 0.3 secs faster.

I think that is well worth doing compared to the costs.

[S4TAN]

I think that is well worth doing compared to the costs.

Thanks okkim for your unbiased and informed conclusion ...

[GrahamS4]

I have some facts about gutting the pre cats. The car (A6 biturbo, tiptronic) has a chip and cat back exhaust, and it was dynoed before and after the gutting. Nothing else was changed.

The difference was +10 HP and +20 Nm, on the 2500-5500 rpm range. And the maximum power and torque came 500 rpm's earlier. On the 1/4 mile the car was 0.3 secs faster.

I think that is well worth doing compared to the costs.

That's exactly the sort of change I am hoping the dyno will show tomorrow. Like I said earlier, if it does, I will change my view. I think all I am really saying is that the difference is that sutble and there is no way I can tell a 10BHP, 20NM change on a 320BHP and 500NM car. Maybe others can, I can't. Of course I WANT the improvement, but having it because you know it's good and really being able to tell the difference are different things to me!

[Peakz]

The fact that it keeps the turbo's cooler is reason enough to have it done, especially with our meagre K03's and as mentioned previously torque is better than outright BHP, you're bound to feel the extra 20Nm of pull.

I was going to wait a while longer until fitting a Milltek but having read this thread I may well badger MRC to fit one asap!

[GrahamS4]

I agree, up to the feeling th 20NM part. Maybe I do not have stig like senses, but I dont believe someone can feel a difference of 20NM on a car that has 500NM already. I just couldn't feel a 4% variation. Show me it on the dyno, great, but this is the tuning equivalent of the Princess and the Pea!

[saf]

I agree, up to the feeling th 20NM part. Maybe I do not have stig like senses, but I dont believe someone can feel a difference of 20NM on a car that has 500NM already. I just couldn't feel a 4% variation. Show me it on the dyno, great, but this is the tuning equivalent of the Princess and the Pea!

I think theres a difference throughout the whole rev range. Car just feels a bit more looser throughout the range.

Theres more of a difference at low revs. When pressing the gas the car seems to rev a lot easier during the first few thousand rpm. Id say very beneficial to those who like to launch.

It feels kinda like using a lightened flywheel but the other way round. Instead of the car revving down easier it revs up noticibly quicker.

Thats what I found.

[Peakz]

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

[s4woody]

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.