pre-cats

[chunky79]

Right people, 2 questions -

If the pre-cats are gutted what needs doing to the car? i.e needs the cel light mapping off???

Also, how much louder does it make the car?

Cheers

Stand down

[Mr V10]

You read my mind Dunc, was about to make a similair thread, you will need to get your exsisting MRC map tweaked to get the best out of your remap.

Can I also ask.

1. How much BHP difference is there between just gutting your pre cats/doing the cats completely.

What I'm trying to establish is, is there a significant difference in BHP in going pre cat/full cat delete and having the associated MOT headaches along with it, worth the headache?

I have decided I am having my car decatted and remapped before my Germany trip now that I've got the tyres and brakes sorted, it would be dumb to de limit and 540 BHP is AFTER a trip to the ring.

[chunky79]

Doug has said he can tweek the map. I just didn't know if the car would be undriveable if i gutted them and couldn't get the tweek done straigt away

[Mr Footlong]

I know this scenario well from my scooby days. I used to have frequent remaps/tweaks as I was changing things multiple times a year. It would have to be a pretty major upgrade normally for a mechanic to declare it undrivable before the remap IMO, but I was always, always told to do was if I had upgrade work done and had to drive the car, try running at no more than about 3000 rpm or so and stay off boost. Basically like you are warming the car up.

My uneducated opinion about driving on gutted precats would be that you could use a bit more than 3000 rpm but I would still try not to use boost, until you have the map tweaked/done.

I loast track of how many boring miles driving like a granny I clocked up in the Fluffy driving either from here or Newbury, to my mapper in Swindon...

[JCviggen]

I had my precats gutted when the box was being rebuilt and it's one of the best mods you can do IMO. And a heck of a lot cheaper than downpipes with race cats with pretty much the same result.

Sound: it is louder, noticably but certainly not too loud. Just perfect I thought, how it should've sounded from the factory. It sounds less like it has its throat pinched shut and more like a V8 (outside)

Performance: bit tricky because I also replaced leaky intercoolers but the difference was considerable. It made 522bhp on the stock map on MRC/Mihnea's dyno. The car felt a little bit flat at lower revs but that's not because it had lost anything there....but because the top end was THAT much better. After 5500 it just took off. Where the completely stock car starts to struggle and level off at 5500/6000 the power just kept climbing all the way to the shift point with the gutted precats. Peak power was literally at redline. After a remap that changed, but it gave me an idea just how restrictive the precats are (if you look at them you'll come to the same conclusion - they are by far the biggest bottleneck of a standard car)

Do they require a remap? I would say no. Car drove great, I took it to 170 on the Autobahn and around the Nordschleife for a few laps and it ran just fine. I also can't think of any reason why a remap would be necessary for this relatively mild alteration. It's not like changing the turbo/WG size or injector size. It's just less backpressure at high rpm, the ECU will request the boost it wants and it keeps an eye on fueling as well so there's nothing to worry about.

Stock car (green line) vs my car gutted precats and IC upgrade stock map - wheel power not flywheel.

[mavada]

...does it influence the mot?

[chunky79]

Down pipe gutting should be ok for mot so I believe.
I wondered if the car would play up due to the cel

[JCviggen]

...does it influence the mot?

No it's fine, when warmed up the main cats are plenty efficient.

[Mr Footlong]

If it is that good/noticeable a mod to make I fail to see how it wouldn't be advisable for the map to be tweaked? Personally if I did anything that altered backpressure then I would be sitting there twitching about the values not all be 100% optimal. Fair enough the ecu has a fair amount of tolerance built in but does the same level of tolerance apply on a remapped ECU?

I appreciate JC's input on this but until Grizz or Doug care to make a comment on this I will stick to my worryguts opinion . The usual applies about taking the car for a good drive to get the cats nice and hot before going in for MOT but as JC said, with the big standard cats still on there, it is unlikely that you will have problems at all.

[chunky79]

Doug said it may need tweeking after gutting them. Would be good to whack it on the dyno aftere to see what difference it does actually make.

[JCviggen]

If it is that good/noticeable a mod to make I fail to see how it wouldn't be advisable for the map to be tweaked?

What would you tweak? I've tuned my own ECU (good old fashion Bosch ME 4.3 however) and I don't see what you would change. Ignition advance can safely be left alone because if anything it could take more rather than less. It will probably start running a bit more spark advance at the top end after a bit of driving but that's because the knock sensors will stay quiet for longer. Fueling should not be affected much at all, well within the ECU's normal adaption range. Boost will not change either, it will still get what it requests. So what else is left? I did sufficient miles and even did a very very hard run on track (up to nearly 140C oil temp) on the stock program with the precats gone that IF anything had gone outside of the allowed adaption range I would have gotten codes and MIL. I didn't (well the normal catalytic efficiency ones obviously) and everything was fine when it was dyno'd on the stock program with Mihnea monitoring VCDS as well.

Typically the only thing that needs doing on turbo cars when you go to free flowing pipes is make sure they don't boost spike. But that's not an issue on these cars due to weak actuators and a sufficiently advanced ECU.

Mind you when you're on the stock map you WILL want to get it done because of the annoying MIL.

[Shoppinit]

Told

[Mr V10]

Well anyway, I'm quite excited about going stage two and will be getting a bespoke map, I want to get fuel droplets into the exhuast (like the RS5 in top gear and the C6) so it does that little V8 burp on every upshift, I cannot wait. I am hoping for 540 BHP with a pre cat delete, and a stage two remap. I'm not sure about upgrading the filters, I bought some OEM ones from Audi a few weeks back and will probably fit them, I've seen a photo of the ITG filters totally destroyed on RS6.com, and it shat me up, plus are they really worth £75 each, really?

http://www.rs6.com/showthread.php/18552-ITG-Air-Filters

[chunky79]

Well anyway, I'm quite excited about going stage two and will be getting a bespoke map, I want to get fuel droplets into the exhuast (like the RS5 in top gear and the C6) so it does that little V8 burp on every upshift, I cannot wait. I am hoping for 540 BHP with a pre cat delete, and a stage two remap. I'm not sure about upgrading the filters, I bought some OEM ones from Audi a few weeks back and will probably fit them, I've seen a photo of the ITG filters totally destroyed on RS6.com, and it shat me up, plus are they really worth £75 each, really?

http://www.rs6.com/showthread.php/18552-ITG-Air-Filters

Mmmm, looks like they haven't been maintained properly mate. Have you asked Doug if he can do the droplet fart thing.

[bilko1]

I'm running Milltek decat downpipes on standard map and engine runs fine, the cel comes on at varying times but a quick mouse click on VCDS turns it off. There's no loss of power when the cel comes on its just annoying. What I noticed with the decat pipes is an increase in turbo whistle and faster spool up.