View Full Version : Cat removal?
FabiaTDi
24-12-2003, 12:59
Has anyone here removed the cat from their TDi?
Is it worthwhile just removing/replacing the cat or is it better to replace the whole system?
How restrictive is the cat and what sort of gains can you expect?
Lots of questions I know! :o
Merry Christmas all! http://www.briskoda.net/forums/images/smilies/xmas.gif
driveforward
24-12-2003, 13:10
Rage removed the cat from his Ibiza TDI and actually found his stats DECREASE... which may be worth noting...
FabiaTDi
24-12-2003, 13:20
Seems strange!
Any reasons why this would happen?
Its a possible mod that has been mentioned by a tuning company.
Cheers.
tdi's have low down torque which may require back pressure.
resistance isn't always a problem.
What were/are Rage's final performance stats?.. did he break the magic 200bhp?
Maybe a sports cat would be the best replacement?
You get some back pressure, keep it legal and gain power.
driveforward
25-12-2003, 17:33
Originally posted by Neo_VR
What were/are Rage's final performance stats?.. did he break the magic 200bhp?
.....no :(
Well at the time Ians TDi had 150 Bhp and could keep up with Simon on the 0 - 60 sprint. I took the pictures myself to prove it. Just ask Ian. :devil:
FabiaTDi
25-12-2003, 20:02
Did Rage get his car RR'd after the new exhaust was fitted?
driveforward
25-12-2003, 22:54
Originally posted by FabiaTDi
Did Rage get his car RR'd after the new exhaust was fitted?
Yes he did, results are confidential... see my earlier post ;) :(
FabiaTDi
26-12-2003, 08:45
Originally posted by driveforward
Yes he did, results are confidential... see my earlier post ;) :(
So not as good as the results in his sig then? :(
Personally I was just thinking of a decat (probably from Powerflow) rather than a whole new exhaust. This should help free up the back box a little as I have heard the cat can be restrictive.
the point being - is back pressure a good thing or a bad thing?
Originally posted by FabiaTDi
So not as good as the results in his sig then? :(
Personally I was just thinking of a decat (probably from Powerflow) rather than a whole new exhaust. This should help free up the back box a little as I have heard the cat can be restrictive.
Just speak to Ross and get your name put down for a Milltek :p
Originally posted by m0rk
the point being - is back pressure a good thing or a bad thing?
I was under the impression that some back pressure is needed. After having a de-cat exhaust and free flow back box Rage's BHP went down.
Its like a trade off, which would you rather do? De-cat it and have a faster turbo spool up time. As theres very little back pressure.
Or get a sports cat and exhaust system? so you have lowered back pressure and gain BHP.
FabiaTDi
26-12-2003, 10:06
So how does a sports cat differ from a standard cat? Does this retain some back pressure?
So if some back pressure is required on a diesel - anyone know why?
Thanks for all the great responses! :cheers:
A catalyst has as such 'elements'. On a sports cat there are more of them and there larger. This allows higher rates of air flow.
As actually proven by Simon, the power went down when he eliminated back pressure. :confused: :redface:
Shock_Xe
26-12-2003, 11:10
my race cat is 100 cell i think where as normal cats are 400-500
Sorry, I'm confused over which has more cells.
Last nights pop is finally wearing off now.
Regular cat on the left, with many small cells. Sports on the right with less, but bigger cells. Borrowed from Milltek.
http://www.milltek.co.uk/images/large/cat_compare.jpg
FabiaTDi
26-12-2003, 21:09
The Milltek sports cat still looks like it would be fairly restrictive in the picture though to me.
Im not 100% sure if a Sports CAT would be applicable for a diesel.
Petrol CAT's are a three way convertor whereas a diesel one is two way. Their chemical make up is different.
Personally i'd just de-cat it. We do this on our PD's alot. Milltek make a large bore downpipe without a CAT and we fit that to a larger bore system with twin round tail pipes. We add a rear valance from a four motion Golf which has the cut out for the silencer so it looks smart. (for the 130 and 150 PD Golf).
Power is usually up a few bhp on a normal remap on the PD and turbo seems to spin up faster.
FabiaTDi
26-12-2003, 21:22
Ross, I was wondering if you'd have any before and after plots of a PD130 with a decat?
:cheers:
I'll have a rummage around at work and see what I can find.
Thing is most of the cars with exhausts/decats we do also are remapped.
What I might be able to get is a graph of a remapped PD with a standard exhaust and one with a decat and Milltek, leave it with me :)
driveforward
27-12-2003, 12:07
Originally posted by techie
What I might be able to get is a graph of a remapped PD with a standard exhaust and one with a decat and Milltek, leave it with me :)
It would be interesting to find some hard evidence on this subject... :think:
slim_boy_fat
27-12-2003, 12:35
I know its not quite the same, but Leo got a full Miltek system including free flow cat on his LCR. It didnt really give much more top end, but it pushed the torque slightly higher and he feels its much less lag.
TDis have the VNT turbos so they are less prone to lag (not saying they dont have it ) than the petrols. VNT is a pretty good set up. Diesels get the benifits because of the lower temps they run than the petrol cars. I doubt that there is much of a difference removing the CAT on tdi engines. At the end of the day its the gearing thats the biggest problem with the tdi. In an attempt to get the very best mpg they fit too high gearing.
Sort the grearing and the car would be fecking rapid..
driveforward
27-12-2003, 12:43
Originally posted by slim_boy_fat
Sort the grearing and the car would be fecking rapid..
Thought yours was fecking rapid!? :p
slim_boy_fat
27-12-2003, 22:18
Originally posted by driveforward
Thought yours was fecking rapid!? :p
I get by...;) But there could be a new project on the horizon.
See how the money is after Christmas.
driveforward
27-12-2003, 23:27
Originally posted by slim_boy_fat
I get by...;) But there could be a new project on the horizon.
See how the money is after Christmas.
New project!? PM me ;) :D
slim_boy_fat
28-12-2003, 08:21
Originally posted by driveforward
New project!? PM me ;) :D
Patience my padawan learner.
driveforward
28-12-2003, 10:02
Originally posted by slim_boy_fat
Patience my padawan learner.
:think:
Originally posted by slim_boy_fat
Patience my padawan learner.
:rotfl:
Bear in mind that Rage's system is a Poweflow and there is no science whatsoever in them, they just drop the old system and make pipes to fit the bottom of the car and chuck a couple of boxes in. I had one too (which I why Rage has one TBH) and when I had mine made up my car felt quicker - maybe that was just the slightly quicker turbo spool-up, maybe it was actually quicker, but it felt different. I didn't get it re-dyno'd (but mine made 189bhp and 306lb/ft on the same rollers on the same day as Rage's signature figures).
A difference in the Powerflows was that my car had 1 more silencer box than Simon's (IIRC), and it was made up by a different fitter, so who knows what else may have been different. Neither car was mapped for the exhaust either; both run the standard Revo TDi map.
Gleistung has several dyno plots of TDi Sports before and after a decat and he was talking a small increase. For me the difference is in the driveability though, because it's less easy to be caught off boost and the shove comes closer to the time you put your foot down without the cat. In any case a chipped TDi can afford to lose some torque in favour of bhp - it might stop them from fading away up the rev range so badly as they do.
Why not get Powerflow just to remove the cat? They charge about £80 and they fit flanges to the cat and to the pipe they use so you can swap it back any time you want - it took me about 10 minutes when I was selling my car.
All turbos need some back pressure to work IIRC, but it isn't a huge amount and the only way the TDi would be different to a petrol engine is if the fancy VNT system had a different need - that I don't know, but Gleistung's posts would suggest the cat is not required.
FabiaTDi
28-12-2003, 10:50
Fen,
Thanks for that - exactly what I was looking for :cheers:
I'll do some searches gor Gleistung's dyno plots :)
Just to confuse you some more we've actually done a couple of these.
(see pic I posted)
http://www.seatcupra.net/forums/showthread.php?s=&threadid=26859
Seems to work better keeping cat and just replacing the rest with tubing of at least 60mm diameter..:D
Will have 2 130 golf's dyno'd in the next couple of weeks. The vnt turbo + cat will muffle the sound so it's not very loud.
removing the cat will reduce back pressure but it's not the same for a turbo car. the turbo is making a big bit of back pressure by it's self.
removing the CAT on my GT made teh turbo spin up quicker, gave me more topend (significatly felt better above 5500 to 6500rpm) but it did fell as if it lost off boost. also the mpg seemed to get worse also. noise increased shit loads. although I liked the sound I prefer the car the way it is with the normal CAT on
Don't think it makes that much difference on the TDI's. Another side effect (I haven't seen it personally, but it is known to happen) is a resonance at certain rpms.
Originally posted by Neil82
.
:confused: :confused:
FabiaTDi
28-12-2003, 15:56
Originally posted by prc
:confused: :confused:
Maybe he was just making a point :laff:
driveforward
28-12-2003, 15:58
Originally posted by FabiaTDi
Maybe he was just making a point :laff:
:hammer:
Wow! This thread is confusing lol. Just for the record, ive decatted and de-backbox my 306 hdi and i wouldnt say its got any power gain (its also remapped aswell), but it certainly sounds lovely.
And yes, Holy Thread Revival :P
I de-catted mine 6 months ago. Before that i would press the throttle, wait, wait and then a surge of power, wheelspin, wasted power IMO.
After de-cat, smoothed air box, egr disconnected I have a smoother power curve. I hear the turbo spooling up earlier, I hear a crisper snap from the diverter valve.
It helped my engine definitely and feels more responsive. It might affect torque, in that I don't have that huge power surge all at once but have it more spread out and earlier, so this would increase bhp, IMO.
I did a lot of research before I did the decat and I'm happy with it.