decat pipes

[Paulbarr73]

I've noticed a massive difference in price between decat pipes (£300) and 100 cell cats (£1300).
I was curious about the benefits and bad points of fitting decats.
I understand they will be louder, but will they put strain on the main slencers?
Will the car (993 c4s) make it through an mot with them on?
Can the heat shields be removed as the cats are not in there causing massive temperatures?
How long do they take to fit them? and is it a DIY job?
Would different back boxes make a more pleasing sound?
Would the noise annoy me too much!?
And any other opinion on them really, as I think the race/ 100 cell cats are way too much money.
Thanks alot guys.

Paul

Found my 993, PPI done, Deposit on, nearly there![]

 

[dommorton]

The car won't legally pass the emissions test without cats so they need to be refitted every year for the inspection.

 

[cobalt911]

Hi Paul - c4s....a man after my heart ha ha...

OK - here is a subject I have been going through for some time now! The main reason I started looking around the exhaust system was to gain a better sound and also 'free up' the engine a little. 1st pass was to fit RSR exhausts. Now, they provide a bassier note by simply removing some soundproofing in the silencer box and a re-route of some piping. That worked ok but I found that between 2 and 3000 revs the 'boom' in the cabin somewhat annoying.

I also looked into the cat side of things. First thing to say is a car without cats will not pass an MOT so unless you are planning to be track day king it is probably not the best idea. I suspect when cats are removed some more work on the ECU needs to be done and, of course, there is an oxygen sensor left dangling. I went the 100-cell cat route but instead of spending £1500 on a Dansk one I went back (yet again) to Gert at Carnewal. He provides a 'swap' system where he sends over an original Bischoff or Gillet cat unit but with 100 cell cores inserted. You simply fit and return the old one to him. Cost is around £700 at todays exchange rates and he also holds a deposit until he receives your old one. I had Tognola fit mine and it has made a discernible difference to the engine, both in revs and noise! The noise is now too much for RSR's (I reckon the increase is about 30%) so I am going back to standard silencers and losing the RSR's. I am also fitting supercups for fun which I expect to scare most TVR owners!

Also worth thinking about is going to see Gert and getting them fitted at his place in Belgium. Its a fun trip and you will love the journey back!!

Plan to buy a new oxygen sensor too if changing the cat as the corrosion on ancilleries can be enough that they will simply break when removed (about £100).

If you are in the Berkshire area feel free to pop along and hear a 100-cell cat and supercups in action - may scare you off!

So, in conclusion, I reckon either a 100-cell cat with standard boxes OR leave the cat as is and try different boxes on the back, cheapest route being the RSR style from Gert (I am also after standard and looking to swap my RSR's)...

Happy to take a call if you want to hear more ponderings but improving the sound without it being annoying is becoming a hobby ha ha...

Cheers,

Mark

 

[p27549]

Paul,
I have Danske De cat pipes and Standard silencers fitted to my 993 C2 Cab. Yes they are loud even with standard silencers. They do make a difference to throttle response, much improved. The Lambda sensor is also located into one of the pipes. I had no issue with re-ussing my original sensor. They are a DIY fit, but the pipes are not that tidy a fit. They do chafe against each other, not sure if Fab speed de-cat pipes would be better. The car will never pass an MOT with them fitted. I re-fit the Cat at MOT time, its a pain but its only once a year.The kit comes with all necessary gaskets and bolts to install. I do have a set of Danske sports boxes but they are really loud when coupled to the de-cats. I have been advised that the Cat also acts as a silencer due to the exhaust gases crossing each other assisting in noise cancelling to a point. I am looking for an old Cat and removing the cores. Hopefully it will give the same free flow gases and maintain a lower noise. Just have to find a second hand Cat to cut open and try.
I thought the 100 cells were to expensive as well. Once you have fitted the de-cats i would recommend a re map of the ECU to get the performance out of the car. Mine has just been tuned by Tim at Autotechnik in Crawley. Very good.

Best of luck

TIM

 

[Paulbarr73]

I think I might have been thinking of doing the job ' old skool'!! is the good old days, a pre 93? car you could just bypass the cats and it still go through a MOT. not any more it seems.
I do think the RSR's may be the way to go. However, maybe I should wait til I get the car and get used to it and see if it's loud enough as standard, (I doubt it!), so only time will tell.

Paul

C4S - in the post[]

 

[jmspear]

Hi Paul, I have been through the following combinations:

1) Std cat and RSR's (RSR's now sold)
2) 100 cell cats and sports boxes and high flow manifolds all Cargraphic
3) As 2) but standard manifolds (heating crap with high flow manifolds and no power advantage (as dyno tested at 9M and by Wayne Schofield) so back to standard)
4) Std boxes (factory) and de cat (dansk)

I prefer the sound of 4) is pretty much always 104 - 105 dbs on sound meter at track days, sounds deep and lovely and no booming, if I fit extra back bomb silencers, from merlin drops to 100db and I can get on pretty much any track.

Interestingly the sound level of 4) and 2) was the same as measured at numerous circuits, the sound of 1) was lower than all other combo's bit still not low enough for castle combe and I much prefer the sound of 4) over all other combo's.

No probs with lambda sensor, but I have a '95 car with only one sensor, power wise, well tough to say as the engine is mapped to option 2) and has billet heads etc, etc, moving to option 4) I haven't had remapped, but my butt dyno tells me I have lost a little low down torque, but I had mountains of this anyway with the billet head conversion, but have made it feel "less restricted" at the top end and it feels like it revs freer and a little more top end power. But pretty subjective, seems to perform just the same on the circuit. I also have a slight knock going over bumps where the dansk pipes clash as they touch when fitted.

They do get very hot, have had them glowing cherry red on the circuit and they are very "heat blued" but no problems with heat affecting bumper etc.

Finally not MoT legal but as has been suggested you can always change come MoT time, or in my case a very good mate owns a garage ;-) . I have swapped all bolts for stainless steel marine grade, totally elimantes corrosion and makes removal etc painless. I strongly recommend this route. I bought the bolts via ebay, make sure you buy right size (thread and length)

HTH

Cheers

John