I went to Longlife exhausts in Walsall today- and I'm getting them to do the exhaust tomorrow. He said £600 including de-catting, which I thought was OK. I just have a nagging feeling that someone recently said you shouldn't de-cat an NA. Is this true? or will I get more power?

 

I read that write-up by MTL and I'll have another look- did you say with an NA you have to be careful with the back pressure. Will de-catting it lower the torque at lower RPMs? Will I end up having to rev it even harder to get it going? If the cats are still there, and that raises the backpressure, does that make the car get more power at lower revs? Tell me if I am totally wrong here

 

The bloke seemed to know what he was doing, but I just wanted to check before I went ahead with it.

 

I have to choose the style for the back pipes too- god knows what I'm going to go for. Definately twin exit, but two pipes at each side or just one?? What should I go for?

theres a lot of talk from people about the good old wifes tail of back pressure. the fact is a couple of people on here have decatted NA's & said it felt better.

 

i would go for it :)

ps, back pressure is bad ;)

Lack of back pressure is also bad!!! You will lose low end torque, but I think you'll get slightly better top end power.

 

I wouldn't do it

 

Paul N

I would for quality headers (millen), and fit a cat back system, but leave the cats alone. It will also reduce hassle come Mot.

less back pressure exhaust will give more horses but often less torque, thats the theory, wich is often right if you look at tuned non turbo cars, like honda's. :slap:

I definately DON'T want to loose low end torque. What should I do? Will I feel any power improvement from the new exhaust alone?

 

This is a fairly big deal for me as being an NA this will probably be my biggest single 'tuning' thing, so I want to try and get it right.

Ive got a mate who's always going on about back pressure lol,

im not an egg spurt but i just cant see how back pressure can be good.

In practical terms surely decatting is the way to go, you dont want those expensive things on there !

aaaaaaaaarg, bhp is directly related to torque.

 

on a dyno they measure torque which then gets converted to power by a calculation.

 

Horsepower = torque x rpm / 5252

 

below 5252 rpm any engine's torque number will always be higher than its horsepower number, and above 5252 rpm any engine's horsepower number will always be higher than its torque number. At 5252 rpm the horsepower and torque numbers will be exactly the same.

 

check it on some dyno sheets!! ;)

ps, back pressure is bad

 

Lack of back pressure is also bad!!!

 

Who is right??!! What should I do? Cats or no cats?

 

Will I get it back de-catted and it feel slower than before, will I not notice apart from a change in sound, or will it go faster? I want the car to accellerate quick from start rather than have a higher top speed.

I have an NA, and a longlife exhaust and I removed the cats. Car drives better and sounds sweet. Nuff said??

 

Also twin rolled pipes on each side, maintains the look of the car and sound awesome

Do rolled pipes make a difference in any way? Just the look? They have basically any shape of pipe I want. Thinking of either single oval rolled, quite fat to fill the space in the bumper, or twin slash cut at each side.

 

Thanks for the answers so far. I was kind of hoping for a definitive answer- opinion seems a bit split on this so I'm still not sure.

Rich,

 

Removing the cats will do 2 things:

1. give you more high rpm horses, and perhaps get you to the red line quicker

however,

2. Loose part throttle driveability. You might also find, your care will run a tad richer without the cat (on an NA, less so on a TT afaik)

 

so... your call really - if you're going to race your Z to race meetings etc, take em off and get a custom chip done, or its it your daily driver for pootling around town / driving to work everyday leave em on.

 

My 2p spent

Simon.

Having read the advice, I think I'm going to leave them on for just now and see how the new exhaust goes. What people seem to be saying is that removing the cats will increase the performance but raise the point where peak power is attained in the rev band.

 

So I would have to rev it harder to get speed/acceleration. This is not what I want, and as I use the car daily/round town etc, I think I'd be best leaving the cats in for the moment. In theory I like the idea of removing the cats as a way of getting the maximum power out of an NA, I have got used to the feel of the revs of the car and the gear changes and I don't really want to mess with that.

 

Am I right in thinking that a cat-back exhaust will still give me some improment in power? If it is freer flowing than stock from the cat back I should see some bhp gain, even if it is failry small?

 

After all this, I think maybe I would like to get improved headers as another way to change the exhaust, but how easily they are available I don't know.

If you're that worried about it Rich do what I did! Longlife made me two direct cat replacement pipes and I keep the original cats in the garage. They even made new flanges for the cats so they will go back on with no problem (just four bolts each side). Much cheaper than some other places I looked at and the quality of workmanship was excellent! They even said they will swap them over for free if I take the car to them on a quiet day (for MOT) etc..

 

Do it mate!

 

Steve

 

Im getting my n/a cats gutted on monday by the local garage ! So i will let you know if you like before you get the job done !?!

ok,

 

1 for MOT's see my write up in the FAQ section on emmission tests on zeds!

 

2 how on earth is it going to make a car run richer by decatting???? is more fuel going to be injected for a given amount of air without the cats then??

 

3 LISTEN TO JOCK!!!! he has(had? ;) ) an N/A which he decatted - proof of the pudding & all that!

But was he looking for more top end power, or preserving low end torque? Or am I just totally misinterpreting what has been said? I'm going to get it done at nine. I'm just worried about it not pulling in low gears as I am used to. To me that's one of the things I like about my NA, I feel it's responsive in second and especially third.

Who is right??!!

 

I'd personally go with our technical "experts" if PaulC or Duffer say it's so then it's usually right !!! (apart from if they are talking about non car related stuff, then they could be deemed to be talking out of thier butt hole :D :rofl: ) but when they are talking about cars, I don't argue, I do as I'm told lmao !!!

Yes- I trust their judgement. I've said I won't do it, I will, I won't. **** it. I'll have made my decision in an hour!! and yes, I do trust the opinion of these guys. Cheers

Im only doing it because im on a quest to get flames from the exhausts! And i was once told that this is the best way ?!

 

Dont know if its true or not

Rich,

 

I use my car as a daily driver and it is fine in traffic. The rolled edges just look good.The bottom line is (and have said this lots of time) the NA makes power right through the rev range on a nice linear curve, maximum power moves a small amount up the rev range, but it is not like your whole power range is going to jump 2000 revs. YOU WILL NOT lose driveability by removing the cats.

 

I wanted a new exhaust cos mine was holed, not looking for power or torque or anything else.

 

My last thought is this, its a 13 yr old car, cats have a life span, so ask yourself what condition those cats are in, and whether they are doing the job you think they are doing? I would suggest that they are probably towards the end of their life span , or past it , in any case.

ok,

 

1 for MOT's see my write up in the FAQ section on emmission tests on zeds!

 

2 how on earth is it going to make a car run richer by decatting???? is more fuel going to be injected for a given amount of air without the cats then??

 

3 LISTEN TO JOCK!!!! he has(had? ;) ) an N/A which he decatted - proof of the pudding & all that!

 

Oops, my mistake! (It early this morning after an 18 hour day at work!)

I was getting confused with using an after market air filter on an NA, which will cause you to run richer, sorry Rich. The first point I mentioned still stands however.

Had the exhaust done- including de-catting. They did de-cat pipes just in case, but I take Jock's point that maybe the cats are past their best and just fouling up a free-er flowing exhaust.

 

I went for the twin 3 inch slash-cut pipes, to keep a stock type look.

 

I asked them to make it quiet(ish) but I appreciate taking the cats out probably adds to the sound. It seems pretty loud to me and I just don't know how anyone could take it louder than it is. I have to say I did like the sound before- you knew it was there, but it didn't take over. I used to be able to hear the engine, now all I hear is the exhaust, so I'm not sure about the sound yet.

 

Driving, I don't know how much is imagination or 'psychosomatic' - telling yourself it's different. What I found on the drive back was that the car felt a little more responsive- it would pick up speed a bit quicker, and I felt I was sitting in a lower gear for longer- I would stay in second till I was revving a bit higher.

 

Another possibly imaginary effect seems to be that changing gear seems smoother, almost as if the power carries on while I'm changing up and it's easier to 'pick up where I left off' after a gear change, where before gear changes could be a little jerky- power would fall off as I changed up and make the take up after the change seem not so smooth. Maybe all that is totally in my head.

 

I have to say, I'm not totally convinced about the sound. I don't know how I'm going to cope with the responance if I'm sitting at 2000 revs. Looks good though :)

 

Big thanks to everyone who posted an opinion.

 

I cant wait for mine !!

Don't know if I'm up for flames. Wouldn't it have to be overfuelled?

 

About the cats- will I get more fumes/vapour out the exhaust now? Just don't want to start worrying about loads of vapour - I am guessing there will be because there's nothing to catch the shite coming through.

Im running an Apexi SAFC so i should be able to fuel it accordingly! Is it much louder ?