De-catting

[toplad]

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Thinking of decatting my 996, has any one gone down a similar route, or maybe headers?

www.design911.co.uk/index.htm?Region=UK

Click on Exhaust for 996

I've decatted before and been happy with the results in the past. With a map, headers, and decat you could be looking at a gain in the region of 40BHP

Anyone else?

Edited October 14, 2004 by toplad

[KarlS]

I doubt you'll see 40 Hp from the mods you mentioned. I put headers, Fabspeed mufflers, and a piggyback chip on a 99 C2 and saw a total of 18 HP on the dyno. I also ran the car on the track without the mufflers using Fabspeed Supercups and while the car was louder and lighter, I doubt there was any more HP.

I'd suggest that rather than removing the cats, that you look into a muffler bypass instead. Muffler bypass pipes are readily available and will save considerable weight, if you can stand the noise. A cat bypass would not only make the car fail emissions, you'll have to get a custom pipe made up. You also have to be very careful when changing the exhaust back pressure on the M96. There are lots of changes and parts out there that will actually decrease HP. I'd suggest working with a reputable tuner and someone who will give you before and after dyno sheets.

Karl

[toplad]

I doubt you'll see 40 Hp from the mods you mentioned. I put headers, Fabspeed mufflers, and a piggyback chip on a 99 C2 and saw a total of 18 HP on the dyno. I also ran the car on the track without the mufflers using Fabspeed Supercups and while the car was louder and lighter, I doubt there was any more HP.

I'd suggest that rather than removing the cats, that you look into a muffler bypass instead. Muffler bypass pipes are readily available and will save considerable weight, if you can stand the noise. A cat bypass would not only make the car fail emissions, you'll have to get a custom pipe made up. You also have to be very careful when changing the exhaust back pressure on the M96. There are lots of changes and parts out there that will actually decrease HP. I'd suggest working with a reputable tuner and someone who will give you before and after dyno sheets.

Karl

<{POST_SNAPBACK}>

Thanks for the Advice Karl, just the sort of input I was hoping for.

I'm just going off the web site info regarding the power gains.

I thought if I used the headers (A claim of 12BHP) and the Decat pipes (a claim of 9 BHP) and a local tuner can add 20BHP with re-programing of the ECU on the rolling road, I'd hoped for the a bit more than 18 BHP. I not worried about the emissions test btw. I'm prepared to have the "cats" reinstalled once a year for the yearly emission test.

I've spoken to a local exhaust manufacturer and can have anything I like made up. I'm not sure I know what you mean when you say muffler bypass, can you explain?

The main thing I'm concerned about is the decreased back pressure in the exhaust system due to cat removal.

Regards

[KarlS]

The exhaust system on the 996 follows this path - headers connect to the cats, cats connect to the mufflers, mufflers connect to the exhaust tips. A muffler bypass pipe eliminates the mufflers by connecting to the cats on one side and has its own exhaust tip. By bypassing the mufflers you save the weight of the mufflers (around 50 lbs) and get a louder exhaust with no impact to emissions since the cats are still in place. You also don't have problems with back pressure, since the initial back pressure that is seen by the heads comes from the cats, not the mufflers which are farther down stream.

A custom exhaust shop can make up a muffler bypass pipe or you can buy them from places like Fabspeed (theirs is called SuperCup).

Karl

[Scouser]

But putting bypass piped on only makes the car sound louder....very much louder....uncomfortably louder imho. They won't give you any HP increase. As you said Karl, the back pressure is seen by the cats not the mufflers so all you are doing by replacing the mufflers with bypass pipes is just making your car more noisy (although there is some slight absorbtion of backbreasure in the mufflers too.).

I accept that you drop 50lbs or so when you get rid of your stock mufflers but this isn't really going to increase HP significantly. You could do the same by getting rid of your spare tyre. Also, the Fabspeed Max flow mufflers are less than half the weight of stock and can better the sound while still losing some weight.

If you want to increase your HP with any real significance you will have to go for an SC. By the time you spend out for exhaust mods, headers, remapped ECU etc for an extra 15HP or so and at the same time blowing out any warranty you may have, you might as well go the whole hog and SC it......or you could of course trade up to a TT ;)

[toplad]

I don't know where you got the 15 BHP, but it's incorrect, the headers give you 12 and a remap at Ninemeister is 20 BHP(ish). The lot would cost a little over a grand, I'd be happy with that for cost per pound stakes. Super Charging is in the area of 6K which is a bit too steep for me.

or TT :clapping: :thumbup:

[umn]

The fallacy is to just add up the numbers. I very much doubt you get an extra 20 HP just from a different intake and exhaust, the system is too finely tuned for that.

Also, I wonder if the remap is supposed to give you 20HP at the top end. Usuallly, re-mapping in naturally aspirated engines is most successful in mid-range where the manufacturers have to be conservative with their mapping to comply with exhaust and noise regulations. It is an old trick of re-mappers to to promise a nice gain but not tell you in what range. Customers always assume it is top end, but that's not sure at all.

I'd be extremely sceptical of anything much in excess of 15hp top end just by the three measures you mentioned. If a tuner was going to promise that, I'd insist on before and after dyno runs on a neutral dyno and put the promised top-end gain +/- 5% in the contract. 50% payment up front, rest upon successful completion.

Neutral dyno is essential, don't trust a dyno graph you haven't falsified yourself.

Cheers,

Uwe

Edited October 18, 2004 by umn

[KarlS]

Headers will not give you 12 HP either. I've seen test results for many of the after market headers and mufflers that were done by a tuning shop (ie neutral party). The majority of them actually made less or equal HP to the stock exhaust system. With CAD systems and what not, the PAG engineers are just not leaving that much on the table. There are a few systems that will make a little more power but to get anywhere near 12 you'd need to swap the entire system, not just the headers.

As for 20 HP from a remap to a NA engine, it's not going to happen. I had one of the leading chip tuners spend a day working on my GT3. After almost 30 dyno runs, the best we could do was 10 HP max. As Scouser said, the only way to get more than about 20 Hp from bolt-ons is to get a supercharger. Anything else is a waste of money although there are a lot of people out there who have spent the money and are now experiencing the placebo effect.

Karl

[Scouser]

Here's a cheap way of getting 50 hp: http://www.angelfire.com/nc2/mycoffeecan/page1.html