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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Guttin Cats on DP's?



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      06-08-2007, 11:19 PM   #1
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Guttin Cats on DP's?

All this talk about dp's on another thread. Has anyone thought about guttin cats. Audi guys used to call this piggie pipes and we made a lot of power on stock pipes. If no one makes a reasonable dp I might do the same. I'll do a dyno b4 and after if I do, do this.
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      06-09-2007, 05:29 AM   #2
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sounds good. The only thing that keeps me cautious about DP modding is the obvious AFR problems, 02 sensor problems, and CEL issues.
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      06-09-2007, 06:27 AM   #3
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Quote:
Originally Posted by 1badE90 View Post
All this talk about dp's on another thread. Has anyone thought about guttin cats. Audi guys used to call this piggie pipes and we made a lot of power on stock pipes. If no one makes a reasonable dp I might do the same. I'll do a dyno b4 and after if I do, do this.
What?
Be so kind and give some explanation, pics etc.
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      06-09-2007, 05:25 PM   #4
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Quote:
Originally Posted by Boost_Nation View Post
sounds good. The only thing that keeps me cautious about DP modding is the obvious AFR problems, 02 sensor problems, and CEL issues.

thats why you get a tune for it.... every mod you do requires a tune to get the full use(power) out of the mod.
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      06-09-2007, 05:48 PM   #5
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no point in gutting the downpipes. Would cause a restriction as mentioned in the other thread due to the sudden increase in pipe diameter then back down again.

Not to mention why would you break apart a set of downpipes that cost somewhere north of $1500 each?
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      06-09-2007, 06:11 PM   #6
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Quote:
Originally Posted by itsbrokeagain View Post
no point in gutting the downpipes. Would


Not to mention why would you break apart a set of downpipes that cost somewhere north of $1500 each?


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      06-09-2007, 06:45 PM   #7
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This worked very , very well on B5 S4s.

I came from the audi world and this, with a tune made GOBS of HP.

Piggie Pipes..........
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      06-09-2007, 07:21 PM   #8
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Quote:
Originally Posted by itsbrokeagain View Post
no point in gutting the downpipes. Would cause a restriction as mentioned in the other thread due to the sudden increase in pipe diameter then back down again.

Not to mention why would you break apart a set of downpipes that cost somewhere north of $1500 each?
Do some research first. I came from the audi tuning world. Guttin the cats on DP's would give the car an increase in HP. Do a search on Audiworld.com
and there are endless dyno charts on piggie pipes.
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      06-09-2007, 07:23 PM   #9
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Originally Posted by Boost_Nation View Post
sounds good. The only thing that keeps me cautious about DP modding is the obvious AFR problems, 02 sensor problems, and CEL issues.

From what i am told that A. this car uses wideband B. the o2's are b4 the cats and c. custom maps from vishnu would solve CEL and AFR issues.
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      06-09-2007, 09:01 PM   #10
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Quote:
Originally Posted by 1badE90 View Post
Do some research first. I came from the audi tuning world. Guttin the cats on DP's would give the car an increase in HP. Do a search on Audiworld.com
and there are endless dyno charts on piggie pipes.

Oh I know they would give an increase in power. You are removing a restriction in the pipe. But you would get MORE hp if you just had a smooth flowing, straight pipe.

IMO I still wouldn't do it.
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      06-09-2007, 09:39 PM   #11
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Yes Piggie Pipes worked very well on the older S4.
I bought aftermarket downpipes for my S4, cost me $1600 plus installation. I did not think the added performance to my stock turbos was worth the 1600. I would have probably had done piggie pipes if my timing was better.

For the S4, upgraded turbos required larger downpipes but getting larger downpipes on the stock turbos was not worth it for me. It did add better top end performance but nothing that blew me away.
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      06-10-2007, 10:43 AM   #12
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Quote:
Originally Posted by itsbrokeagain View Post
Oh I know they would give an increase in power. You are removing a restriction in the pipe. But you would get MORE hp if you just had a smooth flowing, straight pipe.

IMO I still wouldn't do it.
It's common sense you'd get more HP from smoother flowing pipes. I wouldn't gut the cats on a new car, but on an older car, sure - if it yielded decent gains .

Downpipe mod might return the largest gain after the ECU mod. The turbos will spool up faster, so you get more power available at lower RPMs and throughout the power band. The backpressure on turbo'd engines can be alliviated with better flowing exhaust, and there really no limit to power returns (unlike a NA engine). It sucks that there is not enough room provided to do a 3" exhaust on these cars.
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      06-10-2007, 11:35 AM   #13
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Quote:
Originally Posted by judec View Post
What?
Be so kind and give some explanation, pics etc.
Piggie Pipes - a common name for downpipes off of an Audi B5 S4 (2000-2002) that have had the contents of the pre-cat removed.

In B5 S4 forums (mainly AudiWorld), the S4 is referred to as a pig because of the weight of the car. The Audi guys have a pretty good sense of humor and came up with the term piggie pipes for stock downpipes that had the first set of cats (pre-cats) gutted. They were cheap to buy ($300 from Vast Performance or FREE if you DIY) compared to the custom pipes that were going for $1,200+. On a chipped car and even upgraded to a K04, the measurable difference the extra $1,000 made was not really that much. Endless posts were created on this topic on Audiworld.

The actual pre-cat on the S4 are easier to get to compared to ones on a 335 so it was a much simpler procedure.... remove pipes, gut pre-cats using your favorite tools and put it back on. All that was left to do was relocate the second O2 sensor to the rear of the main cat. No check engine light and about 15whp & torque with faster turbo spool times.

Is it better to have a smooth pipe, yes. But you can't beat $300 (or $free) for similar power. I think this option will come around once tuner-built downpipes start to hit the market.

Hollowed out B5 S4 downpipe:



The inside of the Cat:



Anyways... just my $.02
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      06-10-2007, 11:54 AM   #14
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Quote:
Originally Posted by zenmaster View Post
It's common sense you'd get more HP from smoother flowing pipes. I wouldn't gut the cats on a new car, but on an older car, sure - if it yielded decent gains .

Downpipe mod might return the largest gain after the ECU mod. The turbos will spool up faster, so you get more power available at lower RPMs and throughout the power band. The backpressure on turbo'd engines can be alliviated with better flowing exhaust, and there really no limit to power returns (unlike a NA engine). It sucks that there is not enough room provided to do a 3" exhaust on these cars.
If 2x2.5" is a restriction for you and you would need 2x3", you are going to have serious power. 600hp? Beyond?
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      06-10-2007, 12:42 PM   #15
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Quote:
Originally Posted by bnj View Post
If 2x2.5" is a restriction for you and you would need 2x3", you are going to have serious power. 600hp? Beyond?
The thing is, on a turbo'd engine, you should always be able to make use of better flow, regardless of peak power you might want to achieve. 3" should make more power than 2.5", and the power band will probably widen. (Of course larger turbos get even better gains from larger diameter pipes.)
This guy is going to offer one of the first turbo kits for the 335i. Only thing I wonder about is why make all this torque when you know you are going to destroy your stock transmission. Even Alpina, with their hugely expensive B3 edition (the price difference in a stock 335i and B3 335i is over $30,000), limited torque output because installing an upgraded transmission was not an option - probably too costly.
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      06-10-2007, 02:32 PM   #16
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Quote:
Originally Posted by PSI Power View Post
Yes Piggie Pipes worked very well on the older S4.
I bought aftermarket downpipes for my S4, cost me $1600 plus installation. I did not think the added performance to my stock turbos was worth the 1600. I would have probably had done piggie pipes if my timing was better.

For the S4, upgraded turbos required larger downpipes but getting larger downpipes on the stock turbos was not worth it for me. It did add better top end performance but nothing that blew me away.
Thats why I suggested gutting the cats. Why pay for DP's twice. Eventually when they come out I will do a larger turbo upgrade. But for the mean time why not?
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      06-10-2007, 06:04 PM   #17
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Cool

Quote:
Originally Posted by My E90 View Post
Piggie Pipes - a common name for downpipes off of an Audi B5 S4 (2000-2002) that have had the contents of the pre-cat removed.

In B5 S4 forums (mainly AudiWorld), the S4 is referred to as a pig because of the weight of the car. The Audi guys have a pretty good sense of humor and came up with the term piggie pipes for stock downpipes that had the first set of cats (pre-cats) gutted. They were cheap to buy ($300 from Vast Performance or FREE if you DIY) compared to the custom pipes that were going for $1,200+. On a chipped car and even upgraded to a K04, the measurable difference the extra $1,000 made was not really that much. Endless posts were created on this topic on Audiworld...
Thank you for explanation, it's clear to me now.

Quote:
Originally Posted by bnj View Post
If 2x2.5" is a restriction for you and you would need 2x3", you are going to have serious power. 600hp? Beyond?
BS. Bigger is better with turbo car, but fitting 3" pipes into the 335i is PITA.

2x2.5" is similar in volume to 1x3.5", while I've seen 600HP cars with 3" JT exhaust (actually including cat, I guess) and it works and makes ferraris cry on the highway, so everyone telling me 2x2.5" isn't enuff should stop smoking that weed and do the math.
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      06-10-2007, 06:19 PM   #18
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Quote:
Originally Posted by judec View Post
2x2.5" is similar in volume to 1x3.5",
But isn't it one pipe for 3 cylinders? I don't know.
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      06-10-2007, 06:21 PM   #19
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yes, it is. double pipe 2.5" are almost equal single pipe 3.5" (actually a lilbit bigger). It was posted as an example, what's important is the final output of 600+HP on a single 3". it was 4 cylinders, 2.3liter connected to that one. Now in this one we have 3 cylinders 1.5 litre... 2.5" is not the best possible, but simply enuff.
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      06-11-2007, 10:20 AM   #20
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Quote:
Originally Posted by judec View Post
BS. Bigger is better with turbo car, but fitting 3" pipes into the 335i is PITA.

2x2.5" is similar in volume to 1x3.5", while I've seen 600HP cars with 3" JT exhaust (actually including cat, I guess) and it works and makes ferraris cry on the highway, so everyone telling me 2x2.5" isn't enuff should stop smoking that weed and do the math.
Perhaps I don't get what you mean with "BS". Does it mean "I agree"? After "BS" you typed the same stuff that I said with slightly different terms.
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      06-11-2007, 11:07 AM   #21
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BS = BullShit. It was meant as a decent comment on "2x2.5" is a restriction". It's volume is actually bigger like a single 3" used widely on lets say 500-600HP applications and until U reach that output I bet my trousers U'll find a whole lot of more real restrictions like a double 2.5" full exhaust (like turbos, IC, injectors, fuelpump...)
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      06-11-2007, 11:42 AM   #22
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Quote:
Originally Posted by judec View Post
BS = BullShit. It was meant as a decent comment on "2x2.5" is a restriction". It's volume is actually bigger like a single 3" used widely on lets say 500-600HP applications and until U reach that output I bet my trousers U'll find a whole lot of more real restrictions like a double 2.5" full exhaust (like turbos, IC, injectors, fuelpump...)
I said that IF HE THINKS 2 x 2.5 IS RESTRICTION, he must be having > 600 horses.
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