# Decat down pipes or not r35



## slim69 (Nov 2, 2014)

Thinking of getting decat down pipes fitted. Has anyone had them done and wished they left the standard ones on. Am now at stage 4. What price should I expect to pay for the middle of the road quality pipes and fitting. Thanks for any input


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## barry P. (May 9, 2010)

slim69 said:


> Thinking of getting decat down pipes fitted. Has anyone had them done and wished they left the standard ones on. Am now at stage 4. What price should I expect to pay for the middle of the road quality pipes and fitting. Thanks for any input


It's not just buying them and fitting, you will also need a remap.


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## Stealth69 (Jan 6, 2005)

Don't buy middle of the road downpipes, they will crack and then you'll have to replace them etc etc and it's not a small job! 

As Barry says you will also need a remap for the work....... There is also a possibility that you'll need to replace a lambda sensor if you break on the way out so is budget for that as well! 

It's a good mod and worth doing, it's just not all that cheap to do!


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## allsop83 (Nov 20, 2014)

I've been wondering about this- not so much a cost issue but what about the extra noise? Does it make the cabin unbearable or is it pretty similar to fitting the Y-Pipe?


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## allsop83 (Nov 20, 2014)

*un resonated Y-pipe


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## ACspeedtech (Aug 25, 2011)

This is always a little quandary for customers,
Upsides... Noise, a little faster spool, about 15hp/15ftlb, flames (if you like that sort of thing)
Downsides... Noise, road legality, poor bang-for-buck after your last upgrade, MOT.

Cost-wise, a good set of decat downpipes plus fitting will work out around £800 all done, but you will need a remap to suit for sure also so add a little to dial it in over your last tune. Also as noted, the O2 sensors can have a tendency to not want to be removed (we keep OEM ones in stock just in case) and require replacement. The studs on the turbos are well known to cause problems on removel, sometimes requiring the motor to be removed to access to drill out... We've a very good success rate though and rarely have issues, I'd recommend installation by a shop used to the job.
Andy


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## Stealth69 (Jan 6, 2005)

ACSpeedtech had my Downpipes out and changed in no time, zero busted studs, zero O2 sensor issues..... the supplied the downpipes and they look as good as new nearly two years on  

Recommend for sure !


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## mindlessoath (Nov 30, 2007)

with decat downpipes it will be much louder depending on the rest of the cat back.

recommend only cast downpipes. ams, titek, rexspeed, cobb, liney all have cast downpipes. ams being the best as both ends are cast and the profile tapers smoothly. best sound vs the rest too.

as mentioned above non cast will surely crack and the really cheap ones will crack much sooner.

also as mentioned a tune will be required. also those bolts have a tendency to break, so maybe order a spare or two handy.


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## ACspeedtech (Aug 25, 2011)

mindlessoath said:


> non cast will surely crack


Hugely disagree, using high grade steel and correctly purge welding will not crack. We have cars running ours with 60k+ miles on and they're as good as new.
The same welding technique and material quality used on custom turbo manifolds running 50+psi of boost for years on end with zero issues.


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## vxrcymru (Sep 29, 2009)

Two O2 sensor were welded into my stock downpipes and had to be replaced at £400 ish... so it worked out a lot more expensive than I anticipated. Also i had emission warnings that took two trips to the tuner to fix. 

But car has been fine since and the sound is amazing...


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## moofz (Nov 30, 2014)

I had Russ Fellows decatted downpipes fitted when i headed to Litchfield for Stage 4 upgrade. Love them! Much better sound, but isn't overly loud to my ears anyway. Had sports cats in the exhaust and just passed my last MOT. I don't really notice the petrol fumes that some people mention either, well you can notice it a little but nothing too bad.
Definite yes from me


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## rob2005 (Apr 26, 2015)

The fumes are nice :chuckle::chuckle:

I had some fitted and the noise for me (as its not a daily) is acceptable but they add drone when cruising, piss the neighbours off from cold start up and you'll need a compliant MOT tester close to you for emissions. 

And i do enjoy the flames when I'm not trying to get 25+mpg out of the old girl.


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## mindlessoath (Nov 30, 2007)

ACspeedtech said:


> Hugely disagree, using high grade steel and correctly purge welding will not crack. We have cars running ours with 60k+ miles on and they're as good as new.
> The same welding technique and material quality used on custom turbo manifolds running 50+psi of boost for years on end with zero issues.


so your one of very few that do this correctly. glad to hear! tho cast still has its advantage's. non cast will be lighter.


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## dtox (Sep 21, 2009)

Do downpipes come with different noises and sounds... I would want something mentally brutal where as others would want something more quiet. 

Don't buy cheap they can crack and the issue is fitting them not actually buying them.

Does it matter which type for the different pops and bangs and flames or is that purely down to the mapping?


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## Stealth69 (Jan 6, 2005)

Do downpipes come with different noises and sounds... I would want something mentally brutal where as others would want something more quiet. - *Not Really, not like resonated pipes etc*

Don't buy cheap they can crack and the issue is fitting them not actually buying them. *Correct, this will just make you unhappy lol*

Does it matter which type for the different pops and bangs and flames or is that purely down to the mapping? *All down to the mapping, it's achieved by retarding ignition *


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## Joni P. (Nov 13, 2006)

Am I OK mapping-wise as I have a COBB Accessport that should have already Stage 1 to 3 maps in it?
For example is a stage1 mapping sufficient to be used with decats?
If not, who could write me new maps within a week? -I have a street racing event coming soon and really need to be there kicking some V8 asses.

I have a custom exhaust now without any cats until the original rear mufflers. I wanted to keep that look and maybe keep the noise levels more comfortable


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## Stealth69 (Jan 6, 2005)

As far as I am aware none of the maps you have installed (1-3) cater for the removal of the DP CATS...... The Stage1 map is usually JUST Y-pipe and map so I wouldn't want to be running decat downpipes as well on that map! 

Andy at ACSpeedtech is a COBB pro tuner, just depends on his availability I guess.


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## terry lloyd (Feb 12, 2014)

the stage 3 map is the only one suitable for downpipes without cats 

cobb map notes 


Hardware Requirements:
Stage 1 Maps:
1.) Intake: Stock, COBB SF Intake (2.75***8221, or COBB BigSF Intake
(3.00***8221
2.) Exhaust: Stock or upgraded cat-back exhaust

Stage 2 Maps:
1.) Intake: Stock, COBB SF Intake (2.75***8221, or COBB BigSF Intake
(3.00***8221
2.) Exhaust:
***61623; Cobb Y-Pipe REQUIRED
***61623; Stock or upgraded cat-back exhaust



Hardware Requirements:
Stage 3 Maps:
1) Intakes: COBB 3.0***8221; BigSF Intake System - REQUIRED
2) Wastegate Actuators: Stock boost control wastegate actuators
ONLY
3) Injectors: COBB ID1000 cc fuel injectors - REQUIRED
4) Fuel pump upgrade: 255 liters per hour or greater - REQUIRED
5) Exhaust:
***9642; COBB Downpipe - RECOMMENDED
Copyright © 2015 COBB Tuning Products LLC. All Rights Reserved | COBB Tuning - Home page 1
***9642; COBB Intermediate pipe (Y-pipe) - REQUIRED
***9642; High flow cat back exhaust - OPTIONAL
6) Intercooler: COBB Hard Pipe Kit - RECOMMENDED


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## Joni P. (Nov 13, 2006)

terry lloyd said:


> Hardware Requirements:
> Stage 3 Maps:
> 1) Intakes: COBB 3.0***8221; BigSF Intake System - REQUIRED
> 2) Wastegate Actuators: Stock boost control wastegate actuators
> ...


Damn.

This car is my daily driver, I wanted to keep it stock, just wanted to remove the restricting elements to free out the full stock potential to use.
Not really keen on changing bigger injectors or fuel pump etc. I have seen where that road leads to


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## Stealth69 (Jan 6, 2005)

you can change the downpipes and not change the Injectors, just need a specific map for it


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## Joni P. (Nov 13, 2006)

Stealth69 said:


> you can change the downpipes and not change the Injectors, just need a specific map for it


I think I will do that, depends of course if someone has the time to make me a custom map and if the custom map costs more than 1000cc injectors and fuel pump, then of course would be wise to use the current stage3 maps that I already have.


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## terry lloyd (Feb 12, 2014)

You dont need fuel pumps - thats just cobb being over safe i am running the stage 3 without pumps and fueling is fine - most only change pumps if running E85


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## Stealth69 (Jan 6, 2005)

Joni P. said:


> I think I will do that, depends of course if someone has the time to make me a custom map and if the custom map costs more than 1000cc injectors and fuel pump, then of course would be wise to use the current stage3 maps that I already have.


Give Andy (ACSpeedtech) a call on 01925 830889...... given injectors will cost around 600 quid and fuel pump 200 odd quid you'll defo be better off with map LOL


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## Joni P. (Nov 13, 2006)

F**k it, I ordered Bosch EV14 flowmatched 1000cc injectors (420eur /set from Finland) and I already have a couple of 485 Walbros on the shelf.

I guess I have to be next looking at some reinforced circlips for the transmission... 
Or do I really need them if I drag race once a year and rest of the driving is just highway; to work and back.


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## terry lloyd (Feb 12, 2014)

you will need 3" intakes - what cobb do you have v2 or v3


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## Stealth69 (Jan 6, 2005)

And not cheap shit intakes or you'll be caught in a world of poop


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## Joni P. (Nov 13, 2006)

Stealth69 said:


> And not cheap shit intakes or you'll be caught in a world of poop


How could even the Chinese not succeed in the intake pipes? Only thing that matters anyway should be the diameter of the part where the MAF sensor is mounted.

With such simple parts I will not even consider any other option than to manufacture parts that fit 100% to my engine, in my car.


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## Stealth69 (Jan 6, 2005)

Easy to get wrong if you don't understand what is happening in the pipe, any idiot can cut and bend a pipe to fit perfectly LOL ...... it's not just the diameter of where the MAF sits that is the issue, it's all to do with the air flow, the placement of the MAF in the pipe and the diameter. 

Some intakes cause a bonky turbulence which causes all sorts of grief for the MAF's so choose wisely chap.


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## mindlessoath (Nov 30, 2007)

Joni P. said:


> How could even the Chinese not succeed in the intake pipes? Only thing that matters anyway should be the diameter of the part where the MAF sensor is mounted.
> 
> With such simple parts I will not even consider any other option than to manufacture parts that fit 100% to my engine, in my car.


listen to stealth. this is not a simple part, very few get it right. I recommend the gotboost intakes as they were designed to eliminate this issues. and they have an option for green filters which are better than those shit k&n intakes everyone thinks are good (but are not).


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## Anders_R35 (Jul 20, 2011)

I have set of GTC down pipes if you're interested?


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## Joni P. (Nov 13, 2006)

Stealth69 said:


> Give Andy (ACSpeedtech) a call on 01925 830889...... given injectors will cost around 600 quid and fuel pump 200 odd quid you'll defo be better off with map LOL





Anders_R35 said:


> I have set of GTC down pipes if you're interested?


No thanks, I already have custom 3" downpipes and Y-pipe.


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## Stealth69 (Jan 6, 2005)

Man I dread to think what the hell is going on with your engine at the moment, bonky combo of mods and maps lol


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## Joni P. (Nov 13, 2006)

Stealth69 said:


> Man I dread to think what the hell is going on with your engine at the moment, bonky combo of mods and maps lol


Nothing. Since the car is on my lift waiting for the bigger injectors and new intake pipes.


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