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Lambley



Member Since: 20 Apr 2013
Location: Mid Devon
Posts: 1435

United Kingdom 2006 Defender 90 Td5 HT Java Black
Exhaust / catalyst / fuel economy
Anyone know if a catalytic converter makes a difference to fuel economy?

I swapped my decat downpipe for the original yesterday, just to stay on the right side of plod. I've done a few miles in it and it's slightly quieter but doesn't pick up as quick in low revs. It's had a tune and gives good fuel consumption (I got 36.4mpg average on a recent run to Cornwall) but after refitting the cat I'm convinced it's using more fuel - could this be true or is it my imagination? I can live with the loss in low rev power but not at the cost of using extra fuel.
Post #360623 27th Sep 2014 8:52pm
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munch90



Member Since: 26 Oct 2013
Location: guildford
Posts: 3558

England 
are you pushing it a bit harder after changing pipe back , testing so to speak , might be worth leaving it a while before worrying about fuel use to settle back in to normall driving style
Post #360630 27th Sep 2014 9:14pm
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Caterham



Member Since: 06 Nov 2008
Location: Birmingham
Posts: 6260

England 2011 Defender 110 Puma 2.4 XS CSW Stornoway Grey
I know nowt but would be surprised if it wasn’t using more.....

Hence people buy free flow exhausts to get the engine running more efficiently.
Post #360633 27th Sep 2014 9:20pm
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Lambley



Member Since: 20 Apr 2013
Location: Mid Devon
Posts: 1435

United Kingdom 2006 Defender 90 Td5 HT Java Black
Maybe your right, I have probably been testing it a bit, I'll give it a couple of tanks of fuel and work out what the difference is
Post #360714 28th Sep 2014 9:52am
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bga86



Member Since: 17 Jan 2014
Location: Here and there
Posts: 205

2015 Defender 90 Puma 2.2 HT Fuji White
Simple answer lambley is yes it will use more fuel. With the cat in place the exhaust flow is restricted (all be it slightly) so the engine cannot breath as easily. Did this experiment with my last td5. Tested over 3 tank fills with the cat on and 3 with it off I would get between 30 and 35 miles more from a full tank with it removed Thumbs Up
Post #360759 28th Sep 2014 12:42pm
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K9F



Member Since: 12 Nov 2009
Location: Bournemouth
Posts: 9610

United Kingdom 2008 Defender 90 Puma 2.4 XS CSW Stornoway Grey
Turbo will not spool up as quick so you will naturally give it 'more gas' to compensate. Engine running temperatures will also be up a few degrees making the burn less efficient. If you go through life with your head in the sand....all people will see is an ar5e!!

Treat every day as if it is your last....one day you will be right!!
Post #360762 28th Sep 2014 12:51pm
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Lambley



Member Since: 20 Apr 2013
Location: Mid Devon
Posts: 1435

United Kingdom 2006 Defender 90 Td5 HT Java Black
Thanks bga86, that confirms it then. I'm Going to see Gary at Alive on Thursday to make sure everything is running perfectly so I'm not sure wether to change it back again now.
What do you recon is more restrictive- a centre silencer or cat?
Post #360764 28th Sep 2014 12:52pm
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K9F



Member Since: 12 Nov 2009
Location: Bournemouth
Posts: 9610

United Kingdom 2008 Defender 90 Puma 2.4 XS CSW Stornoway Grey
My standard offset centrebox was changed for a straight through. Rearbox was removed. A cat is more restrictive in nature due to the internal 'Cell Per Square Inch' CPSI structure. Think it's 400 on a standard diesel cat.

Thumbs Up If you go through life with your head in the sand....all people will see is an ar5e!!

Treat every day as if it is your last....one day you will be right!!
Post #360766 28th Sep 2014 1:01pm
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munch90



Member Since: 26 Oct 2013
Location: guildford
Posts: 3558

England 
K9F wrote:
Turbo will not spool up as quick so you will naturally give it 'more gas' to compensate. Engine running temperatures will also be up a few degrees making the burn less efficient.


I agree with the " more gas to compensate bit

but with needing a cyl firing temperature of roughly 550 degrees c I cant see a few degrees running temperature really making much differance
Post #360768 28th Sep 2014 1:17pm
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Lambley



Member Since: 20 Apr 2013
Location: Mid Devon
Posts: 1435

United Kingdom 2006 Defender 90 Td5 HT Java Black
Cheers all.
So, to keep the noise down but power up - I'd be better off with a std centre silencer and rear section but decat front pipe?
I've currently got a cherry bomb in the middle
Post #360769 28th Sep 2014 1:23pm
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bga86



Member Since: 17 Jan 2014
Location: Here and there
Posts: 205

2015 Defender 90 Puma 2.2 HT Fuji White
Correct Thumbs Up
Post #360776 28th Sep 2014 2:06pm
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pannawonica



Member Since: 21 Nov 2010
Location: Clackline Western Australia
Posts: 568

Australia 
I have just removed the centre box and cat, not a lot more noise hard to pick really. As I did the mods over a period of time I have to say I was surprised at the gains from removing the centre box. A big plus too reducing the amount of heat coming up the floor. Very Happy I suppose the heat issue is not such a problem for most over there, however when its over 50c well worth it! More to the point is I'm getting about 50k's extra from the tank. Very Happy
Post #361206 30th Sep 2014 9:34am
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Naks



Member Since: 27 Jan 2009
Location: Stellenbosch, ZA
Posts: 2579

South Africa 2010 Defender 90 Puma 2.4 SW Alpine White
Hmm, must also remove the centre box as summer is kicking in over here.

It's going to be a hot one this year, expecting 45C+ Thumbs Up --
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Post #361210 30th Sep 2014 9:56am
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Lambley



Member Since: 20 Apr 2013
Location: Mid Devon
Posts: 1435

United Kingdom 2006 Defender 90 Td5 HT Java Black
Thanks again for the replies, I've decided to go back to the original set up I had, decat front, cherry bomb centre and std rear. I can't see the sense in keeping the cat on the front at the cost of 3/4 mpg, seems to go against the 'saving the planet' argument somehow.

As for heat in the system - what about using wrap? I used to do it on my race bikes, it stops the heat coming through the exhaust and keeps it internally, it's probably a load of tosh but on a race bike it was meant to add about 2 bhp. I was going to do it and see if it helps reduce the noise any, if it was wrapped from the from somewhere near the top of the downpipe to the cherry bomb then surely it'd help reduce that 'tinny' rasp and turbo whistle? Just a thought.
Post #361211 30th Sep 2014 10:06am
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pannawonica



Member Since: 21 Nov 2010
Location: Clackline Western Australia
Posts: 568

Australia 
[quote="Naks"]Hmm, must also remove the centre box as summer is kicking in over here.

It's going to be a hot one this year, expecting 45C+ Thumbs Up[/quote]

makes a big difference to the heat coming up from the floor. Thumbs Up
Post #361357 1st Oct 2014 2:39am
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