Decat = alot less mpg ?

1. classicvin Regular Poster Joined: Aug 2009 Yeovil, somerset, uk Posts: 263 saxo 1.1 expose vtr kit

   #1 28th May 2010, 22:57

   Hello,
   
   I am currently looking into an exhaust system for my 1.1 saxo (single point injection) The section i am looking at will go from the back of the downpipe on the flexibit, right back to the back of the silencer.
   
   I am wanting to get this due to my current exhaust system being ridiculously loud @ motorway speed ( it resonates in your ears ! ).
   And i guess this is due to the fact that i only have the under car cat + a rear backbox (sporty one ofc )
   
   Now i was looking into getting a silencer for the center section. But i dont think there will be alot of room as the cat will be in the way aswell. So the system i am looking at doesnt have a cat, but hopefully that will allow room for me to put a silencer in to quiet it down abit ! I like the noise when it doesnt resonate ! So im thinking this centre silencer will give it a nice noise but not resonate !
   
   
   this is what i'm looking at : http://cgi.ebay.co.uk/CITROEN-SAXO-1...item1e5aeaeba6
   
   and obviously weld a centre silencer into it. (i guess you could say like the ss race section)
   
   But my question is, will having no cat dramatically effect my fuel consumption ?
   
   Thanks alot
2. Oc2 Frequent Poster Joined: Apr 2010 Nottm. Posts: 924 Focus ST2 ASBO

   #2 28th May 2010, 23:03

   Shouldnt do... might be wrong, but the cat is just to clean the emissions going out the back, so it passes goverment enviromental stoof!
   
   Certainly makes the exhaust gases easier to pass without a cat aswell
3. classicvin Regular Poster Joined: Aug 2009 Yeovil, somerset, uk Posts: 263 saxo 1.1 expose vtr kit

   #3 28th May 2010, 23:15

   Yeah well i was thinking that i might lower the back pressure through the exhaust, increasing the head flow rate when both valves are open, so its wasting the fuel / air mixture as such. If you get me
4. Oc2 Frequent Poster Joined: Apr 2010 Nottm. Posts: 924 Focus ST2 ASBO

   #4 28th May 2010, 23:29

   Touché
   
   Would of thought since the restriction so to speak has been removed the engine doesnt have to work as hard to push the exhaust gases out
   
   im probably wrong mind lol sorry
5. KamRacing Saxperience Addict Joined: Nov 2006 A farm shed in Aylesbury Posts: 14916 Corolla AE86 Peugeot 205 B18C (in bits)

   #5 28th May 2010, 23:29

   The cat is a restriction especially as its probably falling apart inside. Binning it is more likely to help mpg.
6. classicvin Regular Poster Joined: Aug 2009 Yeovil, somerset, uk Posts: 263 saxo 1.1 expose vtr kit

   #6 28th May 2010, 23:34

   yeah but i was thinking, when you have valve overlap (if the saxo 1.1 even has valve overlap!) When both valves are open, letting the new air/fuel mixture in, and also the old exhaust gases out, Obviously there is going to be more of a draft on the exhaust side(due to the less back pressure), so more of the new air/fuel mixture will go out of the exhaust port. And this de-crease of mixture will decrease performance no?
   
   Sorry its probably me just being "picky" i'm a vehicle technician for vw and i just think about these things
7. user_26394 Saxperience Addict Joined: Aug 2008 Bedworth Posts: 10221 106 gti

   #7 28th May 2010, 23:53

   i found my mpg went down after having a decat
8. classicvin Regular Poster Joined: Aug 2009 Yeovil, somerset, uk Posts: 263 saxo 1.1 expose vtr kit

   #8 29th May 2010, 00:10

   how much were you getting with a cat? and how much are you getting without ?
   
   Cheers
9. user_26394 Saxperience Addict Joined: Aug 2008 Bedworth Posts: 10221 106 gti

   #9 29th May 2010, 00:12

   with my gti i'm losing about 50 miles a tank i think it was
10. woodyemma Infrequent Poster Joined: Jul 2009 Salisbury Posts: 115 Subaru impreza sport, saxo furio

    #10 29th May 2010, 09:54

    Taking a cat off should increase mpg
11. woodyemma Infrequent Poster Joined: Jul 2009 Salisbury Posts: 115 Subaru impreza sport, saxo furio

    #11 29th May 2010, 09:55

    It releases back pressure thus less power is stolen pushing the gases out
12. woodyemma Infrequent Poster Joined: Jul 2009 Salisbury Posts: 115 Subaru impreza sport, saxo furio

    #12 29th May 2010, 09:58

    An anyone confirm that you'll lose mpg or is this matey tripping
13. woodyemma Infrequent Poster Joined: Jul 2009 Salisbury Posts: 115 Subaru impreza sport, saxo furio

    #13 29th May 2010, 09:59

    Bickerton that is
14. raunchz Saxperience Addict Joined: Jul 2005 Solihull / Bournemouth Posts: 14233 2015 Lapiz Blue Golf R

    #14 29th May 2010, 15:57

    It's a hard one to say whether it reduces mpg tbh it'll be upto the individual I'd say - as to how they drive.
    
    I personally didn't see a change as to my mpg
15. user_38615 Established Member Joined: Oct 2009 Birmingham Posts: 2073 Current - 56 1.9 astra Sri Owned - 54 C2 GT. Ow

    #15 29th May 2010, 16:42

    when i had mine decated not so long ago ive acually noticed i get like 2-3 mpg more than when it was on,
    
    i also bunged half a bottle of redex into a fivers petrol haha which was supposed to be a full tank but thought ill put it to a fiver see what happens that also seemed to help it out alot haha after my car stopped stalling every time i stopped for lights car runs a treat now dont have no crapy idle or nothing aint really related but thought would drop it in
16. classicvin Regular Poster Joined: Aug 2009 Yeovil, somerset, uk Posts: 263 saxo 1.1 expose vtr kit

    #16 29th May 2010, 17:18

    cheers for the help so far seems promissing