Turbo headgasket, why is bigger better?

1. manc Established Member Joined: Dec 2004 Derby Posts: 1945 Pug 207

   #1 5th July 2009, 15:53

   Hi,
   
   Had a quick search round and havent really hit upon a clear cut reason to why a bigger headgasket is required when you turbo a Saxo, the only reason I think you would want a bigger headgasket on a turbo setup is to have/allow more air in the combusion chamber? can someone enlighten me?
   
   Thanks
2. AlexBp West Midlands Joined: Dec 2007 West mids Posts: 23149 Supra,civic GL

   #2 5th July 2009, 15:55

   it lowers the compression ratio
   
   which for boost is benefitial
3. VTRelite Saxperience Forum Bum Joined: Dec 2008 Gloucester Posts: 3000 Citroen Saxo VTR Renault 5

   #3 5th July 2009, 15:58

   as running boost you need a lower compressio ratio as compared to n/a
   
   normal compression ratio is roughly 10:1 wheres turbo can vary from 8-9:1
4. manc Established Member Joined: Dec 2004 Derby Posts: 1945 Pug 207

   #4 5th July 2009, 16:08

   I see, forced induction without a bigger headgasket push's the internal compression ratio as it comes on boost, which you would expect, this increase in compression increases the odds of internal damage? lowering the compression allows the engine to capture more air and put less compression on internal components thus decreasing the odds of internal damage?
   
   Is the above correct in la man terms?
   
   Thanks.
5. VTRelite Saxperience Forum Bum Joined: Dec 2008 Gloucester Posts: 3000 Citroen Saxo VTR Renault 5

   #5 5th July 2009, 17:42

   pretty much
6. LeeM Saxperience Post Whore Joined: Feb 2008 Liverpool Posts: 7393 Black Corsa C SRi

   #6 5th July 2009, 20:40

   more air means more compression, if you compress air and fule enough it can explode without the need for a spark. within an engine this is bad, so the thicker gasket lowers compresion and reduced the risk of this
7. user_15989 Saxperience Forum Bum Joined: May 2007 Posts: 4857

   #7 5th July 2009, 21:16

   In a petrol engine the fuel is under a controlled burn.
   
   However your adding fuel and air in to a very hot engine under pressure. You get to a point what the fuel air mix sill simply explode uncontrollably.
   
   Lowering the static compression significantly reduces the chance of the burning fuel air mix from getting out of control.
   
   A few other options to provide this control is to increase cooling and/or reducing the oxygen to fuel ratio and/or using less volatile fuel.
8. williamsvts Saxperience Post Whore Joined: Feb 2006 northumberland Posts: 7693 pulsar gtir, mk4 astra sxi

   #8 5th July 2009, 21:17

   you would be better off with forge pistons or machining a dish in your standard pistons imo,
9. blackie_2k5 Saxperience Hardcore! Joined: Oct 2008 Birtley Posts: 22253 VTR Turbo, 106 xsi track slag, Transit recovery, B

   #9 5th July 2009, 21:47

   machining pistons is bad idea for a turbo imo, works but stock pistons on boost arent great anyway, to then weaken them seems silly to me, just asking for trouble
10. VTRelite Saxperience Forum Bum Joined: Dec 2008 Gloucester Posts: 3000 Citroen Saxo VTR Renault 5

    #10 5th July 2009, 23:21

    spontaneous combustion on petrol is very unlikely diesel yes but not petrol
11. liam-o Established Member Joined: Apr 2009 Posts: 1346

    #11 5th July 2009, 23:44

    Quote:

    Originally Posted by VTRelite spontaneous combustion on petrol is very unlikely diesel yes but not petrol

    i like how you agree that it is likely with diesel, when in fact it will definitely happen with diesel as this is how the engine works (as you cant ignite diesel)
12. user_15989 Saxperience Forum Bum Joined: May 2007 Posts: 4857

    #12 6th July 2009, 17:00

    Quote:

    Originally Posted by liam-o i like how you agree that it is likely with diesel, when in fact it will definitely happen with diesel as this is how the engine works (as you cant ignite diesel)

    true
13. sliderz Frequent Poster Joined: Jun 2007 warrington Posts: 722 saxo vts turbo

    #13 7th July 2009, 07:57

    ok simple answer pinking = to hot = spark plug dont fire chamber heat dose = engine piston through side of block
14. Mike_08 Established Member Joined: Oct 2006 Birmingham Posts: 2401 Subaru Impreza WRX

    #14 7th July 2009, 08:46

    lol as said