safe compression ratio ?

1. olly-bay Newbie Joined: Feb 2010 bedfordshire Posts: 15

   #1 24th February 2010, 12:23

   firstly hello to every one as it's my first post
   
   now to the question of how high can the compression ratio go in a vtr on standard pistons rods ect as i'm guessing that you could take it from 9.60-1 to the 10.80-1 of a vts as i'm guessing again that the internals are the same would 11.5/6 be possible?
2. raunchz Saxperience Addict Joined: Jul 2005 Solihull / Bournemouth Posts: 14233 2015 Lapiz Blue Golf R

   #2 24th February 2010, 12:27

   I think it'll mainly depend on your valve clearance (depending on what camshaft you are running) and whether you are running a standalone Ecu so that the ignition map can be altered to suit this higher compression.
3. Peter_D Saxperience Post Whore Joined: Jun 2004 Helmsdale Posts: 8832 DC5 Teg

   #3 24th February 2010, 12:36

   What are your plans?
4. olly-bay Newbie Joined: Feb 2010 bedfordshire Posts: 15

   #4 24th February 2010, 12:44

   just getting ideas together but maybe standard cam, bigger competion valves, super flow valve guides, Valve Springs, Ported Inlet manifold, exaust system and induction
5. raunchz Saxperience Addict Joined: Jul 2005 Solihull / Bournemouth Posts: 14233 2015 Lapiz Blue Golf R

   #5 24th February 2010, 12:47

   Quote:

   Originally Posted by olly-bay just getting ideas together but maybe standard cam, bigger competion valves, super flow valve guides, Valve Springs, Ported Inlet manifold, exaust system and induction

   Standard camshaft?
   
   How'd you plan on raising the compression? Just skimming a lot off the head?
   
   The only way you'll gain compression whilst being safe with the valves really is by fitting high compression pistons - even then you'll have to make sure the valves don't hit the cylinder walls/cut-outs in the pistons due to their size (depends how big your competition valves are?)
   
   I'm guessing you'll be running a standalone Ecu ?
6. olly-bay Newbie Joined: Feb 2010 bedfordshire Posts: 15

   #6 24th February 2010, 12:57

   maybe a little of head and 0.7 steel gasket 40mm inlet valves 32.5mm Exhuast valves if possible and why a new ecu? like i said just ideas in my head couldn't find any info on high ratio so started asking questions
7. raunchz Saxperience Addict Joined: Jul 2005 Solihull / Bournemouth Posts: 14233 2015 Lapiz Blue Golf R

   #7 24th February 2010, 13:21

   Quote:

   Originally Posted by olly-bay maybe a little of head and 0.7 steel gasket 40mm inlet valves 32.5mm Exhuast valves if possible and why a new ecu? like i said just ideas in my head couldn't find any info on high ratio so started asking questions

   Well you'll need to be able to create a new ignition and fuel map to make the most of these bigger valves, higher compression etc.
   
   There isn't much point in doing all this work on a standard Ecu map as you simply won't be able to take advantage of all the work that's been done, that's if it runs at all tbh.
   
   I'm sure you can get the standard Ecu remapped if you wanted to, but I'd personally look at OMEX, DTA, Emerald, Megasquirt etc.
   
   40mm inlet valves seem big, I'd definitely be cautious about clearances, dry building the engine and measuring it all carefully !!
   
   
   A good company worth talking to is GMC - they are very experienced doing this sort of tuning and have barrels of knowledge!!
   
   He is a member on here - worth checking out his affiliates section and maybe firing across a quick pm ?
8. user_15989 Saxperience Forum Bum Joined: May 2007 Posts: 4857

   #8 24th February 2010, 14:48

   Quote:

   Originally Posted by olly-bay maybe a little of head and 0.7 steel gasket 40mm inlet valves 32.5mm Exhuast valves if possible and why a new ecu? like i said just ideas in my head couldn't find any info on high ratio so started asking questions

   The higher the compression the more likely the engine is to get uncontrolled detonation. The ignition and fuelling become absolutely critical. The standard map simply will not do the job.
   
   There is no real point putting bigger valves in. The can give real clearance issues and give little gain compared to a cam. Generally you would be wanting to look at the cam before considering valves.
9. axsaxoman Saxperience Forum Bum Joined: Jan 2003 Scotland Posts: 3380

   #9 24th February 2010, 16:56

   on std cam ,yes you can ghange gasket to the 0.6mm ,with no clash problems
   std ecu has knock sensor so unlikely to cause any problems ,but the extra power you wold get by fitting larger vlaves would be minimal without cam change ,,ecu ,manifold etc
   32.5 ex valves will not fit on std seats and 40mm inlets --would be very close,but you could machine them down a little 39,5 will fit on inlet seats,remeber to upgrade spings at same time as they are now heavier,and for best comp make sure you use flat faced valves ,not ones with a dish in

   1 user thanked this post: olly-bay
10. olly-bay Newbie Joined: Feb 2010 bedfordshire Posts: 15

    #10 24th February 2010, 17:27

    so are you saying it's could possibly be ok to fit the larger 40mm inlet valves 32.5mm Exhuast valves with new valve seats and raise compression with a .7mm steel gasket and be ok on clearance
    
    if it is then other bits i was thinking of and don't know if there worth while or work would be super flow valve guides, Valve Springs, Ported Inlet manifold, 4-2-1 Manifold, induction kit
    
    if the head was off any else worth doing
11. olly-bay Newbie Joined: Feb 2010 bedfordshire Posts: 15

    #11 24th February 2010, 17:28

    and any idea what the ratio would be and are the other standard internals ok