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[QUOTE="jescombe, post: 337994, member: 28670"]
Ok, I've got my hands on a stock YZ400 head that I'm going to run until I get my valve seats fixed. I've measured the head volume and it's a couple of cc's less than my flowed 426 head.

Using this head will push compression from 12.5:1 to ~13:1 unless I run a looser squish clearance, and I'm getting nervous about staying with (97 RON) pump fuel. It seems UK race fuel is more expensive and lower octane than you get in the US. However, the consistency can only be a good thing, so I'm hoping for some advice on specs..

Atol ([url]http://www.atolfuel.co.uk/[/url]) seem to have the market pretty much cornered, and have two fuels aimed at 4stroke motorcycle engines. The first fuel is the cheaper @ £50/25L vs £70/25L, but the high end of the distillation curve seems very high compared to (for instance) the Phillips fuels that have been discussed here?
 
[B]ATOL ULR[/B] 
 
 Density  Kg/l at 15 C
  0.745
 
 Reid Vapor Pressure  bar at 37,8 C
  670
 
 Research Octane Number  
  99.0
 
 Motor Octane Number  
  88.0
 
 Distillation (c)  
  30%  66
  50%  100
  90%  170
  FBP  195 
 
 Oxygen %  % Mass
  1.3%
 
 Benzene %  % Vol
  0.60
 
 Lead Content  g/litre
  <0.005

[B]ELF MOTO 4T[/B] 
 
 Density  Kg/l at 15 C
  0.766
 
 Reid Vapour Pressure  bar at 37,8 C
  0.502
 
 Research Octane Number  
  101.5
 
 Motor Octane Number  
  88
 
 Distillation (c)  
  30%  70
  50%  82
  90%  119
  FBP  139
 
 Oxygen %  % Mass
  2.68
 
 Benzene %  % Vol
  0.1
 
 Lead Content  g/litre
  <0.005

Any pointers before I rush out and buy the wrong one would be gratefully received..  :eek:
[/QUOTE]

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