hi compressions

[Todd King]

  <<<   From: Todd Knighton <knighton at net-quest.com>
  Date: Thu, 05 Sep 1996 13:25:09 +0000
  Subject: Re: hi compressions: wasDIY_EFI Digest V1 #258
  John Faubion wrote:
  > Actually the big reason for multivalve chambers is more area is exposed
  > around the valve to flow fuel. Two small valves have much more flow
  > capacity than 1 large valve but is more expensive that manufacture.
  That's also what Yamaha though, they went to 5 valves to get even more
  flow.  They did pick up flow, but on the F1 motors the 4 valve engines
  made more power still.
  Point is.  It's not all flow, but combustion chamber shape and flame
  propogation as well.   >>>
  
  Ahh, Yamaha's 5 valve with the lens-shaped comb. chamber.  The 3 smaller
  valves maximize the use of the available chamber area plus expose much 
  more total opening (perimeter) quicker than two (or one) larger valves,
  kind of like getting a free increase in cam ramp steepness. As Todd said, 
  people were puzzled that the engine was down on power compared to the 4 
  valve; one symptom I heard about was that it liked a surprising amount 
  of ignition advance, indicating a slow burn, although the chamber was
  "engineered" for a fast burn. A benefit of the fast burn chambers is the
  ability to increase compression ratio ("outrun the fuse", as someone had
  recently posted) so the street version was set up for around 11:1 CR. I
  wonder if Yamaha had enough of a squish area in their chamber? All that
  valve stuffing may have cut down on the available squish area... Wish
  I had a job like that, designing chambers, playin' on the dyno, etc. 
  Gee Todd K., need any help over there? :-)
  
  Todd  Todd_King at ccm.co.intel.com