Too good to let go by - Miller Cycle

[Seth]

On Mon, 11 Aug 1997, Robert Harris wrote:

> Most Miller Cycle engines ASSUME adequate power is available and
> there fore trade POWER for FUEL Efficiency.  The specific mechanism
> is that raising the compression ratio raise's the efficiency of an engine
> quite startlingly.  Research suggests that POWER and EFFICIENCY
> increase  with compression ratio up to about 17 to one.  The problem
> is detonation.  A Miller Cycle conversion made by Crane or Crower 
> after the 79 Crude Control Crisis ran a small block Chevy at a 15 to
> one compression on unleaded low octane pump gas.  They had to 
> stroke the crap out of it to both get the compression and regain the
> power.   By limiting intake charge, you can safely compress the 
> reduced charge back to the original low compression chamber pressure
> of say 9:1  and have an EXPANSION ratio of 15 or 16 to one and all
> the bennies of really good forced exhaust extraction.
> 
> Running a higher octane fuel reduces the advantages of extreme compression
> and by the time you are running methane - there is no advantage.
> 
> Increasing the charge density by mechanical means simply means the 
> Miller Cycle becomes detonation limited at ridiculously LOW manifold 
> pressures.  Just drop the compression and put a power cam in.
> 
> One thing tho - every one of you has watched Miller Cycle engines in 
> triple digit competion - pret near every weekend.  NASCAR. Yup.  The
> restrictor plate effectively turns the engine into a Miller Cycle at RPM
> and thats why they are limited to 14 to one.  Some smart ass's figured
> out that with restricted intake, you could go to 18 to one or more and
> get back most of the lost power without detonation.  Cam's aren't the
> only way to limit the charge to less than 100% VE
> 
> "When some one gets something for nothing -
>              some one else gets nothing for something "
> 
> If the first ingredient ain't Habanero, then the rest don't matter.
> Robert Harris <bob at bobthecomputerguy.com>
> 
> 

Mr. Harris,

That's quite an intriguing insight into the NASCAR CR limit.  With a lot 
of overlap, you get miller cycle at low RPM, then as the VE climbs with 
RPM, the intake chokes.  An interesting idea.

Seth