V<VV> Milled head tech tip (per CORSA Tech Guide)

[BobHelt at aol.com]

Somebody below mentioned my name. So I'd better comment.
 
First, the article referenced was specific in detail that one shouldn't  just 
mill the gasket step, and step-cut the pistons and GO!   It told  the readers 
to set the CR to a desired value first. That CR is critical. You  MUST relate 
the CR to the fuel octane you desire to use.
 
Next, if you will take a look at the article, you will see a chart (Figure  
2) on page 5. This chart clearly shows that for a quench gap of 0.035 in., a CR 
 of about 9:1 will support REGULAR gas.   (PS, Corvair engines actually  had 
lower CRs than advertised.)  Higher CRs need higher fuel octane. So if  you 
were to make the modifications mentioned and wound up with a CR of, say,  10:1, 
you are most likely going to need premium fuel.
 
Regards to all,
Bob Helt
 
 
In a message dated 8/31/2006 5:11:36 AM US Mountain Standard Time,  
dkdewald at pasty.net writes:

A point  of reference; the Tech Guide article "Running on Regular" was 
written by  Bob Helt in either 1980 or 1981.  If you remember those days, 
leaded  gasoline was still commonly available as 89 PON and was referred to 
as  "regular gas."  "Unleaded gas" was available as it still is today at 87  
PON and most places had "premium unleaded" at 91-92 PON.

I believe  that the basic science of the article is sound, it is just that 
technology  and terminology has changed in the past 25 years.  Based on my  
experience, I think that the modifications are good for about 2-4 points  of 
octane tolerance depending on the engine--140's seem to respond better  than 
110's. In most cases it is about enough to use mid-grade unleaded 89  PON 
instead of 92 PON premium in a 140, and permit a 110 to operate on any  
91-92 PON fuel instead of only the best quality 93 PON  stuff.