<VV> low vacuum

[BobHelt at aol.com]

Please see below for some comments.
Regards, Bob Helt
 
In a message dated 9/2/2006 6:32:52 PM US Mountain Standard Time,  
iscdirector at yahoo.com writes:

All the  corvairs I own as well as all the ones I have checked belonging to 
other  people have readings about 12 to 14 Hg. in neutral gets worse in drive 8 
to 10  Hg. Also the readings are very erratic the needle on my handheld gage 
vibrates  and jumps. 
That should be telling you something....hi perf Corvairs have this kind of  
vacuum at idle speeds. Probably the same for the base engines too.
 
 

All the  engines I have checked have aftermarket lifters, some with many 
miles, some  fresh. This indicates valves not closing. 
 
No. Not true.What's happening is that the high degree of valve overlap  built 
into the cams makes the idle vacuum erratic as you have found out. The  
vacuum builds rapidly at speeds over idle and then drops under engine  loading.
 

I have  tried replacing valve springs and it no effect. The only thing that 
seems to  raise the vacuum any is to run rockers at zero lash then it gets much 
better.  This problem is bad with powerglide as the modulator quits working 
when vacuum  drops below 15 Hg. 
Never measured it, but that just doesn't sound right. The modulator  responds 
to vacuums around 3-6 in-hg as I remember.
 
 

Any one  else addressed this problem it seems to a common one as others in 
our club say  they are having the same trouble. 
 
Not sure just what the problem is from what you stated.
 I personally don't see a problem.
Regards,
Bbob Helt