Alternatives Re: <VV> Rebulding Retard?

[FrankCB at aol.com]

Lou,
    I would strongly advise that you NOT try drilling  into the carb.   
Unfortunately, unlike all the Corvair Rochester  carbs, the stock turbo Corvair 
Carter YH throttle body has NO connection for a  ported vacuum advance.  You'd 
have to find a YH throttle body that came off  an early 6 cyl Corvette, or a 
Nash or some other early car that used ported  vacuum advance in a YH.  (That's 
what I have on my 180) Instead, you can  switch the stock Corvair turbo retard 
unit for a Dale unit that has both vacuum  advance AND pressure retard.  This 
connects to the same intake manifold  source that the stock turbo retard uses 
so its just a simple matter of using the  same rubber hose that already 
exists.  
    However, this setup now provides manifold vacuum to  the advance at idle 
conditions, where you don't really want it since  it tends to cause "bogging" 
as the car is accelerated above idle  speed.  Carb ported vacuum advances have 
NO vacuum advance at idle because  the slotted carb vacuum port is located on 
the UPSTREAM atmospheric  pressure side of the throttle plate.  As the 
throttle plate opens (to go  above idle speed) the throttle plate MOVES to the other 
side of the vacuum  port thereby putting it under DOWNSTREAM conditions of 
intake manifold  vacuum and sending vacuum to the vacuum advance unit.  All the  
non-turbo Corvair carbs work this way.  If you use the Dale unit, to avoid  
vacuum advance at idle you can install a 12 volt solenoid valve in the vacuum  
line to the intake manifold and use a microswitch in the throttle linkage to  
keep the solenoid valve closed at idle (no vacuum to the advance) until the  
throttle is opened.  I believe Ray Sedman offers  a solenoid/microswitch kit to 
do exactly what I describe.
    There are other ways to accomplish having  vacuum advance ABOVE idle 
speed and pressure retard once the turbo  boost comes up.  On my 180 I use a 
Vette/Nash YH throttle body that  has the vacuum advance port.  This gives me the 
vacuum advance above idle,  but does NOT provide detonation control when the 
boost comes up.  For that  I use an electronic knock sensor that senses 
knock/detonation  and electronically retards the ignition.  My EKE unit retards ALL 
the  spark timing when knock is sensed.  Ray Sedman has a more sophisticated  
unit (the SafeGuard) that selectively retards only  the cylinder(s) originating 
the knock and can even display the AMOUNT  of retard to the driver.
    More information on this subject can be found  in my Turbocharging 
chapter of the Corvair Basics Manual available from  CORSA.
    I'd estimate that the Dale unit with added  solenoid/microswitch kit 
could be installed in one day assuming you've laid out  the location of the parts 
and wiring ahead of time and secured all the tools and  hardware that will be 
needed.
    Regards,
    Frank "likes boost" Burkhard  
 
 
In a message dated 2/20/2007 7:05:54 PM Eastern Standard Time,  
louis at suffolknet.org writes:

How  difficult is it to do this?  I've always thought about doing it - but  I
get nervous when I think I read something about drilling into the  carb....

Is this a one day  project?

Regards,

Lou




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