<VV> Answers on Questions Re: Turbo Mileage

[FrankCB@aol.com]

Hi Norm,
    Sorry I didn't make it clearer in the Corvair Basics Manual.  What you 
need is to provide vacuum advance (similar to every non-turbo Corvair) while 
also having provision for retarding the ignition timing when the engine goes into 
boost (as in the stock turbo 150/180 engine).  This can be accomplished in a 
number of ways.  One is to use a Dale vacuum advance/pressure retard unit (but 
add a means of shutting off the vacuum advance at idle.)  Strictly speaking, 
since the Dale provides the pressure retard, you don't really NEED the 
SafeGuard to accomplish the same thing.  However, the SafeGuard is a vastly more 
sophisticated means of having pressure retard, since it can retard only those 
specific cylinders that are exhibiting knocking/detonation and not ALL the 
cylinders as the Dale does.  The SafeGuard also has provision for a dashboard 
indication of how much retard is being provided so it is ideal for use in setting up 
a water injection system to flow only enough water to just suppress 
detonation.  Since it responds virtually instantly, the SafeGuard can also "fill in the 
gap" until the water can actually start flowing into the engine.
    Another way of having vacuum advance/pressure retard is to replace the 
stock 150/180 pressure retard "pot" with a vacuum advance "pot" from a normally 
aspirated (NA) Corvair.  But you still need to add a retard device that will 
retard the timing when the engine goes into boost.  The SafeGuard is the best 
for this job, although other EKE (electronic knock eliminators) are also 
available which may be less expensive, but, unlike the SafeGuard, operate in an 
analog manner and retard the timing of ALL cylinders when knocking/detonation is 
detected.  This latter setup is what I used many years ago before the SafeGuard 
became available.  The problem of using an NA vacuum advance unit is where to 
connect the vacuum line.  Unfortunately, the stock Corvair YH turbo carbs 
(unlike the Nash and early Corvette YHs) do NOT have a ported vacuum advance hole 
drilled and tapped in the throttle body.  I my case, I replaced my 180 
throttle body with one from a Nash/Corvette and connected the vacuum advance "pot" 
to its ported vacuum advance hole.  An alternative would be to connect the 
vacuum advance line to the intake manifold and add a vacuum solenoid to the line.  
Use a microswitch located in the throttle linkage to open the solenoid valve 
only when the throttle plate moves above idle speed.  This will shut off the 
vacuum advance at idle, but bring it in as soon as the throttle begins opening, 
exactly as happens in the NA Corvairs which do use ported vacuum advance from 
their downdraft Rochesters.
    As far as using a SafeGuard with a Petronix, I think that would be an 
excellent combination.  The Petronix corrects for the wear in the stock 
distributor since it doesn't depend on physical contact between the distributor cam and 
the points.  Therefore, the Petronix will fire a cylinder every 120 
crankshaft degrees while the points in a worn stock distributor will tend to fire each 
cylinder a few degrees early or late due to bushing wear.  You'll notice this 
with a smoother idle, as we did when we installed one on son Jim's purple 
Corsavertible a few years ago at a national convention.  The Petronix II can 
handle a much larger primary current flow so you can use it with lower resistance 
ignition coils, like the Flamethrower 2 that has only 0.6 ohms resistance.  
This comes in handy particularly if you run high boost levels which put a heavy 
load on the ignition system.
    As far as changing the distributor, if you look at the specs for the 
65/66 180 distributor shown in the shop manuals, you'll find that the timing is 
FIXED until 4000 rpm at which point the centrifugal advance STARTS, or until 
boost rises above 2.25 psi at which point the pressure retard begins.  So in 
normal street driving, the stock distributor operates at CONSTANT timing for most 
of the time (thus the big improvement resulting from the addition of vacuum 
advance).  While I have no experience with having done so, I suspect that a 
changeover to a 95 hp distributor would also make some improvement.  Does anyone 
have any actual experience with doing this?  By the way, the 95 hp distributors 
for standard trans and for PG have different centrifugal advance specs, the 
manual trans one is 0 deg. at 700 rpm and peaks out at 28 deg. at 4200 rpm 
while the PG one is 0 deg. at 1700 rpm and peaks out at 20 deg. at 4200 rpm.
    Can anyone else add some more info to this discussion?
    Frank "finally running out of words" Burkhard
    
In a message dated 11/15/04 1:42:26 PM Eastern Standard Time, 
ncwitte@wittelaw.com writes:
In order to get reasonable mileage with a turbo Corvair driven on the
street, you need to include a vacuum advance.  When I did this years ago on
my turbo 180 that I was driving to work every day, the mileage went up from
18 mpg to 22 mpg AND the part throttle acceleration improved considerably.
How else can you "have your cake and eat it too"??  Detail on
how to accomplish this are described in the Turbocharging chapter of the
Corvair Basics Manual.

snip


Frank, I was actually reading p 151 of the Basics Manual today, and I was a
little confused.  I have a whole lot of questions, like:

*    Is there a need to run both the Dale pressure retard/vac advance with a
Safeguard?
*    Do you run a vacuum advance with a Safeguard at all?
*    Would it be desireable to use a Safeguard with a Pertronix?
*    I or II?
*    Could a setup like this benefit from running a 95 hp distributor?  Or is
that necessary?

Thanks,

Norm Witte