<VV> Corvair a City Car

[James Davis]

It is not that hard to build a Corvair highway cruiser.  A 3.27 rear 
gear with 195/75-14 tires gives 2,585 rpm at 60 or 3,015 rpm at 70 
mph.  To get the car rolling use a 64-65 FC 4-sp with the 3.65 low 
gear.  This gives about the same total 1st gear reduction as the 
64-65 car transmission with a 3.55 rear gear and 7.00 x 13 tires. 
This combo with a 140 using a 304 cam straight up and a  9.2:1 cr 
with modified squish combustion chamber will yield 30 m/g at 60mph 
and 26 m/g at 70 mph on 91/93 octane.  (My Corsa has been that way 
since 1986).
Many of you know of my Rampside.  It regularly gets 22 mpg at 70 mph 
with the A/C on.  It is a 140 with modified squish heads (9.7:1 cr); 
using a Ray Sedman flat cam.  With a 3.55 rear gear turning 27.4" dia 
tires, it turns 3,050 mph at 70 mph.  With a 4.26:1 first gear, 
getting rolling with a 2,000 tow and 1,000 in the bed is not a problem.

Changing an engine from a cr of 9:1 to 8:1 with no other changes will 
drop the power by  5% and the fuel mileage by 7% on the 
average.  Using a thicker head gasket on a 140 or 110 will decrease 
the squish dramatically; enough to actually increasing the octane 
requirements.
Jim Davis


At 07:37 PM 5/7/2006, P.H. Raker wrote:
>Hello, All,
>      I agree completely with Padgett's analysis of the matter.  So,
>what is the solution for those who wish to use 'Vairs as long distance
>cruisers?  Two possibilities come to mind.
>      Alternative final drive gears are available.  If 3.55 gears give
>3000rpm at 60mph, then 3.08 gears should give 2603rpm (all other things
>being equal).  I believe I have read that 3.08 final drive gears are
>readily available to fit in Corvair differentials.  Of course, larger
>rear tires would also help to lower curise rpm, but would also hurt
>acceleration performance.
>      The aftermarket 5-speed transmission with 0.73 (overdrive) top
>gear would give 2190rpm with 3.55 gears and 1900rpm with 3.08 gears.
>(With the 308 gears and 0.73 overdrive that works out to 2375rpm @
>75mph, right at peak torque.)  Now THAT should give some fuel economy
>more comparable to the so-called "modern" vehicles.
>      Of course, your mileage may vary.
>           Phil Raker
>
> > Point is that the curves say to me that GM really wanted the
> > engine to run in the 2400-2800 rpm range (torque peak is at
> > 2400) and not 3600 and since few speed limits required
> > anything above that, the mix was right. Today (at least in
> > the souf) things are different.
> >
> > So my contention is that a stock Corvair is really designed for
> > speeds under 60 mph and going beyond that is going to have a
> > considerable cost.
> > DID NOT say it could not handle 70 well (mine keeps trying to
> > creep higher), just that it is outside of the normal design
> > parameters and will have a cost.
> >
> > Padgett