<VV> Restoring a turbo (long message)

[Jim Simpson]

I don't know what your budget is, what your goal might be, nor do I know 
what your ultimate expectations for the car.  But I've only owned one 
Corvair -- a '66 Corsa turbo.  I've owned the car since 1968 (!), having 
purchased it off a Chrysler dealer's used car lot.  It was about 15 months 
old and looked immaculate.  (As it turned out, it wasn't -- the previous 
owner had a dog and there was plenty of evidence of that under the back 
seat.  (Just hair!))  But it ran well and by contemporary standards was 
quick, handled well, and had decent brakes (as long as you weren't hauling 
it down from much more than 75 or so -- they would fade otherwise...)

I drove this car for about 10 years, autocrossed it a bit, drove it across 
the country three times, and learned a fair bit about the idiosyncrasies of 
the turbo engine.  There were some minor problems over they years -- 
snapped clutch cables twice, replaced the clutch once, stripped spark plug 
threads once, burned the exhaust valves (though that may have been from the 
previous owner), and ran through several sets of tires.  I had one major 
problem -- it ate valve seat in 1973 or 74.  The local Chevy dealer put new 
heads on it -- for a price -- since I didn't have either the time or place 
to do it.  (I was active duty in the Navy at the time.)

The car was "retired" in the mid-70's and in '79 we started what must be 
the world's longest running restoration.  (We'd just bought a house and had 
a garage in which to do the work.)  That restoration ran until 1997, 
completing the car just in time to drive it to the Lake Placid CORSA 
National Convention.  We had the good fortune of winning a gold medal and 
being promoted to Senior Division on that, it's first, outing.

Now what do I think about turbo Corvairs?  I like them, obviously.  But 
they aren't perfect by any means.  They run just like a 95/110 at lower 
speeds and part throttle.  Even when you stomp on them, it takes a bit for 
the exhaust system to heat up and the turbo to spool up.  But more 
importantly, you have to be in the right rpm range -- above 2500 for a 
stock turbo to have any measurable boost.  So if you are running up through 
the gears, you normally run out of first before you have time for boost to 
build -- maybe slightly into the positive pressure range.  Second, full 
throttle, you'll see some.  Third and fourth will have full boost from 3000 
to 5000 rpm after which it drops off pretty rapidly.  But 5000 rpm in 
fourth is ~100 mph with stock gears and tires, so that shouldn't be a major 
issue.

Overall, the "turbo lag" is mostly due to the peaky nature of the turbo 
Corvair's power curve.  All four late engines have similar torque (and hp) 
curves from idle up to 2500-3000 rpm.  The higher compression engines (110 
and 140) have a slight advantage but not enough that would show on a 
graph.  Where the three non-turbo's differ is in their ability to 
breath.  This shows up in the torque curves -- they're more important than 
hp curves since that's really what you feel in the seat of your pants.  If 
you look at the torque curves, you'll see the 95 hp engine torque dropping 
off first at about 3600 rpm.  The 110 is next reaching about 3000 rpm with 
a bit more torque, then the 140 at about 4200 rpm.  Interestingly, they all 
produce about the same peak torque -- ~160 lb-ft gross.  (Note that 
horsepower = torque x rpm/5252.  So the higher the rpm at peak torque, the 
higher the horsepower even though the actual peak torque is the same.)

The turbo is a different animal.  Up to the point where the turbo starts 
spooling up, the torque (and hp) curves pretty much overlay the other three 
engines.  But once the turbo starts spooling up at ~2500 rpm, the torque 
curve soars, peaking at 3400 rpm with 264 lb-ft gross torque.  That's 100+ 
lb-ft more torque than the naturally aspirated engines.  Since it has small 
valves and a fairly restrictive carb, the torque drops off fairly rapidly 
after that, but never drops back to anywhere near that of the normally 
aspirated engines.  So once the turbo "comes alive" it's a much more 
exciting engine!  They aren't as sharp or responsive feeling as a 140, but 
that's deceptive.

(I can send the curves to anyone who's interested.  The data is available 
from a number of sources; I've compiled the late engine data into an Excel 
spreadsheet.)

It takes the best premium gas you can find.  Turbo's were designed with 
(then) 98 octane gasoline in mind.  I find current 93 octane marginal at 
best.  (Current 93 octane is close to 96 - 97 "old" octane.)  To 
compensate, I have one of American Pi's knock sensors.  It works to protect 
the engine, but I find it definitely cuts engine power when it intervenes.

Turbo carbs are a bit fussy, but work pretty well once they're set up 
right.  I did have a float since and start flooding the engine once, but 
that's a 40 year old float.  Resoldered the seams and it works fine.

Specialized turbo parts are more expensive than "normal" Corvair parts, but 
still a lot cheaper than similar parts for newer cars.

My advice?  Drive the car with the current engine and start building a new 
turbo engine for it.  The parts are out there so you could build one from 
scratch over time.  The best way, would be to find a complete engine and do 
a full and careful rebuild.

Jim Simpson, Group Corvair, '66 Corsa turbo coupe.