<VV>Cheap Gaz

[Cepak, Tom A]

I've had my '63 vert since March of '05.  I've read over the past year
how many have been running premium to keep your vairs from pinging, but
I didn't think about it much.  I guess I have an anomolous vehicle.
I've never have run anything but 87 octane and I haven't had any
knocking or pinging.  Living in Fort Worth Texas, with summer
temporatures from the mid 90s to around 105, from reading your posts I'd
have expected heat related problems.  From checking the numbers on my
engine and heads, I have a 102hp engine that has the 9:1 compression
ratio.  I had Wolf Enterprizes rebuild my carberators with 52 jets.  I
never removed the lower shrouds.  Maybe there are other factors envolved
as well.  It has a 4-speed with a 3.89 diff., and the tires are WAY too
small.  I believe they are 165/??/13s. 

I haven't filled up yet with the new fuel mix (may contain up to 10%
ethonal), so it will be interesting to see how this effects the engines
performance.

Tom

-----Original Message-----
From: virtualvairs-bounces at corvair.org
[mailto:virtualvairs-bounces at corvair.org] On Behalf Of Padgett
Sent: Monday, May 08, 2006 8:07 AM
To: virtualvairs at corvair.org
Subject: <VV>Cheap Gaz


>Retarding the timing ONLY  to use lower octane is the sign of an
amateur!

Point was that to make a Corvair suitable for Iterstate speeds,you have
to change things, it was not designed that way.

Living in Florida, to me, long gears are the way to go. The difficulty
is that to get a PG in Low to 70 (and make drive an Interstate gear
would take a 2.13 rear end. So we are left with kludges. 3.08 gears are
apparently not very common so economy on the Interstate is going to cost
quite a bit of money.

Relatively easily I can go to 27" tires in the rear (about as much as
will fit - clearance issue seems to be at the front edge to the rocker.

Back at the gas you get two things as you go up in octane:
1) fuel burns slower (why you need more advance with premium than
regular)
2) premium has a higher "flash" (detonation) temperature, and this is
important in an aircooled engine

other than that there is actually little difference between regular and
premium.

Now pressure and temperature are directly related, as you squeeze
something, the temperature goes up so 9:1 is going to have a higher
initial charge temperature than 8:1 *at wide open throttle* (why pinging
is most common al low speeds with high throttle openings. If you could
avoid WOT at low speeds, you would not need higher octanes. Water
injection at high throttle openings helps cool the intake charge and
also allows more compression on lesser gasolines.

The biggest issue is ignition. Just tuning the initial back a few
degrees is a guess and you really have a choice. regular burns faster
than premium  so the whole advance curve is going to be wrong & just
retarding a premium fuel curve means that if you get it right for 1000
rpm, it will be retarded at 4500. Set the advance for 4500 rpm and it
will be liable to ping around town. Vaccuum advance will also be wrong
for the same reason, the fuel combustion speed will change differently
depending on the charge density.

Now there are some out there who have already been though all of this. I
just know the theory and can't hear ping anyway so I just run premium
even though it is not very efficient. I also run at 70 mph where legal
and have
66 (power valve) carbs with 52 jets on a 3.55/PG combo which is about as
far from peak efficiency as possible (was worse, when I bought the car
one power valve was missing entirely. PO said it never pinged on regular
and that was all he ran.

Does seem that the first rule for running on regular would be to keep
the engine as cool as possible which would mean no or modified (doors
removed) lower shrouds. Have heard it mentioned that 4 degrees ATDC does
not ping but kills top end (and I would expect runs hotter since
retarded which is exacly what you do not want). I suspect that 10
degrees would be better coupled with moderation on the loud pedal below
2000-2500. Anyone ever tried this with 87 PON ?

As to a ball bearing on the PE needle, I would rather not & think that
at higher throttle openings the normal PE would richen the mixture and
make it run cooler so long as it had enough advance.

Best starting place for running regular though would be a recurved
distributer designed for a lot less advance on the bottom and not as
much less on the top  than a normal 110 and perhaps more aggressive
vacuum advance as well and as much help for cooling as you can give it.

It just feels to me that even with as bad a chamber as the Corvair's, if
you can keep it cool and provide the right advance curve,  then with
under
9:1 cr (see the stock engine tests) it should be able to run well on
regular.

Padgett 

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