<VV>Cheap Gaz

[Padgett]

>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