Right on. I suggested a mix of 93 and 110.
For the testing, not in the lab mind you but on the street, I used 99 octane. Here's some of it;

First, I have to fill in the blanks on the test subject. It's a 69 Firebird that is so close to stock that it's easier to point out what's not like original 1969 equipment. The original 400 engine has a stock rebuild meaning original pistons, heads, intake, carb, exhaust..... So, it's running 10.75 to one compression. It has less than 1000 miles since rebuild so it's just broke in. The one part that's not like original is the distributor. It has the Accel electronic HEI and the Accel Supercoil. To accommodate these components, they are hardwired to the full output of the charging system(18-24 volts while running). The trans is the original TH400 with a fresh rebuild. The rear end has the original, special order, 3.55 safety track and that too has been freshly rebuilt. So, what you basically have is factory 1969 Firebird 400 non ram air exactly like you would buy it in 68/69 except for the ignition upgrade.


Test materials:
BP 93 octane unleaded pump gas.


Sunoco 110 octane racing fuel.


Max Lead 2000 Tetraethyl Lead Additive (Donated by Greg Fielder for the purpose of study)



The first test was done some time ago and that was straight 93 octane alone. The car ran ok on this fuel up to about 150 degrees when it started spark knocking to beat the band and I scurried over to Sunoco to add some octane.


Since I had 10 gallons of 93 already in the tank I decided to add 5 gallons of 110. This calculates out to about 99 octane. With this octane level, the car came to life! I'm going to use this level as a base line for the rest of the test for comparison. It's difficult to describe performance without experiencing it first hand. I will use three tests to try to convey the results.
First and foremost, sparkknock.
Second, what kind of a burnout it would do from a dead stop.
Third, how it hits the gears.

Results at baseline 99 octane:
No sparkknock at all.
It burns the tires for just under a second and then scoots.
The tires break loose momentarily when it hits second and third gears.

Results with 12 gallons of 93 octane unleaded fuel and one quart of lead additive
No sparkknock at all.
A slight burn out from a dead stop. Definitely a drop in performance.
The tires still have a slight chirp when hitting the gears. I noticed a slight bogg at times when trying a heavy acceleration.
There was a noticeable drop in operating temperature. The temp never reached 180 which is passed when using baseline 99 octane. Temps reach 220 at times with 99 octane.

Results with 12 gallons of 93 octane with 5 gallons on 110 octane and one quart of lead additive.
Same performance levels as baseline 99 octane with one difference, lower operating temperature. Again, the temps never crept over 180.


Of course it was more interesting the first time I posted it because it had pictures. Hey I found one of the original pictures from the testing.