I can purchase 90 octane non-ethanol gas. would it be beneficial to add octane booster and if so which brand is best. Car 1973 L82 with aluminum intake and holley carb. otherwise original.

 

90 octane by itself should be just fine for that 9:1 engine. Ethanol is fine too as long as you’re not letting it sit for long periods of time.

 

If you use the 90, listen carefully for any pinging with a load like when going up a steep hill. GM made the '70s engines to run on regular unleaded. If you hear pinging, there's nothing wrong using ethanol with higher octane.

 

Clearly it does depend on how you have it tuned. But a basically stock L82 should run just fine on that 90 octane.

 

I am not a big believer is using/wasting Higher Octane fuels in engines that don't need the octane. If the engine works on 87 octane then why not use the 87 octane all year round? My 1988 C4 has a L98 engine in it and it lives very happily with the 87 octane fuel here in Northern Virginia.

Before trying the lower octane fuels it would be a great idea to verify that the knock sensor is still working as it was designed to. On the C4 while idling you simply tap the engine block or cylinder head with a metal wrench. The tap/knock if heard should make a quick idle speed re-adjustment and go right back to idling smoothly.

If your car can run fine on the 87 octane and I was planning a quick trip in the summer heat then I might give it a dose of 90 octane fuel to help prevent problems. The C4 fuel injection system does have a knock sensor which can and will retard all 8 spark plugs when knocking is detected, unfortunately the system retards all eight spark plugs versus the offending one like the newer cars have on them.

When I first built my High Compression 427 I installed a MSD multi-retard digital switch that lets me pull the amount of timing I want. The idea is for the engine to run on "non-retarded" but once a knock or ping has been detected I can start by pulling timing while driving the car. I had it set different ways but normally I pulled small bites of timing like 2* at a time and they all added up to give my engine enough retard for it to run on even cheap low octane fuel.

In a low compression stock engine you are very likely not going to need the extra octane of premium fuels nor will your engine require any kind of Fuel Booster.

If the engine is running Hotter than normal it will likely need the timing looked at. Having the timing set too retarded will make excessive heat. Having a partially filled radiator will do it, Having a bad vacuum hose on the vacuum advance can even cause an engine to run hotter than normal. Having carbon inside the engine causing pre-Ignition will drive a poor engine nuts. To eliminate the carbon from the combustion chambers you might try the old trick of S-L-O-W-L-Y pouring ~ 8-12 ounces of cool water down the throat of the carburetor while holding the rpm's up high enough to burn the water. This will cause the carbon on the pistons or in the combustion chamber to break off and exit the engine.

On the later C4 engines they used an EGR and when the EGR had failed, the engine will run much higher combustion chamber temperatures until the EGR is replaced or the code is re-written eliminating the EGR. Emissions equipment needs to be maintained to keep it working properly. On many older Corvettes, the EGR is a necessary gadget and it needs to work properly for the engine to run normally.

 

You don't need any octane "booster" with a stock '73 engine. Mid-grade unleaded should work fine in your L-82 if ignition timing is reasonable.