Fuel recommendations for 1966 Olds 98

oldscharm · 05-23-2003, 12:24 PM

I am acquiring a 1966 Olds 98 convertible with 65,000 miles. This has the 425 cu in engine rated at 360 hp, compression ratio 10.25 to 1. I am looking for advice and recommendations on how to handle fueling this vehicle, what additives in what modern fuels will yield a happy long life engine?
Thanks.

sed1945 · 11-07-2005, 09:44 PM

In My 64 I run Premium unleaded with a bottle of STP Octane booster per every ten Gal. plus 2 ounces of 2 stroke oil per tyank full for the valves. Works great in my 64 and the oil's to help keep the valve seats from wearing. No it don't smoke.

jdorour · 11-09-2005, 11:14 AM

Nice car.
I have a 1966 Ninety Eight myself and love the car.

You will be very happy running 93 Octane or better. Octane Boosters are ethanol or methanol and are not all that good for the car. Both forms of alcohol will retain water and can rust the mild steel fuel lines used in these cars. It can also cause rust in the fuel tank. Tests have shown that the octane boosters generally only increase the octane one or two points over the pump octane (not a big advantage) if at all. The component that is missing is tetraethyl lead. TEL was used to lubricate the exhaust valve and increase octane rating. There are sources in Hemming’s Motor News that sell TEL but it is very expensive. In reality if you are not driving your car daily and or driving it hard it will run on 93 octane pump gas just fine. You do not have to add anything to the fuel. Keep the engine in good tune, run the coldest spark plug specified for the 425, keep the ignition timing at the recommended setting (or slightly retarded a degree or two), if you hear the engine making a pinging sound back off the throttle.

Two cycle motor oil will do more harm than good. The TEL was intended to lubricate the exhaust valves. The two cycle oil will not provide any lubrication effect for the engine top end (it does not provide any lubrication for the two cycle engine past the combustion chamber). The two cycle motor oil will combust and significantly increase the carbon build up on the valves, cylinder head and piston crown. It will cause the rings to stick. Who knows what it will do to the secondary metering jets in the QuadraJet carburetor.

Lastly when it is time to overhaul the engine you can do some minor modifications to eliminate the problem altogether. Install hardened valve seats and lower the compression ratio to about 9.0:1 or 9.5:1.

John

[ November 09, 2005: Message edited by: jdorour ]</p>

11-09-2005, 11:14 AM	#3 (permalink)
jdorour Senior Member Join Date: Feb 2004 Location: Atlanta, GA. Posts: 123	Nice car. I have a 1966 Ninety Eight myself and love the car. You will be very happy running 93 Octane or better. Octane Boosters are ethanol or methanol and are not all that good for the car. Both forms of alcohol will retain water and can rust the mild steel fuel lines used in these cars. It can also cause rust in the fuel tank. Tests have shown that the octane boosters generally only increase the octane one or two points over the pump octane (not a big advantage) if at all. The component that is missing is tetraethyl lead. TEL was used to lubricate the exhaust valve and increase octane rating. There are sources in Hemming’s Motor News that sell TEL but it is very expensive. In reality if you are not driving your car daily and or driving it hard it will run on 93 octane pump gas just fine. You do not have to add anything to the fuel. Keep the engine in good tune, run the coldest spark plug specified for the 425, keep the ignition timing at the recommended setting (or slightly retarded a degree or two), if you hear the engine making a pinging sound back off the throttle. Two cycle motor oil will do more harm than good. The TEL was intended to lubricate the exhaust valves. The two cycle oil will not provide any lubrication effect for the engine top end (it does not provide any lubrication for the two cycle engine past the combustion chamber). The two cycle motor oil will combust and significantly increase the carbon build up on the valves, cylinder head and piston crown. It will cause the rings to stick. Who knows what it will do to the secondary metering jets in the QuadraJet carburetor. Lastly when it is time to overhaul the engine you can do some minor modifications to eliminate the problem altogether. Install hardened valve seats and lower the compression ratio to about 9.0:1 or 9.5:1. John [ November 09, 2005: Message edited by: jdorour ]</p> __________________ 1966 Ninety Eight Convertible - 425 Tri-Carb, Factory Dual Exh, Switch-Pitch THM400, 3.54 Posi. 1966 Catalina Wagon - 421 Tri-Power, M21, 4.11 Saf-T-Trac, 8 Bolt Wheels 1989 IROC-Z - 5.7TPI

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05-23-2003, 12:24 PM	#1 (permalink)
oldscharm Junior Member Join Date: May 2003 Posts: 1	I am acquiring a 1966 Olds 98 convertible with 65,000 miles. This has the 425 cu in engine rated at 360 hp, compression ratio 10.25 to 1. I am looking for advice and recommendations on how to handle fueling this vehicle, what additives in what modern fuels will yield a happy long life engine? Thanks.

11-07-2005, 09:44 PM	#2 (permalink)
sed1945 Junior Member Join Date: Oct 2005 Location: Mo Posts: 7	In My 64 I run Premium unleaded with a bottle of STP Octane booster per every ten Gal. plus 2 ounces of 2 stroke oil per tyank full for the valves. Works great in my 64 and the oil's to help keep the valve seats from wearing. No it don't smoke.