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Would I need to use high octane gasoline in a 1971 Impala with a 400cid 2bbl or would regular gas (89 octane) work?
 

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In 1971 , all GM cars had lower compression to deal with lower lead content gasoline and soon to be unleaded gasoline. A 400CI with 2 barrel carb would be something like 8,4:1 compression. Try 89 octane, and if it doesn't ping al lot, ok. If it does ping a lot, try 93 octane. If 93 pings a lot, retart the timing till it stops.
 

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In 1971 , all GM cars had lower compression to deal with lower lead content gasoline and soon to be unleaded gasoline. A 400CI with 2 barrel carb would be something like 8,4:1 compression. Try 89 octane, and if it doesn't ping al lot, ok. If it does ping a lot, try 93 octane. If 93 pings a lot, retart the timing till it stops.

I agree with you , My newer 350- 4 barrel has a compression of 9.1 to 1 , so I run 91 and 94 octane (no ethanol) but 89 works ok , no pinging , I just don't want ethanol in my $1000 Holly . Let us know how you make out :beer:
 
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