Which Octane?
03-09-2016, 11:55 AM
#1
Drifting
Thread Starter
Which Octane?
I'm getting ready to pull my '74 L48 M20 out of the garage and one of the first things I need to do is fill it up. I purchased the roadster last summer and this will be my first gas stop. The only thing available here is E10 in 87,89 and 92 octane. What fuel would you recommend I use? The engine is stock original with 37K miles on the clock. It runs strong with no noticeable smoke or ping. Thanks in advance.
03-09-2016, 12:01 PM
#2
Le Mans Master
I'm getting ready to pull my '74 L48 M20 out of the garage and one of the first things I need to do is fill it up. I purchased the roadster last summer and this will be my first gas stop. The only thing available here is E10 in 87,89 and 92 octane. What fuel would you recommend I use? The engine is stock original with 37K miles on the clock. It runs strong with no noticeable smoke or ping. Thanks in advance.
03-09-2016, 03:00 PM
#4
Team Owner
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03-09-2016, 05:53 PM
#6
Race Director
Starting in 1971, Chevrolet reduced the compression ratio on all of their engines, to allow them to run on regular unleaded. A stock 74 L-48, should run just fine, on any of today's regulars.
03-09-2016, 05:58 PM
#7
Drifting
Put in the 92, really how much are you driving the car that a little extra savings at the pump is going to make a difference. I think you will notice the difference in performance with the 92 anyway.
03-09-2016, 06:57 PM
#8
Had a 1976 L-82, 4-sp
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Royal Canadian Navy
The calorific value of all pump gas is the same. Higher octane will not increase the performance of his car.
03-09-2016, 07:11 PM
#9
Le Mans Master
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I too say go for the lowest. When I bought my 78 I made the mistake of putting 91 in it, and it ran like crap. Followed a friend's advice and used 85 (regular in Colorado), and it runs like a charm. 
03-09-2016, 07:35 PM
#11
Drifting
Thanks
03-09-2016, 07:54 PM
#12
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Royal Canadian Navy
He has a low compression engine so low octane gas is all that is required. Older hipo cars had a lot higher compression and required high octane. Todays hipo cars are a whole new breed with lots more power, higher compressions like a lot of older hipo cars but can run on 91 octane.
03-09-2016, 08:03 PM
#13
Drifting
He has a low compression engine so low octane gas is all that is required. Older hipo cars had a lot higher compression and required high octane. Todays hipo cars are a whole new breed with lots more power, higher compressions like a lot of older hipo cars but can run on 91 octane.
03-10-2016, 08:04 AM
#14
Drifting
Octane rating is simply the fuels ability to resist igniting under pressure before the spark plug fires.. { DETONATION} 93 Oct produces no more power than 87 octane .. It only allows high compression pressures without detonating before spark. Putting 93 in a car designed for 87 will not improve performance or cleaning , engine life or anything else .. Its a MYTH
03-10-2016, 08:15 AM
#15
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Royal Canadian Navy
On the flip side to the above, if you put 87 in an engine that requires 93, then you will get ping. On newer cars, the engine knock sensor will detect the ping and retard the timing i.e. loss in power.
03-10-2016, 09:27 AM
#16
Pro
03-10-2016, 09:36 AM
#17
Pro
Octane rating is simply the fuels ability to resist igniting under pressure before the spark plug fires.. { DETONATION} 93 Oct produces no more power than 87 octane .. It only allows high compression pressures without detonating before spark. Putting 93 in a car designed for 87 will not improve performance or cleaning , engine life or anything else .. Its a MYTH
03-10-2016, 08:32 PM
#18
Race Director
03-11-2016, 07:23 AM
#19
Drifting
The OP stated it had not been.. and if it is modified ,then its no longer as designed, hence the word MODIFIED ... I stand by my statement, if the engine is designed to run on 87 octane, there is absolutely no benefit to using 93 octane. None. Its a myth 
03-12-2016, 06:28 PM
#20
Instructor
I'm getting ready to pull my '74 L48 M20 out of the garage and one of the first things I need to do is fill it up. I purchased the roadster last summer and this will be my first gas stop. The only thing available here is E10 in 87,89 and 92 octane. What fuel would you recommend I use? The engine is stock original with 37K miles on the clock. It runs strong with no noticeable smoke or ping. Thanks in advance.