Octane Question
Thread Starter
Melting Slicks
Joined: Sep 2002
Posts: 2,390
Likes: 2
From: New Castle DE
Octane Question
So i went to fill up at Sunoco today clicked on high test and it was like 
regular is all we have. So i filled the 74 up with 87 
MY question is this, will it really make any difference? I mean it is an l48 with a whopping what 8.5:1 compression ratio 
I did notice tonight on the way home that the car did seem to stink a little more then usual but that was it. I did get into it and din't hear any pinging all though it was cool out.
regular is all we have. So i filled the 74 up with 87 MY question is this, will it really make any difference? I mean it is an l48 with a whopping what 8.5:1 compression ratio I did notice tonight on the way home that the car did seem to stink a little more then usual but that was it. I did get into it and din't hear any pinging all though it was cool out.
Instructor
Joined: Jun 2004
Posts: 162
Likes: 1
From: Johnsburg IL
Unless you have increased the original 8.5 or even 9.0 engine comp you don't need high test. Saves money and prevents carbon build up which can happen with low compression engines using high test.
Race Director
Joined: Jul 2001
Posts: 15,892
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All '74s were designed to run on regular gas right from the factory. There is no benefit whatsoever in running higher octane than that. Think of the thousands of dollars that people waste by buying high octane gas. 
Pro
Joined: Nov 2004
Posts: 575
Likes: 0
From: Nice Lake Ontario
"All '74s were designed to run on regular gas right from the factory. There is no benefit whatsoever in running higher octane than that. Think of the thousands of dollars that people waste by buying high octane gas. "
X2
All "high test" does is provide a more controlled burn (so you can run more ignition & compression). It is actually a slower burning fuel than reg. Unless your car requires it please just send me your extra cash, I have a better use for it
X2
All "high test" does is provide a more controlled burn (so you can run more ignition & compression). It is actually a slower burning fuel than reg. Unless your car requires it please just send me your extra cash, I have a better use for it
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
Don't forget that you will get the BEST performance from the LOWEST octane rated fuel that your car can safely use. Using higher octane rated fuel than is necessary not only wastes your money, but actually LOWERS your performance!!!
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Drifting
Joined: May 2004
Posts: 1,442
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From: Flanders NJ
Originally Posted by tpiini
Don't forget that you will get the BEST performance from the LOWEST octane rated fuel that your car can safely use. Using higher octane rated fuel than is necessary not only wastes your money, but actually LOWERS your performance!!!
He's right 
Race Director
Joined: Feb 2005
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Originally Posted by WhichVette?
Most engines below about 10:1 or so don't need premium. Just wasting your money...
Rich
Drifting
Joined: Dec 2004
Posts: 1,345
Likes: 3
Originally Posted by sjr1971
GM saw this comming. My '71 owners manual for an LS5 454 , 8.5:1 comp. recommends 91 Octane. I don't have to go to an airport for gas
Remember when there WAS such a thing as 'cheap' stuff ?
Remember when there WAS such a thing as 'cheap' stuff ?
Melting Slicks
Joined: Jul 2005
Posts: 2,545
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From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM
My 71 RPO LS6 454-425 HP does not like low octane gas, so she gets noting but high test.
Now my 79 L-82 350-375HP (lots of motor work) runs best with high test also. This one hesitates when it gets reg gas only, as soon as it gets high test it doesn't. For all I drive them in a season, I don't mind the extra cost. I know most here say they will run on reg, I know the differents in sound and reaction when I ask them to Mooove. My 0.2 only.
Now my 79 L-82 350-375HP (lots of motor work) runs best with high test also. This one hesitates when it gets reg gas only, as soon as it gets high test it doesn't. For all I drive them in a season, I don't mind the extra cost. I know most here say they will run on reg, I know the differents in sound and reaction when I ask them to Mooove. My 0.2 only.
Race Director
Joined: Jul 2001
Posts: 15,892
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Originally Posted by StickShiftCorvette
I think the 91 recommendation is based on the research octane number, not the current (R+M)/2 , average of research and motor octane numbers. ALL C3s made after '70 ('71 and later) were made to run on regular unleaded gas.
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
Originally Posted by Glass Act
My 71 RPO LS6 454-425 HP does not like low octane gas, so she gets noting but high test.
Now my 79 L-82 350-375HP (lots of motor work) runs best with high test also. This one hesitates when it gets reg gas only, as soon as it gets high test it doesn't. For all I drive them in a season, I don't mind the extra cost. I know most here say they will run on reg, I know the differents in sound and reaction when I ask them to Mooove. My 0.2 only.
Now my 79 L-82 350-375HP (lots of motor work) runs best with high test also. This one hesitates when it gets reg gas only, as soon as it gets high test it doesn't. For all I drive them in a season, I don't mind the extra cost. I know most here say they will run on reg, I know the differents in sound and reaction when I ask them to Mooove. My 0.2 only.
Melting Slicks
Joined: Apr 2004
Posts: 2,083
Likes: 2
From: Montreal Qc.
If one was running lots more timing advance than stock (like any of us who tune ala Lars) would that have any effect on pre-ignition/knock using low-grade with low compression (stock-ish 79 L-48)
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
Late 70`s Vettes were low compression and the use of low grade fuels are compatible. As far as advance, you cant put more into the engine than it can use with out having harder starts. The engine itself will almost tell you how much it will take. `
East bound and down...
Joined: Dec 2004
Posts: 987
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From: Jonesboro Arkansas
Originally Posted by Star79
If one was running lots more timing advance than stock (like any of us who tune ala Lars) would that have any effect on pre-ignition/knock using low-grade with low compression (stock-ish 79 L-48)
This is a good point. If you are running more advance than stock, you certainly will notice a difference in how well your car runs depending on the grade of gas you are putting in your car. Also you may have a slightly higher compression ratio than what you think that you have due to carbon build up, if you put a tank of 93 or higher in your tank and your car seems to run better, it may not be just your imagination. Just some food for thought.
East bound and down...
Joined: Dec 2004
Posts: 987
Likes: 3
From: Jonesboro Arkansas
Originally Posted by El_Cid
now does this work with all C3s? I run 93 on my stock 82, but if its doing nothing, id like to know.
I am not that familiar with the TBI that those cars use, but I know on late model fuel injected cars your car will run more advance if the computer does not detect spark knock, therefore, if you are running a higher grade of gas you may feel more power. This is especially evident with performance chips and programmers. The increase in most cases wouldn't be worth the extra cost at today's prices though, so I don't advocate running 93 octane in your corolla, but now you know that it can make a difference.