Octane Requirements 1979
 

I don't want to open too big a can of worms here but..

My new to me 79 came with all sorts of documents and factory manual but no owner's manual.

What is the recommened octane level for the 79 L82 engine, been using high test to be safe?

Adrian

1979 Unleaded Fuel
 

According to the Owners Manual, Page 5-1, "Your gasoline engine is designed to use ONLY UNLEADED gasoline. Unleaded gasoline must be used for proper emissions control system operation." There is no mention of the octane requirement. On Page 7-2, the Compression Ratio for the L-82 engine is only 8.9 - 1. My guess is that the car would probably run on regular, but to be safe, a mid-grade or premium, would probably be better. Maybe someone more familiar with the engineering aspects of engines could shed more info on this.

Your 79 will run on 87 which is regular. if it pings run the next higher octane. it can't hurt to run premium most do and the cost is less then a $1.80 more to fill the tank w/the good stuff.

If I remember correctly, there was no such thing as 'super' unleaded in 1979.

Your only choice was what we now call 'regular' unleaded, or 87 octane.

In '79 you could still find stations that had upwards of 100 octane (if you knew where to find them). But your '79 C3 only needs regular unleaded gas. As mentioned, if you get some pinging, adjust the advance or buy the mid-grade of gas. Premium gas in that car is a waste of money, IMO.

I understand regular will work assuming stock timing..
But

What about those that have the timing advanced per the Lars Papers?
Does that make any differance?
I use premium anyway and don't mind wasting the money that way as I find many other ways to waste it on this car. lol

Regular 87 octane is fine.

If it pings, you have 2 choices; retard timing or switch to higher octane.

Just to help clarify.... Lars instructs us as to the BEST way to set up your engine for best performance and operation. The factories DIDN'T set them up for optimum performance for two reasons: 1) it took more time and, therefore, cost more to do; 2) retarded timing might generate less emissions, but it definitely produces less power...which translates to LOWER WARRANTY COSTS. Lars knows that your engine can operate properly (better, IMO) when mechanical advace is set to 34-36 degrees max and when it all comes in around 2500-2800 rpm. The engine is designed to handle that and not ping. GM didn't go to that trouble. I just had Lars redo my carb and distributor for my '71 [low compression] engine. It never ran better since I've had it, it doesn't ping on regular gas and it is more economical than before. What's not to love?

My 80 was to run on 87, but I rarely did. My crate is also to run on 87. Ive only put 87 in once and didnt think it was worth the risk. When fuel is in the $3 range, what is another 20 cents....:willy:

Just my opinion

Order a reproduction owner's manual or shop for an original on eBay. All Corvettes love 97 or higher octane, but they'll run on the lower grades.

:)

Higher octane = higher horsepower = better power performance = more $$$. Higher octane will not hurt the car (other than you will wear the engine out sooner). Lower octane will not hurt the car as long as it is not pinging. Use whichever you like for your "reasons".

Is this the same for a 77 with an L82????:bigears

Yep. My '80 L-82 likes 97 octane (so does my '68), but she runs fine on 87.

:)

Run the lowest octane gas that doesnt allow detonation (ping) anything more doesnt improve performance and just spends your money.

If you modify the engine, the same holds true...higher compression - more advance - run whichever octane eliminates ping..(probably a higher grade)..but dont run any more than you need...thats just money down the t*let.

no harm will come to your engine if you run higher than necessary octane, but all things being equal, higher octane will not improve performance unless you need it.

:bs I can't believe that this myth is still around.:nono:

But that was LEADED gas, not unleaded. Leaded gas in a catalytic converter car was certain death.

Mike,

1) Please explain how a higher octane fuel..with better burn characteristics...would NOT generate more power out of an engine.

2) There were lots of (older) C3 cars that didn't have catalytic converters in 1979. The statement made above was that no such "hi-test" gas was available in '79. Not true.

1) Do some basic research yourself. I've put some easy to find links below. High octane gas is 'regular' gas with additives (in the old days tetra-ethyl lead or TEL) that INHIBIT the spontaneous combustion of the gasoline ie- pinging, knocking etc. There are no other processes or ingredients that would increase the BTU content of the gasoline that would produce 'more power'. In an esoteric sense a given volume of regular gas potentially has more 'energy' than an identical volume of high octane. In practice, this difference is not noticeable.

http://en.wikipedia.org/wiki/Octane_rating

http://chemistry.about.com/gi/dynami...tos/octane.htm

The availability of high octane gas allows either OEMs or home builders to configure engines with higher compression ratios, more adventurous ignition maps and/or cam characteristics. It is these features in the engine that produce the increased power, not the gas itself.

2) Please re-read my post. I said no super UNLEADED gas in 1979. There was plenty of leaded super gas available, as well as regular leaded. If you had super unleaded available in your area, that's nice. None was available here.

There was unleaded (regular), low-lead, and leaded. Sunoco 260 was 103 octane and leaded.

Paul,

Do you remember when hi-octane unleaded gas became widely available? I'm thinking mid-late 80s?

When I bought my 78 in 1979,there was one choice:87 unleaded....run 91 oct now...

Mike,
My memory is failing me. There was a phase-in period in Canada for unleaded when leaded was still being used. There were two gas-fill nozzle sizes and you could not get the Sunoco 240 and 260 nozzles into the narrow 1979 Corvette fill tube. In fact that started in 1975 when the cat cons arrived. But the 1979s did work with 87 octane unleaded. I drove one for 17 years. You had to set the timing very carefully to avoid ping. We have to remember that the 1979 L-48 compression ratio was 8.5:1 and the "high-perfomance" L-82 was a mere 8.9:1.

When the Canadian government completely banned ethyl (lead) I simply can't remember. But I believe it was timed with the auto makers move to hardened valve seats. I can only guess at mid-1980s when MTBE was added as an octane enhancer to replace lead. That introduced a host of other emissions problems of course, in recent years with a lawsuit between Shell Canada and GM Canada.

My 1967 327/300 with a 10.25:1 CR is cranky with 89 octane but lives well with 91 and I tend to 93. But my timing is tweaked from the original factory setting. As you know the cost per liter (converted) is well over $5.00/imperial gallon now and as I am getting 14-16mpg in the city, that is my cost of driving 14 miles. I tend not to use Sunoco as all but their 94 is up to 10% ethanol and that plays havoc with rubber fuel-management components in these old cars. Newer cars with advanced polymer fittings are fine.

Sorry my memory does not serve me well.

My memory is no better than yours! Thanks for your note.

I guess it was mid 80s then. :cheers:

Fuel octane for L82
 

That engine does not require anything but 87 Octane. I have 11.6 compression and run on 91 to 93 octane. High octane fuel burns slower and make less power so running any higher than you need is a waste. Your stock distrubutor most likely has a very slow advance ramp up which helps on that too.

Gear ratios, and stall speeds on the converter have a great affect too.

Just trying to help.

David

A Newbee

I beg to differ. You will realize no benefit from using a higher octane than your car requires for proper operation. Octane is merely a combustion inhibitor, not a power adder. Octane is a linear strain of molecules. The greater the octane you use, the higher compression you NEED to efficiently burn it. If you put 93 octane in your carburated low compression car, more gas is likely to not get burnt in the combustion chamber and clog sh*t up because as stated octane is a combustion inhibitor..

The only exception to this is a turbocharged/supercharged car with knock sensors that will retard timing at the first hint of detonation....which would allow the car to operate under most conditions safely regardless of the octane fuel you put in, at a penalty for performance.

My 8.25 compression L48 needs nothing more than 87 octane. Nobdy can tell me that I will get more power from 93 octane. Same with our 8.9 compression L82 friend who started this post. Even though the cost difference is minimal, save the 1.80 per tank and put it in the tank for when your rear wheel bearing fail or your radiator pukes milky antifreeze all over your garage. :toetap: