My motor is a stock 1977 L48. What octane fuel is required?
How will premium fuel effect (help) performance?
I have been using premium fuel for about six years and just recently read the motor only required regular fuel.
What is the consensus?
Thanks for responses.

 

Premium fuel is a waste of money for your stock engine. Octane stops detonation, period! If your engine does not knock with regular (and with the low compression you have, it won't), there is no advantage to using premium.

God bless, Sensei

 

I use 87 Octane in my 81 with no problems....

 

Use the lowest grade it will run on and you will be fine. No need to run higher octane if it is not needed. It will not give you more performance. It actually could hurt it slightly since higher octane fuel will burn slower. Probably nothing you can feel by the seat of your pants but it may knock of 1 or 2 HP.

 

im running 87 in my 77.. just took a 520 mile trip and got 16 mile to the gl.
I have tried 89 and 91 with no difference. ...

 

Personally, I think the only reason I can still get 93 octane gas is because people think it will make their cars go faster ( the number of cars on the road that actually require 93 octane is so low they would discontinue making it ) I hope that never changes

So if anyone ever asks you about it, tell them to fill er up

 

If it runs on 87 do it if it feels good!

 

The ECMs on later model Vettes, etc, will run the spark on up until knock is sensed and then back off till knock is cleared. So, even tho they will run (by law) on 87 octane, later mo Vettes w/ ECMs and knock sensors will take advantage of the increased octane, if available; more power and greater mileage too.

Gotta love computers.

P.

 

Sorry Dude, but that's just plain BS. If an engine was designed and certified to run acceptably on 87 octane, it will NOT run better on high octane. The computer has no ability to increase cylinder compression and no ability to advance timing more than factory settings.

This is one of the more recent myths that people have invented.

 

If you put reg in your ls2 engine (designed for premium) the computer will retard the timing so it doesen"t knock. Results would be less power an less mileage.

Allthough it sounds like the valves rattleing, it"s actually the piston skirts hitting the cylinder walls.

 

Thanks for info.....another question, if I go to regular will I have to adjust timing? Motor runs great on premium from idle to top end.

 

I do love my computer, but lets be real here. They didn't put computers in Vettes until '81 ("80 Cali), so the OP's Vette does not have one. Also, the computer does not "run the spark on up until knock is sensed". It has a pre-set timing curve that it runs (designed for the specific engine, with low octane gas), but if it does detect knock, it retards ignition 2 degrees. I have a performance chip, aftermarket heads, pistons and cam, (higher compression etc.) and I advance my base timing a good bit.

My car requires premium. I recently traveled out of state and was running out of gas in an area where the hurricane scare caused a gas rush and I had to buy regular from one of the few stations that had anything. Even with 2 bottles of octane booster additive, it was knocking. I really had to baby it. It finally went away when I got some good fuel half a tank later.

God bless, Sensei

 

You may be able to run more advance on premium, but just start out putting in the regular and listen as you accelerate hard, especially up hill. If the engine makes a rattling sound, you may need to back the timing off a bit, but if it is tuned to original specs, I doubt you will have any problems.

God bless, Sensei

 

No, the setting you have now is probably optimum. Almost all SBCs run best with a total advance of 36 degrees, irrespective of gasoline type.

 

I actually tried something in my truck at the beginning of the summer and recommend everyone try it at least once.

I typically get 17.4 mpg on regular, but ran the tank down and filled it with premium (20 cents more per gallon). At the next fill up, I had clocked an extra 1.5 mpg.

Now thats a heavily regulated by computer fuel system in my 08 ranger, compared to the weaker than an Atari 2600 in an '81... So considering we're all dealing with 30+ year old technologies, I would recommend testing a few tank fulls. It's obviously a better grade than the homogenized stuff you're "saving money with" pumping regular.

saving money.... 20 cents / 10 gallons .. 2 bucks.

wow....

 

some motors markedly more efficient on premium & others not ... try it w/ yours for your results. And add this to the reg-prem mix ... if the fuel has ethanol in it, it'll usually yield less mpg than straight gas ... as in: straight 87 usually more mpg than ethanol 87. But, for several months now, I dunno of any straight pump gas in my immediate area.

But check yours & see ... if it costs 6% more $ to get 8% more mpg then it's a bargain.

 

Just numbers.

If gas is $3.00/gallon and you realize 18 mpg your cost is $0.167/mile. With a 6% increase in cost and 8% improvement in mileage the numbers are; $3.18/gallon, 19.94 mpg of a cost of $0.164/mile.

An improvement, however I spill mor gas than this.

 

I know when I did my little test, I saved 50 cents on the yield from the tank. But it gave me another day as well (being my daily driver)

with the limited use our C3's see on average, I would recommend people ante up and buy some decent gas.

nobody ever bought a vette for it's gas mileage.

 

(Most) performance chips/tunes optimize performance based on premium gas performance and retard spark if knock is detected resulting from lower octane, etc. If driving with such a tune on 87 octane, and one switches back to premium, the ECM will reduce the spark retard i.e. "run up" the spark to the settings in the tables...is perhaps a better way to put it. The ZR-1 will run on 87 octane, in spite of it's 11.25:1 compression...retarded, however. No question it runs better on the "good stuff"; read: retarding removed.

Today's engines make more power today on unleaded fuels because of the sensors and computers. My point was that with the modern computer systems, the old adage of "if it don't knock on 87 octane, then running higher octane is a waste" is IF the tune was designed around 93+ octane to begin with.

Combustion chamber design has soooo much to do with optimum spark advance settings and octane requirements that any generalizations about performance advantages of 87 vs. 93 octane, or even 100+ octane is really very limited to just a very narrow set of engine situations. Books have been written on the subject, and there is no way to do the topic justice here, methinks.

P.

 

Boy has this become a discussion!!!!!!
My original question was "what octane gas was the 1977 L48 engine designed to run on?"
If I was running 93 octane fuel and changed to 87 octane fuel would other adjustments be required?
The motor is strictly stock....NO COMPUTER!!!!!! The car is a daily driver
The responses have been interesting....from what I've read there would be very little difference in engine performance but I could save .40-.50 cents a gallon.
12 gallons = $6.00 at each fill. Not bad, eh?