Hello - I just purchased a 1972 with the original engine still in it. I asked the dealer what type of fuel to put in it, assuming it needed leaded or I'd have to use unleaded and add something to it.

He indicated it should take regular unleaded.

Does that sound right? Should I be adding something to it?

 

In the Forum there is a "search" function.... It will become very useful with your great new purchase.... The answer is your engine will run fine on today's gas... I put the highest octane in because it makes ME feel better !!!

 

Of course from a practical and scientific standpoint the higher octane fuel will have no performance gain or otherwise over regular unleaded in a low compression engine such as an L48 or even the LT1 that year. Unfortunately the marketing schemes that higher octane is actually a "premium" fuel and better for all engines is so burned into many peoples heads that they buy it and use it in the lower compression engines where its faster burn rate has not benefit or use...(it makes them "feel better" while spending more for nothing... I say give it to charity for same feeling and actually do some good :-) ). some people don't know it can burn up smaller engines ( jet ski and motorcycles) I was warned not to use it when I bought my jet ski.

If you want to spend extra money to show how much you care I recommend a lead substitute with regular fuel over the high octane stuff if anything it will have more benefit. I recommend fuel stabilizer if your car sits for weeks... had my brand new Carb plug with a clear jelly substance this spring from sitting for three months.... what a mess.

 

All '72 Corvettes were built to run on regular unleaded gas.

 

Yes.

No. It will love 92 octane, but it will run fine on cheapo.

 

Whether or not higher octane fuel should be used is dependant on the ignition timing of the car.

If your timing is setup as most here will recommend, to achieve maximum performance, and you run 87 octane fuel, you will most likely experience pinging under heavy acceleration.

Try using lower octane fuel, and see if you get any pinging under heavy acceleration. If you do, then either switch to higher octane, or retard your timing.

 

Good to know... for some reason I though I read elsewhere that the 74 was the first year they started building them for unleaded.

I totally overlooked the timing.... guess I was thinking that was more for guys running recurved distributors that stock setup.. OK I'll eat crow on some of what I said earlier...being a carved engine It seems changes things a bit vs fuel injection...

http://chemistry.about.com/od/chemis...ine-to-buy.htm

 

At 9:1, even an optimized timing curve may not induce detonation with 87 octane.

 

I run my 72 on 89 octane mid range and have had no problems with detonation.

 

Thanks for the replies.

I took it in for a general inspection. The auto shop indicated that in the older cars the lead served as a lubricant for the valves. When they switched to unleaded, most owners replaced the softer valves with hardened valves.

Running unleaded if it wasn't converted could damage to the valves. They said there was no way to know if this was done without pulling it apart.

Therefore, they recommended I add a lead enhancer every time I filled it up. They said it wouldn't hurt either way and would protect the engine if they hadn't been replaced.

Does that make sense or sound off?

 

That was what I originally thought...
But after a quick Google search I can confirm that the 72 was designed for leaded or unleaded fuel.

 

In 1971 is when all engine manufacturers had to start building engine for Unleaded Fuel and not all lowered the compression ratios this model year but by 1972 the L48s were all at about 8 to 1 compression ratios but still producing about 200 HP and during this time they also had to report real HP and Torque on the engines instead of Lab results.

In my research the lowest HP L48 engines were produced in 1975 and in 1976 they started to learn how the increase the HP again with the 8 to 1 compression making way for the unleaded fuels. Most of the late 60s engines were false reported when it came to actual drive train for HP and Torque they took the results straight off the engine with open exhaust systems when on the Dyno.

Many of the Big 4 of the time would lie on the actual HP in the late 60s when Muscle Cars were so powerful they could kill you on the engine so the buyer would have lower Insurance premiums.

The only engines at the time were the L82 engines with 9 to 1 compression that needed the higher octane fuels and this continued till they did away with L82 in 1982.

Here is a little history thanks to Wiki

http://en.wikipedia.org/wiki/Chevrolet_Corvette_(C3)

 

In was in the early 1980s I think 1986 was the last you saw leaded fuel in rural areas and the USA quite selling Leaded Fuels they added fuel additives to use in older engines. Most of the leaded fuels were used in Rural areas of the country but most of the urban areas you could not purchase it anymore.

 

I'd say 90% crap.

1) cars from '71 onwards came factory equipped with hardened valve seats

2) nobody pulled engines part back then just for the fun of it. Very very few had hardened seats installed just 'because the sky might fall'

3) 40 years later we know that cars, especially light weight sports cars like Corvettes, never ever have valve seat problems, even pre '71 engines.

But the myths still persist and the misinformed just can't seem to stop spreading them.

 

I've run 87 octane in my big block 72 for the 13 years I have owned it. No problems with running this grade at all. Save your money!!

 

Mike is 100% correct. Starting in 1971, all GM engines came with induction hardened valve seats with the anticipation of the upcoming switch to unleaded.

In later studies done by the SAE in the mid-70's (I get the papers), they found that the hardened seats were not required except in rare cases of heavy vehicles pulling continuous heavy loads up extended inclines at or near WOT, such as a 3/4 ton truck pulling a loaded horsetrailer up the Eisenhower Pass on I-70 in Colorado. In this case, the Exhaust Gas Temperature (EGT) could get high enough to start exhaust valve erosion in some cases. Unless you plan on pulling an 8-horse horsetrailer at WOT with your Vette, there is no gain (and considerable risk from faulty installation) of installing hardened seats. The engines we build out here with original pre-'70 heads are never built with hardened seats, and they perform flawlessly. Anybody who tells you that hardened seat wives' tale is technically not aware of the facts on the subject.

As for octane, the advertised comp ratio on your 72 is only 9 to 1. This means that the actual ratio is under 8.5 to 1. There is no gain whatsoever running higher octane than neccessary to suppress detonation, and you can't get detonation, no matter how aggressive your timing curve is, on an 8.5 to 1 engine. Just run regular unleaded and forget all the BS you hear about the "gas problem."

Lars

 

Thanks Lars.

I stand corrected. Very sorry for the bad info.

I have had my base engine 72 for 5 years, and the block is original, and the numbers and dates on the heads make them appear to be original, so I assumed everything in the motor was original.

I've set up my carb, and distributor according to your papers, the car runs greats. But when I run regular unleaded, I definately get some pinging under WOT at higher RPM.

What do you think could be causing that? Would a cam change in the past be causing it? Or should I look at the timing some more? I have about 10 initial, 36 total mechanical, and 56 total.

Thanks!

 

I agree with Kim72....save your money I've had no problems running 87 octane @ $1.25 a litre $5.50 a gallon!

 

I remember back in the early 80s just before the USA dumped Leaded fuel off the market there was a craze in the classic car world. We will Burn our Valves NO Worries the gas companies added lubricants to the fuel to prevent burning up all the old engines. Lead was a lubricant in the early years not a Octane additive.

Hell I should be brain dead with all the lead I breathed as a child and not to mention all the paint chips I consumed from lead in the paint LOL

 

Sorry for bringing up an old thread, but that's what you get when using the search engine. I'm looking at purchasing a 72 350/200HP. I was worried about the lack of lead in the gas, it's good to know it won't be a problem. Although I will probably burn premium in the car if I purchase it, because around here the premium is alcohol free. Do you have to worry about alcohols effect on the fuel system?