Guys, I just bought a '65 with the 327/365 HP engine. With 11:1 compression pistons, I do not think that premium 93 octane pump gasoline is sufficient. I do not intend to race this engine but I do like to "run it through the gears" sometimes.

What I need from the experts on high compression C2 Corvette engines is: Will my current practice of running 93 octane premium with 3/4 bottle of 104 Max octane booster and two cupfuls of lead substitute be enough? I am really fighting the urge to order a 55 gallon drum of (105 octane?) racing fuel. That is the last thing that I want taking up space in my garage!

What says you?

 

I'm not an expert.

If your engine is built and tuned to factory specs, there's no reason 93 octane pump gas wouldn't be sufficient.

The archives have plenty of information about fuel requirements, adverse effects of using octane booster, and the waste of money of lead substitutes.

 

even with the 11.to1 pistons, the L76 motor is not true 11 to 1... unless it was blueprinted, which would have required bigger domes, significant cutting of the heads, or shim type headgaskets...

none of which are standard practice on rebuilding one of these motors...

having said that.... my L76 was blueprinted and makes true 11.25 to one. I have the 30-30 cam advanced about 4-6 degrees (can't remember off the top of my head) and I run 92-93 octane in it regularly with no issues whatsoever.

Now, if someone did you a favor by installing the LT1 camshaft... then all bets are off, as that has less duration and will bleed off less cylendar pressure and raise the potential for pre-ignition.

If you are sure you have the 30-30... then no worries...
if you have any other cam.... and just about anything streetable has less seat duration than the 30-30 and could have problems.

Thanks

Aaron

 

If you have the factory "30-30" cam and your timing/advance map is set up to factory specs, there's no reason it shouldn't run fine with no detonation on ordinary 93-octane pump gas. If it has a different cam and an unknown timing/advance map, all bets are off.

All the 104 octane booster and "lead additive" will do is eat the plating off the inside of your float bowls and empty your wallet.

 

You should be fine! If you get some ping, try to back off the timing one to two degrees.

 

Isnt the lead substitute a good thing for the valve seats?

 

Its supposed to help if the rebuild did not include hardened valve seats.

However, I ran without lead substitute in my '66 Mustang (with original heads) for years and when I pulled the heads the valve seats just showed ordinary wear. Unless you are 'all out' racing I think its unnecessary.

 

I don't think it's necessary, unless, possibly, you drive tens of thousands of miles in a very aggressive manner.

 

Clark:

93 octane premium gas of today is rated based on the average of Research Octane Number (RON) and Motor Octane Number (MON). It is roughly equivalent to 98 octane RON rated gas from the 1960's period when your car was new. The octane rating numbers changed over the years.

As others have already said, your car should be fine on today's 93 octane IF the cam, compression, and distributor advance curve are original. If not, you could have some issues. Check your advance curve and initial advance with a dial-back timimg light and your car tachometer to see if it is close to the original. If it is, fill up with a good 93 octane gas and drive the car. If you get some pinging under load, you can reduce the initial advance some to compensate.

Experience over the last twenty-five or so years has confirmed that lead is not needed for valve protection if the car is driven/operated normally.

Checkout the advance map (including vacuum advance) and give 93 octane a try first. Then...if needed....you can make adjustments.

My 1967 327/350 HP car has 11.1 compression, so I am advising from personal experience.

Larry

 

If you could advise what's in the "lead substitute" bottle/cans it would be helpful in giving you an answer?

 

an old wives tale that caused panic when unleaded gasoline first came out.
Bill

 

Bill:

If you go back and read the history of tetraethyl lead in gasoline, you will find that many claims and half truths were from the automakers themselves. The reason was $$$.

GM pushed heavily for the use of tetraethyl lead (TEL). The person who invented/patented it was a GM engineer/scientist. The two largest manufacturers of TEL in the United States were ETHYL CORP which was a joint venture between GM and Exxon, and DUPONT which owned a large share of General Motors Corp stock at this time. The third USA manufacturer was Houston Chemical Corp in Texas.

I worked for Houston Chemical at this time as an engineer, so I am familiar with the uses and history of organic lead for gasoline.

Lead will definitely raise octane level, and will help prevent valve seat recession for motors operated under continuous, heavy load. Our 40 year old hobby cars and occassional drivers don't fall into this latter category very often anymore.

Larry

 

To answer the questions, the engine is the stock Special High Performance 327/365 with 30/30 Duntov cam, solid lifters, domed 11:1 pistons, and 4150 Holley #2818A carb. The engine block numbers show this engine and the appropriate numbers match the VIN. I bought the car from Pro Team and they told me that it appears to be the REAL DEAL, numbers matching. With only 46K original miles, I doubt that the engine has ever been apart, so, it should have all the correct internal parts. I am no expert on Corvettes, but it runs like a scalded cat!

There was no ownership documentation provided with this car. My research shows a long succession of speculators/dealers owning this car since it was restored in '05. It has hopped all over the country in the process. These greedy bastards only kept it long enough to resell it at a higher price to another speculator. I intend to keep this car away from those rats and lovingly care for and drive this car for the rest of my life. It deserves it.

I have had a Corvette expert (a former NCRS judge who runs a Corvette restoration/repair shop) remove and go through the distributor (take out the slop, etc.) and install a popular electronic module kit to replace the mechanical points. This shop also replaced the coil and the ignition timing was then set to specs. Other than vatting and rebuilding the carb, and correcting an intake manifold leak with a new FelPro gasket set, nothing else has been done to the engine.

I have had various supposedly knowledgeable Corvette experts/mechanics tell me conflicting things. One told me that I should only use racing fuel or Avgas. The Pro Team salesman told me that "unless I am going to hammer" the car, pump premium (93 octane) would be fine with no mods. Another told me that 93 octane unleaded with octane booster and lead sub would be good "insurance". I can afford any fuel, including the additives I am currently using.

I would feel more confident if everyone agreed on one thing, even you Forum guys. If some of you are correct about this engine running fine on modern 93 octane premium unleaded, that is what I will use, which is what I am using currently. But, I have been putting in 3/4 bottle of "104" Brand octane booster in the tank when I refill. I also have been using CD2 Brand Lead Substitute - 1-1/2 oz. to 15-16 gals. of 93 octane unleaded fuel. This bottle is clearly marked for "offroad use only" (ha-ha). -Clark

 

"104" Brand octane booster only raises the octane by a small amount.

.2 or .3 pts at most, it will take 93 octane to 93.2 or 93.4, so it really doesn't do much.

If you need to boost your octane you need to run racing fuel or toluene along with your 93 octane gas to bring it up enough to make a difference.

 

Clark:

Try the 93 octane pump gas. If it pings, DOUBLE-CHECK the distributor initial, centrifugal, and vacuum advance versus OEM.

If you want or need additional octane, or simply want the tetraethyl lead, then buy OCTANE SUPREME 130 from Kemco in Utah. This is the real deal TEL with EDC and EDB lead scavengers added to make things work as intended. But it is sold "for off-road use only" as you might expect. This stuff will work, just like it did in 1965 when your car was new.

Others mix (leaded) AVGAS or LEADED RACING GAS with unleaded pump gas. I would not do this except as a last resort. And I don't think it will ever come to that. Leaded race gas can be bought in 5-gallon thru 55-gallon containers, but is $$$ and a real PIA if you don't really need it. Few of us are lucky enough to have a dragstrip nearby that sells racing gas.

Typically the guys that need and use Avgas or Leaded racing fuel have modified engines with non-OEM cams and recurved distributors.

Larry

 

the short version is: if it doesn't spark knock with 93 octane at the correct timing required for that engine; it ain't broke, so don't try to fix it. if it does ping, and the distributor curve is correct, then try backing the timing down from whatever it is set at until it stops pinging (this shouldn't require more than a few degrees..).

forget the snake oil.
Bill

 

Exactly!

 

My cars range from 10:25 to 11:1 compression and they all run fine on 93 octane with no pinging. You should be fine. As suggested, if it pings, dial it back until it doesn't. Sounds like a nice car

 

I have an L79 4-speed car with a couple of minor mods (bigger 2.02 etc..... valves and bigger 750 cfm carb). The true compression ratio as measured by the engine builder was exactly 11.1:1. I've been running 93 and/or 94 pump gas without a problem for years. Timing is where it should be and prmary jets are 72 (w/metering plate on the vacume secondaries). I dump in some CD-2 lead substitute from time to time just for the hell of it..........

 

I went thought the same exercise you are going through now soon after taking possession of my '66.

After some research on the additives, I came to the conclusion that I was never going to see a big increase in octane beyond a couple of "points" as mentioned by others here.

Was adding lead substitute for a while until I became convinced it had all been hype and perhaps needed only by extreme duty vehicles.

I was able to get racing fuel when I lived in California and adding a quarter to half tank of 104 octane did seem to make the old girl run/sound a bit better - but this may have just been all in my mind. I do think it smelled better.

I have never had a pinging problem with (91 in California and Hawaii, 93 in Texas) pump gas in my L72 while using recommended timing ranges.

Haven't added anything for a while and no longer give it much thought.

Lance