Gas for 11:1 compression

[Bob B.]

Hi all,

I know a lot of you have 11:1 compression engines and was wondering how they do on the 93 octane gas we can normally get at the pump?

If there are problems with running only 93 with 11:1 then, other than additives, what is the best solution? Would using an extra head gasket or two lower the compression enough for 93 to work?

Thanks,

Bob

[Donald T.]

Re: Gas for 11:1 compression

If there is no knock/ping then there's no problem. Most vintage cars will run just fine on 93 octane. You can also retard the ignition timing if necessary. I would not bother going to the extreme of attempting to lower the compression.

[Jim T.]

Re: Gas for 11:1 compression

Original owner of 1968 327/350 L79 with 11:1. Have no problems using 93 premium. I don't lug the engine, it starts great when hot or cold.

[Bruce B.]

Re: Gas for 11:1 compression

My 62 Corvette 340 HP has 11.25 to 1 compression and runs great on 93 octane gas. No pings or other problems.
I understand that the 10% ethanol which is now in most gas does increase the octane number to some degree. Maybe thats the tradeoff for reduced gas mileage...

[Terry B.]

Re: Gas for 11:1 compression

I recently drove my recently acquired 62 from Phoenix to Seattle and on the first two tank fills the engine dieselled (ran on) when I shut it off. There after I purchased octane boost and/or lead substitute additives and no more running on. It's my belief that I really should use the lead substitute additive/octane boost because the lead substitute will act as a lubricant for the valves. Is this still accepted practice/belief?

[Bob B.]

Re: Gas for 11:1 compression

Terry,

For adding octane, the additives may be okay, but I believe that the idea that valves need the lead is an urban legend. This was a major question back when unleaded was first introduced and the automobile companies all did extensive testing to determine whether unleaded was damaging. The result was that there was no difference at all, except when the engines were run extensively under the most extreme racing conditions.

Thanks,

Bob

[Bruce B.]

Re: Gas for 11:1 compression

No lead additive, no octane boost and after 20,000+ miles my 340 HP 62 Corvette still runs fine in both cold and hot weather.
Most additives are a waste of time and money.
But if they work for you, use them.

[Duke W.]

Re: Gas for 11:1 compression

Advertised compression ratios of the era are about as accurate as advertised horsepower. As built, sixties vintage engines are typically a half-point lower than advertised, and many that have been rebuilt have lowered CR, some to the point where they can run on regular, but you pay a price of 5-10 percent loss of torque, power, and fuel economy.

Current "93 octane", which is the arithmetic average of RON and MON is equivalent to about 97-99 RON, and owners' manuals of the era recommended 98-100 RON, which is the range of typical sixties premiums. So detonation due to insufficient octane should not be an issue if 93 PON is available in your locale.

Some areas of the country, like California, might only have 91 PON, which is about equal to 95-96 RON, so some detonation may occur, but it can usually be tamed with 2-4 degrees less spark advance at a cost of about one percent torque, power, and fuel economy.

Ethanol has a high octane rating, but the base stock gasoline it's blended with has lower octane than gasolines that are not designed for added ethanol, so the final PON ends up the same for the specific grade of fuel regardless of ethanol content.

Vintage Corvette engines don't need so-called lead additives, most of which don't have any TEL, anyway. TEL combustion products can protect integral cast iron valve seats from receeding, but it's only an issue in heavy duty use like trucks or racing.

Run-on is usually caused by hot combustion chamber boundaries, which can be a result of too little total idle timing. It was a problem on early emission controlled engines because initial timing specs were reduced and vacuum advance disabled in order to heat up the exhaust gas so oxidation would occur in the manifolds with injected air, and this also heated up the combustion chamber boundaries.

Ideal total idle timing - lowest EGT and minimum idle fuel flow requires low twenties to low thirties total idle timing. On most pre-emission engines this was achieved with the combination of initial timing and full vacuum advance. Low overlap cams can be in the lower end of the range and high overlap cams need to be in the upper half. High overlap cams leave a lot of exhaust residual in the combustion chambers at idle and low load, which slows flame propagation speed, so they need more spark advance under these conditions for optimum efficiency.

Duke

[John F.]

Re: Gas for 11:1 compression

The Max Lead 2000 has worked real well in my 427/390 when mixed with non ethonol 93 octane gasoline. The engine has not been into and has 51,000 miles on it. I really don't want to have to have the heads taken off and rebuilt. Can you still get the real lead additive? I am about out and have been unsuccessful in locating a supplier.

[Larry M.]

Re: Gas for 11:1 compression

The Max Lead 2000 has worked real well in my 427/390 when mixed with non ethonol 93 octane gasoline. The engine has not been into and has 51,000 miles on it. I really don't want to have to have the heads taken off and rebuilt. Can you still get the real lead additive? I am about out and have been unsuccessful in locating a supplier.

Try this link: http://www.jackpodellfuelinjections.com/maxlead.htm

Normally his ads are in the Driveline.

Larry

[John F.]

Re: Gas for 11:1 compression

No ad for Jack this issue. Tried his number and left message on answering machine last week. No response. Heard from someone that he no longer sells the Max Lead 2000. Does anyone know any other source for lead additive?

[Michael W.]

Re: Gas for 11:1 compression

Try running on straight pump gas, you might be surprised. If it does make a difference, best look into repairing or adjusting what's wrong. No need for lead on any Corvette and no need for higher octane than pump on a 427/390.

[Larry M.]

Re: Gas for 11:1 compression

Try running on straight pump gas, you might be surprised. If it does make a difference, best look into repairing or adjusting what's wrong. No need for lead on any Corvette and no need for higher octane than pump on a 427/390.

I agree with Mike if you have a stock/OEM motor.

However, if you want a source for the TEL additive, then GOOGLE "max lead 2000" or "octane supreme 130" and contact one of the listed suppliers. There are a few listed.

It appears that the source of the TEL additive (KEMCO OIL and CHEMICALS in Utah) has allowed their website license to expire. This could mean that they are selling the business or going out of business. I don't know??

Their phone number is (was) 801-768-4408. Try and call them on Monday. Even if they are closed, there should be adequate inventory still within the system through a few of their suppliers. GOOGLE is your friend.

Larry

[John H.]

Re: Gas for 11:1 compression

It appears that the source of the TEL additive (KEMCO OIL and CHEMICALS in Utah) has allowed their website license to expire. This could mean that they are selling the business or going out of business. I don't know??Larry

Larry -

The Kemco outfit folded their tent about a month ago.

[Larry M.]

Re: Gas for 11:1 compression

Larry -

The Kemco outfit folded their tent about a month ago.

Thanks John. Now we know what happened. They sold a number of products including racing gasoline, as well as the controversial TEL additive.

Do you know the reason why?? Government/environmental issues?? Financial?? Legal issues??

Larry