VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc How Do I reduce Octane Level in Gas.

I herd that using today’s gas in a old car will damage the valves so I was wondering what type of additive can I use to reduce the octane level?

Someone told me I can add diesel fuel to my regular gas to reduce the octane but I don’t know if this is recommended.

It's for a 1927 Chevy.

Any thoughts?

Idon't think that is necessary. I usually add some Seafoam to keep the new gasoline from screwing up my carb , also add some Marvel Mystery oil for upper lube.

today's gasoline will not damage these old vehicles. there's a myth the absence of lead in modern fuel will damage valves. but it's just that, a myth. octane will not damage an engine in any way, shape, or form. filler up, add a little MMO if you prefer and drive to your heart's content.

I put 80,000 miles on a set of heads that were manufactured long before unleaded fuel and they showed no ill effects. and I worked that old truck hard

I know that I have not put anything in my 31 coupe since the rebuild and it runs fine. But I was wondering about my new project the 67 El Camino. Should that have something added to the gas?

Burned valves on older engines that have not been rebuilt with hardened ones will only happen with sustained high speed driving, like a lot of long road trips between cities. the driving most of us do cruising, going to shows, etc. should not pose a problem. If you are really paranoid, you could rebuild the engine with hardened valves. I personally would not bother. And don't even bother with the lead substitutes found in the stores. It has minimal value raising octane and has nothing in it that will protect the valves. One more thing, I did read an article that said that if the car was run on leased fuel for any amount of time, the valves will typically be 'protected' for the life of the engine. However there is no way to substantiate this claim.

There is absolutely no relation between octane and valve wear.

Tetraethyl lead supposedly has two purposes: raising octane and lubricating the valve seats. Only the lubricating property could have any effect on the valves. As far as I know, excess valve wear from lack of lead has never been proven.

Adding diesel is a crude way to raise octane. There is no conceivable reason to raise octane for that vehicle.

When your 1927 was new the majority of gas was unleaded. Lead did only one thing to gas and that was to make it burn slower. It had nothing to do with the valves. Today better refining raises the octane. The removal of lead can actually make the valves last longer because it prevents lead deposits from forming on the valve seats and preventing the valves from closing tight. The lead also shortened the life of the bearings, exhaust system and spark plugs.Modern engines would never go 200,000 or more if they used leaded as. Years ago it was common to grind valves by 20,000 miles.

Really, so even the commonly mentioned effect of lubrication is false? Who started all of these rumors? Lead companies?

I will join the dudes above and also say that lead additive is not necessary! Your car will run just fine without it....period!

What about the lead paint we ate as children? Do they make a lead substitute paint chip?

My 1968 Impala Sport Coupe with a 275HP 327 and 400HT runs fine on tours and Interstate driving on regular and also premium unleaded, sometimes I will treat it to a tankful of premium, without any extra additives , It is an original engine with 104,000 actual miles on the odometer. It uses a bit of oil (a Qt about every 800 miles.) "Betsy" will burn rubber any time you want to. Of course the real owner (the boss lady) jumps on the old hotrodder driver for any street raceing. Sometimes I just gotta blow away one of those Dodge Rams. Ha!

Yeah, Home Depot had a liquid paint kit for anyone addicted to lead paint chips (window sill) and it has to dry for 5 years to mature, it is not really lead, but tastes good anyway!

after a highway run back in the day, tail pipes would be light gray to almost white due to the lead. it would be used as an indication of the condition of the engine. plugs would have small globs of lead on them.

I knew I could count on Mack to catch that.

I know the thread is about lead and burnt valves, but for completeness of information, here is another tidbit.

When I got my 28 in Feb, I too had the same questions since the PO had mentioned the engine knocked and gave me some 'lead additive'. Actually, it was the clutch that was thunking away. None the less, in my quest for info, I found a good article on the history of gas that said that back in the 20's the octane was around 40-60. Needless to say today's 87 is more that sufficient.

Yes, I would say that the old 4 cylinder (roaring fours!) are quite adaptable to fuel octane quality, The new unleaded will do a job of gunking up the fuel supply system if it is left in for a while without running the car. I am using Seafoam to counteract the detiriation and short storage life of the gasoline. I haven't been using it in the 28 very long, but I use it in the tanks of the outboard boats. Marine use is what Seafoam was originally made for.

Thanks to all for the answers to my question. I thought so but it never hurts to ask. Thanks again. :vcca:

Thanks everyone for your help. I will just add MMO & Seafoam to the gas.