Fuel- 1967 427/435

[Michael B.]

I just purchased this 427 and would like opinions on fuel/additives.It is more of a show car than a daily driver and is stock.I would appreciate your comments. thanks

[Don H.]

Re: Fuel- 1967 427/435

Hey Michael
welcome to NCRS and the tech board. The Big Block boys will have their own answers to your question, but you can read past threads on this topic until the cows come home if you see the small box on upper right of this page, enter fuel and additives (all three words) and hit the search button. Lots has been written and discussed.

[Don H.]

Re: Fuel- 1967 427/435

In my opinion (and just that) you will be far better off running aviation fuel or racing gas rather than any additive. Especially if it is going to do a lot of sitting - it will not go bad nearly as fast as pump gas as well as the performance benefits. Welcome to NCRS & good luck, Don H.

[Michael J.]

Re: Fuel- 1967 427/435

My stock '67 L71 coupe gets nothing but ethanol free premium, no additives ever. I am lucky I have a station close to me that has it. In my experience, it helps a great deal with hot starts, cold starts after long times sitting, and smooth running. But, you will find others who's experience may vary…...

[Jim T.]

Re: Fuel- 1967 427/435

An additional thought Michael is putting fuel in the fuel bowl when your 427/435HP Corvette is not being driven. If the fuel bowl has added fuel before start -up or cranking the engine you will be saving your starter from turning over the engine to fill the carburetor with fuel so you can start your Corvette. I use this procedure on my Holley equipped Corvettes and they start immediately after long periods of non use. Put ounces of fuel through the vertical vent tube after removing the air cleaner lid. Fuel in Holley's does evaporate.

[Jimmy G.]

Re: Fuel- 1967 427/435

Avgas all the way !!!!!

[Michael B.]

Re: Fuel- 1967 427/435

Thanks Jimmy, i tend to agree.Should i use 100ll or Jet A

[Michael B.]

Re: Fuel- 1967 427/435

Jim, Thanks for this great idea.

[Michael B.]

Re: Fuel- 1967 427/435

Thanks Michael. is what you use unleaded? Can you be specific as to what you use.

[Michael B.]

Re: Fuel- 1967 427/435

Thank you Donald.Can you reccomend a specific racing fuel?

[Michael W.]

Re: Fuel- 1967 427/435

Thanks Jimmy, i tend to agree.Should i use 100ll or Jet A

Jet A? That's not gasoline.

Your car should run acceptably on pump premium. This topic has bee thrashed extensively.

[Duke W.]

Re: Fuel- 1967 427/435

Jet A is basically No. 1 diesel fuel, which has an octane rating of less than 50.

The first thing you should do is determine how the engine runs on pump premium. Do a detonation test. Load it up at low revs in top gear and listen.

The second thing you should do is wire the heat riser open and convert the OE ported vacuum advance to full time if it has not already been done. This will lower operating temperatures in stop and go traffic and reduce the tendency for fuel bowl percolation. You will also need to replace the OE "MS 201 15" VAC with a B26.

This subject has been discussed extensively on the TDB including a recent thread no more than a month old.

Most OE engines will operate satisfactorily on pump premium without any snake oil additives or need to dope pump premium with avgas or racegas, and some "high compression" engines will even operate satisfactorily on regular unleaded because they were rebuilt with low compression pistons and thick head gaskets.

Many owner's may think they have an "11:1" compression ratio engine, but most actually have no idea what the actual compression ratio is because the engine was rebuilt two or three owners ago. and there is no documentation on what actual parts were installed and other data necessary to calculate the actual compression ratio. Most OE engines are rebuilt with lower compression than when they left Flint or Tonawanda, and advertised compression ratios were typically 0.5 higher than as originally built.

One thing you can do is use feeler gages to measure head gasket thickness at the corners of the head-block interface. The OE shim type gasket was .028". Likely your engine, like most others has a thick composition gasket that lowers the CR another 0.5 even with the OE type pistons, so at best it may be 10:1.

The only way to understand what is needed for your specific engine is to run these simple tests.

Duke

[Michael J.]

Re: Fuel- 1967 427/435

Thanks Michael. is what you use unleaded? Can you be specific as to what you use.

I guess you meant me, too many Michaels….but yes it is unleaded and is only 91 octane, as premium at my altitude (8000'+) is all that way, except this has no ethanol. However, as I have the changes Duke specifies to the timing, VAC, etc. I have never had an issue with pinging or knocking or overheating. And also, I use the same fuel in my '64 L76 that has a B28 VAC, but runs just as well in all ways.

[Mike E.]

Re: Fuel- 1967 427/435

This map linked has been posted before on this topic, one more time can't hurt, zoom in on your area. I found a station about 5 miles from me that has e-free fuel. If you have a Smart Phone bookmark it for road trips.

http://pure-gas.org/extensions/map.html

Mike

[Duke W.]

Re: Fuel- 1967 427/435

Thanks Michael. is what you use unleaded? Can you be specific as to what you use.

Nowadays, there is so much statutory and regulatory control of gasolilne blends that it makes no difference what "brand" you buy. Refiners have to blend gasolines with the same chemical and physical characteristics depending on region and season, so buy gasoline based on price and convenience.

Like many new owners of vintage Corvettes your head is full of myths and misinformation from reading dire warnings on the Web, etc. It's not that complicated, but you do need to run some simple experiments and think about making some simple modifications to the spark advance map if you want to opitmize performance, fuel economy, and make buying gasoline as simple as with your daily driver.

Duke