Fuel 1970 LT-1

[George C.]

I have a 1970 LT-1 (11:1 compression) and was told that I could not mix 100 octane low lead avgas with 91 octane pump gas.

Has anyone had any problems mixing these two fuels together?

[Duke W.]

Re: Fuel 1970 LT-1

I wish I had a nickle for every time someone said "I was told..." without any discussion of the source or its credibility. You can mix any and all kinds of fuel called "gasoline" to achieve the necessary octane requirement, but how do you know if the engine needs more than the highest commercial octane available to you. If it doesn't detonate, you don't need more octane than whatever you can buy at local gas stations.

If the engine is still original Flint-built... never overhauled, the actual CR is likely closer to 10.5 than the advertised 11:1. If it has been rebuilt it likely has lower compression. You can get an idea by measuring the head gasket thickness at the corners of the head-block interface. The OE shim gasket is .018" thick. If it has a thick composition gasket the CR is likely not more than 10:1. If it was rebuilt with "low compression pistons" it may be as little as 9:1.

The '71/'72 LT-1s had an advertised CR of 9:1 - probably closer to 8.5 in reality - and the specified fuel was 91 RON, which is equivalent to today's 87 PON due to a a different octane rating methodology, so if your engine was rebuilt with "low compression" it may not even need the highest commercially available octane.

Duke

[Larry M.]

Re: Fuel 1970 LT-1

Agree with Duke. But when I blend leaded gasoline with current pump gas I try and get "no ethanol" gas. Leaded fuel (AV gas or Racing gas) contains chlorides and bromides as lead scavengers that will increase corrosion in your fuel system if moisture is present. At least for me here in SE Louisiana, commercial gas with ethanol seems to absorb moisture from the air much more readily than "no ethanol" gas.

For that reason I use the gas without ethanol for my blending. So far no issues in MANY years. Something to consider.

Larry

[Kenneth B.]

Re: Fuel 1970 LT-1

Duke is right. My 70 LT-1 ran just fine on 91 pump gas. I guess if you want to drag race and rev. it to 7000 RPM you might want to use racing gas.

[Michael W.]

Re: Fuel 1970 LT-1

Has anyone had any problems mixing these two fuels together?

Yes, it emptied my wallet faster than I could refill it, all for no apparent gain.

Your car should run just fine on straight pump gas, 91 octane or higher.

[Ed H.]

Re: Fuel 1970 LT-1



I have to work that out this Spring. I was told by a respected engine builder (who oversaw this portion of the project) that it should run OK with 91 commercial pump gas. He did suggest, if I was to do extensive highway travel that I should add 'lead substitute' every other tankful. Another respected engine guy suggested the mix might need to be richened a bit. For around the town trips for ice cream, they agree, no need for 'lead substitute.'


YMMV

[Michael W.]

Re: Fuel 1970 LT-1

No Corvette engine ever works hard enough long enough to endanger the valves or valve seats. Lead or lead substitutes for this purpose are a waste of money.

[Larry E.]

Re: Fuel 1970 LT-1

FWIW: If the car is not to used very much I would use straight Av Gas(100LL). Not so much for the octane
and lead but it tends to last longer before it turns sour. I have used it for years with no complaints. Larry
P.S. It can be bought at local airports and brought back to your garage in 5 Gal Cans.

[Patrick H.]

Re: Fuel 1970 LT-1

YMMV

Ed,

If you are interested in any comments about the chassis shown, especially if you are thinking of judging, just let us/me know.
I can send comments offline if you prefer.

Patrick

[Daniel S.]

Re: Fuel 1970 LT-1



My 70 LT1 runs better on 110 or Cam 2 than it goes pump gas but we have no issue running solely pump gas...

[Bill L.]

Re: Fuel 1970 LT-1

I have a 70 L46 with same compression. All i will say is set the car up to a factory tune and run it on pump gas. Then run it with maybe 5 gallons of 100 octane leaded or unleaded with 93 pump gas and see if there is a difference.

My L46 idles better with much better throttle response and I can wind it up to the redline with absolutely no issue with the mix. I have to detune a bit for pump gas and it does not idle nearly as well and it will run on once in a while. It has never been apart except to replace the timing chain, clean up the intake, and replace the oil pan gasket. I am sure there is some carbon build up that may contribute to the problem, but she sure runs perfectly with a little more octane.

The difference is noticeable in the seat of the pants and at stop lights.

Bill

[Ed H.]

Re: Fuel 1970 LT-1

Ed,

If you are interested in any comments about the chassis shown, especially if you are thinking of judging, just let us/me know.
I can send comments offline if you prefer.

Patrick

Hi Patrick, Appreciate your interest - we've been together since 1976, over a lot of miles, stories, etc, etc, etc. It (known affectionately as The Plastic Pig) has been sitting in our garage for quite a few years now, but I managed to come up with a fair pile of cash to get it back together and road worthy. It is fairly original, but has had, counting me, at least 4 owners (I now know 2 of them, but haven't been able to figure out who #2 is.), each of whom has made their changes to the car, and I simply can't afford to correct them all, so I really don't see us going for an NCRS trophy anytime soon.

I've been chastised about a number of items with respect to paint, color, finish, etc, but if you see something beyond that that is a concern, please feel free to let me know.

Thank you!

[Patrick H.]

Re: Fuel 1970 LT-1

Hi Patrick, Appreciate your interest - we've been together since 1976, over a lot of miles, stories, etc, etc, etc. It (known affectionately as The Plastic Pig) has been sitting in our garage for quite a few years now, but I managed to come up with a fair pile of cash to get it back together and road worthy. It is fairly original, but has had, counting me, at least 4 owners (I now know 2 of them, but haven't been able to figure out who #2 is.), each of whom has made their changes to the car, and I simply can't afford to correct them all, so I really don't see us going for an NCRS trophy anytime soon.

I've been chastised about a number of items with respect to paint, color, finish, etc, but if you see something beyond that that is a concern, please feel free to let me know.

Thank you!

Ed,

Wasn't sure how particular you were going to be in the restoration. If you've already gotten advice, then I'll leave well enough alone. Sounds like a fun car!

Patrick

[Ed H.]

Re: Fuel 1970 LT-1

Ed,
... Sounds like a fun car!

Patrick

Huntington Beach, CA to Watkins Glen, NY, < 44 hours, solo.



Keepsake from first date. Spare you the long story, but was doing >90 mph



Took a while, but here's the result of that first date.

(Sorry for the thread drift)