WayneB_LT1

We built that engine very carefully to spec and it was broken down again by a shop that specialized in high performance and racing cars. We all scratched our heads. We're sure heat is the culprit but adding items to block the heat take it off original (I was rebuilding it for NCRS judging). You need to understand another thing about heat here in Georgia, that car draws its cooling air from under the car, not through the front grill. You have to live in the South to appreciate how hot asphalt gets in July and August and it is just four inches below your car, you could cook a steak on it. Gas has a variety of formulas in bigger metro areas, depending how close to town you are (I'm in town), those formulas just don't like the gas. I drop a five gallon can of AV fuel in (or 103 octane leaded racing fuel) and it purred perfectly. Not hard to draw a line from bad running to fuel type. I could tell a quick and noticeable heat difference when it tried to run todays ethanol laden gas...it got hot and got hot quick. Another thing that made it miserable was that 4:11 rear end. That may be fun in a quarter mile drag strip but it was pure misery cruising around, especially pumping out heat.

It was a fun journey rebuilding it, met lots of great people here, NCRS, and other forums but, that is one car I just don't miss. Nice to own a fairly rare car once and scratch that off the bucket list. I had owned sports cars since I was a teenager (I'm 63 now) and after that car was gone, I bought a new Yukon. I was tired of my backside six inches off the road in cars that jar your teeth driving over shadows for four decades. I looked back at the long list of sports cars I have owned and have no problem with three tons of steel wrapped around me and a luxury ride...above the traffic. I used to go to the Vette shows and would see C1, C2, and C3 cars restomoded where they dropped the old body on C6 frames...old school styling with modern guts. Shook my head because I had that "purist" mentality rebuilding mine. Doesn't seem so crazy to me now. I like air conditioning that works, smooth ride, modern accouterments. When you do a full restoration of one of the old C3's, you just have to get honest and admit to yourself they were truly a bucket of bolts. Fabulous styling but hey, that was a GM assembly line before the Japanese made us get religion about quality and durability. "Planned obsolescence" was real and fervently practiced. Todays Vettes are world class sports cars, those past eras were basically, craftsmanship wise, an embarrassment.

Now, I understand all of you younger guys getting into the nostalgia thing but, remember, I'm a Baby Boomer, those WERE the cars of the day when we started driving. As much "more cubic inch" thinking as we had back then, the cars just don't measure up to today's cars. A carb was an incredibly inefficient fuel system, you had peak performance at a certain RPM range and that was it. That was why NASCAR rigs were constantly changing settings in a race. Today a computer and fuel injection keep your engine running at its peak mix of fuel, air to perfectly match whatever RPM you throw at it, something you didn't get back then. I started driving in 1969, had a 68 350 Firebird (wish I had that one back), a 67 400 Firebird, 69 Camaro, 70 Camaro, Triumph GT6 (don't get me started on my opinion of British Leyland) 70 Malibu, 240Z when it first came out, 280Z, 300Z, 84 Vette, 71 Vette, that 70 LT1 and several more. Throw in the Chryslers and Dodge's my friends had and we ran the gamut of the prime of the muscle car era...while it WAS the muscle car era. So, for us guys and gals that were born when there were still forty eight stars on the American Flag, there does come a time when you can say "Ok, that was fun but, been there done that". Yesterday's cars and todays environmentalists just do not make a match.

AirBusPilot

AV fuel is kind of a band aid, it won’t make the power of race fuel.

The main reason is the incredibly slow burn rate. It was designed for air cooled, low rpm engines with very large combustion chambers. Those aircraft engines also use 2 spark plugs, each located on opposite sides of the combustion chamber. Each lights off the fuel, and the flame front meets in the middle. When pilots do a mag check, they shut off one plug and the rpm drops a few hundred rpm, then they switch to the other ignition and repeat. Redundancy is also a factor.

F4Gary

LT-1 fuel pump does not have a return line to the tank.

E10 gas may need a larger jet to get a richer mixture because of the ethanol.

Not having lead in the gas didn't have anything to do with his pinging.

He sold the car a few years ago.

He doesn't have the car anymore.

statik

Have you tried http://www.pure-gas.org They track which stations offer ethanol free gas. There were 2 that popped up in Atlanta. I dont know Atlanta well enough to not which other city names to check for.

DABall

I had my 70 LS5 454 rebuilt professionally to original specs. Compression ratio is 10.5 to 1. I had problems with 93 octane ethanol free gas. I found that some Sunoco stations in New England sell 5 gallon containers of 110 octane, leaded race fuel. I mix 10 gallons of the 93 ethanol free with 5 gallons of the 110 race fuel. Engine runs great!!

leigh1322

My tuning experience:
The original problem stated was the ethanol causing vapor lock. I agree it would. Octane in gasoline has a boiling point of 257 F and ethanol has a boiling point of only 173 F. (Chemist here).
I never had that problem with my 70 LT1 in a Z28, but in the hotter underhood environment of a C3, I could see it being a problem on a lot of these old C3s. with the newer gas ( I also never ran 10% ethanol tho). Blocking off the manifold heat riser and using the factory undercarb heat shield would both help with the vapor lock. So would more fuel pressure. If it is boiling in the bowls, you need the heat shield. Use a IR thermometer and check fuel bowl and manifold temps...If the large heat shield is too noticeable for judging purposes, use a thicker carb gasket, or make a heat shield the same size as the gasket. If the fuel bowl is that hot, you're gonna have trouble with ethanol.

The pinging problem is a whole different issue, and completely unavoidable with todays octane and 11:1 engines, and stock timing. .My stone stock but blue-printed 11:1 LT1 actually CC'd out to 10.5 to 1. (And that was also common.) Even then it required 99 octane to run the factory timing, or the ideal power timing. 93 Octane required many adjustments, but after much experimentation my best friend ( a speed shop owner) and I got it to run fine on 93 Octane. It did affect the power output though. Here's our recipe IIRC: Custom distributor curve limited to less than factory about 20 degrees IIRC. (It's been 20 years) The Centrifugal all-in by 2600 with weak springs. Inital timing at only 6-8 degrees for 93 octane, yields around 28 total. Bump initial up to 14-16 degrees inital for 36-38 total for max power with 99 octane.Check timing both at idle and 3000 rpm..Power probably dropped 30HP on 93 with de-tuned timing, but it worked. Still rev'd like mad. That fixed the full-throttle pinging.
Vacuum advance was also extremely critical for no part-throttle pinging. My Vacuum was only 10.5-11 at 900 rpm idle. Vacuum was "cutting-in or out" too early, even causing timing fluctuations at idle, and a wandering idle. With an adjustable vac can, we loosened up the vac diaphragm spring so it didn't cut the timing until 8-9 inches or below. We also limited vacuum advance (Brazed slot shut) to around 10-12 degrees.That's the one that killed most of the pinging.
After all that, it idled like a champ, nice and steady, never pinged, at either part or full-throttle. And I could switch to 99 octane and the "power" tune at will with a quick initial timing change, and a fuel change. Our 99 Octane formula (15 gal 93 octane plus five gal race gas). My recipe basically came straight out of the Chevy Power Book, with some tweaks.
Ran it that way for 27 years. Mostly on 93, except for "special" occasions.
I am sure with a little ingenuity, that "tune" could be duplicated and still be NCRS "corrrect". After all, they don't pull the distributor cap do they? The rest of it could be hidden.
Hope that our experimenting helps some of you with these old high compression engines.
My "new" ride is a 72 454 C3. It will look stock, but the motor will not be inside. No way am I putting up with 8.5 compression. It'll be at least 9.5 and probably 10.5, I'll just "fix" the timing. Oh yeah, don't say anything, but the cam just might be an LS6 grind (shhh...).
Can hardly wait!! Torque!!!
Z28Lee

gavino

I just came across this post so I am putting my two cents in. I have a L71 11:1 compression ratio BB.Pretty much needs the same gas. Sometimes things get confusing with gas. Aside from having ethanol(up to 10%) the 93 octane gas is equal to 1970 99 octane gas of the late 60s and early 70s. Different rating methods. So essentially todays min 93 octane gas should work in an LT 1. One thing that may have been overlooked is the low manifold vacuum that these high compression engines had. Doing the timing change and manifold vacuum switch helps. The only thing I wonder about after rebuilding the carb is what size power valve was installed. The power valve opens with engine vacuum and shoots in more gas. They should be of a lower value than the manifold vacuum so they don't open sitting in traffic. Very important to check the number on the power valve and fit to your engine accordingly.The lower the engine vacuum the lower the power valve number. I would put a vacuum secondary Holly 780-cfm-3310 and make sure the correct power valve and correct secondary spring diaphragm tension is installed.The 3310 carburetor has been inducted into the Hot Rod Hall of Fame! When you pounce on it fuel and air will be blended correctly. It'l fly. Its all about the carburetor.