Todays unleaded gas just won't work in 70 LT1 high compression engine
01-03-2018, 11:54 PM
#21
Team Owner
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Location: Southern Cal Ca
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St. Jude Donor '22
heat is the enemy.
carb jetting, dist advance, vacuum advance
power valve.
I tried the 100 low lead av gas. live by an airport
and had field access.
don't like the stuff.
different burn rate is all i can say.
now a days, with cheap plug in oxeg sensors and readers
you should try checking the mix your carb is putting out.
01-04-2018, 02:15 AM
#22
Melting Slicks
The physics don't fit your analogy. Gasoline has a starting boiling point of 95 degrees fahrenheit. Ethanol has a starting boiling point of 173 degrees fahrenheit. Gasoline also has a higher reid vapor pressure than ethanol, which means at 100 degrees F, gas is vaporizing more than ethanol. In other words, ethanol will not cause vapor lock. There have been a lot of studies on these kind of effects.
The reid vapor pressure is raised for cold seasons in pump gas, so in the winter it will vaporize better for starting engines. Winter gas will vapor lock easier in warm weather.
Avgas has a lower reid vapor pressure and higher boiling point than pump gas so it does not vapor lock at altitude. It makes sense that it helped your vapor lock problem.
I remember a lot of old cars having vapor lock problems back in the 60's, long before the ethanol gas mix. Better operating cooling systems and shielded fuel lines and carbs help prevent vapor lock. And yes, sometimes clothespins on the fuel line helped.
I believe the problem was with your car, not the fuel. The fuel was getting too warm somewhere in the system.
Mike
The reid vapor pressure is raised for cold seasons in pump gas, so in the winter it will vaporize better for starting engines. Winter gas will vapor lock easier in warm weather.
Avgas has a lower reid vapor pressure and higher boiling point than pump gas so it does not vapor lock at altitude. It makes sense that it helped your vapor lock problem.
I remember a lot of old cars having vapor lock problems back in the 60's, long before the ethanol gas mix. Better operating cooling systems and shielded fuel lines and carbs help prevent vapor lock. And yes, sometimes clothespins on the fuel line helped.
I believe the problem was with your car, not the fuel. The fuel was getting too warm somewhere in the system.
Mike
01-04-2018, 06:51 AM
#23
Melting Slicks
Before I found a local source for 100 octane unleaded I used use what I call "Frankengas". 3 gallons 93 pump gas, 1 gallon zylene, and an ounce r so of Marvel Mystery oil. Also used it it my GN running 21 pounds of boost.
01-04-2018, 09:20 AM
#24
Drifting
I do not have an LT-1 car, but the engine that was in my car was an absolutely 100% factory assembled service replacement LT-1 engine. Every single number was correct to service replacement parts, the pistons were absolutely correct, the rods, crank, 4-bolt, lifters, TI Ignition...everything. It even still had the plastic-tooth timing gear on the correct LT-1 solid cam. The block date-coded to 1977-78. We estimated that the engine had maybe 10,000 miles on it.
My point: 100% true blue LT-1 engine and it ran just fine on premium fuel. When we cracked the engine open, there was a VERY, VERY small amount of wear that looked like it could have been attributed to detonation, but I have no idea what fuel the PO ran in the car. I could not hear any detonation.
Not sure if it helps or hurts, but I'd politely offer that it sounds like something else is amiss in your motor.
My point: 100% true blue LT-1 engine and it ran just fine on premium fuel. When we cracked the engine open, there was a VERY, VERY small amount of wear that looked like it could have been attributed to detonation, but I have no idea what fuel the PO ran in the car. I could not hear any detonation.
Not sure if it helps or hurts, but I'd politely offer that it sounds like something else is amiss in your motor.
Last edited by keithinspace; 01-04-2018 at 09:20 AM.
01-04-2018, 12:32 PM
#25
Team Owner
Settle a small argument, please.
Ok, here's a problem we had when I restored my 70 LT1; engine rebuilt to specs, engine parts and everything but, we could not get the thing to run on todays gas. The high compression engine needs high octane but todays falls short. Also needs leaded gas. We tried every timing/carb combination known to man (done by pro race car builders to boot) and couldn't get a smooth run. Even when we ran it awhile it would cut out after it got hot - the gas line runs over the top of the manifold and the alcohol in todays gas would evaporate and cause vapor lock...just like it would do in an airplane. So, the only thing that would work, we tried racing fuel (over 100 octane, leaded) and ran like a charm, of course, that is crazy expensive. Next we put in 100 octane leaded fuel...yes, they still sell it and it is called "aviation fuel" and you get it at small air fields. That's a little better on the pocketbook but, a real hassle to get, especially in the Atlanta area where the Department of Homeland Security keeps the airports in the metro area from selling it in cans or cars so you have to go outside the metro area to get the stuff. Driving forty five miles to fill up five gallon cans is a little crazy. Get an idle but spits and sputters elsewhere. Miss at low RPM and it going at higher. Get it warm and it cuts out because of vapor lock. We tried it all, timing, carb, valves...the only thing that worked was gas.
So, given that we tried every setting known to man to get it to eat todays crappy gas, anyone else come up with a solution...short of putting the engine on blocks and dropping in a crate engine? keep in mind, the engine was built to spec, including rods, pistons, the whole bundle, and runs an 11:1 compression. Meticulously calibrated.
I argued that it needed leaded gas to go with the high octane to handle the same problems prop plane engines run into (they are high compression too), and, that "ethanol" is just another vapor lock problem.
Anybody else rebuild a 70 LT1 to spec and get it running on todays gas? If so, I have no idea how, we worked settings on that thing for six months before sticking with 100 octane leaded gas or, the higher octane racing leaded gas.
Ok, here's a problem we had when I restored my 70 LT1; engine rebuilt to specs, engine parts and everything but, we could not get the thing to run on todays gas. The high compression engine needs high octane but todays falls short. Also needs leaded gas. We tried every timing/carb combination known to man (done by pro race car builders to boot) and couldn't get a smooth run. Even when we ran it awhile it would cut out after it got hot - the gas line runs over the top of the manifold and the alcohol in todays gas would evaporate and cause vapor lock...just like it would do in an airplane. So, the only thing that would work, we tried racing fuel (over 100 octane, leaded) and ran like a charm, of course, that is crazy expensive. Next we put in 100 octane leaded fuel...yes, they still sell it and it is called "aviation fuel" and you get it at small air fields. That's a little better on the pocketbook but, a real hassle to get, especially in the Atlanta area where the Department of Homeland Security keeps the airports in the metro area from selling it in cans or cars so you have to go outside the metro area to get the stuff. Driving forty five miles to fill up five gallon cans is a little crazy. Get an idle but spits and sputters elsewhere. Miss at low RPM and it going at higher. Get it warm and it cuts out because of vapor lock. We tried it all, timing, carb, valves...the only thing that worked was gas.
So, given that we tried every setting known to man to get it to eat todays crappy gas, anyone else come up with a solution...short of putting the engine on blocks and dropping in a crate engine? keep in mind, the engine was built to spec, including rods, pistons, the whole bundle, and runs an 11:1 compression. Meticulously calibrated.
I argued that it needed leaded gas to go with the high octane to handle the same problems prop plane engines run into (they are high compression too), and, that "ethanol" is just another vapor lock problem.
Anybody else rebuild a 70 LT1 to spec and get it running on todays gas? If so, I have no idea how, we worked settings on that thing for six months before sticking with 100 octane leaded gas or, the higher octane racing leaded gas.
Read up on Avgas. It is made to run at high altitude and low temperatures. Not as in old wives tails in your car on the ground. Just used by people that are clueless!
To deal with vapor lock GM had the answer before your car was built it is called the AC-delco bypass fuel pump that requires a return line to the tank. If it is heating of the fuel in the line from the pump to the carb, you can insulate the fuel line. If your carb boils over when you come to a stop after driving is called Carb Heat soaking. The metal shields is a dumb idea they still transmit the manifold heat. The best cure is a 4 hole 1/2 inch wood spacer as a thermal block.
My two Vette motors exceed your compression, but it was a learning curve because I built a high compression 383 ci years that pinging problems.
When the engine was built did they install domed pistons? They would have to if it was really 11.00 C/R. Did they polish the iron head combustion chamber? Did they pay close attention to the valve seats especially the exhaust side? You have to grind the seat and the valve for a wide contact area and the valve sunk down into the seat and not protruding into the chamber. Did they try several heat ranges of spark plugs? Did they install different spring weights in the dizzy to delay full advance? Was the cam dialed in when it was installed? You can try advancing the cam 2 test first and then 4 degrees to lower dynamic C/R.
People that tell you to use full vacuum on the vacuum advance don't understand that all you have to do is put a mechanical stop in the dizzy to limit total advance. So you install a stop that says limits you to 20 degrees. So you can run 16 initial for a total of 36 degrees total. Then you install a vacuum advance can that is adjustable and limit it to say 8 degrees additional.
If you have all this stuff dialed in and it still pings (you actually said not running smooth) on 93 unleaded from your service station there is only one cure and I came to this conclusion after fighting with octane boosters and every timing curve setting that I could come up with. when dynamic compression is to high the ONLY fix is to get a cam with higher .050 duration numbers. The cams designed in the 60's were not made to make the power of a modern cam. They were limited by spring technology. I've built friends Lt1 motors with modern Crane Cams solid lifters and they run much better that the 60's grinds. The 238/248 @.050 114 It makes the lobes on a lt1 cam look wimpy and no detonation even on our local 91 octane. If you sell the car just hand him the junky LT1 cam, springs, spring caps, and rotators
01-04-2018, 12:40 PM
#26
Team Owner
Ethanol in fuel will cause it to boil around 10 degrees lower temp than regular fuel. If you engine is running hot, it could cause vapor lock; fuel shouldn't be hot from the pump as it had a return line. Pump-to-carb fuel line should be insulated with outer foil surface, and carb needs insulator for intake manifold.
Perhaps your plug heat range is too high or timing is retarded to make engine run hotter than it should.
Personally, I think you have other "set-up" issues that are the source of your problems.
Perhaps your plug heat range is too high or timing is retarded to make engine run hotter than it should.
Personally, I think you have other "set-up" issues that are the source of your problems.
01-04-2018, 12:55 PM
#27
Team Owner
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01-04-2018, 02:14 PM
#28
Team Owner
Hello, a few things, LL 100 av gas is very low in lead, prop planes usually have low compression. Many piston driven aircraft engines are 7.6 - 9.0 compression. I am fortunate that I run a supercharged IGSO 540 Lycoming in my boat and have fuel on hand. In my L-46 I use a 50/50 mixture of 89 non alcohol and av gas, works well for me.
Carbs, fuel injectors and other components are designed with the dye in mind. Our street carbs/injectors are NOT designed to run this gas for very long as the dye is very sticky and will gunk up your carb if the gas is allowed to evaporate.
When I was an A&P working on Cessna's etc. we'd replaced a gas tank for some reason I'd always take the used Avgas and put it in my Fiero. It made a performance difference but after a few tanks I had to remove my TBI and clean it because of the dye.
My ZZ4 runs 10.5:1 compression and I've always struggled with pinging. It seems to be better in the winter when they come out with the winter blends and the air is cool. I have rung octane booter and that helps alot. I usually run that in the summer.
If you're looking for non-ethanol gas try this website:
https://www.pure-gas.org/
Last edited by theandies; 01-04-2018 at 02:17 PM.
01-04-2018, 02:34 PM
#29
as others have pointed out we can recommend adjustments but you dont have the car any more.
I have a 69 with a 70 LT-1 short block I installed many years ago. It uses an Edelbrock RPM Airgap and has hooker side mount headers, a rejetted 780 Holley, early version of Chevy slant plug heads, recurved distributor, 160 thermostat.
The car has run for decades on 93 octane, 10% ethanol gas. It runs better on 100 unleaded mix or 110 leaded mix but the 93 does not make it a problem to drive.
I have a 69 with a 70 LT-1 short block I installed many years ago. It uses an Edelbrock RPM Airgap and has hooker side mount headers, a rejetted 780 Holley, early version of Chevy slant plug heads, recurved distributor, 160 thermostat.
The car has run for decades on 93 octane, 10% ethanol gas. It runs better on 100 unleaded mix or 110 leaded mix but the 93 does not make it a problem to drive.
01-04-2018, 05:07 PM
#30
Melting Slicks
OK, I am one to admit when I am wrong. I have seen the "10% ethanol raises the reid vapor pressure of gasoline 1 PSI" claim before, but it did not make sense to me since ethanol has a much lower RVP than gasoline. I did some searching today and found a paper on RVP laws for gasoline with and without ethanol. I found this explanation in the paper.
"Blending of ethanol into gasoline at 10 volume percent causes the RVP to increase by about 1 psi
despite the fact that fuel grade ethanol has a lower vapor pressure than gasoline (see Figure 1).
The low vapor pressure of fuel grade ethanol is caused by attractive forces between the ethanol
molecules. The strongly electronegative oxygen atom in each ethanol molecule is attracted to
the somewhat positive hydrogen atoms in other ethanol molecules. The attraction between
ethanol molecules means that it has a stronger tendency to stay as a liquid and not vaporize into
the more dispersed gaseous state. However, when blended into gasoline at relatively low
concentrations the more numerous gasoline molecules disrupt the attractive forces between
ethanol molecules and allow the ethanol to readily evaporate, raising the vapor pressure of the
blend. Not surprisingly this increase in vapor pressure with ethanol is more marked with the
lower RVP hydrocarbon blendstocks. This would be true with the addition of any component
which raises vapor pressure, as the final pressure is a weighted average of the pressure
contributions of all of the components. As ethanol content is increased above about 20% the
vapor pressure increase becomes less, and above about 50% ethanol vapor pressure for the blend
is less than that of the gasoline."
Seems I was wrong, ethanol at 10% could contribute to vapor lock. However, RVP on 10% ethanol is still much lower than RVP of gasoline that was available when these cars were new, so E10 is still less likely to cause vapor lock than fuels of yesteryear.
Mike
"Blending of ethanol into gasoline at 10 volume percent causes the RVP to increase by about 1 psi
despite the fact that fuel grade ethanol has a lower vapor pressure than gasoline (see Figure 1).
The low vapor pressure of fuel grade ethanol is caused by attractive forces between the ethanol
molecules. The strongly electronegative oxygen atom in each ethanol molecule is attracted to
the somewhat positive hydrogen atoms in other ethanol molecules. The attraction between
ethanol molecules means that it has a stronger tendency to stay as a liquid and not vaporize into
the more dispersed gaseous state. However, when blended into gasoline at relatively low
concentrations the more numerous gasoline molecules disrupt the attractive forces between
ethanol molecules and allow the ethanol to readily evaporate, raising the vapor pressure of the
blend. Not surprisingly this increase in vapor pressure with ethanol is more marked with the
lower RVP hydrocarbon blendstocks. This would be true with the addition of any component
which raises vapor pressure, as the final pressure is a weighted average of the pressure
contributions of all of the components. As ethanol content is increased above about 20% the
vapor pressure increase becomes less, and above about 50% ethanol vapor pressure for the blend
is less than that of the gasoline."
Seems I was wrong, ethanol at 10% could contribute to vapor lock. However, RVP on 10% ethanol is still much lower than RVP of gasoline that was available when these cars were new, so E10 is still less likely to cause vapor lock than fuels of yesteryear.
Mike
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PainfullySlow (01-06-2018)
01-05-2018, 12:31 AM
#31
Team Owner
Not my experience over these many years. But, lots of things have changed over that same time.
01-05-2018, 11:35 PM
#32
Old Pro Solo Guy
I too think something else is going on here. BTDT. I Suggest you try a different carb just for a quick test. Then you'll know if it is carb related. I know, you rebuilt the factory one several times. But I too had severe problems with my factory GM 70 LT1 Holley. It turned out the factory carbs have adjustable air bleeds that the aftermarket ones do not have. They are hard to spot, clean, or adjust during a rebuild. Look at the primary air bleeds, they are wide open and have no small diameter insert. Look in front of the choke horn, near the gasket, there are two dimples covered in something like body putty. Once you dig that out, there are two hidden air bleed screws you can use to adjust the air bleeds. They have a huge effect on part-throttle. Aftermarket carbs are set much richer, these are much leaner part-throttle. Holley can also re-calibrate it if you prefer.
FWIW Mine would run great on pump gas, but I had to pull like 8 degrees timing out of it. With better gas (99+) and the timing back it really screamed with 20-30 more HP.
Good luck;
FWIW Mine would run great on pump gas, but I had to pull like 8 degrees timing out of it. With better gas (99+) and the timing back it really screamed with 20-30 more HP.
Good luck;
01-06-2018, 07:46 AM
#33
Le Mans Master
OP, have you tried running any Torco Octane booster in the 70' LT1 just to see if it improves the pinging?
I think I would either try some Torco or even some VP race gas just to see if it alleviates the pinging. If it does, then you KNOW for sure you don't anything else weird going on. You may have to feed it a steady diet of Torco from now on, but at least you'll be able to keep some timing in it and keep it making power.
I think I would either try some Torco or even some VP race gas just to see if it alleviates the pinging. If it does, then you KNOW for sure you don't anything else weird going on. You may have to feed it a steady diet of Torco from now on, but at least you'll be able to keep some timing in it and keep it making power.
01-06-2018, 11:20 AM
#34
all the people or are still suggesting great ideas, do you realize the OP no longer has the car so he can not try out anybodies suggestions.
01-07-2018, 12:13 AM
#35
Team Owner
It's a worthwhile topic to discuss...whether the OP still has the car or not. Maybe some other LT-1 owners will chime in with their experiences on this issue.
01-07-2018, 10:57 AM
#36
Melting Slicks
Seems to have been two different, yet partially related issues going on:
1. Overheating of the fuel causing vapor lock
2. Dynamic Compression+Combustion heat too high for the fuel
Gkull provided some great solutions for both.
If you're going to go with Octane Boosters, personally science has moved beyond Torco; no need to have the orange manganese deposits from Torco. Go with Boostane with less manganese and all the manganese in solution.
Adam
1. Overheating of the fuel causing vapor lock
2. Dynamic Compression+Combustion heat too high for the fuel
Gkull provided some great solutions for both.
If you're going to go with Octane Boosters, personally science has moved beyond Torco; no need to have the orange manganese deposits from Torco. Go with Boostane with less manganese and all the manganese in solution.
Adam
01-07-2018, 09:50 PM
#37
Take the lid of the air cleaner assembly. Close the hood and take the car for a ride. The culprit is pressure buildup in the carb and limited air. If you are using a reproduction intake assembly or not using a 3 inch filter element it will cause a wildly rich condition that is hard to diagnose. The Holleys need 3/4 inch clearance for the air tubes to work properly on the 780 carb . If not it will run pig rich under load all the time. If you have the stock assembly measure the distance of your air tubes and the lid. I chased a similar problem for months on my LT-1 that was beyond frustrating. Lars has commented on this very subject also.
I’m going to do a write up on it soon
I’m going to do a write up on it soon
Last edited by LT3; 01-07-2018 at 09:59 PM.
01-07-2018, 10:02 PM
#38
Safety Car
Get the "Pure Gas" app for your phone/tablet. Ethanol free gas isn't that hard to find in Metro Atlanta area. There are several stations on the north side of Atlanta with 91 to 93 octane ethanol free. It's more common around the lakes (Lanier and Altoona ), but there are stations with it closers in, too.
01-08-2018, 07:22 PM
#39
Burning Brakes
Member Since: Aug 2013
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I have had the same problems with the "crap gas, and all my fun cars were high compression engines built to GM specks because they (GM) could out spend me when it came to designing a engine.
I tried most everything to stop the ping with the factory tune up specks.
Nothing worked on pump gas here in CA. I blend avgas in my tank and my engines run great. I tried some methods advised and my engine dieseled so bad when I turned it off that it cracked a piston skirt. It was a automatic transmission and I finally had to put it in gear, turn the A/C on to get it to stop.
I retarded the timing and it ran like crap and would barely lay rubber. Put the avgas in and advanced the timing and laid about 300 feet of rubber.
No matter what I do to my engines with pump gas, they loose HP big time.
I was trumped on about every post I wrote telling me I was everything from a pee brain to whatever, but the bottom line is HANDS DOWN avgas has worked for me on all my high compression cars and I don't mind being called names by those that never tried higher octane fuel like we had when the engines were designed. Yes something did change, The gas!! On long trips I used water injection to stop the pinging when I couldn't mix avgas with my fuel.
The gas thing has been beaten to death, even to the point of engine damage. I learned my lesson, do what works. No more cracked piston skirts for me, and no more HP loss.
I understand that some can't get what we need to drive our hobby cars and we have to give something up to get original factory performance out of a engine that was designed for a different fuel that is available at the pumps.
I am happy with what has worked for me for all these years.
Dom
I tried most everything to stop the ping with the factory tune up specks.
Nothing worked on pump gas here in CA. I blend avgas in my tank and my engines run great. I tried some methods advised and my engine dieseled so bad when I turned it off that it cracked a piston skirt. It was a automatic transmission and I finally had to put it in gear, turn the A/C on to get it to stop.
I retarded the timing and it ran like crap and would barely lay rubber. Put the avgas in and advanced the timing and laid about 300 feet of rubber.
No matter what I do to my engines with pump gas, they loose HP big time.
I was trumped on about every post I wrote telling me I was everything from a pee brain to whatever, but the bottom line is HANDS DOWN avgas has worked for me on all my high compression cars and I don't mind being called names by those that never tried higher octane fuel like we had when the engines were designed. Yes something did change, The gas!! On long trips I used water injection to stop the pinging when I couldn't mix avgas with my fuel.
The gas thing has been beaten to death, even to the point of engine damage. I learned my lesson, do what works. No more cracked piston skirts for me, and no more HP loss.
I understand that some can't get what we need to drive our hobby cars and we have to give something up to get original factory performance out of a engine that was designed for a different fuel that is available at the pumps.
I am happy with what has worked for me for all these years.
Dom
01-18-2018, 09:27 PM
#40
Ethanol free gasoline
I have 2 cars that will not run well with ethanol gas. One is a 91 Mercedes 560SEL (fuel injected) and the other is my 64 Corvette, rebuilt 327 with a cam. Octane level matters more to the 327 than the 560, but neither of them like the EtOH...at all. If you can't find ethanol free gas in Atlanta you're not using www.puregas.org They have a great app that slides you into googlemaps to help you navigate cross country on EtOH free gas. There are dozens of locations around Atlanta. So, did you sell the car?