Question for our gasoline experts on AV Gas. (100LL)

[Larry E.]

Had my 70LT1 out on a short run yesterday. (1/2 hour run) Outside temp was extremely high 95 degrees. When it got home
I stopped in the driveway and shut off. Would not restart until it cooled down. I run straight 100LL Av Gas in the car. Here is my
question: Would running straight AV Gas make the engine run a little hotter? This was a common problem (hot start) with the 70 LT1's especially in the "F" cars because of the close proximity of the exhaust manifolds to the Starter/Solenoid area. In fact GM came out with a special solenoid spring to cure the problem(which is in there now). Never had a problem till now. Comments Please. Thanks -- Larry P.S. Anybody else ever had this problem either in a Corvette or Camaro LT-1??

[Stuart F.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Does the engine crank over under the heat soak conditions?

Stu Fox

[Larry E.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Does the engine crank over under the heat soak conditions?

Stu Fox

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No; nothing. Silent till it cools down; then works perfect. Larry

[Duke W.]

Re: Question for our gasoline experts on AV Gas. (100LL)

No, avgas does not make the engine run hotter. One thing you can do to reduce internal heat generation/heat soak issues is to convert the ported vacuum advance to full time, disable TCS if equipped, and install a B28 VAC.

You should also install some light centrifugal springs to bring the 26 degrees centrifugal in before the OE 5000 RPM, and run initial timing of 12 to achieve 38 deg. total WOT advance at 2500-3000.

The OE spark advance map was set up to maintain high EGT to oxidize HC and CO in the exhaust system, and much of this heat is transferred to the coolant as the exhaust gas traverses the exhaust port. The hot exhaust manifolds and head pipes also radiate a lot of heat to nearby engine components. This has a considerable cost to fuel economy and performance. The ideal spark advance map for your engine is as close to the OE 327-365/375 HP as possible.

If you use an IR gun to measure exhaust manifold temperature at idle with the engine fully warmed up after a drive you will likely find they are somewhere near 900F. With the above recommended spark advance map, they should be no more than 500, and that will likey cure your starting issue. Radiant heat transfer increases with the fourth power of temperature, so the reduction in radiant heat transfer from the cooler manifolds and head pipes is dramatic.

Duke

[Jim T.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Although not an LT-1, my 1970 Corvette was changed to full time advance the the TCS disconnected about a week after buying my new 1970 Corvette. Full time advance gave better gas mileage in city driving and cooler driving temperatures in city traffic. Still using full time vacuum for 45 years.

[Gene M.]

Re: Question for our gasoline experts on AV Gas. (100LL)

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No; nothing. Silent till it cools down; then works perfect. Larry

Since you get NOTHING AT ALL, I would do the simple things first. Check that connections are tight. If that is ok try the firewall connector too. Could be bad cut out switch if it's the green knob type. Remove the solenoid and take it apart and see if the contacts are buggered up. NOTHING AT ALL means no clicking, not engaging or turning over. Gotta be electrical issue, something with HIGH resistance, since when cooled down it works.

[Larry E.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Since you get NOTHING AT ALL, I would do the simple things first. Check that connections are tight. If that is ok try the firewall connector too. Could be bad cut out switch if it's the green knob type. Remove the solenoid and take it apart and see if the contacts are buggered up. NOTHING AT ALL means no clicking, not engaging or turning over. Gotta be electrical issue, something with HIGH resistance, since when cooled down it works.

Gene/Stu: Thanks for the suggestion but I know the problem. It's too much heat by the starter/solenoid area. Like I said in the above GM issued
a new spring for the solenoid. IIRC GM issued a bulletin on this problem for the Camaro Z28. Could also be a problem in the Vettes. The problem is one that I can live with since the car
is trailered 95% of the time; just will not take a ride in it when it gets about 90 degrees. Will take the spring issue up with Joe Lucia. Thanks; Larry P.S. Thanks Duke for the insight; and telling about the AVGas. Larry

[Gene M.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Larry, you should at least have a click at solenoid. I would not be happy because that 5% of the time you may not be starting...... remember Murphy's law if it can go wrong it will.

[John D.]

Re: Question for our gasoline experts on AV Gas. (100LL)

I remember showing off with my 63 FI car at a Seven Springs, PA Regional in 2008. It was 93 plus degrees outside. A bunch of us were waiting for the ops teams or teamleaders to show up.
My FI car had pure 100LL in it. I ran the engine for 45 mintues with the hood closed. It just sat there and idled. Tuned the key off and the temp gauge pegged.
Opened the hood and the hot air just blasted out. I wait a couple of minutes.
Then I didn't practice what I preach. I reached in the window. Turned the key (wrong way to start a hot FI car) and the LWC started right uyp and ran like a clock.
Guys were saying it's because of the FI unit, etc. I said well a little bit but it's mainly because of the 100LL fuel. True story. JD

[Edward J.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Larry you can try wrapping the exhaust pipe or a heat blanket on the starter. to see if this helps. years ago this was a common issue with exhaust headers. Hot soak condition on starter was a common issue with big blocks, and suppose it can be with a small block. GM use to use a high temp.gasket between the solenoid and motor to help with heat on big blocks.

[Bill C.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Larry --

have you checked all the frame and battery grounds? I had a very similar issues on my BB 72. turned out that a bolt came loose from the starter to frame ground.

also -
there is at least one usable link wire connected to the solenoid. maybe there is an issue with it ???

Bill

[Joe L.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Gene/Stu: Thanks for the suggestion but I know the problem. It's too much heat by the starter/solenoid area. Like I said in the above GM issued
a new spring for the solenoid. IIRC GM issued a bulletin on this problem for the Camaro Z28. Could also be a problem in the Vettes. The problem is one that I can live with since the car
is trailered 95% of the time; just will not take a ride in it when it gets about 90 degrees. Will take the spring issue up with Joe Lucia. Thanks; Larry P.S. Thanks Duke for the insight; and telling about the AVGas. Larry

Larry-------


The solenoid spring will not solve the problem. I tried that among many other things once-upon-a-time. I had this problem in my original owner 1969 300/350 since practically the time it was new.

The only thing I ever found that solved the problem PERMANENTLY was the installation of a slave (remote) solenoid. After I did that, hot restarts in Death Valley in the summer were no problem.

[Paul Y.]

Re: Question for our gasoline experts on AV Gas. (100LL)

Larry-------
I agree Joe, I have several installed on my vehicles and they are fail proof.

The solenoid spring will not solve the problem. I tried that among many other things once-upon-a-time. I had this problem in my original owner 1969 300/350 since practically the time it was new.

The only thing I ever found that solved the problem PERMANENTLY was the installation of a slave (remote) solenoid. After I did that, hot restarts in Death Valley in the summer were no problem.

I agree Joe, as I have several installed on my vehicles and they are trouble free starts in the heat.