Fuel/additive recommendations
I just took delivery off the car hauler of my new '67 L71 coupe this morning (just before the snow hit) and as usual it came with about a 1/2 gallon of gas in the tank. I went and filled it up with the normal 90 octane unleaded (the max we have here at 7000 feet) that I have been using in my '66 L79 and got to wondering if that octane and unleaded is OK for the new Vette. As I said, I have had no issues with 90 octane unleaded in my L79, and it is a stock engine as far as I know. Does the stock L71 need anything more? Like an octane booster? I understand the lead additive is long gone from the shelves. Thanks for any advice.
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Big Tanks In the High Mountains of New Mexico -
Re: Fuel/additive recommendations
Here's a few hundred threads to keep you busy reading:
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Re: Fuel/additive recommendations
This subject has been discussed a zillion times. Most OE engines will operate without significant detonation on pump premium, but it's a matter of each individual engine due to production variance and different operating conditions.
So you're at 7000 feet and only have 90 PON fuel. Try it an see what happens.
There are no silver bullets.
DukeLast edited by Duke W.; December 7, 2009, 05:57 PM.Comment
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Re: Fuel/additive recommendations
They were there earlier.....as I read some of them. Don't know what happened.
Suggest searching on your own, using terms like "fuel additives", "lead additives", "TEL", or "octane booster".
90 octane ( (R+M) /2) may be a bit low for this engine. I think 93 octane will be okay if engine is stock.
But as Michael Ward said previously.....lots of information is in the archives. This topic has been discussed about as much as "What motor oil to use" or "What car wax to use".
LarryComment
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Re: Fuel/additive recommendations
OK, thanks I did search and found lots of things useful and lots of junk with the words in it, but I am running the experiemnt. In my shakedown cruise I did not notice any pinging or other issues, after the snow melts I will run it more. Thanks for the info everyone.
On another issue, is there any timing and/or carb adjustments I should make for a car coming from near sea level to 7000 feet? I did nothing on my L79 and it runs great, so I am assuming no adjustments are necessary for the L71 either, but I have never had a big block solid lifter, multi-carb engine before.Big Tanks In the High Mountains of New MexicoComment
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Re: Fuel/additive recommendations
If a carbureted engine is set up at sea level it will loose idle speed as altitude increases.
You should perform the idle speed mixture adjustment procedure per the CSM, and I recommend about 900 RPM idle speed for SHP big blocks.
It's a good idea on any old Corvette to take the spark advance map and compare it to specs in the CSM and AMA specs.
Beyond that I recommend converting the ported vacuum advance to full time. Selecting logical search words will yield many threads on this subject that tell you how to make the conversion along with the different than OE VAC that you should install along with the conversion.
DukeComment
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Re: Fuel/additive recommendations
the area of the jetting should be leaned 2% for every 1500 feet above sea level for max performance. running it a little rich should help keep it out of detonation.Comment
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Re: Fuel/additive recommendations
To sum up the archive info in 4 words - no knock no need.Comment
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Re: Fuel/additive recommendations
Thanks for the tips I will do them, the idle was about 600 rpm, but you gotta love that lope and rumble out the sidepipes! I am also wondering if it has TI, the tank sticker says it came that way, what should I look for to confirm it still has TI?Big Tanks In the High Mountains of New MexicoComment
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Re: Fuel/additive recommendations
TI was a mandatory option with L-71. The control unit is located behind the left side of the grille mounted on the front of the inner fender skirt and the harness runs below the left fender gutter.
The dist. has two short wires exiting with a connector to the TI harness, and there is no ballast on the cowl. If you lift the dist. cap window, you won't see points.
I equate severe "lope" with poor idle quality. As you increase idle speed lope is reduced and idle quality is better.
You should also search for the BB first design valve spring problem and consider changing them to the second design if this hasn't already been done.
Manifold vacuum should be about 14"@900 - maybe somewhat less at 7000 feet. If it's significantly less someone has installed a higher overlap cam, which is NOT the way to go.
DukeLast edited by Duke W.; December 8, 2009, 09:14 AM.Comment
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Re: Fuel/additive recommendations
Thanks, it has been removed, no control unit or harness (though the clips are still there for it and the harness) and a ballast is on the FW. Looks like it was replaced by a Petronix unit under the dist. cap. Guess that won't affect the timing, advance, etc.Big Tanks In the High Mountains of New MexicoComment
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Re: Fuel/additive recommendations
I live at 7930' and have logged just about 60K miles on my '71 SB. During engine restoration, I used the '70 350/350 components for 11:1 CR. I run just fine on pump premium no lead with ethanol mix...
The only other changes made were to convert the ignition to a Breakerless SE, re-jet the stock QJet for my altitude and 'deep six' the carb's nitryle float for a brass substitute to thwart alcohol deterioration of the nitryle coated foam based float.
BTW, I've driven the car across country on many NCRS National Road Tour trips and I make no adjustments for lower altitude operation other than re-tweaking the curb idle.
Also, I used to have a condo in Vail and drove the car frequently over the Continental Divide (+11K feet) without hiccups...Comment
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