New 71 Cutlass owner
February 21st, 2014, 11:20 AM
#1
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Join Date: Feb 2014
Location: Canton Ga.
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New 71 Cutlass owner
I just bought a 71 Cutlass convertible 442 clone. It has the 390 w 4bbl edelbrook. My first question is, what kind of gas should I use. As you know, we cannot buy leaded gas anymore. So do I use 87, 89 or premium unleaded... Do I need to add any kind of additive.
February 21st, 2014, 11:41 AM
#3
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Location: Canton Ga.
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Yea... the 390 was a typo. It is a 350 Rocket. I have a compression gauge. I could measure it. I assume, just remove all the plugs and distributor wire and crank it. What kind of reading am I looking for.
February 21st, 2014, 12:00 PM
#4
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Location: Phoenix, AZ
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Welcome aboard. As droptopron posted, without knowing the specifics there's no way to tell you which grade of gasoline your engine needs. An original, un-rebuilt '71 engine had ~8.5:1 compression ratio so it should run on 87 octane. Timing, temperature, and engine condition may affect that, though.
For the compression test, you should also ensure the throttle is fully open while cranking. Cranking pressure readings could be anywhere from 120 psi to 200 psi, depending upon what type of pistons and camshaft are in there.
For the compression test, you should also ensure the throttle is fully open while cranking. Cranking pressure readings could be anywhere from 120 psi to 200 psi, depending upon what type of pistons and camshaft are in there.
February 21st, 2014, 12:17 PM
#5
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Location: Poteau, Ok
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Welcome to the site and congrats on the new ride. I'd go with what Ken said above. If the engine sounds like it has a cam you may consider hi-test until you figure it out. The other option is call the previous owner and ask.
February 21st, 2014, 12:35 PM
#6
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Location: Forest Ranch Ca.
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Welcome, even though a compression test is a good idea on a unknown new to you engine and useful information will be told by that reading it will not tell what compression ratio is. If you can find the head numbers that will tell a lot of what you have or what you could have if nothing has been altered from what it was new......Just a thought.
...Tedd
...Tedd
February 21st, 2014, 02:44 PM
#9
Just an Olds Guy
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
There's no need for anything but regular fuel, unless you have a lot of methanol gas in your area. Today's 87 reg octane is the same as the 91 octane of 1971. If you find your engine pinging, either adjust the timing or go to higher grade (mid) octane. Whichever suits your needs better.
The cylinders are numbered as follows
Drivers side from front 1, 3, 5, 7
Passenger side from from 2, 4, 6, 8
Here ya go in diagram format
February 21st, 2014, 04:17 PM
#10
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Location: Phoenix, AZ
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Does the engine idle smoothly, with no lope sound? Just trying to get a feel if the cam is a typical factory style or something with a bit more overlap. The reason I ask is the cranking pressure is greatly affected by the camshaft valve opening/closing events. An engine with a small cam will have higher cranking compression than the exact same engine with a larger cam. Allan's mention of the engine being a bit tired due to the slightly low pressure readings could also be an indication of an aftermarket cam in the otherwise stock engine.
Last edited by Fun71; February 21st, 2014 at 10:09 PM.
February 21st, 2014, 06:27 PM
#12
Just an Olds Guy
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
WTH?? The dickens you say - no tetraethyline in your area??? Of course it's gone the way of the dodo, but the good thing about your 71 engine is the valve seats are hardened right out of the factory for unleaded gas. So no worries about that.
Fun71 brings up an interesting point. It's possible the engine has been somewhat modified. My comment about compression is based on an original engine just going through normal wear/tear over the years. IIRC the original compression was around 150 psi/cylinder, so overall it's not terrible.
If it's smooth running, I'd just go for the grade of gas it seems to run smoothest on. That may not end up being 94 octane either.
Fun71 brings up an interesting point. It's possible the engine has been somewhat modified. My comment about compression is based on an original engine just going through normal wear/tear over the years. IIRC the original compression was around 150 psi/cylinder, so overall it's not terrible.
If it's smooth running, I'd just go for the grade of gas it seems to run smoothest on. That may not end up being 94 octane either.
February 26th, 2014, 08:15 PM
#16
Welcome to CO, nice looking car. As a point of reference, I have an original unmolested 71 CS with a 350 and run 89. I have the timing advanced a little more than stock otherwise 87 should work fine for you, assuming everything is stock.
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