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what gas to use

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keiths 70 AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote keiths 70 AMX Quote  Post ReplyReply Direct Link To This Post Topic: what gas to use
    Posted: Apr/28/2018 at 5:45pm
 I have a 1970 AMX with the original 360 V8 with a 4 barrel holley carb. I have been using premium gas. 93 octain, and when ever I get gas I use the STA-BIL 360. My question is should I also be using a lead additive in the gas as well, or is the STA-BIL enough. Thanks for any information or advice you could give me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6768rogues Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2018 at 6:12pm
I have a 360 that is lightly modified and I use the middle grade of gas with no additives. If you have a stock engine, no additives are needed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote akimmet Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2018 at 9:13pm
The original 4bbl 360 engines for 1970 were high compression, so premium is required. The sta-bil additive is completely unnecessary unless the car sits for long periods of time.

You probably don't need the lead substitute either. I have found valve seat erosion only seems to be a problem on freshly cut valve seats on non hardened exhaust valve seat head castings. If the heads already had some significant miles on them they seem to last just fine without hardened seats or lead substitute.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2018 at 10:04pm
Don't need to add a thing, and like they said, the Sta-bil is only needed for storage or longer term sitting (like if you park it for a month or so, etc.)
I add it before I park my cars for the winter.
I run 91 (or when I can find it, better) in my 70, 87 in my 4.0 liter Eagle and 87 in my 73 Javelin with 360
No additives.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2018 at 11:28pm
Here in Denver, Maverik stations sell "clear gas".  It's mid-grade octane rating (87), but ethanol free.  It's usually priced between ethanol mid-grade and ethanol premium.  I've been running it exclusively in my motorcycle and AMX for 2 years, and I can't feel any difference in performance, and even at 10.1:1, my AMX doesn't ping.  It doesn't seem as prone to vapor lock in hot weather as ethanol gas does.

Bob
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Apr/29/2018 at 8:18am
TEL (LEAD) is bad, pure evil. It's poison and
wears out the upper cylinders and rings.

However it is required for pre 1970 exhaust
valves and seats.

If you do not need TEL or other lead substitutes, don't use it.

93 RM2 "octane" in leaded provides the same or better
anti detonation protection as leaded premium of the late
1960s and early 1970s.

Automotive Octane ratings are different today.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote akimmet Quote  Post ReplyReply Direct Link To This Post Posted: Apr/29/2018 at 9:21am
TEL and lead substitutes protect non-hardened valve seats by leaving deposits behind on exhaust valve seats.

I find it amusing people still mourn the loss of leaded gas, not realizing it was one of the major causes  of engine wear.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Apr/29/2018 at 9:22am
The added wear from not having lead (or a substitute) in a STOCK engine is marginal. It would be fine in any AMC engine, but wear may be a bit more with one of the early 60s big three performance engines -- the rarer ones like the 428 Cobra Jet and such. If you have stiffer valve springs due to a high lift cam wear is accelerated, so you might want to run an additive. Other than that you will be fine. There may be as much as a 20% increase in wear in a pre 70 engine, but usually it's between 10 and 20%. So if you would have a valve job done at 100K miles, with unleaded gasoline you would have to get a valve job at 80-90K miles. You can usually get 2-3 valve jobs out of a head. Putting valve seats in is pretty common and affordable now. If the heads need rebuilding, even if for other reasons (say the guides need to be replaced), I'd consider getting seats put in at the same time. You generally only need exhaust valve seat inserts, as the cooler running intake valve seats don't wear as fast. But until the heads need a rebuild, don't worry about it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ccowx Quote  Post ReplyReply Direct Link To This Post Posted: Apr/29/2018 at 10:17am
I run 91 octane no ethanol in my 10.4: 1 compression 1970 390. I am a bit careful about timing and have slowed the rate of advance down a bit, but basically it works fine. As for valve seats, I have not had any negative effects that I can see and I am running 280# double valve springs.

Chris
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Post Options Post Options   Thanks (0) Thanks(0)   Quote keiths 70 AMX Quote  Post ReplyReply Direct Link To This Post Posted: Apr/29/2018 at 10:51am
 Thank you all for the information, I'll be able to save some $ on the additives.
   Thanks againSmile 
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1980 Spirit DL
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