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1968 390 heads

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White70JavelinSST View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Feb/13/2020 at 8:43am
Looks like you win !

You got the correct heads on your 68 390.

Look where the motor mounts are bolted to the engine, there should be "390" cast into the block.

That will definitely confirm which engine you have.
70 Javelin SST, second owner, purchased 1972
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/13/2020 at 8:49am
Standard issue 343/390 head. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gnrand Quote  Post ReplyReply Direct Link To This Post Posted: Feb/13/2020 at 1:13pm
Originally posted by White70JavelinSST White70JavelinSST wrote:

Looks like you win !

You got the correct heads on your 68 390.

Look where the motor mounts are bolted to the engine, there should be "390" cast into the block.

That will definitely confirm which engine you have.



Yes 390 on the block. I just got the build sheet form the previous owner when it was rebuilt and it was open up .040" over. So it might be closer to 400 cu inch.
1968 AMX X
1986 Buick GN
1965 Corvair Corsa
1966 V8 Corvair
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXFSTBK390 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/13/2020 at 2:34pm
You have the same heads I took off my 390 when I rebuilt it. AMC in 1968 considered the 1968 AMX 390 to be a high compression engine and recommended 110 octane leaded gas. The ...558 heads have 50.60 cc's and 390 engine rated at 10.2:1 compression. Unfortunately 99% of Calif gas station offer up to 91 octane. I therefor installed rebuilt 73 401 cyl heads with 57.92 cc's combustion chambers to reduce the compression ratio to ~9.65:1. Also installed dog-leg free flow exh manifolds. If you notice knocking or pinging you should adjust the timing. There is a Union 76 at the Citrus Off ramp that sells 100 octane at $8.99 a gallon. 

Edited by AMXFSTBK390 - Feb/13/2020 at 9:48pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gnrand Quote  Post ReplyReply Direct Link To This Post Posted: Feb/13/2020 at 7:21pm
Originally posted by AMXFSTBK390 AMXFSTBK390 wrote:

You have the same heads I took off my 390 when I rebuilt it. AMC in 1968 considered the 1968 AMX 390 to be a high compression engine and recommended 110 octane leaded gas. The ...558 heads have 50.60 cc's and 390 engine rated at 10.2:1 compression. Unfortunately 99% of Calif gas station offer up to 91 octane. I therefor installed rebuilt 73 401 cyl heads with 57.92 cc's combustion chambers to reduce the compression ratio to ~96.5:1. Also installed dog-leg free flow exh manifolds. If you notice knocking or pinging you should adjust the timing.<span style="white-space:pre">     </span>There is a Union 76 at the Citrus Off ramp that sells 100 octane at $8.99 a gallon. 


I did a bunch of drag racing with an '87 GN (8 sec V6 GN car NHRA approved) and I still have unopened VP C16 (116 octane) but honestly I don't hear any detonation.
BTY putting gas in this car with the Ca nozzles is a PITA. You almost have to lay down to access the gas spout.
Jeff
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1986 Buick GN
1965 Corvair Corsa
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ccowx Quote  Post ReplyReply Direct Link To This Post Posted: Feb/13/2020 at 8:53pm
96.5:1 compression ratio?! What octane does THAT require? Just kidding....

As for the fuel needs, I have a 1970 390 with stock 291C heads and with the .030 overbore I get around 10.4:1 compression ratio. I am able to use 91 octane gas with no ethanol and it seems to work ok. I have the advance set fairly conservatively and the total advance is around 36 degrees total. 

Chris 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXFSTBK390 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/13/2020 at 10:57pm

BTY putting gas in this car with the Ca nozzles is a PITA. You almost have to lay down to access the gas spout.
Jeff [/QUOTE]last month, member AMXTSY posted photos of a license plate stay-open tool he made. This make refueling easier. Search "license plate tool." See photo.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gnrand Quote  Post ReplyReply Direct Link To This Post Posted: Feb/14/2020 at 8:34am
Originally posted by AMXFSTBK390 AMXFSTBK390 wrote:


BTY putting gas in this car with the Ca nozzles is a PITA. You almost have to lay down to access the gas spout.
Jeff
last month, member AMXTSY posted photos of a license plate stay-open tool he made. This make refueling easier. Search "license plate tool." See photo.[/QUOTE]

Very clever. My GN has the spout higher and the gas cap actually holds the same type of license plate door open. One of the problems is; the Ca. gas nozzles are massive.
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1986 Buick GN
1965 Corvair Corsa
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/14/2020 at 9:31am
Yeah, I remember those. It's like a swollen gas strut boot on the pump nozzle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXFSTBK390 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/14/2020 at 11:38am
I installed a billet gas filler neck and gas cap assembly on my 68 Camaro. It caused gas to back up because of the bend in the neck. So I would push a 10" long fuel hose (7/8" dia?) onto the nozzle and push it past the bend and fill up. Worked great. This might make filling up an AMX easier. So, in the trunk store a piece of hose, license plate stay-open tool, and a small rubber mat to place your knee on. Cheers  
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