1968 390 heads
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=104001
Printed Date: Apr/23/2024 at 11:03am
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com
Topic: 1968 390 heads
Posted By: gnrand
Subject: 1968 390 heads
Date Posted: Feb/12/2020 at 8:21am
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Is there an easy way to determine if my 390 heads are stock or "Dog leg". Thank you Jeff ------------- 1968 AMX 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
Replies:
Posted By: bbgjc
Date Posted: Feb/12/2020 at 8:52am
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The exhaust ports are rectangular on early heads. From 70 up they look like boots/doglegs |
Posted By: White70JavelinSST
Date Posted: Feb/12/2020 at 9:21am
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Dogleg exhaust port looks like this  ------------- 70 Javelin SST, second owner, purchased 1972 |
Posted By: AMXFSTBK390
Date Posted: Feb/12/2020 at 11:41am
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Pull a valve cove and post the casting number, or look it up yourself. ------------- Questions are powerful tools...what's in your toolbox? |
Posted By: Heavy 488
Date Posted: Feb/12/2020 at 12:00pm
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If it still has manifolds, you can make out the shape at the head mounting flange. |
Posted By: gnrand
Date Posted: Feb/12/2020 at 8:31pm
Maybe this pic will help. ------------- 1968 AMX 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
Posted By: AMXFSTBK390
Date Posted: Feb/12/2020 at 9:09pm
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How do you know the heads are not 290 or 304 heads without pulling the valve covers? ------------- Questions are powerful tools...what's in your toolbox? |
Posted By: Heavy 488
Date Posted: Feb/12/2020 at 9:32pm
| Looks like square port to me at least compared to the log manifolds on my 70. |
Posted By: gnrand
Date Posted: Feb/12/2020 at 9:40pm
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OK, I have some minor surgery tomorrow but should be able to pull the valve cover and snap a picture. ------------- 1968 AMX 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
Posted By: gnrand
Date Posted: Feb/12/2020 at 10:15pm
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Got ambitious and pulled the pass side valve cover. The number is 3188558-2. Looking it up it is a 68/69 AMX and it has rectangular exhaust ports, if I am reading it correctly. Jeff ------------- 1968 AMX 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
Posted By: White70JavelinSST
Date Posted: Feb/13/2020 at 8:43am
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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 |
Posted By: Heavy 488
Date Posted: Feb/13/2020 at 8:49am
| Standard issue 343/390 head. |
Posted By: gnrand
Date Posted: Feb/13/2020 at 1:13pm
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 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
White70JavelinSST wrote:Posted By: AMXFSTBK390
Date Posted: Feb/13/2020 at 2:34pm
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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.
------------- Questions are powerful tools...what's in your toolbox? |
Posted By: gnrand
Date Posted: Feb/13/2020 at 7:21pm
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 ------------- 1968 AMX 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
Posted By: ccowx
Date Posted: Feb/13/2020 at 8:53pm
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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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Posted By: AMXFSTBK390
Date Posted: Feb/13/2020 at 10:57pm
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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.  ------------- Questions are powerful tools...what's in your toolbox? |
Posted By: gnrand
Date Posted: Feb/14/2020 at 8:34am
[/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. ------------- 1968 AMX 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
Posted By: Heavy 488
Date Posted: Feb/14/2020 at 9:31am
| Yeah, I remember those. It's like a swollen gas strut boot on the pump nozzle. |
Posted By: AMXFSTBK390
Date 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 ------------- Questions are powerful tools...what's in your toolbox? |
Posted By: White70JavelinSST
Date Posted: Feb/14/2020 at 11:49am
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I just use the gas cap on the White70 and wedge it in between the license plate frame and the lower valance panel. The homemade tool is definitely awesome though.
------------- 70 Javelin SST, second owner, purchased 1972 |
Posted By: gnrand
Date Posted: Feb/14/2020 at 11:51am
Maybe a metal extension that would be similar to a gas cap fitting with clamping ears so the two will attach. Could have a slight bent in the extension that would tilt up. ------------- 1968 AMX 1986 Buick GN 1965 Corvair Corsa 1966 V8 Corvair 1969 Scrambler Stock 1969 Scrambler Modified |
Posted By: 1948kaiser
Date Posted: Feb/14/2020 at 2:14pm
| saw at amx at daytona one time that had the amxs on the sides modified so they would open and then ran a hose to the gas tank. was a big y in the truck. |
Posted By: Tunaspanker
Date Posted: Feb/15/2020 at 8:07pm
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I also made a fill spout for my cars. I cut a piece of 1 inch Home Depot schedule 80 pipe stock. They sell a 2 foot stick that worked just right. Cut it into 2 pieces about 9 inches and 11 inches. 45 degree ell (elbow) in between the 2 pieces. Finished it off with a long-neck filler spout cut to fit into the upper end. Gravity flows just fine to keep up with gas going in. Bungee'd it to the trunk latch. I made it after I pissed off a gas station attendant for spilling gas.
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Posted By: AMXFSTBK390
Date Posted: Feb/16/2020 at 12:16am
Is this the AMX at Daytona with  rear 1/4 panel gas tank access? ------------- Questions are powerful tools...what's in your toolbox? |