|
|
|
Your donations help keep this valuable resource free and growing. Thank you.
|
New heads for 343 |
Post Reply 
|
Page 12> |
| Author | |
Jav69 
AMC Apprentice 
Joined: Aug/30/2016 Location: Lake Bluff IL Status: Offline Points: 56 |
 Post Options
 Thanks(0)
 Quote Reply
 Topic: New heads for 343Posted: Jun/26/2019 at 6:39am |
|
looking to start swapping out heads on my 1968 343. Just wondering if 360 heads would work.
Thanks
|
|
 |
|
|
Midnight Rambler
AMC Addicted 
Joined: Jan/17/2011 Location: SoCT Status: Offline Points: 1670 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/26/2019 at 7:59am |
|
343 used the same heads as the 390. Your money might be better spent on new valves and maybe some port work.
|
|
 '66 American 440 Convertible 290/M-40/AMC 20 3.15/PS/PB '04 Jeep Wrangler X Rocky Mountain Edition 4.0 5sp |
|
|
|
|
bigbad69
Supporter of TheAMCForum 
Joined: Jul/02/2007 Location: Ottawa, Ont. Status: Offline Points: 6685 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/26/2019 at 8:07am |
|
FYI 343/390 (square port) heads are the same. 360/401/390 (dog leg) heads are the same. 360 heads will work on your 343. You would need step dowels to locate the heads. You would also need to slot the intake to head mounting holesoin the intake, or use a 70-up intake and mill it to fit your low deck engine. It's a pretty common swap. I have 6090 heads on my low deck 390.
|
|
|
69 Javelin SST BBO 390 T10
|
|
|
|
|
Jav69
AMC Apprentice
Joined: Aug/30/2016 Location: Lake Bluff IL Status: Offline Points: 56 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/26/2019 at 11:04am |
|
If I use 390 heads will I have to make any modifications
|
|
|
|
|
tufcj
Supporter of TheAMCForum
Supporter of TheAMCForum Joined: Jul/10/2007 Location: Watkins, CO Status: Online Points: 4097 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/26/2019 at 1:27pm |
68/69 390 heads (square port) are identical to 343, no mods needed. 70 390 (dogleg port) would require step dowels and modification/change of the intake. Bob tufcj
|
|
|
69 AMX
74 Javelin AMX 67 Rogue If you need a tool and don't buy it... you'll eventually pay for it... and not have it. Henry Ford |
|
|
|
|
BassBoat
AMC Addicted
Joined: Aug/29/2008 Status: Offline Points: 1719 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/26/2019 at 7:40pm |
|
most 360 heads will have larger combustion chambers, and result in lower compression. That might not be a bad thing depending on what octane is available in your area.
|
|
|
|
|
WesternRed
AMC Addicted
Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5808 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/26/2019 at 7:47pm |
|
If you want new heads then look at Edelbrock.
Minor differences mostly covered above, 343/390 uses 7/16" bolts, later heads use 1/2", you use step dowels and step washers to allow the 7/16" bolts to work within the 1/2" holes. Some intake fitment issues as detailed above. Also the exhaust port shape is different so you either need to find 1970 log manifolds to work with your existing exhaust or change to later manifolds/headers with a modified exhaust system. Another thing to keep in mind is that later 360 heads have a larger combustion chamber so there is a drop in compression unless you can find a set of the 291C 360/401 heads with small chambers like the 343/390 heads.
|
|
|
I've finally given up drinking for good...........now I only drink for evil.
|
|
|
|
|
farna
Supporter of TheAMCForum
Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19689 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/27/2019 at 6:40am |
|
Or change at least two of the 7/16" head bolts to 1/2" (one on each end of the head). That takes drilling the hole in the block and tapping though. The step dowels just replace the original head locating dowels. Getting the old ones out is harder than putting the new in, but they should pull right out with a little effort. Stepped washers aren't really necessary, the standard head bolt washers are just fine. If you're running the engine really hard (racing) or it's built high compression (over 10:1) they might add some strength, I'm not sure they do though. The dowels locate the head, the bolts don't shift in the holes once torqued. AFAIK the step washers don't affect torque, just prevent any possible shifting while tightening. Many engines have been built without them. Certainly won't hurt though, even if just for peace of mind. It's not like they cost much...
|
|
|
Frank Swygert
|
|
|
|
|
Greyhounds_AMX
AMC Addicted
Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/27/2019 at 7:13am |
|
If it's basically the original 1969 343 from the Javelin it would have been a 10.2:1 compression ratio. Moving to 58cc dogleg heads from a later model 360 would be a step in the right direction (assuming you would want to use pump gas), moving the CR to 9.6:1.
I did just that on my 1968 390, using late model 360 heads opened up from 58cc to 61cc. I used the step dowels and stock 1969 head bolts. It's been 20 years and 10,000 miles, works great. I took a different approach to handle the intake manifold bolt hole issue. Instead of slotting the hole in the intake I drilled and tapped a new hole in the heads, one size down from the standard hole size. That way the engine can use a stock 1969 intake manifold. The head swap to dogleg heads is a great performance boost, and with factory parts no less! Pretty cool. Don't forget that you'll need some dogleg freeflow exhaust manifolds too - that's all parts of the upgrade. While you are at it you might consider blocking the exhaust heat crossover in the intake, and "Machine-ing" the intake manifold as well. |
|
|
1968 AMX 390 w/T5
|
|
|
|
|
amcenthusiast
AMC Addicted
Joined: Jul/02/2012 Location: SW Atlanta GA Status: Offline Points: 1778 |
Post Options
Thanks(0)
Quote Reply
Posted: Jun/27/2019 at 9:06am |
|
Get your own copy of American Motor's book named "Performance American Style".
The $15 spent could save you $500 for things you don't need (or want). Remember, the flip side of hopping up the engine is weight reduction; it's all about increasing the car's power to weight ratio. 12 lbs. to every 1 hp. is/was Muscle Car Club of America's qualifying ratio. 10 to 1 is getting into 'race car' category (where the car should be driven by a trained driver) This is arguably main reason why aluminum heads are a higher performance mod. (same goes for lightweight aluminum intake manifold, even headers -as noted in Performance American Style) https://www.amclives.com/collections/engine/products/1967-1991-amc-v-8-edelbrock-performer-rpm-aluminum-cylinder-heads-w-o-exhaust-crossover-fully-assembled They're more costly though, maybe after other things are done to the car like fiberglass hood and aluminum radiator? https://www.amclives.com/collections/fiberglass (both these mods are good to remove weight 'up high', on the front of the car, to improve front to rear weight bias, lower center of gravity and increase power to weight ratio) |
|
|
443 XRV8 Gremlin YouTube video: https://www.youtube.com/watch?reload=9&v=2DmFOKRuzUc
XRV8 Race Parts website: http://amcramblermarlin.1colony.com/ |
|
|
|
|
Post Reply
|
Page 12> |
Tweet
|
| Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |
Click for TheAMCForum Rules
Topic Options
Jav69 wrote: