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70-73 & 74-up 304 head difference |
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814Kustoms 
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Joined: Sep/07/2013 Location: United States Status: Offline Points: 130 |
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 Topic: 70-73 & 74-up 304 head differencePosted: Aug/19/2018 at 9:53am |
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Is there any parts differences between the 1970-73 & 1970-up 304 heads? I have a 1973 304 i'm looking to take the heads off for rebuild. I also have a 1974 304 on my engine stand torn down but ran well when it was in a jeep but smoked a little bit. Took the heads off yesterday to find a handful of bad valves so those will have to be rebuilt too. Finally, I have an extra set of rebuilt heads off a 1974 304 as well.
The plan was to put the rebuilt set of heads on my 1973 block with new pushrods, rockers/bushings/bridges and run the engine in my Javelin until I got the 304 on the stand built. As I looked up parts I could only find them in 1974 and up AMC/Jeep applications. I haven't taken my valve covers off my engine in the Javelin to visually verify since it doesn't leak a drop of oil from the valve covers and the car is still mobile. My thought was getting all the parts needed prior to starting the head swap, but if newer heads are a different setup and it's not feasible then I can just leave it be until I build the 304 on the stand. Any information is very much appreciated! Thank you!
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304-dude
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Aug/19/2018 at 9:59am |
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73 and 74 are basically the same for fitment and parts interchange.
Pre 73 are stud mounted, while on up are bridged rocker design. 70 heads are high compression design. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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814Kustoms
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Joined: Sep/07/2013 Location: United States Status: Offline Points: 130 |
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Posted: Aug/19/2018 at 10:14am |
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304-dude - Thanks for the info! I found a website that states the head casting numbers (3216086) for both '73/'74 which was more confusing about why the parts were labeled 74-up.
http://www.purpleized.com/AMX/head.shtml
Had a feeling that I may have opened up the valve cover on the engine that's in the car and answered my own question with a completely different design, but figured i'd ask here first. So verdict is I can interchange all the heads I have (73/74) with all parts/fitment being the same for either 304s I have. Thanks again for the confirmation! |
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814Kustoms
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Posted: Apr/30/2019 at 7:37pm |
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Ok have finally opened up my 304 (almost a year later) inside the Javelin to discover that I do have the stud mounted rockers and the '72 stamped on the inside. Also found the reason it was running bad due to backed off rockers as well as a few that were angled horribly which wore into the tops of the valves/retainers. It's a shame too because when I opened it up it's the cleanest engine i've ever seen.
I have all the parts for the pair of '73 heads ready to go on. So I just need a sanity check to be sure that I can put these newer heads on the older block and they'll perform the same as the stock (stud mount) heads I'll be pulling off? From what i've gathered the only difference is how the rockers are mounted to the head. I'm just unsure of if the pushrods will be the same length (have new ones for the bridged style) or if there will be any other issues using the new style heads on the old block. I'll be moving across the US in about 2 months and need to have my Javelin running in order to have it shipped so i've procrastinated way too much. Hopefully, i'll get some good news from one of the reliable sources on here so I can get things buttoned up! Thanks for all the help so far! |
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ramblinrev
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Joined: Dec/28/2008 Location: Wisconsin Status: Offline Points: 11528 |
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Posted: Apr/30/2019 at 7:44pm |
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The fit will be perfect, between those years. No worries on that!
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74 Hornet Hatchback X twins (since 1977)
62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981) |
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304-dude
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Apr/30/2019 at 7:44pm |
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In 73 only the 401 had studs on the heads. Please post the part number from the 73 heads for verification. Its not good for anyone to blindly swap heads on any 304 engine, as only the 360 and 401 have enough bore to use larger valves. You can run small valve heads on the 360 or 401 for added torque
Same with my 304... though its a 71 and not many want them, so i pieced it out with less than 27k on the rebuild. A bit of a shame as the tranny too had been rebuilt as well. Edited by 304-dude - Apr/30/2019 at 7:48pm |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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Shawn_Watson
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Joined: Dec/05/2018 Location: Carlsbad, NM Status: Offline Points: 117 |
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Posted: May/01/2019 at 1:21pm |
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Which head has the best detonation resistance? 91 octane pump swill.
Shawn
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ADAM12MATADOR
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Joined: Dec/03/2011 Location: New City, N.Y. Status: Offline Points: 518 |
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Posted: May/01/2019 at 4:01pm |
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If i am not mistaken all 71 and up heads had 58 cc chambers. Those would give you the least amount of detonation. That is on a stock engine, stock cam and compression.
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purple72Gremlin
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Posted: May/01/2019 at 4:26pm |
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Trader
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Posted: May/01/2019 at 5:24pm |
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You don't necessarily want low compression for "swill", higher then 10% ethanol.
9.0:1 or higher will do better to stop Low Speed Pre-Ignition (LSPI). Manufactures now for turbo or supercharged factory engines are going 9.5:1 to 10.5:1 and requiring SN Plus motor oil. If you have it torn down now, my opinion would be to build to 9.5:1 CR. You have a better chance to control high RPM detonation. LSPI is like high RPM detonation, but you don't know it's happening and your pistons just erode away at the upper ring land area. There is is lots of info out there but this is a good site to scroll through as a start: Know one, at this point in time, seems to know how ethanol which has higher octane is pre-igniting at low speed on low compression engines. And the higher the ethanol content, the more likely this is happening. I,ve seen this in 360's, not so much 401's and no idea on a 304. AMC I6 also looks to be vulnerable. |
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304-dude wrote: