Author Topic: 308 heads or magnums?  (Read 351 times)

Offline RCCDrew

  • Sr. Member
  • ****
  • Posts: 1377
308 heads or magnums?
« on: June 19, 2017 - 06:18:32 pm »
I did a search but couldn't find what I was looking for. Looking to upgrade the J heads on my 340. I have a set of 308s and a set of magnums. Which would you use on a pure street car? I was thinking the 1.6 rockers and closed chamber of the magnums would be a worthwhile addition.




Offline RCCDrew

  • Sr. Member
  • ****
  • Posts: 1377
Re: 308 heads or magnums?
« Reply #1 on: June 20, 2017 - 04:47:18 pm »
No opinions?

Offline HP2

  • Resident
  • *****
  • Posts: 4477
Re: 308 heads or magnums?
« Reply #2 on: June 20, 2017 - 05:36:30 pm »
Magnums have better ports and improved flow. They will require oil through pushrods as they don't have the rocker shaft.


Offline Beekeeper

  • Full Member
  • ***
  • Posts: 786
Re: 308 heads or magnums?
« Reply #3 on: June 20, 2017 - 09:01:54 pm »
Not to hijack the thread but where were you able to find a set of the 308 heads? I keep reading in here that those were the best iron heads you could use. I'd love to find a set for my 340.

If you used the magnum heads, wouldn't that create other issues with intake alignment and valvetrain?

Offline jimynick

  • Resident
  • *****
  • Posts: 3853
Re: 308 heads or magnums?
« Reply #4 on: June 20, 2017 - 10:35:49 pm »
The trick with the magnum heads is to run AMC lifters as they're the same size and oil through the push rods which you've also got to replace. I bought a set through my local Mopar dealer but don't know if they're still available or not and if not, them you'd have to go aftermarket. I, also hear that the 308's are the hot setup for a factory head. Good luck.  :cheers:

Offline RCCDrew

  • Sr. Member
  • ****
  • Posts: 1377
Re: 308 heads or magnums?
« Reply #5 on: June 21, 2017 - 04:47:03 am »
Not to hijack the thread but where were you able to find a set of the 308 heads? I keep reading in here that those were the best iron heads you could use. I'd love to find a set for my 340.

If you used the magnum heads, wouldn't that create other issues with intake alignment and valvetrain?
I found the 308s at the local u pull it. You just have to know what you're looking for. If you see an 89-91 pickup with a 360 and TBI then you probably have the heads you are looking for. I think they were $75 for the pair.

If I used the magnum heads I would have other issues but I am ready to address them. I have a complete magnum engine ready as a donor, and I have a dual pattern intake. It's just pushrods and lifters after that. I think.

Offline HP2

  • Resident
  • *****
  • Posts: 4477
Re: 308 heads or magnums?
« Reply #6 on: June 21, 2017 - 11:06:26 am »
I don't know that 308s are the best iron head out there but they are a pretty significant improvement over the early heads and are the most widely available at a reasonable price. IMO, I'd say W2s are the best iron head with some of the Mopar Performance hybrid LA/Magnum heads offered through the 90s coming in second.

Yes, AMC lifters were the hot ticket for this conversion, back in the 90s. Since then, I believe a couple of lifter companies have closed and/or been bought out and I believe now all Mopar/AMC lifters are considered interchangeable and oil through the body. Use hollow pushrods for rocker oiling or solid pushrods to plug em off. I'd verify it with your favorite cam company before installing though.

Yes, this conversion requires the heads, lifters, pushrods and a modified intake. If you already have the dual pattern intake and the magnum engine, most the parts are there for you already.

Offline RCCDrew

  • Sr. Member
  • ****
  • Posts: 1377
Re: 308 heads or magnums?
« Reply #7 on: June 21, 2017 - 02:06:57 pm »
I'm hoping to start the ball rolling on this in a month or so. I think I'll use the magnums IF they aren't cracked and IF I don't have high comp. pistons. Think I can see the piston height with a borescope?

I was hoping Chryco would chime in before I made a decision on which way to go.

Offline Chryco Psycho

  • Administrator
  • C-C.com Guru
  • *****
  • Posts: 36621
  • 70 Challenger R/T SE 70 tube Chassis Cuda now sold
Re: 308 heads or magnums?
« Reply #8 on: June 21, 2017 - 10:16:01 pm »
I have used both , both work well different resons to use either
 Lifrter companies are in short supply Johnson is the only one to use now
 Basically I agree with HP2
« Last Edit: June 21, 2017 - 10:18:21 pm by Chryco Psycho »

Challenger - You`ll wish You Hadn`t

Offline duodec

  • Full Member
  • ***
  • Posts: 665
Re: 308 heads or magnums?
« Reply #9 on: June 24, 2017 - 11:26:16 pm »
Who is the best supplier for Johnson lifters for our Mopars?