The heads are interchangeable, but you must match the intake to the heads..
the intake bolt holes go straight into the head (~45deg angle) on
pre-magnums, but on magnums they are vertical... Mopar Muscle did an article
late last year that showed about 70 HP more by putting Magnum heads on a
340...
The valvetrain is also different... the pre-magnums used a oiled shaft that
the rockers pivoted on, while the Magnum heads use a hollow pushrod for
oiling, and use a rocker stud setup... so actually, the Magnum heads don't
need oiling holes.. (they get oil through the pushrod)
I also think that the pre-Magnum didn't use a roller cam (Magnum does) and I
think they went from a dual-plane intake design to the keg-barrel style the
Magnum uses
I could probably find more exact descriptions if you like, let me know if
this answers your questions adequately.
Gary Shook
>My '91 Ramcharger was a pre-mag motor. It had throttle body injection (the
>magnums have multi port). The main difference is the heads. The way the
>intake bolts to the heads is different, and I believe the oil passages
>might not line up the same (not sure about this).
>
>----------
>> From: Dan Matthews <dakota_v6_89@hotmail.com>
>> To: dakota-truck@buffnet.net
>> Subject: Re: DML: RE: Premag vs. Mag
>> Date: Friday, February 26, 1999 6:29 PM
>>
>> Thanks for the horsepower comparison , but i was really wondering what
>> made the Mag different from the Premag. What kinda component differences
>> on the engine.
>
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