Re: [AMC-list] 4.0 to 4.2 question

[adh@xxxxxxxxxxxxxxxxx (Sandwich Maker)]

" From: Frank Swygert <farna@xxxxxxx>
" 
" Mark got you on the casting number. But what will you be doing with
" this engine? For better low speed power (normal driving) the later
" model head should be a better choice. The only thing is you need a
" 2001 or later model. The 99-00 head has a thin spot in the center
" that's prone to cracking with age. I think I have that problem solved
" as I'm running a 2000 head on my J-10 (258 with carb) and have had no
" problems... yet. Been running it about a year now. 

from what i've read, the revised #0331 head appeared '02/'03 and has
'TUPY' cast between the #3cyl rocker studs where the original #0331 is
blank.

" The later head has smaller exhaust ports but has a bit better flow at
" low speeds due to higher velocities. It will fall off in power quicker
" than the 7120 head though -- peaks out at 3500 or so rpm instead of
" 4500 or so (with stock or near-stock cam). But below 3500 it does a
" bit better. So for a street vehicle the later model is better, but for
" total performance the 7120 is the better head. 

also read: the exhaust ports lost area on the bottom side with little
or no effect on flow, and the intake ports are actually bigger than
earlier heads.  the iron exhaust manifolds used with this head may be
more restrictive than the fabricated tubular ones on earlier heads.
________________________________________________________________________
Andrew Hay                                  the genius nature
internet rambler                            is to see what all have seen
adh@xxxxxxxxxxxxxxxxx                       and think what none thought
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