In the past some 347's had some problems with burning lots of oil and longevity(sp?) issues. I think most of the new ones from good companies have taken care of this but some people still feel that a 331 will last longer and is a "safer" stroke. This is just what i've heard, if i'm wrong don't flame me.
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92 AOD GT, K&N, ram air, pulleys, 2 ch. flowmasters, 4:10's, shift kit, 1 5/8 mac longtubes and offroad hpipe 14.249 @ 97.34 mph before the headers and hpipe