larger flow capacity, larger valves etc ( 1.84 / 1.54 ) if i remember correctly.. although, you could suffer a bit of a compression loss going to these heads, so , having them milled a bit would be a good idea to up the compression for more power...i really want to do something like this for my car bc its alot cheaper than buying brand new aluminum heads for 1200 samolians
It's a good swap. Obviously it won't be as good as some nice aluminum heads, but it can be done for a fraction of the cost of aluminum heads. The 2 issues are the head bolts and the already mentioned compression loss because of the bigger combustion chambers in the 351w heads.
I have 351w heads with screw in studs, guide plates and roller rockers on my 289 in my '66 coupe. I used ARP 289/302 head bolts with TrickFlow shoulders for bolts (351w uses a 1/2" bolt, 260/289/302 uses a 3/8" bolt), and instead of shaving the heads, I built the engine with 10:1 flat tops, keeping my compression at a very streetable ~9.5:1 compression ratio. The car is my daily driver, and so far, best ET is 14.334 in the 1/4 mile (now I have to fix my traction-lock :
From 77' and up, the chambers for the 351's get pretty big. The valve and runner sizes for the later 351 heads are the same as the 302's, (75' and up?), so you should stick to the earlier 351 heads if you do the swap.