Hey im trying to restore a 85 gmc sierra its got the factory 305 engine in it. What would i need to do to make this a 350. Do all i need is the Heads or is there several other things im gonna need. Thanks

 

take it to a machine shop and get it bored out to a 350 the cubic inch comes from the bore size and crank shaft stroke.

 

 

Buy a 350 from GMPP. The 305 is a different block for the much to small bore, and I believe the crank is different even though the stroke is the same to accomidate the lighter pistons. Its a balance issue as explained to me.

Also I've talked to a couple of guys who love their 383HT. It pretty is pretty much max for the 89-98 trucks but it will work in your truck with a electric fuel pump for the carb.

 

The crank has the same stroke but is set up for a lighter bob weight. The circle track guys use the 305 cranks with the lightest pistons and rods they can find to make engine rap quickly. You can not bore a 305 out to 4 inches unless you want to sleeve the block. You will need a block with a four inch bore. You need to cc the heads I think the 305 heads have a 58cc chamber and smallish valves. Most 350s have 64 or 76cc heads. Some circle track guys put larger valves in the 305 heads and use the smaller chamber to raise the compresion.