so what determines max lift on heads? is it something to do with the heads or something to do with the valves springs? im asking this because im looking at heads and cams. also how much room for porting does the GM vortec heads have and how much horse power can you really get out of these.

 

You can get stupidly large amounts of power from vortecs. You don't need to remove much material from them (or do you want to).
Vortecs experience port stall around .500" lift. So don't go above that. Use a longer duration cam if you want, keep lift at .480-.500" max.

Max lift is a combo of things;
coil spring bind
but usually ; retainer to valve guide boss.

You can machine the guide boss down (and set it up for positive valve stem seals as well).

 

allright cool. also i was wondering what is the differnce between 86 and earlyer 350s and 87 and later blocks? in my summit magazine its allways saying this. do they have differnt bolt patterns as in the heads bolt on differnt of anything

 

A summary of SBC block significant changes (that I can think of off of the top of my head):

1955 - SBC introduced. No side mounts or oil filter provision. Dipstick on driver's side of engine.
1957 - Full flow oil filter provision introduced
1958 - Side engine mounts introduced
1967 - 350 cid introduced (Camaro only); also eliminated the "draft tube" crankcase ventilation casting in the rear of the block.
1968 - "Large" crank bearing journals introduced, 350 available across the board
1970 - Siemesed cylinder wall 4.125" bore 400 cid introduced, main bearings even larger than the 1968 "large" journals (400 cid engines only, the other SBC's remained as they were)
1980 - Passenger side dipstick introduced
1986 - One-piece rear main seal introduced
1987 - Roller lifter provisions introduced

That will take you through the "Generation I" small blocks. Does not include LT1 or LS1-family engines introduced in the 90's.

Things that have never changed:
- Basic external dimensions (length, height, width, deck height, etc.)
- Head bolt pattern
- Bellhousing bolt pattern
- Water pump mounting
- Timing cover bolt pattern
- Cam bearing size, spacing, and lobe spacing, distributor drive