Head and cam swap

[Dirtybird]

Currently running a 350 with 47 heads and ‘72 4 barrel intake stock 2 barrel cam. I have two sets of heads to swap in, a set of #13’s or a set of #18’s. Looking for advise on which is the better head to use and what cam to use (likely a 068 right?) Will the 18’s be too much compression for pump gas? Should i rebuild the 13’s with a little smaller intake valve?

[TWO LANE BLACK TOP]

Pontiac 350 CID engine = 3.875 (3 7/8) inch bore with a 3.750 (3 3/4) inch stroke for a total of 354 (353.8) Cubic inches...

The main disadvantage of building good power with a 350 Pontiac engine is the small bore size...Also the long stroke severely limits the amount of RPMs that you can turn...Anything at or above 5000/5500 RPMs ...Creates hyper piston speeds...And the engine will Not survive for any extended period time at or above those RPMs...

The small bore limits the amount of air that you can pull into the cylinders + Flame shrouding and related flame spread/burn efficiency... Issues associated with that....High duration/lift cams will compound the airflow issues into the small bores/ combustion chambers...

The # 13 D port cylinder heads have... 72cc combustion chambers with 2.11 sized intake valves with 1.77 exhaust valves...Using the 400 CID heads with the larger intake/exhaust valves on the small bore 350 engine can create a restriction in the air flow/swirl/ velocity of the air flowing into/out of the cylinders/combustion chambers....

The #47 D port (1968/69 350) cylinder head...72cc combustion chambers with 1.96 sized intake valves with 1.66 exhaust valve...Would probably be the best ones to use....When the heads are cut/surfaced to insure that they have a good flat sealing surface...Usually about .020 or so...It will also decrease the size of the combustion chambers...slightly raising the compression ratio...And burning 93 octane pump gas would not be an issue..Which with the #18 68cc combustion chambers May/May Not..Be an issue...Also whatever heads you decide to use would have to have the valve seats cut and replaced with hardened seats...To be compatible with Unleaded gas If they haven't been replaced already..

As far as the camshafts go...The "068" 400 HO cam...Or the "744" Ram Air 3 cam...Would not work well with the small bores of the 350 CID engine (even if bored .60 over)....And you would be very dissatisfied with the results...Especially when a Smart car embarrasses  you at the stoplight...

Best advice on a camshaft  would be to contact someone who specializes in camshafts...(Comp Cams...Butler...  Lunati..ETC...Tell them what you have/want... Then go from there...Please keep us informed...I'm  (other members also)   curious as to what grind they reccomend for the small bore long stroke engine...

TLBT

Edited June 7, 2023 by TWO LANE BLACK TOP

[64 kiwi boni]

3 hours ago, TWO LANE BLACK TOP said:

Pontiac 350 CID engine = 3.875 (3 7/8) inch bore with a 3.750 (3 3/4) inch stroke for a total of 354 (353.8) Cubic inches...

The main disadvantage of building good power with a 350 Pontiac engine is the small bore size...Also the long stroke severely limits the amount of RPMs that you can turn...Anything at or above 5000/5500 RPMs ...Creates hyper piston speeds...And the engine will Not survive for any extended period time at or above those RPMs...

The small bore limits the amount of air that you can pull into the cylinders + Flame shrouding and related flame spread/burn efficiency... Issues associated with that....High duration/lift cams will compound the airflow issues into the small bores/ combustion chambers...

The # 13 D port cylinder heads have... 72cc combustion chambers with 2.11 sized intake valves with 1.77 exhaust valves...Using the 400 CID heads with the larger intake/exhaust valves on the small bore 350 engine can create a restriction in the air flow/swirl/ velocity of the air flowing into/out of the cylinders/combustion chambers....

The #47 D port (1968/69 350) cylinder head...72cc combustion chambers with 1.96 sized intake valves with 1.66 exhaust valve...Would probably be the best ones to use....When the heads are cut/surfaced to insure that they have a good flat sealing surface...Usually about .020 or so...It will also decrease the size of the combustion chambers...slightly raising the compression ratio...And burning 93 octane pump gas would not be an issue..Which with the #18 68cc combustion chambers May/May Not..Be an issue...Also whatever heads you decide to use would have to have the valve seats cut and replaced with hardened seats...To be compatible with Unleaded gas If they haven't been replaced already..

As far as the camshafts go...The "068" 400 HO cam...Or the "744" Ram Air 3 cam...Would not work well with the small bores of the 350 CID engine (even if bored .60 over)....And you would be very dissatisfied with the results...Especially when a Smart car embarrasses  you at the stoplight...

Best advice on a camshaft  would be to contact someone who specializes in camshafts...(Comp Cams...Butler...  Lunati..ETC...Tell them what you have/want... Then go from there...Please keep us informed...I'm  (other members also)   curious as to what grind they reccomend for the small bore long stroke engine...

TLBT

two lane black top  knows his ponti motors 

[oldredgoat1966]

I just joined forever pontiacs I have a brand new never used melling cam and lifters with a ram air grind went with hydralic roller cam instead