head # 353049
Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
head # 353049
good morning
what are the flow characteristics of these heads made in 1973 vs earlier bb heads? any other differences? i'm looking for mid speed torque in my rebuild, not high rpm power. any thoughts?
jeff
what are the flow characteristics of these heads made in 1973 vs earlier bb heads? any other differences? i'm looking for mid speed torque in my rebuild, not high rpm power. any thoughts?
jeff
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Good head, 113cc open chamber, 206/1.72 valves. valve sizes are small
for a 454 size engine, consider putting the 2.19/1.88 rectangle port
seats and valves in them, the open chambers unshrould the big valves
well. Earlier 65-70 oval port heads were basicly the same but with a bathtub
style 101cc chamber, easier to make compression with the smaller chamber
but the flat steep wall beside the valves shrouds the valves more then
the open chamber. Valve sizes, runner sizes virtually the same on the
closed or open chamber heads. Open chambers showed up in 69 on the
L/88 to help unshround the 219/188 valves, the bigger chamber in
71 was just an easy fix to help lower comp, for the new lower octain
fuel.
for a 454 size engine, consider putting the 2.19/1.88 rectangle port
seats and valves in them, the open chambers unshrould the big valves
well. Earlier 65-70 oval port heads were basicly the same but with a bathtub
style 101cc chamber, easier to make compression with the smaller chamber
but the flat steep wall beside the valves shrouds the valves more then
the open chamber. Valve sizes, runner sizes virtually the same on the
closed or open chamber heads. Open chambers showed up in 69 on the
L/88 to help unshround the 219/188 valves, the bigger chamber in
71 was just an easy fix to help lower comp, for the new lower octain
fuel.
Last edited by Little Mouse; Dec 17, 2007 at 09:48 AM.
Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
thanks little mouse
if i put in the larger valves, would the flow slow down enough in middle throttle and rpm ranges to effect performance? this engine will seldom see 5000 rpm, mostly a torquer for impressing the honda boys around town.
jeff
if i put in the larger valves, would the flow slow down enough in middle throttle and rpm ranges to effect performance? this engine will seldom see 5000 rpm, mostly a torquer for impressing the honda boys around town.
jeff
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
of the runners on the old rectangle port heads around 305cc to
the oval ports around 254cc is what causes them to have a slower
air filling of the cylinder at lower rpms, the big runners were nice at higher rpms when the engine has less time to get a gulp of air.
Big blocks are known to have a small percentage of valve area to the amount of cubes they have, even if you had the 2.19/1.88 valves
if you consider the percentage of valve area to just a set of 2.02/1.60
valves in a 350 its not nearly as good. with 206/1.72 valves problem is
even worse. The nice thing about your open chamber it helps unshroud
the bigger 2.19/1.88 valves.
Last edited by Little Mouse; Dec 17, 2007 at 11:35 AM.
