[goatless]

Well, you learn something new everyday. So the heat riser flapper thing went away in '69 and came back again as part of the emission control system in the mid '70s?

Jack, that center port divider is another thing the Pontiac engineers changed their mind on- I've got a bunch of sets of logs and only a couple have the divider. I don't recall the dates on the ones with them or without.

The set on my Lemans right now are '70 castings that don't have the divider.
BTW, my lemans ran a 12.76 at Lebanon Valley yesterday with logs... and G70-14 Polyglas tires. Those log manifolds aren't the hinderance that most people believe!

[70Steve]

Jack, that center port divider is another thing the Pontiac engineers changed their mind on- I've got a bunch of sets of logs and only a couple have the divider. I don't recall the dates on the ones with them or without.

My 70 GTO got one of each!! Early Nov. 69 car,....... manifolds weren't that much earlier from memory.

Thanks for the thread too b-man.

[zeebo]

Originally Posted by goatless

Well, you learn something new everyday. So the heat riser flapper thing went away in '69 and came back again as part of the emission control system in the mid '70s?

Jack, that center port divider is another thing the Pontiac engineers changed their mind on- I've got a bunch of sets of logs and only a couple have the divider. I don't recall the dates on the ones with them or without.

The set on my Lemans right now are '70 castings that don't have the divider.
BTW, my lemans ran a 12.76 at Lebanon Valley yesterday with logs... and G70-14 Polyglas tires. Those log manifolds aren't the hinderance that most people believe!

correct..i do not know the exact date they stopped with the heat riser valve, but i know that 72 thru 74 pontiacs do not have them..they returned in 75 with the cat. converter. i personally dislike these, not only for the restriction, but for the fact that they can seize up and stick closed, severely damaging your engine.

unless you are doing a 100 point resto, id leave it out, and even if you do a 100 point resto, id tack weld it open..

i think opening up the log outlet and extrude hone polishing sure cant hurt..plus with good mandrel pipes that dont neck down you should be good up to 1hp/cu in....

[sixtysix]

Is the heat riser necessary with an automatic choke?

[goatless]

Some years didn't have the flapper at all. So, no not necessary.