396 Cam change for 1971

[davepl]

And yes, I know it was the 402. But I was doing some research yesterday on what cams actually came in the 396s, and noticed that as of 1971 they added more exhaust lift and duration (still a very mild cam).

I'm wondering what this might have coincided with, like a switch to open port cylinder heads perhaps?

Curious as to what else in the motor changed for '71 that would have necessitated a cam change, or if it was "just because".

[hamjet]

I haven't checked, just shooting from the hip from what I remember. 1971 was the first year they started dropping compression. they probably played with lift and duration to coincide with the drop.Open port heads, (we used to call them rectangle port) were for the 375 HP and up 396/402s. more compression, if you mean larger combustion chamber, I don't know for a fact if they dished the pistons, opened the combustion chamber, or both when they lowered the compression in 71.

[davepl]

I do see gross horsepower dropped by 10 to 300hp for 1971. I like that in the heritage center docs they list gross and net, so you can see what the difference actually is.

Anyone find a reference on what the compression change might have been, or if the cylinder heads changed? I can likely find it, but is a forum, not a monologue!

[davepl]

For 1972, compression was down to 8.5:1 and net horsepower had fallen from 242 down to 210, so a significant drop. SAE net torque on the big block was still 320, but that's less than half what comes in the new Z06 :-)

Still not sure on head changes, but I think there was a chamber change.

[SS Tim]

Originally Posted by davepl

And yes, I know it was the 402. But I was doing some research yesterday on what cams actually came in the 396s, and noticed that as of 1971 they added more exhaust lift and duration (still a very mild cam).

I'm wondering what this might have coincided with, like a switch to open port cylinder heads perhaps?

Curious as to what else in the motor changed for '71 that would have necessitated a cam change, or if it was "just because".

Most likely it was for NOX reduction.