I was the person that went through a 2 year ordeal with NHRA on the early # 163 intake manifold with the cut plenum. This is legal only on the 1970 (375hp-402), 1970 (450hp-454) and the 1971 (425hp-454) as a replacement manifold for the very rare high rise #474 that also had a factory cut plenum.
The cut plenum #163 manifolds were very popular as an over the counter GM part until sometime in the mid eighties. This was a "Snowflake" logo style for the Winters foundry.
In the 1990's a different foundry and pattern equipment was used and NONE of those #163 manifolds had a factory cut plenum. They did however have slightly more volume.
Some racers thought that just because it had the same #163 casting number the cut-plenum version would be legal for all years and models. NHRA nipped this idea in the bud
and almost rescinded acceptance for the 70 and 71 model years. The early cut plenum #163 intake manifolds are still available at swap meets and ebay but are quite expensive.
Keith Lynch and I tested Bruce Bachelder and Travis Miller's patience with this deal back in 2004 but if you look at the NHRA engine specifications for the 1971 Chevrolet engines you will see that it is still legal.
It is a tricky to jet this cut plenum intake correctly but you can pick up some power with EGT's on every cylinder and a dyno. I would put a cut-plenum #163 up against a #359 anytime. I still have a cut-plenum intake manifold here and Dave Lebrun has one that I lent him if anybody wants to dyno test after the optimum stagger jetting is found. Call 231-740-5534 or email
mark4gen6@yahoo.com if anyone is interested in trying my cut-plenum #163 intake. Fred Lee