Senior Tech Team
Join Date: Sep 1998
Location: Mustang, OK USA
If you want to get started with the LEAST AMOUNT OF EXPENSE FOR HEADS, use 70-74 stock 400 heads. The 400 ports are as big as any SB heads and they come with 1.94-1.5 valves. The first upgrade you can do is to open them to 2.02 or 2.05 intake valves and 1.6 exhaust valves. If you have a VERY GOOD head person in your area who will not charge an arm and a leg, you could have them port matched and have some light bowl blending done. The STOCK 70-74 heads, which are 76cc heads, used with 5.7 (350) rods and flat top pistons, will produce about 9.6 comp.
DO NOT USE ANY STOCK 75-LATER CHEVY HEADS ON A 400. In 1975, Chevy started cutting corners on their heads to save a little weight. In 75 the heads had a second exhaust crossover port added which produced more head heat. And by the late 70s, all SB heads (except the Bowtie heads) were light weight, thin wall castings. ANY machinist who has lots of experience with SB heads will tell you that Mid-70s and later heads are either cracked when they come in, or, they probably will crack soon.
For performance, endurance and longevity, your VERY BEST investment in a head will be one of the iron, BIG PORT aftermarket heads, such as World or Dart with 225cc or larger intake ports will be the most ideal head to use. A 235-245cc port will provide the best performance. I don't think there are ANY alum heads with ports this big right out of the box. Also, heads with the 2.08 valves will be the best to use.
I have pointed this out here many times before. Performance wise, a BB 396-402 will blow the doors off of a SB400, even though they are the same displacement. The reason is because BB heads can BREATHE! PERIOD! The BB heads with the the smallest valves and ports (such as a bone stock oval port BB head) ARE STILL BIGGER THAN SB HEADS WITH THE BIGGEST PORTS AND VALVES. You physically CANNOT install a valve in a SB head that is as big as a small BB valve. So, the bottom line is, there is no such thing as a head with ports/valves too big for a SB400. When you have 400+ cubic inches, it needs to be able to breathe, so don't be concerned about using big port/valve heads.
And last, keep in mind, as displacement increases, the engine can handle a cam with a larger profile. For a SB400, a lift of .500 is no problem. But, then this brings up another issue. Most SB heads come with pressed in rocker studs. For a cam with .450 or more lift, it is almost mandatory to have screw in studs installed. The reason is because BOTH the bigger lift AND the amount of spring pressure required to handle this much lift will possibly cause the pressed in studs to pull out. ALMOST ALL aftermarket heads come with screw in studs.
[This message has been edited by DZAUTO (edited 12-27-2001).]