Big Block heads are a find. Buick
made numerous different sets throughout the years. Some of these heads
flowed better than others. Identifying heads (engine size and year),
however, can be a difficult job. This chart will help by providing you
with casting numbers so you can determine what you've got, or know what to
look for at your local parts yards.
Chart Based upon Information from Kenne-Bell
and Buick Service Bulletins
Production Head Casting Number
Service Replacement Head Casting
Cylinder Block Casting Number
Head Chamber Size in cc's
||66cc (455 Stg 1)
Heads in Bold are "Big Port"
heads. These flow about 5% better than regular heads.
What Heads Flow the Best?
Through the years, Buick made numerous sets of heads for the 400, 430 and
455 engines. These heads are largely interchangably. Generally, the rule
is that early heads can be used on later blocks but later heads will not fit
early blocks. I can't say that this is true, however, later heads
(certainly 72 and after) came with larger chambers (for reduced compression
engines) and various smog and emissions modifications. So, from a
performance standpoint, most people will want to use 71 and earlier heads.
The question is what heads flow the best. The following is a list of the
stock factory non-stage heads that flowed the best.
NOTE: If using earlier heads on a later
block (67-69 heads on a 71 or later 455 Block), you need to block the upper
front oil passage hole (located beside the upper front head bolt hole) on
the drivers side of the block. If left unplugged, serious oil
leakage will result when 455 rocker shafts are used.
1. 67-68 400-430 "Big Port" Heads (These heads
flow about 5% better due to
larger intake ports).
2. 70-71 455 Heads
3. 69 430 Heads
4. 72-74 455 Heads
5. 75-76 455 Heads
The information listed above does not
include porting. Ported heads will obviously flow better than any
non-ported heads. Good port jobs, however, are EXPENSIVE. The list is
intended to identify the best flowing heads for people who don't have the
bucks to port their heads. My suggestion is to take a set of the 67-68 Big
Port 430 heads and cut them for stage 1 valves, back cut the valves, match
the intake manifold ports to the intake ports of the head. If funds permit,
then go a little further and unshroud the area around the new big valves in
the combustion chamber, and polish the combustion chambers.
Big Block Performance Heads Tips
Block Exhaust Crossover
Install cap plugs (2 per head) to block off the crossover
passages. If you remove your cylinder heads, the better course of action
is to have a quality head shop fill these passages flush to the exhaust
port. This keeps hot exhaust gases out of the intake manifold giving you a
denser and cooler air/fuel mixture and equalizing the exhaust port flow by
eliminating turbulence in the 2 center exhaust ports.
Back Cutting Valves
Stock valves restrict the air flow into and out of the head. Back cutting
the valves 28 to 30 degrees is a huge bang for the buck on any Buick, big
or small block. Back cutting will enhance low and mid lift flow numbers.
Intake Port Matching
Ideally, intake manifold port openings and cylinder head port openings
should match perfectly. Match porting will help achieve this. One thing
to remember, a perfect match is almost impossible to attain, so it is
better that the intake manifold openings be slightly smaller than the
cylinder head port openings. UNDER NO CIRCUMSTANCES do you want the
intake port opening larger than the head port. This will cause turbulence
and reduce air flow, thereby hampering performance.
Exhaust Port Matching
If using stock exhaust manifolds, match porting the head exhaust openings
to the exhaust manifold openings will benefit performance. DO NOT enlarge
the exhaust port flange on a Stage 1 head. The manifold needs to be
larger than the head port to prevent or reduce exhaust gas reversion.
Unshrouding Valves in Combustion
If you install Stage 1 valves in a standard small valve head, you MUST
relieve the combustion chambers around the valves. If you do not, you
will most likely not increase airflow or horsepower. In fact, air flow
reduction may occur.
- Polishing Combustion Chambers
This is beneficial not only for race engines, but for street
driven engines too. Polishing will remove sharp edges that could cause hot
spots in the chamber and result in early detonation.