Heads

[Chryco Psycho]

etting a Head
having discussed the short block & cams in previous articles it is time to look into heads
there are some basic differences to start with
we will start �with the production iron heads there are 5 types of chambers used by Mopar
Hemi- this is a dome , litterally a bowl inverted ] with the valves at close to 90* angle &
directly in line with each other , the spark plug is placed at the top of the dome so the flame
travel is even & equal in all directions which resists detonation , causes a more even burn & is
extremely efficient the new Hemi have a quench ring all around the edge to drive the air fuel
into the center of the chamber for evem more effecientcy & power & use 2 plugs at the top of
cylinder as did some of the rare 60s race Hemi heads , the first true hemis were developed for use
in aircraft �as early as the first world war , Chryslers use of the Hemi is more to do with marketing
than them actually designing the cylinder heads

Pent roof - the modern Quasi Hemis use this design , typically used on 4 cylinders like Neon 16v
engine these use a single spark plug in the center of the chamber with a slightly domed roof
typlically � more like 45* & 2 intake valve & 2 exhaust valve to get more effective valve size in
a smaller dioameter cylinder where space for larger valves is limited

Closed Chamber - this is often misunderstood but in most cases this is a D shaped chamber with 40%
of the chaber closed off flush to the deck & the vlaves set in at an 18* angle to the piston & the
spark plug on the side of the chamber , generally this design has a smaller combustion chambner to
increase compression , the Big advantage to this style of head is Quench , I often swap these heads
onto lower compression engine to increase compression without changing pistons , this is termed the
wedge design

Open Chamber - this is virtuall identical to the closed chamber , the valve angle is identical as is
the position of the valves & spark plug to one side of the chamber the difference is that the closed
area across from the spark plug is also raised above deck level , this nullifies the quench effect But
it aids in pollution control so the highly prized 906 big block heads are really the first pollution
control head , all production 340/360 heads are open chamber design these are also wedge design

Heart shaped design - these are a more recent design , thses are trully a closed chamber design ,
valve angle reamins the same as the wedge heads but the closed section is not D shaped but actually
Vees in between the valves to aid in swirl , by carefully shaping both the port & chamber the air is
rolled �instead of dumped into the cylinders this aids in mixing the air fuel & evaporation of the fuel
which increases the power & efficiency of a given amout of fuel , it also increases flow as the air
twists past the valve instead of flowing off the back of the valve & having to make a 90* turn into the
cylinders thes were used from the mid 80s

Lasty the Poly - this head was unique in that the valves were twisted 45* so not side by side like the
wedge or across from each other like the Hemi the plug was on the side of the cylinder like the wedge &
the valves were Canted like the Hemi but at maybe 25* not 90* like the Hemi � �

An interesting tidbit Mopars Wedge engines were designed in the 50s with 18* valve angle , the Chev
Small blocks were also designed then but use a 25* valve angle [in relation to the piston top] in the
late 90s Chev came up with a new head design for Nascar & eventually general performance& street use ,
the big change was to a 18* valve angle , took a long time to figure that out !!!!

Valve sizing is critical in a short storke large bore engine a large valve is easy to install but in
smaller bore engines like the 318 273 & 225 �small valves kill the breathing potential oftem the
cylinder �bores need to be notched to gain clearance for larger valves, this is where swirl can help �

Basic terminology

Valve clearance - this needs to be measured with any engineusing over .500 lift , there are 2
considerations here , first to make sure the valve guides are trimmed down enough so that the spring
retainer does not pinch the seal at max lift & secondly to insure there is enough clearance between
the piston top & valve head so they do not hit , you need �.100 clearance minimum & the interferance
point is generally *8 before TDC for the exhaust & *8 after TDC for the intake valve �
CCs - this is the volume of either the ports or combudstion chamber used for calculating compression
ratio also the chambers can be measured to equalize the chamber volume so each chamber or port is
exactly the same size, �as the CC size of a port increases the velocity has an inverse effect , so the
bigger the port the slower the air flows throught it at a given cylinder volume , there is a fine line
between increasing �port size for more flow & losing too much velocity �

Quench - this is effect of having the piston come very close to the head .040 minimum , this forces the
air �between the piston & head to be forced out at very high velocity & directly into the flame front
from the spark plug �this increases power output & efficient use of the fuel by more completely burning
it this also has the benefit of decreasing the possibility of detonation so slighgtly higher compression
ratios can be used

Milling - this is done to reduce the hieght of the head & decrease the size of the conbustion chamber ,
the block can also be milled to create the same effect �. Generally when the heads are milled the
intake surface has to be milled also , for every .010 removed from the block deck or head deck you need
to mill �.012 from the intake surface or the intake is going to be very tough to get on if at all

Core shift - this is when the water jacket molds or the port molds were not aligned properly with the
external mold so if porting these heads you can very easily break through the casting into a water jacket
, the other problem is the casting can be thin & easily crack with heating & colling cycles , this can be
present in both alum & iron heads

The best heads heads are rumored to be the K heads or early alum Hemi heads, �
the best bet for the big block is the 1 year only 915 head or the early Max wedge heads if you
want to match up all the ports to use them ,When ported the Open Chamber heads are very much equal
with maybe 10 cfm difference between all of them the last 452 casting offers induction hardened seats
but doing a valve jod may cut through the shallow hardening
with the small blocks the best castings are the 87-92 pre magnum high swirl heads , 302 for the 273/ 318
& 308 for the 340 / 360 strokers
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[Chryco Psycho]

On to atfermarket heads
in the last 12 years or so we have been offered a lot more choices
Off the top of my head we have
Stage 5, Barton , Mopar , Indy all offering alum & some iron Hemi heads
Mopar  for the big block  Stage 6 Alum Heads in std or max wedge port
which require special intakes these have a small 78 cc heart shaped chamber   
, Stage V Iron heads  using stock intakes , Max wedge Iron heads , an alum street head
for the small block - Alum commando heads in samll & large port for the LA blocks
we have the Iron W2 in 8 versions  3 for LA blocks & 5 for new R3 blocks with reworked 48* lifter angle
ther is also the W8 alum heads with 6 bolt / cyl mounting
& the top of the line W 9 alum heads alos with 6 bolt  mounting , these engine have been proven to put
a lightweight Prostock chassisinto the 7.10 range in the 1/4 mile all W & P series heads require special
intakes & rockers , most have heart shaped chambers 
then we have the P5 heads fro use with the R4 block & the P7 for use with the new R5 Nascar blocks

Koffells / B1 / Brodix make at least 4 versions of the alum bigblock heads with varying port sizes &
volumes for different applications from the TS all out race head to the streetable BS heads which use
stock rockers but have raised ports & long stem valves & a tiny 65 cc chamber , they also offer 2 good
small block alum heads   

Indy Also has a number of choices with the huge 440-1 requiring external oiling & custom intake ,
the Sr medium head in both iron & alum heart shaped cham,ber & again with external oiling but stock
intakes  & the base  EZ series heads which do not offer external oiling but have the max or std port
size & use stock rockers with raised ports & longer valves & use stock intakes & have heart shaped
chambers & are available in iron or alum also. Small block heads are available as well in a race large
port or small port street version

Bulldog offers a great head with reasonable cost  in both std or max wedge port , these are a true
bolt on head with a heart shaped chamber , long valves & use stock rocker arms & are reasonably priced
for big blocks only so far 

Edelbrock has 2 heads available the base performer which is decent but has unsolved problems like the
nonstock valve location causing piston to valve problems & rocker alignment problems & way to large
combustion chambers & poor shape of the chambers these accept stock intake & rockers
edelbrock is just coming out with a better designed victor head but it si a larger head more aimed at
racing than street use , I have no tseen these yet , they also offer 2 small block RPM castings ,1 for
the 340 with extra clearance for the piston above deck height & a a generic head for any other small
block application but the castings I have seen were badly core shifted & still sent out from the factory 

Stage5 Makes some of the best hemi heads

Barton

There is also the Predator Head , this a monster with 495 cfm intake port flow rating & is basically
a big block chev head designed to fit the Mopar wedge no intakes are available you have to make your
own out of sheet alum , no idea what rocker it uses or where you would need a head this big

the Advantages to alum are lighter weight , repairability better cooling & better more modern design

with Any alum head you need a top quality head gasket , alum expands far faster & more than iron so
the constant pulling against the gasket between the different metalswill eventually cause the gasket
to fail, the best technology is a 3 piece metal shim gasket that can slide between layers without
tearing  , A company - Cometic makes a great gasket for this , they are available in various bore sizes
& thicknesses ranging from .027 - .078 with .004 increments to accuratly adjust the compression ratio ,I
highly recommend using these unless you enjoy pulling the heads off once / year or so 
they also offer a variety of other gaskets including header gaskets in pure copper from .005 - .094
thick

When considering heads for any project from a sway to a complete build there are a lot of varibles to
consider to get the best head for the combination you are building , sk a lot of questions & do a lot
of reasearch to learn as much as possible about what you need for your project
this needs updating as there are a number of new choices such as the Trick Flow heads