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- Stephen Sadler
September 27, 2009, 2:16 pm
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- Speaker of the Truth
September 27, 2009, 6:13 pm
The open chamber heads were circular in shape and closed were oval (bath tub
shape). The open chamber ones breath better.
The better Big Block Heads are cast with "HD" on them near the casting
numbers as I remember. These are the only good Big Block Heads . All the
rest are junk or nothing to write home about. (I'm sure someone will respond
and say they are running truck high deck heads and running in the 8.0's)
Since we live in the era of "the money has all gone to it's rightful owners"
or "Barrett Jackson". The heads were expensive 15 years ago. Now in the new
era they are almost priceless museum pieces.
You know after looking at this stuff for 25+ years. GM made the big and
small block the same way. The basic and slightly high po engines (big and
small) all had regular parts. Then there was the best, high performance
engines that were like racing grade. These parts were not as plentiful as
the regular parts.
Example the 1962 327/340hp had all the high performance parts and it had HP.
Funny the 1968 -69 Camera Z-28 engine was almost the same engine. Funny how
they both had a lot of balls and funny there both had almost the same parts
(most expensive/highest HP). The LT-1 was very similar too. It all boiled
down to that one HP intake, HP cam, Double hump heads, forged pistons, HD
crank, solid lifters. A friend said to me 10 years ago and I doubted him,
"it will cost you $4,000 to rebuild one of those engines)
My friends 68 Corvette 427/435 had all the engine castings cast with "HP"
Example, my friend had a 1967 Corvette conv't. Number didn't match 307 cid
engine. He had a holley 4 barrel. 3:25 axle 4 speed. He couldn't light the
tires up off the line in 1st. Then his neighbor gave him a 327/365 HP holley
intake. (I thought a 327/365 was a Fuel injected engine). After installing
the manifold he could light up the tires all day in 1st if he wanted. Look
at what the manifold is worth if you can find one today.
The days of finding any of this stuff for $25 bucks (Bloomington in the
1970's ) is over. In it's day the HP Gm stuff was better than any edelbrock,
mickey thompson, holley after market stuff.
Don't forget, this stuff was made back in the old days of GM, before GM
decided to have it head up it's ass.
You don't get nothing for nothing anymore.
- Stephen Sadler
September 27, 2009, 10:03 pm
Thanks for the information. Maybe I should better state my question. The
long block I'm building now has flat top pistons. The original heads that
came off the motor are (14092360...86-90...oval...OPEN...454 Truck, "peanut"
round ports from http://www.mortec.com/bbc.htm ) stock. Correct me if I'm
wrong, from what I understand the open style heads are suited to take a dome
type piston to get a really high compression ratio. With My flat top
pistons my compression ration would suffer because of the open chamber
volume. I think for a flat top piston one would want a closed camber to
help further raise the compression ratio to gain more power. Is this
correct? Are there any known recommended Chevy castings that you know of?
Are there any other things I need to know about?
If you arent concerned with originality, and you are going to use
your car for street only use...seriously consider Edelbrocks Aluminum
Oval Port Heads with their AirGap RPM Dual Plane Intake . I swapped
out my 454 cid stock Heads and Intake with these...and I could
actually feel at least a 30 percent greater airflow at the exhaust
tips. The weight is considerably less versus the stock iron heads/
intake , and, based on this motor having the EDL Heads, Intake,
bumpier Cam with Headers...their website dyno chart shows 540 h.p.
Thats an increase of 150 h.p. over stock for an LS5 Motor. I then
added an 800 cfm Mighty Demon Carb with annular boosters/mech
secs....and the car is a real screamer with maximum low end to mid-
range torque . Its darn scary sometimes when you jump on it. The
EDL Heads are high quality CNC'd .
I had a 69 427-435 (tri power manifold) a few years ago.
I was not going to replace that manifold (there is a small port tri power
manifold also) so I was stuck with big port, open chamber heads. My pistons
were not stock and were not flat. They had a very slight dome.
Are your sure your pistons are flat?
I think I would have done better with small port heads which would give you
closed chamber heads. Like you said, only flat pistons here.
The increased torque of the small port, closed chamber head is the way you
want to go with the low octane gas these days.
You cannot use the high compression setup and the open chamber heads do not
get the compression ratio up without a large dome piston. With a large dome
piston the CR would be too high. With a flat it is too low. That is why I
push for the closed chamber head