This section of
“Jim’s Old Firebird” will cover the engine I built for it, why
I made the choices I did, the parts I bought, and how it worked out.
This section covers the block and rotating assembly, commonly called
the short block.
Design Philosophy -
In deciding what I
wanted (It HAD to be a Pontiac engine!), I looked at what was
available for my intended purpose, which was high-performance street
usage, and road racing. Since I didn’t want maximum torque at
minimum RPM, I went with a 400 CID engine size. This gave me what I
considered the “best” bore-to-stroke ratio, allowing good torque
at midrange RPM (important for exiting corners), while winding high
enough to produce good horsepower for the straightaways.
Durability was to be
paramount in this engine build, so I had to look carefully at certain
items, namely the crankshaft and connecting rods. Good, reliable
pistons were easily available from companies like TRW at very
reasonable prices, along with high-quality piston rings, main and rod
bearings, oil pumps, timing chain and gears, and other things, and
the block was deemed suitable by several knowledgeable people. I’ll
cover the crank and rods decision, and why I used those pieces, in
the “Rotating Assembly” section.
My selection of
parts, and this design philosophy, was guided by the wisdom of the
guys at H-O Racing Specialties in Hawthorne, California. They had run
a series of NHRA record holding cars, and published a book that laid
out everything they’d learned about making Pontiacs run strong and
last. They also knew the difference between squirting down a
quarter-mile, and competing in a road race, and were great guys to
talk to on the phone. My selection of a machinist/engine builder was
based on reputation and recommendations from several local guys who
knew what they were talking about.
Block -
All good structures
start with a good foundation, and an engine is no exception. After
consulting with H-O Racing Specialties in Hawthorne, California, and
my engine builder Jack Waldvogel, I decided to keep the two-bolt main
block that came in the car. H-O confirmed that for my intended
application, the stock block was plenty “good enough”, and my
engine builder confirmed that he’d never seen a two-bolt main
Pontiac block fail except under the most extreme use, and then it was
almost always a rod letting go, and ventilating the block. This was
also a “seasoned” block, having gone 24,676 miles in a street
car, and numerous heat/cool cycles which help stabilize the cast-iron
in the block.
I spent many hours
with my Sears die grinder deburring the block of any and all casting
flash and “dingleberries” inside the block that could possibly
break off and contaminate the oiling system. There were several small
pockets of casting sand/cast iron mixture inside the block that I
knocked out, and a ton of casting flash. My strategy was if it didn’t
look like it belonged there, it probably didn’t, so I ground it
down. The lifter gallery in particular had a huge amount of casting
flash which I ground away. I also “radiused” all the oil
drainback holes and passages, and broke all the sharp edges inside
and outside of the block to eliminate any possible “stress risers”
where cracks could start. I didn’t go to the extreme of polishing
things inside like the NASCAR and Road Race guys do, as I didn’t
see the benefit of it. It was pretty shiny by the time I was done,
though. I also didn’t paint the inside of the block with either
General Electric “Glyptal”, an oil-resistant electric motor
paint, or Rustoleum, as I’d heard too many horror stories of the
paint coming loose and causing extensive damage to the engine. Unless
the surface is EXTREMELY clean, the chances of the paint peeling off
were just too high for me to accept.
As soon as I’d
collected enough parts for Jack to get started, I took them all down
to his shop so he could get started.
Jack was a great
guy, and it’s sad that he’s no longer with us. He was a
first-class machinist, welder, and assembly guru, as well as being an
all-around Good Guy. My Dad knew his Dad from the Navy, and my Dad
sold Jack his Bridgeport milling machine, a variable speed “2J”
head, and a ton of tooling; a first-class Bridgeport setup. Jack had
also served in the US. Navy, and served time as a Machinist Mate on a
nuclear submarine.
Jack bored the block
.060” oversize, honed the cylinders on his Sunnen machine, and also
decked the block to “square it up”, and align-bored the main
bearing bores. He drilled and tapped one of the small press-in plug
holes in the block so he could install an Allen setscrew in there
that had a small hole drilled in it to squirt oil on the
distributor/cam gears. This was a modification suggested by H-O
Racing to keep the gears properly oiled. “High Tech” stuff at the
time, and in common use these days. All other “small” pressed-in
plugs were replaced with Allen setscrews, and the “freeze plugs”
were replaced with brass ones. The completed short block was painted
black after final assembly. I requested Jack leave the oil pan off
the engine, as I wanted to get some pictures of the bottom end, with
those pretty Carillo rods. Sadly, I lost those pictures many years
ago.
Rotating Assembly -
Since the connecting
rods are generally considered to be the most highly-stressed parts in
the engine, getting “good” rods is a must. The rods alternately
get stretched/pulled apart when the piston is being yanked down the
bore during the intake and power stokes, and then squeezed together
as the piston goes back up the bore during the compression and
exhaust strokes. So, you need to make the rods out of a material that
can withstand both tension loading (“stretching”) and compression
loading (“squeezing”) without failing. Forged steel is the ideal
material for this application, and it’s what almost all “good”
connecting rods are made from.
Unfortunately,
Pontiac didn’t make most of their rods from forged steel, opting
instead to save some money and make them from CAST steel, which they
called “ArmaSteel”. For most purposes, like the 400 2-bbl in
Mom’s Catalina station wagon, it’s plenty “good enough”. For
a 400 CID engine spinning 6,500RPM it’s borderline, and for a 455
turning anything more than 5,700RPM, it’s a disaster. The bad thing
about cast materials is that when they fail, they FAIL, almost always
by coming apart, a Real Bad Thing to happen to a connecting rod.
So, what choices did
I have? Well, I could try and hunt down some 389 Super Duty rods
(somewhat available), I could try and beg, borrow, and spend my way
into a set of 455 Super Duty rods (chances were slim to none, and
Slim just left town), I could get some aluminum rods (NOT! Aluminum
lacks the cyclic fatigue strength needed), or I could bite the bullet
and order some Carillo Rods. These rods were absolutely the best you
could buy at the time, and had an unbeatable reputation. I was told
by my engine builder that he’d sent one back that was bent due to
an engine failure, and Carillo straightened it, Magnafluxed it,
installed new bolts, completely checked it out, pronounced it fit for
service again, and sent it back to him “NO CHARGE”. That’s
about as good as it gets!
So, taking some
advice from H-O Racing, I went ahead and ordered a set of rods
through Sontag Speed Supplies but had them made .230” LONGER than
stock. The advice from H-O was, as long as you’re paying to have
these rods custom-made for you, why not take advantage of the fact
that they’ll make them any way you want, and get them made longer?
This way, you get the benefits of a basically indestructible
connecting rod, AND you get the benefit of a “better” rod
length-to-stroke ratio. The rod length-to-stroke ratio is one of
those things that you never hear talked about much, especially “Back
In The Day”. The benefits are lower peak piston speed and
acceleration (reduces stress on the piston, pin, and rod), longer
piston “dwell time” at TDC and BDC, and lower piston side
loading, which is how hard the piston pushes against the cylinder
wall.
Why the importance
of longer dwell time? Well, for one, it lets the cylinder both fill
better, and evacuate better, making the engine more efficient, and
maximizing the cam timing it has.
Since I’d be using
longer rods, I’d have to buy special, custom made pistons, right?
Wrong! I chose the length to be .230” longer than stock, which is
exactly the difference in where the piston pin hole is located
between a 400 piston and a 455 piston. I was able to get a set of “30
over” 455 Super Duty forged pistons ordered through Bert Adams
Pontiac. These pistons were made by TRW, and had the advantage of
having a single “eyebrow” valve relief in them, rather than an
“upper” and a “lower” valve relief. This raised the
compression ratio slightly, and was proven to flow better than having
two valve reliefs in the piston. Remember the longer “Dwell Time”
I mentioned? Since the piston is now spending more time at TDC, the
piston crown essentially becomes a part of the combustion
chamber/intake port “system”, and things you do here can have a
big impact on the “Total Flow” in and out of the engine. All I
did to them was break the sharp edges with a Dremel tool. The rods
needed exactly ZERO work
done to them. Jack told me they were balanced as good as he could do
it right out of the box. The day they came in at Sontag’s, Bill
Sontag asked me if could open the box so he could check one out. He
looked at it, smiled, and said “Yep, it’s a Carillo rod”. About
the same time Ron Menzer came running out of the back like a kid on
Christmas morning, and asked if he could hold one. He oohed and ahhed
for a few minutes and then handed it back and said “THANKS”.
So, with rods and
pistons covered, I moved on to the crank, flywheel, clutch, and
harmonic balancer.
There were few
Pontiac cranks made from forged steel that had the required 3.00”
diameter main bearing journals. The 389 Super Duty had one, as well
as the mythical Ram Air V engines, but that was it. Moldex was about
the only company at the time that would make you whatever you wanted,
but that wasn’t in the budget for me. I looked around and contacted
a few people, but nobody had any 389 SD cranks for sale. SO….turning
to H-O Racing again for guidance, I decided a 1970 Ram Air IV cast
nodular iron crank would be my choice. It was made of a better grade
of cast iron than my 1973 crank, had better heat treating, “rolled”
journals, generous “fillets” on the journals, and some other nice
things I forget now. Best of all, it “only” cost about $135! Jack
“micropolished” the journals after he radiused the oil holes, and
did some deburring of it, but that was it for the crank.
I wanted to use an
aluminum flywheel because a lighter flywheel has less rotational
inertia, meaning you can accelerate it faster which translates into
faster acceleration once you’re moving.
This means you can accelerate harder out of corners, a perfect fit
for a car I planned to road race. Why do drag racers use heavy
flywheels? Because a heavy flywheel can store a lot of energy which
gets released when the clutch gets popped, making the car accelerate
harder from a standstill
IF you have the traction (Slicks) to use it. Otherwise you’ll just
blow the tires away. The first flywheel I bought didn’t fit the
crank, so I talked to Tony at the parts counter, and he confirmed
that the early and late flywheels all the had the same number of
teeth on the ring gear, so I told Jack to go ahead and machine the
flywheel to fit the crank. BIG mistake! It turns out the older
flywheels were “flatter” than newer ones, and the first time I
tried to crank the engine in the car I was greeted with the stater
going “ZIIIING!”, and not engaging the flywheel. I checked the
part number I ordered with Sontag, and sure enough, it was for a very
early Pontiac V8.
I should have suspected something as the box it came in looked older
than me, and had an inch of dust on it. Oh, well, order another
flywheel, and this time make sure it fits a 1970 Pontiac!
In
order to keep rotating mass small (because….Road
Race!), I stayed with a
10.5” pressure plate and clutch disc. The pressure plate was a
Borg-Warner “Power Brute” unit, and the disc was for an L88
Corvette. I used a
Borg-Warner “Power Brute” clutch release (throw out) bearing as
it had a different bearing design than an OEM release bearing, which
was supposedly longer lasting when used at high RPM. I never had any
trouble with the clutch, and it engaged solidly, never slipping. The
pilot bearing in the end of the crank was a standard GM pilot
bearing.
The
harmonic balancer was for a 1970 Ram Air IV engine, and I had Jack
“degree” it, cutting timing marks and stamping numbers on it so I
could easily set the initial timing, and check the total timing.
Other
Engine Related Parts
-
I
used an OEM Ram Air IV oil pump along with an H-O Racing higher
pressure relief spring. I took the pump apart and brazed the pickup
tube and screen into the body so it couldn’t fall out, and also
checked the clearance between the gears, the gears and the body, and
the gears and the end plate. I carefully sanded the open end of the
pump body using some 600 grit wet-or-dry sandpaper on a glass plate,
with plenty of oil, and did the same to the end plate to make sure
they were FLAT, and had a polished finish. This ensured there was no
gap between them, reducing any chance of losing oil pressure.
Since
this engine didn’t come with one, I ordered one of the “3/4
length” windage trays listed in the Pontiac
parts catalog. I
used the stock oil pan as it had a baffle in it to keep the oil in
the pan near the pickup, but it only worked well in left turns! The
car cornered so hard that I constantly had to watch the oil pressure
in right hand turns, as I could make the pressure drop just
“twitching” the steering wheel hard to the right! Even running a
quart over didn’t help too much, and this was an issue that plagued
me the entire time I owned the car.
The
water pump, was a Moroso aluminum unit that saved a little over two
pounds. As I mention later, weight saving was another big item to me,
and eventually the car wound up about 400 pounds
lighter than when it rolled out of Norwood. The
front cover was the one that came with the car. I had Jack check the
timing badge to make sure it agreed with the degreed harmonic
balancer, and it did.
In
the end, the only parts that I used that came with the car were the
block, the valve covers, the valley cover, the front cover, the oil
pan, and the oil filter adapter. I had a set of chrome valve covers
from a GTO, but they didn’t have the oil “dripper” rails
inside. Since I read that this could cause your rocker arms to fail
from lack of lubrication, I painted the stock valve covers wrinkle
finish black, and put them back on the car. I also kept the Unitized Ignition distributor. I carefully shimmed all the end-play out of the gear at the bottom, and replaced the stock gear with a bronze driven gear I bought from H-O racing. This turned out to be a mistake, as about 1,000 miles after I got the car running, the teeth wore through, and the engine quit running when I was at the Car Craft Street Machine Nationals in Indianapolis. I was lucky that it was my last night at the hotel. My friend Marvin gave me a ride home, and then took me back the next day to fix the car, and get it back to Joliet.
"Car People" are good people, always willing to help a buddy in trouble!
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