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.
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!
"Car People" are good people, always willing to help a buddy in trouble!