Since I am also building a 455 I have been looking around at different write ups.
Here is something interesting and a fun read.
The 455-cu.in. V-8 debuted in 1970 and was the largest displacement Pontiac engine ever built for the street. It is likely also one of the best, said Jim Taylor, the legendary Pontiac engine builder from Phillipsburg, New Jersey. "I love Pontiac engines, and the engineers who built them were tremendous, absolutely at the top of their game," he said.
Taylor shies away from aftermarket stroker cranks to make power with a 455.
"When I build up a 455 engine, I use the original block and crankshaft, because that Pontiac crank is the best that was ever made," he said.
He admits Pontiacs have engine failures, but it's not because of the crankshaft, rather it is a failed connecting rod or rod bolt.
"I've never seen a nodular iron crankshaft break on a Pontiac," Taylor said.
Like all other American carmakers, engineers at Pontiac in 1970 were in a transition year as they saw tightening emissions standards forcing them to give up high-compression engines. High compression causes a spike in combustion temperatures, which enhances the buildup of nitrogen emissions. Along with emissions regulations, weight was increasing and the only other way to keep up performance was to increase displacement. The Ram Air IV 400-cu.in. V-8, with 370hp, could be ordered through most of the 1970 model year, but Pontiac intended the 455 to phase out the Ram Air IV, even though the RAIV could outperform a 455 in the quarter mile. For specific power output, Hanks believes the 1969-1970 Ram Air IV was the best Pontiac engine ever. "The factory rating was conservative at 370hp and later weight/mph calculations in quarter-mile performance indicate that the engine produced the rated power at the rear wheels," Hanks says. However, at part throttle, the 455's milder cam and smaller ports gave it better throttle response and the 455 was more adaptable to high-speed cruising. The 455 was also burly enough to handle all the power accessories, such as air conditioning, that GTO owners were beginning to order. In 1970, the 455 had the no. 64 cylinder heads.
"Cube for cube, carb for carb, when you put a Pontiac 455 on a dyno and add up the points, which are torque and horsepower, there is no better engine," Taylor said. "Power is all about torque. A Pontiac will pull away quicker and will put you back in the seat. A Pontiac 455 is more responsive than a Chevy or a Ford. In a Pontiac, the torque is most efficient in the rpm range in which you drive. A 400 Pontiac is not a torque maker. And a 428 makes torque, but nothing like a 455. The 455 SD is not the most powerful engine Pontiac built, due to lower compression. One point lost in compression equals 50-lbs.ft. of torque and 50 hp."
Taylor said the 428 engine is very efficient and has a good bore-to-stroke ratio. Pontiac kept its ports small and the 428 is one of only a few engines that had fully machined combustion chambers from the factory, which delivers exceptional cylinder balance.
Taylor maintains that a 455 produces high vacuum at idle, which leads to instant throttle response. "It gives you what you want when you hit the gas pedal," he said. "The 455 has relatively small ports for the size of the engine. In contrast, a big-block Chevy and the bigger Fords have huge ports and that isn't always the best combination for the street. A Pontiac engine has low cubic-feet-per-minute flow through the carburetor, but high velocity through the cylinder heads for more efficiency."
While Taylor sings the 455's praises, like the quality of the cast iron in the blocks, he reveals one major weakness--the lifter bores. "You can't put a big cam in a 455. The weakness is particularly in number two and number six cylinders. The cam tends to pick the lifter bore right off the block," he said. "The proper webbing can be installed if you know what you are doing, but because of this weakness I will not build, say an 800hp engine for a customer, and I absolutely refuse to build one with nitrous. I can build it, but with nitrous it just won't last."
Let's take a look inside a 455 V-8 and see what makes it tick, er, scream. Basically, a 455 is a 400 stroked 0.46 inches. The gross torque rating computed to 480 foot pounds and in 1971, GM rated everything net, so in reality the engine produced 410 foot pounds of torque at 3,600 rpm. This increase now meant the engine was oversquare, meaning the stroke was longer than the diameter of the cylinder bore (4.12 inches) which all adds up to a 5,500 redline. Because the 455 was an oversquare engine, Pontiac engineers used lighter parts in the reciprocating assembly to cut down on mass, which in turn relieved stress. For example, each piston now weighed 1.5 ounces less than in 1970, but at the same time, engineers worked to keep the engine strong by increasing the crankshaft's main bearing journals from 3 inches in the 400 to 3.25 inches in the 455. To further increase toughness in 1971, all crankshafts were cast of nodular iron, in contrast to standard cast iron, and the new 197 casting number heads retained screw-in rocker arm studs from 1970.
By 1972, Pontiac's 400-cu.in. V-8 topped out at 250hp, and the 455 Ram Air IV boasted 300hp despite its 8.4:1 compression ratio. The next year, Pontiac introduced the 455 SD, which put out 290hp in both automatic and manual transmission equipped cars. Considered one of the ultimate Pontiac engines, it suffered from an oil pump with extremely high pressure. In 1973, Pontiac tried to get around the new exhaust gas recirculation regulations (EGR). To accomplish this, engineers provided a solenoid within the system to render the EGR useless. They got caught and the Environmental Protection Agency required that the solenoids be removed.
In 1974, after America suffered through its first energy crisis, Pontiac offered the 455 SD one more time before the advent of catalytic converters in 1975. Thirty years ago, you could still buy a 455, but it was emasculated and breathing through a single exhaust and produced just 200hp at 3,500 rpm. Worse yet, the 400-cu.in. engine wheezed out only 185hp, a shadow of its former self. At least during the 455's last year in 1976, the engine still made 200hp, but performance for the brand was all but dead.