Check out Part 2 of our engine build!
Here’s the fresh 421 on the dyno. More about what it achieved will be published next month
It is a known fact that a person's pupils dilate slightly when viewing something pleasant to the eyes. Well, gaze upon these numbers—a 421ci Pontiac with Tri-Power carburetion.
Wide-eyed yet? We are.
Here is another number to ponder: 370 hp. That's the factory rating of the legendary 421 H.O. Tri-Power equipped Pontiac hot rod—a stout piece by anyone's standards.
Ever wonder what it would take to increase that number by 100? Jim Taylor, well-known Pontiac engine builder, had that question on his bucket list for years. Jim told HPP, "Since I was a young man in the '60s, I always thought how great it would be to find a true 100hp in a legendary 421 Tri-Power setup that retained its iron heads and intake. I don't know if it can be done, but I'm going to try." HPP decided to follow this exciting exercise; we show you the highlights in this two-part primer.
True Pontiac engines were designed and built in Detroit—not on a computer, but often by GI-bill-educated engineers who grew up working with their hands and now had a slide rule in their pocket instead of a greasy rag. These guys lived by mathematics since every function of an engine that converts chemical to mechanical energy can be assigned a number. Math, not gasoline, makes horsepower under the hood of a Pontiac. Jim Taylor knows this, so he took a mathematical engineering-style approach to finding 100 hp in a relatively optimized engine.
It's well documented that an internal combustion engine is nothing more than an air pump. Greater throughput mixed with the proper amount of fuel and ignited at the ideal time for the flame to expand against the piston will result in more power. Thus, the quest to find 100 hp in a 421 started on the flow bench, before a wrench or machine tool touched any part of the 49-year-old engine. Not where most enthusiasts go first.
Using an equation the author has provided in HPP many times—most recently with The Mule engine series—it was revealed that around 228.6-cfm flow though the intake port of the cylinder head is required to produce the desired 470 hp.
2. The original ’64 cast crankshaft boasts a 4.00-inch stroke. The balance drill holes can
3. Over the years, Jim has had metallurgical analysis performed on many factory and afterm
4. This engine employed the Howard’s 4340 billet-steel connecting rod, which is a stock le
5. The rods come with a specification card that is used to determine the bob weights for b
6. Icon 428 forged pistons are in the 421. While a stock 421 had a bore of 4.097 inches, t
7. TDC was confirmed during the build, not only to phase the cam properly but also to dete
For those who may not be familiar with the equation, here it is again:
Required airflow at 28 in/H2O = HP/ # of cylinders/0.257
To determine horsepower from airflow, invert the equation:
HP = flow at 28 in/H2O x 0.257 x # of cylinders
Though airflow is paramount in making power, there are other aspects of the engine that are just as important. Where else will the extra 100 horses come from?
Starting at the bottom, Jim will employ lighter and stronger parts in the reciprocating assembly, as evidenced by the choice of Howards billet rods and forged Icon pistons. The rod weighs 751 grams versus the stock rod at 958 grams. The piston weighs 630 grams with the pin versus the stock piston and pin weight of 790 grams. Reductions in reciprocating weight free up horsepower.
For a few more ponies through better oil control, a factory full-length windage tray will be added, since Pontiac didn't use one on this engine originally. Cam choice is always extremely important, and Jim decided to go with an aggressive Crower mechanical flat-tappet stick with 247/252-degrees duration at 0.050 and 0.515/0.525 lift (0.495/0.505 with 0.020 lash) with 1.6:1 rockers. Crower identifies this cam as a Level 4, which means it provides strong midrange and top-end power for heavily modified engines.
The company says engines running this cam benefit from headers, cylinder-head port work, a large-cfm carb, and an ignition upgrade. It requires a compression ratio of at least 10.25:1. By comparison, the factory 421 H.O. cam specs out at 215/225-degrees duration at 0.050 and has just 0.407/0.407 lift with the factory 1.50:1 rockers.