At top, the stock TPI manifold...
At top, the stock TPI manifold (SBC pattern) and the Vortec-pattern manifold (bottom) with each others gaskets on them (right photo) help illustrate the difference in port shapes. The taller Vortec gaskets over the older SBC intake ports show a visible gap between the port roof of the stock TPI casting and the hole in the Vortec gasket.
Pistons And Rings
The pistons don't receive a lot of attention from horsepower junkies, but professional engine builders spend considerable time and effort on them. Perhaps most critical for power, weight saved on the piston causes a cascade effect throughout the engine as the connecting rod can now be lighter, the crank pins can be smaller, everything is less stressed, and the engine can spin higher with less energy expended.
Another consideration that pays dividends in both performance and economy is ring seal. Remember, the rings seal on the cylinder wall and against the piston ring lands as well. Our research brought us three distinct options in price. Since we will be making enough power and our strokers' piston speed will be punishing to our candidates, we set our sights pretty high for this critical component.
Coming in at a great deal for a set of pistons and rings are the venerable KB hypereutectics. The term hypereuctectic refers to an excess of silicon in the aluminum alloy that forms crystals, giving the pistons better thermal properties, allowing tighter tolerances and keeping the heat in the top of the piston. A full set runs about $260 including pins and rings. Although they're cast pistons, they have proven to be durable and efficient.
A bottom view of a stout Ross...
A bottom view of a stout Ross Racing piston that was at Pacific Performance Products shows the thickness of the piston-pin bosses and the ledge inside the dome. This piston is built for extreme abuse.
Our next level of pistons is the Mahle power pack. These are a fully detailed forging with many expensive options and a Formula One pedigree. The technology used to attain better ring seal and lighter yet stronger pistons is quite impressive. As we learned more, we appreciated where the extra money goes for these. We chose a fully matched set that runs about $600 with rings, pins, and locks.
The final level is represented by Ross Racing Pistons. If you are a serious racer and are committed to the optimum combo, Ross pistons are custom-made to order, and the company has computer maps of most high-performance head's combustion chambers to be able to deliver the maximum compression ratio or valve clearance for any combination you want. These pistons are designed specifically for the application, so there are no "shelf" pistons for our use. While we just can't justify space shuttle technology for our TPI Trans Am, it's nice to know where it is if we need it. Prices vary substantially with different designs and features, but if you are looking for big horsepower-adder pistons that need to hold up to racing abuse, Ross Pistons would be the obvious choice.
Spare The Rod, Spoil The Engine
The rods really should be considered along with the crank, but frankly, there are a lot more options here than we could possibly deal with in the scope of this story. This is one of the places where the part is 100 percent interchangeable with a small-block Chevy, whereas the crank is specific to only a few corporate blocks, so our options on the connecting rods are plentiful and reasonably priced. We won't split hairs here by offering even a fraction of the choices before you, but we would like to go with a rod that is as long, strong, and light as practical at around $350 for the set.
The semi-dome and the depth...
The semi-dome and the depth to the first compression ring indicate this piston is designed for a number of stages of nitrous, run after run. Also note how the slipper skirts are tied together below the piston pin with a large, strengthening rib.
As this is such a critical component in the longevity of the build, we were wary of low prices. We consulted with our friendly engine builder, Troy Bowen at Pacific Performance Products. He cleared the air by recommending an RPM International forged crank and either its I-beam or H-beam, 6-inch, forged connecting rods. Since RPM International doesn't sell direct, we placed our order through Pacific Performance Products, which went with H-beams for their twist resistance and clearance for the stroker combination in the block.
Crank Shaft
As we intended to sack our incumbent 3.45-inch-stroke cast crank in favor of a 3.75 stroker, we selected several candidates for evaluation such as the budget-minded Ohio Crankshaft 3.75-inch-stroke, nodular-iron cast crank with a 1pc rear main seal ($195) and a Scat "lightweight"-cast, 3.75-inch stroker crank ($231). Each would give us a substantial increase in torque, and since the 383-cid stroke version of the SBC has enjoyed so much development, we have a lot of information on what to use with this combination.
Our next option is to upgrade to a forged-5140-steel, 3.75-inch stroker crankshaft from RPM International ($369, which we ultimately chose) or a Scat 4130 forged-steel, 3.75-inch stroker crank ($630), and on up to the beautiful Callies CompStar 4340 forged-steel crank ($730). Obviously, there are significant differences in the quality and finish of these cranks, the most important being the quality of the forging, consistency and accuracy of heat treat, quality and detail in machining (which often creates a substantially lighter crank), and optional coatings.
For a show or strictly street-performance car, the cast crank will be fine for your needs, as we've been told that a good pearlitic iron-cast crank can support well over 500 hp. Keeping in mind that cast-iron and lesser steels are also more brittle materials, and when it does let go, it comes apart with gusto, we emphatically recommend that for all-out racing, a builder will never regret spending the extra money on the high-quality forging. Know your needs and cast (or forge) your vote.
This is an I-beam connecting...
This is an I-beam connecting rod. The red arrow indicates the use of a connecting rod bolt/nut, where the top portion of the bolt hole must be machined along the axis of the rod to squarely seat the bolt head. This creates a stress area where the orange arrow indicates, as the material makes a complex shape transition there. This area and the corresponding area where the bottom cap is cut away for the bottom nut are the weakest points due to stress concentration on this rod design.
Camshaft
At long last, we get to perhaps the most critical key of this combination besides the heads: the camshaft. Our stock cam is a power killer, even in this wimpy-headed engine. Its lobe-separation angle is 117 degrees, which the factory decided was necessary to pass smog requirements, but there is such little overlap that it kills all high midrange-and-up power potential. Troy suggested we go with a Comp or Crane camshaft, and spec'd it for our combination at 225/228 degrees of duration at 0.050 with 0.560 net lift using 1.6-ratio rockers. He also emphasized that we needed about 112 degrees of lobe-separation angle to both pass smog and also enable our combo to rev a bit.
The Cabinet
Since we have the "big" parts out of the way, all that is left is the smaller necessities that make the package work and pretty much blow our budget out of the water. We will probably swap out the included springs on the Edelbrock heads for the proper Comp Cams parts.
Since Pacific Performance Products is a complete machine shop as well as cylinder-head development shop, when we get the E-Tecs apart, we want to put a professional eyeball to them and see if there are any easy gains to be had. Jay, Pacific Performance Products' cylinder-head guru, stated that a racing valve job and a little detail around the bowls can often bring easy gains even on well-developed production heads.
We will also use an oil pump from Dynamic Performance, a Pro Gear timing set, one of Pacific Performance Products' main girdles, a Milodon oil pan to make room for it, Harland Sharp roller rockers, Comp Cams pushrods, stock-style lifters, Fel-Pro Gaskets, and Michigan Racing bearings.