From Chevy 350 to Ground-Pounding 383 Stroker

The first machining operation Jim Grubbs Motorsports’ Joe Meza performed on our block was drilling the main cap bolt counterbores larger to provide clearance for the ARP main cap studs. This keeps the studs, which are slightly wider than stock bolts, from binding in the holes.

Then he ran a 7/16-14 bottoming tap into each hole to clean up the threads and cut them to maximum depth. On most holes we gained 11/2 to 2 full threads. This procedure ensures maximum thread engagement and seats each stud at the same depth in the block.

Next, Meza chamfered the edge of each bolt hole to remove burrs. Then he blew out the debris with compressed air.

With the front and rear caps installed, the block’s next stop was JGM’s Rottler boring machine, where each cylinder was enlarged to 4.0265 inches. The final 4.030-inch bore will be achieved on the bore-honing machine after each piston has been measured.

To prepare for align honing, each main cap is mounted in a jig and milled 0.002-0.003 inch. This shortens the caps and reduces the diameter of the main bore.

Then JGM’s Pete Christensen installed the 18 main cap studs. Never install studs more than hand-tight, because they must be allowed to float and stretch as they’re tightened in order to work properly.

Christensen seated each cap with a soft blow from a brass-faced hammer to ensure they were flush with the bottom of the block.

Finally, he lubed the stud threads with ARP moly assembly lube and torqued each one to 70 lb-ft. The advantage of using studs is that each cap is fastened by the stretching of the stud rather than by the threads in the block. Not only is this stronger, it extends the life of the threads.

JGM always uses an oil pump torque plate to simulate the installation of the pump on the main cap. According to Christensen, this can alter the bore diameter by up to 0.001 inch.

With the block set up in the align-honing machine, the main bore is enlarged back to factory specifications. This procedure ensures that the main saddles line up so the crankshaft will spin without binding.

Since the correct final bore diameter is determined by the machinist, not the machine, Christensen periodically uses a dial indicator to check the main bore diameter during the honing process.

To deck the block, the engine was mocked up by temporarily installing the crankshaft and the piston/rod combo at each of the four corners and measuring the depth of the piston below the block deck at TDC.

After the deck has been measured, the block is set up in a milling machine and decked to the proper height. In our case, we wanted the pistons to sit approximately 0.010 inch “in the hole” to achieve our target 9.6:1 compression ratio.

Andy Hairfield carefully checked the distance from the deck to the crankshaft centerline several times during the decking process. In addition to fine-tuning compression, the decking procedure also ensures that the top surface of the block is square to the crankshaft centerline.

To prepare for bore honing, each piston is measured and marked as to which cylinder it will fit so each bore can be accurately sized to fit its piston.

With the block positioned in a Sunnen honing machine, Christensen installs a torque plate on the block deck. The torque plate duplicates the stress placed on the deck and fore walls when the cylinder heads are installed.

Christensen hones each bore, using the proper cross-hatch pattern for the plasma-moly piston rings we’ll be using.

As with align honing, the final cylinder bore dimension is determined by the machinist, so Christensen alternately hones and measures until the 4.030-inch dimension is achieved. With the honing complete, the machine work is finished. In next month’s installment, we’ll assemble the engine and put it on a dyno to see just how much power we can muster.

Rather than throw cash at a set of rebuilt junkyard heads, we opted for a pair of World Products’ cast-iron S/R Torquers. For not much more than the cost of a good head rebuild, we got brand-new castings assembled with 2.02-inch intake/1.6-inch-exhaust Manley valves, new guides, and valvesprings and retainers. We threw in an additional $150 to have Bill Mitchell Products bowl-blend the area around the valves to improve flow even further.

We knew from the outset of this project that we wanted to do more than a basic engine rebuild, yet we were also wary of falling into the age-old trap of More’s Syndrome, which afflicts the engine builder with the desire for more of everything—more compression, more cam, more trick parts (basically, more time, effort, and money spent). Usually that translates into more power, but not necessarily in an rpm range that you can use in a street truck (when was the last time you wound your motor up to 8 grand?).

Our goal, on the other hand, is an engine that produces its power down low, where we can use it every day. We expect this engine to be strong off-idle and produce peak power around 5,500 rpm, which is the range where most street motors perform. Although many magazine buildups stress top-end horsepower, our goal is to maximize torque. Torque is what gets you moving from the stoplight, and it’s also the ultimate determiner of horsepower. After all, horsepower is just rpm times torque divided by 5,252, and as one engine builder told us, “If you give me torque and you take horsepower, I’ll beat you every time.”

The keys to achieving our goals are good machine work, reasonable compression, and the selection of parts that will work together to produce power.

Why A Stroker, You Ask?

The biggest advantage to putting a crankshaft from a Chevy 400 into a 350 block to produce 383 cubic inches is that more displacement equals more power. Also, the longer crank throw produces more downward thrust, which translates into torque. And torque is what we’re after, especially in a truck.

Although a 383 can still be built using a stock GM 400 crank with ground-down main journals, the popularity of this combination has resulted in the availability of new 3.75-inch crankshafts manufactured to fit in a standard 350 block. We opted to go this route, and we further simplified the parts-selection process by ordering an internally balanced 383 rotating assembly from Racing Head Service. The RHS kit comes complete with a new cast-iron stroker crank, cast hypereutectic pistons, reconditioned 350 rods, moly rings, and a new flexplate, as well as camshaft, rod, and main bearings. We also ordered a Comp Cams Xtreme Energy camshaft and lifter set to fill out our short-block assembly. The bumpstick recommended by the experts at RHS specs out at 212/218 degrees of duration at 0.050 lift with 110-degree lobe centers and 0.447/0.454 lift on the intake and exhaust. This profile should produce gobs of torque between 1,000 and 5,200 rpm, making it ideal for our purposes.

The next major decision we had to make was selecting a set of cylinder heads. Since one of the heads that came with our junkyard core was cracked, we were facing a pretty steep machine-shop bill had we had opted to rebuild them. Rather than invest a bunch of money in junkyard heads, we decided to go with aftermarket heads. The cast-iron World Products S/R Torquers that we chose are generally regarded as one of the best deals going in aftermarket cylinder heads. For about the same out-of-pocket cost of a good head rebuild, you get brand-new castings with better flow characteristics than any stock GM small-block cylinder head, and they come assembled with 2.02-inch intake/ 1.6-inch exhaust Manley valves, new guides, and valvesprings and retainers. If you spend any time investigating the cost of a quality rebuild, you’ll find that the World heads, priced at around $700 per pair assembled, are a deal that’s hard to beat. Rather than reuse our junkyard parts, we completed the valvetrain with a set of reasonably-priced Comp Cams Magnum roller rocker arms and new pushrods.

Then we called Summit Racing Equipment to order all the other necessary items to assemble the long block, such as a gasket set, freeze plugs, an oil pump, an oil pan, a timing set, and valve covers. We plan to top the engine off with a Holley dual-plane Dominator intake manifold and a 750-cfm, vacuum-secondary four-barrel carb. With all the parts gathered, we headed up to Jim Grubbs Motorsports in Valencia, California, to have our block machined. The importance of a knowledgeable machine shop to the success of an engine buildup cannot be overstated. Not only is good block prep critical to power production and engine life, the experts at Jim Grubbs Motorsports gave us tons of tips and insight into the right way to build an engine.

Follow along as the crew at JGM whips our block into shape.