500 LB-FT Small Block in Six Easy Steps
—courtesy, Hot Rod magazine
This time it’s a quest for torque. Luckily, we got horsepower as a bonus. By
the time we were done hangin’ a few speed parts off of a brand-new GM
Performance Parts HT383 crate engine, it made 500 lb-ft at 4,200 rpm and
460 hp at 5,400 rpm. That’s gruntin’ for a daily driveable 383.
The HT383 has been available for a couple years now, but we’ve yet to see even one in a car, and we kinda wonder why. It’s probably because GMPP markets it as a “high-torque truck engine” with 325 hp at 4,500 rpm and 415 lb-ft of torque at 3,500. Most speed freaks will shun the truck connotation and guffaw at those power numbers, opting instead for GM’s aluminum-headed Fast Burn 350 that makes 385 / 385 for just an extra Franklin over the HT383’s typical mail-order price. However, we’ll show you that an out-of-the-box HT383 is no slouch, and just a few well-chosen add-ons can make it scream. Best of all, you can add the stuff as your budget allows.
But first, buy the engine. It’s PN 12497317, available for $3,895 from Scoggin-Dickey. The HT383 comes as a complete long-block with all the tin plus a water pump and an aluminum dual-plane intake. It’s based on a brand-new production block with four-bolt mains and a one-piece rear-main seal plus a set of the highly touted Vortec iron heads with 62cc chambers that mate with hypereutectic pistons (18cc dish, 0.026 in the hole) for 9.1:1 compression. The cam is a very tiny hydraulic roller with 196 / 207 duration at 0.050 with 0.431 / 0.451 lift. The rods are powdered metal, but the crank is forged.
Most curiously, the HT383 uses a slightly different combo than the pedestrian 383 kits. Whereas a typical stroker uses a 400-Chevy-type crank with 3.750 stroke in a 350-type block with 4.030 bore, the new GM crate engine has a standard bore of 4.000 inches with a longer 3.800 stroke. The rods are 5.7 inches, which is stock for a 350. We initially considered comparing the 3.8-inch-stroke HT383 to an otherwise identical 3.750-stroke 383, but decided the 0.050 additional stroke length just wouldn't make that big of a difference in torque. We may be wrong, as our tuned-up crate engine made more average torque than our dyno guys had ever seen from a low-compression 383. Read on to learn how.
Step One: Get It Running
Your new HT383 will come out of the box complete with valve covers, a timing cover, an oil pan, an iron water pump, an 8-inch harmonic balancer, an auto-trans flexplate, and a dipstick. You’ll need to provide a carb, ignition, and headers, which we did with components from Demon, Pertronix, and Hedman. We also opted to upgrade the stock oil pan with a Milodon claimer pan that has an integral windage tray, because we’ve found them to add a few horsepower. We were surprised to discover that the HT383 comes with both a partial windage tray and a full pan baffle, so in back-to-back tests, the Milodon unit didn’t help us out this time. With the timing set to 34 degrees (36 degrees produced the same power), the jets at 70 / 76, and an electric water pump in place, the HT383 overdelivered on the dyno, spitting out 338 hp at 4,400 rpm and 444 lb-ft at 3,400 rpm. That’s more than GM claims, with peaks 100 rpm lower than advertised. Perfect. Stab it in a big ol’ heavy 3,600-pounder-even with a mild TH350 and tame 3.00 rear gears-and we’d expect you to run in the mid 13s.
GM recommends a 750 carb for the HT383, but we’ve had
such great luck with the little 625-cfm Road Demon that we used it for
the initial run-in and first few stages of testing the engine.
Right: We wanted to keep this engine simple, so our dyno
ignition included nothing more than a Pertronix Flame-Thrower HEI. These
all-new distributors include a coil and module specifically engineered
to complement each other, plus a cap with brass terminals. We’ve found
them among the best of the budget-priced HEIs. The wires are Pertronix
Flame-Thrower 8mm dual-cores.
| Description | Part Number | Price |
|---|---|---|
| GMPP HT383 crate engine | 12497317 | $3,895.00 at Scoggin-Dickey |
| Hedman Tork-Step Hedders | 68274 | $199.95 (uncoated) at Summit |
| Pertronix Flame-Thrower HEI | D1000 | $219.95 |
| Speed Demon carb | 4282010V | $299.50 at Summit |
| Milodon claimer pan | 31503 | $99.95 at Summit |
| Milodon oil-pump drive | 23050 | $13.95 at Summit |
| Milodon oil pump | 18750 | $40.39 at Summit |
| Milodon pan baffle | 32500 | $5.25 at Summit |
| Power | |
|---|---|
| Peak HP | 338.1 @ 4,400 |
| Peak Torque | 444.3 @ 3.400 |
| Average HP 2,500-4,800 | 292.6S |
| Average Torque 2,500-4,800 | 424.0 |
| Torque At 2,500 | 431 lb-ft |
Above: We wanted torque, so we chose Hedman’s Tork-Step headers in an early Camaro design. The Tork-Step offerings propose to boost bottom end by using small, 1 ½-inch tubing for the first several inches of each pipe, then stepping up to 1 5/8 tubing. Once our 383 made horsepower in the mid-400s, we tried a swap to regular 1 5/8 headers and ended up gaining a few horsepower while losing a few lb-ft of torque. As a result, the Tork-Steps remained on the engine for every dyno test in this story.
Above: While Milodon pans with windage trays have made proven power in our other tests, the HT383’s factory tray seemed to match its performance. We also used a Milodan high-pressure / high-volume pump-which boosted pressure by 20 psi at every rpm point as compared to the stock HT383 pump-and a Milodan hardened oil-pump driveshaft and rear-pan baffle.
