500 lb-ft Small Block in Six Easy Steps - Royal Purple

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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.
page 1 2 3
—courtesy, Hot Rod magazine
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