500 LB-FT Small Block in Six Easy Steps cont’d
—courtesy, Hot Rod magazine
Step Five: Bigger Cam
The HT383 responded impressively to external bolt-ons. With total investment of about $5,300 with the headers, ignition, and upgraded rockers, carb, and intake, it makes a serious 380 hp and 474 lf-ft with very flat power curves that’d put a smirk on your mug in any street car or tow vehicle. We made 54 extra horsepower and 59 more lb-ft compared to the HT383’s advertised numbers. You’d be lame if you couldn’t get a 3,600-pound car to run in the 12s with this engine, a TH350 (no expensive overdrive), and 3.50:1 gears.
But we always want more. This time, we tore into the HT383 to try a bigger camshaft-namely a Comp Cams XE282HR in place of the original hydraulic roller. The new cam had 230 / 236 duration at 0.050 and 0.510 / 0.520 lift (or 0.544 / 0.555 with our 1.6:1 rockers) with a 110-degree lobe-separation angle. The HT383 uses ‘87-‘98-type factory roller-cam hardware and requires a step-nosed cam to accommodate the factory-style cam retainer. And because the HT383’s stock Vortec valvesprings and guides can’t take more than about 0.490 lift (sometimes less), we sent the heads to Dougan’s Machine to have the seats enlarged for Comp’s specified springs. Since the heads were off anyway, we replaced the gaskets with Fel-Pro rubber-coated steel shims to bump the compression ratio to 9.6:1 from the original 9.1:1.
The reward was a whopping 76 hp and 19 lb-ft. Of course, the cam changed the entire character of the engine; the rpm at peak increased by 1,000 rpm (horsepower) and 500 rpm (torque). A 4,800-rpm-redline engine became a 5,800-rpm buzz. Sadly, the larger cam gave up as much as 25 lb-ft of torque at every data point below 3,600 rpm, yet with 426 lb-ft at 2,500 rpm, it was still no low-end slouch. Also, whereas it formerly idled at 650 rpm and 19 inches of vacuum, the new cam idled at 950 and 12 inches. The tiny cam idled like the Rock of Gibraltar, but we felt the XE282 was acceptably streetable.
Ultimately, the XE282 cam and the half-point bump in compression changed this 383 from an ideal towing / daily driver engine to a hot rod engine that could easily be driven anywhere with some nice bragging rights. It’ll turn our theoretical 3,600-pound land yacht into a beast that’ll probably go 11s on slicks, though the new power curve might prefer 3.73 rear gears.
The stock Vortec spring on the left has a 0.980 diameter
while the replacement Comp Cams spring is 1.430, requiring the spring
seat in the heads to be enlarged.
In addition to the seat work, the valve
guides must also be cut down in overall diameter to accept small Viton
valve seals, and the height of the guides needs to be trimmed to avoid
retainer-to-guide interference with valve lift over 0.490 inch.
| Description | Part Number | Price |
|---|---|---|
| Comp XE282HR | 08-432-8 | $239.95 at Summit |
| Comp 143 springs | 986-16 | $82.95 at Summit |
| Comp retainers | 740-16 | $59.99 at Summit |
| Comp Viton seals | 50316 | $24.95 at Summit |
| Machine labor | N / A | $75.00 at Dougan’s |
| Power | |
|---|---|
| Peak HP | 455.3 @ 5,600 |
| Peak Torque | 493.0 @ 4,200 |
| Average HP 2,500-4,800 | 327.4 |
| Average Torque 2,500-4,800 | 467.7 |
| Average HP 4,000-5,700 | 427.4 |
| Average Torque 4,000-5,700 | 465.3 |
| Torque At 2,500 | 426.3 |
When reinstalling the heads, we used Fe-lPro number 1094
gaskets made of a rubber-coated steel shim. The 1094 gaskets are thinner
(0.015 compressed) and have a smaller bore (4.100) than composite gaskets,
thereby giving the 383 another half point of compression (to 9.6:1).
Step Six: Slippery Oil
We were so close to 500 lb-ft that we decided to pull out the magic wand: synthetic oil. It’s generally worth a few power numbers, so we drained the 10W30 dinosaur sauce and poured in Royal Purple’s 5W30 street oil (lighter-weight racing oil is also available). It took three dyno pulls for the synthetic to do its thing, then it made the repeatable power we wanted: 502.9 lb-ft and 463 hp. As an average from 2,500 to 5,800 rpm, the Royal Purple bought us 7 hp and 10 lb-ft. Combined with the extra engine protection and heat resistance, this is a no-brainer.
The spec oil for the HT383 is 5W30, so we tried it in
a full-synthetic blend from Royal Purple, one of the more affordable brands
of synth. We were so impressed that we’re planning a full chassis-dyno
test of Royal Purple products for the engine, trans, rearend, and wheel
bearing.
| Description | Part Number | Price |
|---|---|---|
| Royal Purple 5W30 | 01530 | $4.99 / quart via mail order |
| Power | |
|---|---|
| Peak HP | 463.1 @ 5,600 |
| Peak Torque | 502.9 @ 4,200 |
| Average HP 2,500-4,800 | 334.8 |
| Average Torque 2,500-4,800 | 478.1 |
| Average HP 4,000-5,700 | 436.4 |
| Average Torque 4,000-5,700 | 475.1 |
| Torque At 2,500 | 434.7 |
Accessory Pulley Shootout
We’ve
seen lots of articles about underdrive accessory pulleys for late-model
cars, but you may not be aware that March Performance also sells them
for carbureted performance applications. In the case of the long-water-pump
small-block Chevy, you’ve got a choice of Performance Ratios or High Water
Flow Ratios in either V-belt or six-rib-belt designs. Either way, you
can use March’s high-performance alternator brackets, as seen on this
month’s cover, to replace the ungainly stock bracket.
While March always recommends High Flow pulleys for stroker applications such as the HT383, or for nearly any real street car, we decided to compare them to the Performance Ratio set on the dyno. March warned that the biggest power gains are seen when underdriving accessories such as power steering, smog pumps, and air conditioning, but we tried them with an alternator alone. First came the Performance Ratio, and to our surprise, it made perhaps one horsepower less than the electric water pump. Call that testing variance. For practical purposes, it was the same. However, the High Flow Ratio must truly flow more water, since it drew an extra 7 hp and 7 lb-ft on average throughout the curve. We’d gladly give that up for the extra cooling; it’s nothing like the horror stories we’ve heard of losing 20 hp to a water pump.
This is the trick six-rib-belt setup from March;
it tends to slip less and throw belts off less often than a V-belt setup.
Regardless of your choice of belt style, we wholeheartedly recommend the
March alternator bracket. It’s far better looking than the stock bracket,
more rigid, easier to adjust, lighter, and won’t cause hassles with the
intake-manifold design like a stocker can.
The difference in ratios is obvious. The
Performance Ratio uses a 5 ½ crank pulley with a 6 ¼-inch
water-pump pulley (0.88:1), and the High Flow has a 7-inch crank
pulley and a 5 ½ on the water pump (1.27:1). For example,
at 5,500 rpm, the Performance setup spins the water pump 4,840 rpm;
the High Flow moves it at 6,985 rpm.
