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Get The Lead Out

The Perfect Way to Motivate Your Large Barge

Mike Petralia Aug 27, 2004

Heavy hitters for heavy rides. That's what we need. Few street cars are lightweights, a fact that challenges their power to "get up and go." What we need is torque--lots of torque--because that's what makes cars go. Horsepower is cool for racing, but our rides need torque. Luckily for us, the folks at GM Performance Parts (GMPP) have already worked out a plan to build lots of torque into a package that's affordable and easy to get. We're talking about GMPP's HT 383 small-block crate engine. Designed and built to produce torque in the low-rpm range that rods and trucks see, the HT 383 is a fine choice for our heavy rides. Plus, it's easy to install; just about everyone has, or can make, headers for it, and hooking up transmissions is a piece of cake. All these benefits make the HT 383 even more desirable. So if you're looking to transplant some new muscle into your old rod, this is something you should check out.

Too often, horsepower is the concern of an engine builder and the topic of much discussion on Saturday nights. Torque gets left out of the picture. But our heavy machines need torque so we have to be concerned with it. Otherwise, we'll be left in the dust by some stinkin' little import! With its advertised 435 lb-ft peak torque rating, and an observed 429 lb-ft in our dyno test, this little brute can take on any comer. Plus, with more than 407 lb-ft of average torque all the way from 2,500 to its 5,000 rpm redline, this little puppy will plant you back in the seat and never let you out until your foot gets off the gas! And, with the skyrocketing prices of gasoline today, it's also nice to know that this motor was engineered to run on cheap 87-octane so you won't go broke feeding it every week.

For our test we wanted to build something a little retro, yet something a little extreme. GMPP usually offers its HT 383 as a complete long-block assembly including late-model Vortec iron heads, or even the hot, Fast-Burn aluminum heads, and a complete top end package. But we didn't want the look of newer heads under our hood, so we went with GMPP's new "492" reproduction heads. These heads feature all the performance of the rare classics, but also include some accessory boltholes on the ends to hang stuff like alternators and A/C, and to fool the cruise night gawkers, too. We also wanted to upgrade the unseen internals of this engine a bit as well. After all, we may be building a retro powerplant, but that doesn't mean we can't take advantage of some trick power parts. So we installed GMPP's recommended hydraulic roller camshaft and all its related parts. Sure, that added to the overall cost of the engine, but the increases in power, longevity, and even fuel economy made it all worthwhile. Not only is GMPP's HT 383 powerful, it's also beautiful, in a low-key sort of way. The engine's black and bare metal appearance fits right under our hoods. And the cost of it won't rob you blind. It's under $4k price tag puts it at less than you'd probably pay to have someone custom build one for you. All of this in a package that's only one phone call away. It's almost too easy to get the lead out today.


Before testing our HT 383 on Dyno-Motive's DTS engine dyno, John Beck, owner of Pro Machine, did a few tweaks on it for us.

The GMPP short-block we ordered comes like this. Heads, cam, intake manifold, and all the top end components must be ordered separately.

Beck wanted to show us the trick goods hidden underneath the oil pan of this GMPP stroker. Check out the one-piece oil pan gasket and partial windage tray.

Beck chose to install GMPP's recommended hydraulic roller camshaft and its related accessories. Since this is a roller cam, GM engineered a lock-plate into the front of the block to keep the cam from "walking" out. It also has a special drive gear that'll work with any stock distributor.

Since the GMPP iron heads have a small combustion chamber, and the crank has lots of stroke, the pistons need quite a large dish to keep compression manageable. Also, Mr. Gasket Solicore head gaskets will keep pressures in check.

The stock-appearing harmonic dampener is deceiving, since a counter-weight has been added to the back of it. The weight is necessary to offset the added stroke of the crank.

Here's a nice tip from Beck. Once you've found true TDC when assembling the engine, use some nail polish or paint to permanently mark the dampener so it'll be easier to see with the timing light.

GMPP's complete hydraulic roller valvetrain is hidden under the intake manifold. The lifter valley "spider" holds the roller lifters in their bores and the "dog bone" keeps them from rotating.

These are the new "492" reproduction heads we ran. They come with accessory boltholes on the ends for things like A/C and alternators, but do not include rocker studs or pushrod guide plates.

Beck disassembled the heads to touch up the valve seats himself by hand-lapping them.

GMPP's cylinder head hardware kit comes with bolts pre-coated with sealant to prevent water leaks. This is much easier to work with than gooey sealants you apply yourself.

Beck checked the pushrod length before installing GM's recommended pieces, just to be sure.

GMPP's full roller aluminum rocker arms are self-aligning on the valve stem tip, so pushrod guide plates are not needed.

In addition to the Edelbrock intake manifold and carburetor we tested, we also installed an Edelbrock fuel pump and water pump.

A steady spark is important to making maximum torque, especially under the heavy loads our engines operate with. Mallory's new totally electronic distributor kept us fired up for the entire day.

Short block PN 12499106
CID 383
CR 9.1:1
Stroke 3.80
Bore 4.00
Cam Hyd roller
Specs 196/207 degrees @ .050, .431/.451 lift Rockers 12370838 (roller, self-aligning)
Crank Forged steel
Heads PN 12480092 cast iron
Valves 2.02/1.60
Intake Edelbrock 7501 (RPM Air-Gap)
Carb Edelbrock AVS 650
GM's rated HP 340 @ 4,500
GM's rated TQ 435 @ 4,000
Observed HP 327 @ 4,600
Observed TQ 429 @ 3,300

Factory rated performance figures are cool, but we wanted to see for ourselves. So we picked up an HT 383 and hauled it over to our friends at Pro Machine for a complete teardown and inspection. After Pro Machine was done with it, they rolled it into their next-door neighbor's shop, Dyno-Motive, and hooked it up to the DTS engine dyno for some power pulls. When the day was done, our HT 383 never quite made the power that GMPP claimed it would. But we did make more power than some of the mail-order dealers are claiming for this engine on their Web sites. All told, the figures we saw were within just a few percent of all the others, which tells us that this is one rock-solid performer. We were probably down on power simply as a result of us testing on a very hot, humid day and because our dyno headers (1 7/8 inch) were a little too big to make the best torque (1 5/8 inch would have been better).

2,600 415 205
2,800 417 222
3,000 424 242
3,200 428 261
3,400 428 277
3,600 425 291
3,800 419 303
4,000 410 312
4,200 401 321
4,400 388 325
4,600 373 327
4,800 356 325
MAX 429 327
AVG 408 282

0411cr_gmpp_17_z 19/18

We tested two different Edelbrock intakes and carbs on this motor: the EPS and Air-Gap manifolds and the AVS 650 and AVS 800 carbs. Both carbs worked about the same on the dyno at wide-open throttle, but the smaller 650 would definitely work better around town with lots of stop-and-go driving. The large size of this engine craved the large-volume Air-Gap intake, so it'll stay.

Even though we know GMPP's intake manifolds are good pieces, we wanted to try something different. So we tested Edelbrock's new EPS intake against its Performer RPM Air-Gap to see which would work best. It turned out that both worked equally well, producing almost identical power figures in either test. The slightest advantage went to the Air-Gap, probably because of this engine's larger displacement, so we left it in place. Also, the carb shown here, the AVS 650, is the one that ran the best so it'll live on the engine as well.






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