383 Chevy: Beyond the Crate!
by John Baechtel
That's easy to believe based on the number of rotating assemblies sold by Scat Enterprises. It's also noteworthy that the 383 originated from the performance community in the late seventies and became so popular that Chevrolet later
adopted it as a crate engine.
|425 HP Chevrolet ZZ383 Crate Engine|
Chevrolet engineers lengthened the stroke slightly so they could base it on existing 4-inch bore 350 small block architecture, but they recognized the curb appeal of the 383ci displacement where the small block V8 has almost completely eclipsed the memory of the 383 Mopar V8 popularized in late sixties Road Runners and the like. If someone says 383 today most people think of Chevrolet. No disrespect to the earlier Plymouth crowd, but in today's world almost everyone recognizes a 383 as a Chevrolet engine.
To the best of our knowledge no one has ever laid claim to conceiving the first home-grown 383 by grinding down the mains on a 400 crank to fit in a 350 block with a .030-inch overbore to achieve the original budget stroker combination. The stroke is increased from 3.48 to 3.75-inch to realize 382.6 cubic inches, commonly rounded off to 383. The GM crate version uses a 4.00-inch bore block with a 3.80-inch stroke to achieve slightly over 382 cubic inches, again rounded up to 383 to capitalize on the engine's popularity.
The first 383 this writer ever saw was built by performance engine builder Joe Sherman in 1978 when he was working as a machinist at Edelbrock. I remember it vividly as Joe pirated the valve cover hold down clamps off a 327 small block I was testing for Car Craft magazine at the time. Over the years we have shared a few laughs about when they might be returned. I can't remember specific numbers, but I seem to recall that Joe had already cracked the 600 horsepower mark even then.
|Here's the original 383 project engine for the Car Craft Underground Camaro in 1980. Fully ported and nitrous-fed engine was painted corporate blue and had no external giveaways except for the Moroso road racing oil pan.|
That led to my choice of a 383 build for the 1980 Car Craft Underground Camaro project car which was the first 383 magazine story I am personally aware of back in 1980. There may have been others.That was a milder street piece that produced about 410 horsepower and 450 lb-ft of torque with iron Chevrolet heads, an Edelbrock StreetMaster dual plane and a Quadrajet carb. With the hidden under-manifold Marvin Miller plumbed nitrous system it cranked up to 570 horsepower. Years later with the original short block, Summit Trick Flow heads, Edelbrock Performer RPM dual plane, 750 Demon carb and a small roller cam if twisted out 505 horsepower and 525 lb-ft of torque without nitrous. That same 36 year old engine still runs strong today and is being fitted into a 1966 Nova.
The point is that the 383 Chevy was spawned in the true spirit of hot rodding. Back then there were no easy or inexpensive ways to obtain stroker cranks so you polled local machine shops until you found a 400 crank they could turn down to the 350 main size (2.65" down to 2.45"). Then you were still stuck with the shorter 400 rods (5.565" versus standard 350 at 5.7"). Note: the 350 and the 400 share the same piston compression height. The 400 rods caused some cylinder wear problems from angularity so it was desirable to maintain the longer 350 rod by working with the piston pin height. today you can get ready-to-run rotating assemblies with 5.7-inch or 6.0-inch rods straight from Scat.
|In this 1980 build the top ring land was also tapered 3 degrees to accommodate piston rock with the nitrous application.|
That old Car Craft engine used .030-over TRW reverse deflector dome turbo pistons that stuck out of the bore .135-inch with the 5.7-inch 350 rods. Note that is about half of the stroke increase. But the piston decks were so thick for the turbo application you could mill them down a lot and still have more than .200-inch deck thickness and a very slight dish of about .050 at zero deck. That got the package to fit the block, but the 350 "Pink rod" rod bolts hit the cam on multiple cylinders. Copying a dubious trick I learned from Joe, I rounded off the top of the rod bolt shank and the bolt head itself on a belt sander for clearance. It was ugly and by any standards, the wrong thing to do, but it it has survived 36 years of constant abuse along with the humble cast factory crank resurrected from a pile of machine shop discards.
Through the miracle of the aftermarket, you can now purchase purpose-built rotating assemblies specifically for the 383 small block from SCAT Enterprises. The cranks are made for the application, the rods are configured to miss the camshaft and the pistons are optimized for the compression ratio you desire.
You can obtain complete 383 Scat kits with cast or forged internals direct from Summit Racing. Which one depends on your budget and intended use. With an early block or a good aftermarket block you can go .060-over and make it a 388 if you wish. Today the 383 is as commonplace as as any original Chevy V8. Factory 383 crate motors are easily tweaked to 500 horsepower and the average 383 build typically achieves somewhere between 450-475 horsepower in street trim while more serious race oriented versions easily top 600-650 horsepower.
That early 383 that I built was machined and assembled at Valley Head Service in Northridge, California. Decades later they remain a highly reputable engine shop performing rebuilds, restorations, performance builds and race builds for all types of engines. Industry veteran Lyle Larson drives the seven second A/Gas 1969 Camaro they sponsor and he mentioned that they were going to build a mid-level LT1 based 383 for a '95 Corvette. Since the LT1 guys never get much love we decided to follow along on their build to show how easy it is to generate strong street performance with the 383 engine that has become a staple of the performance aftermarket. At any given time probably hundreds of 383s are being built all around the country so the project enjoys broad appeal.
This build is based on an OEM '95 LT1 Corvette block and will use a set of ported aluminum heads bearing special significance as they were ported by the late Rod Sokalofsky, a respected head porter who worked with Lyle at Edelbrock and later at Jim Mcfarland's skunkworks facility. The heads were done for former GM performance engineer Mark McPhail and he passed them to Lyle for the project so they're kinda special in memory of an old friend. The ports are mildly revised, but not enlarged. The short side radius is lightly massaged, the port walls and bowl area are cleaned of any casting restrictions and the valve guide bosses are reduced and cleaned up The goal of this project is a 425-450 horse engine with a moderate cam for strong low end torque in a Corvette street cruiser; the same kind of performance the 383 is known to deliver with relative ease.
The short block is derived from the original '95 Corvette cylinder block. A complete rotating assembly from SCAT Enterprises transforms it into a powerful 383 street engine. SCAT components include a forged crank, Pro Stock I-Beam connecting rods with 3/8" cap screws, customer specified forged pistons, rod bearings, main bearings & piston rings. This is an internally balanced assembly with a 1-piece rear main seal.
Scat kits are unique in that they address a peculiar problem with LT1 based engines. The harmonic balancer mounts to a separate hub that uses a slip fit on the crank snout. The hubs are often replaced during rebuilds and in the case of inferior parts they often do not seat correctly. Recognizing this common problem Scat relieves the front of its cranks for proper timing gear seating so there is never a question of the timing gear and hub seating correctly and in the correct location.
The keyway is a problem area because the LT1 uses a stepped crank key arrangement. The balancer hub does not have a internal keyway slot. It is used to properly position the balancer for for the front drive system. The raised portion of the stepped key goes toward the crank side to properly locate the crankshaft timing gear. Then the hub slips over the front portion of the keyway which does not protrude above the slot. A second standard crank key toward the front key slot locates the balancer. The hub, bolted to the balancer is essentially a spacer between the timing gear and the balancer. It positions the balancer in proper alignment for the drive belt system and it provides the sealing surface for the timing cover seal.
Two different stepped keys are used depending on the year of the engine. When a crank position sensor was added for OBD II engines in 1996, the stepped area on the key was modified so it protruded (about 0.100") beyond the face of the timing gear to properly index the notched timing disc for the new crank position sensor. 1992-1995 engines use the key with the shorter step (GM PN 10128303) as they do not have to accommodate the timing disc. The Part No for a 1996-98 Woodruff key is (GM PN 12561513). It is 1.475" long x 0.300" at the raised part (rear) x 0.087 at the shortest part (front).
The LT1 differs slightly from the GEN 1 small block, but not so much that all the same technology cannot be applied to building a reliable engine with a strong power curve. To complement the ported heads and upgraded intake manifold they selected the factory Chevrolet Performance LT4 Hot Cam, P/N 24502586. It measures 218°/228° duration at 0.050 tappet lift, 0.525-inch intake and exhaust valve lift with 1.6 ratio rockers and is ground with 112° lobe separation. In turn, the cam is complemented by the appropriate Trick Flow narrow body 1.6 ratio roller rockers, Summit PN TFS-31400513.
The beauty of 383 rotating assemblies is that you can build the engine relatively inexpensively with standard performance parts and upgrade only the pieces you feel require it. You can build a low-buck engine with cast crank and hypereutectic pistons or pick and choose as you see fit with higher grade comp0nents if you plan on leaning on the engine or running a power adder. Scat's broad range of rotating assemblies allows you to custom tailor your package to perfectly suit your specific application.
Complementing the factory "Hot Cam" selection are aftermarket supporting parts specifically chosen to ensure top performance. That starts with high precision hydraulic roller lifters with tie bars from Johnson Lifters. These lifters were selected because they offer greater dimensional accuracy than other brands. In particular they offer the fastest recovery rate for the high pressure chamber to ensure optimum cam timing and performance under any conditions. And they don't suffer excessive bleed down like stock lifters. Johnson precision lifters for LT1/LT4 applications are available in two versions; stock style roller lifter keyway guides or with traditional tie bars. Either version is capable of delivering top performance as the lifter itself is the primary contributing component. The preload adjustment on this application was set at 1/2 turn down from zero lash.
A stock factory oil pump and pickup was retained along with the stock oil pan installed with ARP pan bolts. Flipping the short block over, the cylinder heads were installed using ARP black oxided head bolts and SCE copper gaskets. High quality SCE seals and gaskets were used throughout this build (see parts list). For optimum quality the builder also selected ARP black oxided cylinder head and main bolts.
LT1-LT4 Tips and Tricks
LT1-LT4 front covers have changed twice because of the changes that were made to the distributor and for OBD II compliance. The early cover had three holes, one for the crank, a small .070-inch hole for the water pump drive and a second one for the distributor drive shaft. The second front cover had the small hole for the water pump shaft and a much larger 2.63-inch hole that sealed on the outside of the distributor housing . The second cover was revised again in 1996 to accommodate the crank position sensor located in the lower corner of the cover on the passenger side.
To ensure optimum performance, a Granatelli Motorsports mass air meter was installed in the inlet system. This unit, PN GRN-350111-C is CARB approved under EO number D-471-1. It features a rugged hard plastic housing which tends to reduce the heat soak associated with metal units.
HEAD GASKETSLT1 350 head gaskets are not compatible with standard Gen 1 350 Chevy head gaskets because of the revised water passages for reverse cooling. Original factory head gaskets on the LT1 were wider and had holes to hold the pushrods in place on the assembly line. Replacement gaskets look more like regular 350 gaskets. Be certain you get the specific gaskets for your application.
There is no keyway in the hub to index the harmonic balancer. A special cutback key that is flush with the front of the timing gear on the 1992-’95 engines is required, PN 10128303. In 1996 the cutback area on the key was shortened so it stuck out far enough (about 0.100") beyond the face of the timing gear to index the notched disc for the crank position sensor. The keys are not interchangeable.
HARMONIC DAMPER AND HUB
The damper is a two-piece assembly with a pulley that bolts onto the hub. The holes in the hub are offset so the balancer only fits on it one way, but there’s no keyway in the hub to index the hub on the crank. This isn't normally a problem unless the damper was drilled at the factory to "trim" the final engine balance. If you have a balance problem on a re-built LT1, try rotating the balancer assembly on the crank 90° at a time to see if it smooths out the engine.
WATER PUMP DRIVE SHAFTCheck the seal surface on the geared shaft that drives the water pump. It must be smooth with no wear groove or it will leak. If necessary purchase a new one from GM (PN 10219554).
EXTERNAL COOLANT LINESAn external coolant transfer line connects the holes on the back side of each head to a reservoir that vents vapors trapped in the head that could cause hot spots.If the external water manifold is damaged it should be replaced. Because the heads are interchangeable there are holes on both ends. The front holes should be plugged.
TRICK FLOW OIL SEPARATORA Trick Flow® Specialties billet oil vapor separator tank system is incorporated into the crankcase system to pre-clean crankcase ventilation gasses before they are reintroduced into your intake manifold or the atmosphere.The separator removes oil mist, vapors, and contaminants that would otherwise enter the intake manifold to be burned in the engine. These contaminants affect the consistency of the air-fuel charge and promote less efficient combustion. Removing them ensure a cleaner air supply entering the runners ahead of the fuel injectors. Pressure drawn from the crankcase is routed through the separator. Internal baffles separate oil, moisture, and contaminants from the crankcase air. Separated oil and contaminants drain to the bottom of the canister and cleaner air is then routed to the intake system. The Trick Flow unit incorporates a sight plug to indicate when the unit needs servicing.
EXHAUST SYSTEMTo ensure maximum performance from this engine package a full exhaust system upgrade was initiated. It starts with ceramic coated Hooker Super Competition headers and ends with a Flowmaster Force II cat-back exhaust system, PN 817670. Flowmaster also supports its exhaust systems with a full range of 50 state legal catalytic converters so you can remain compliant with your new supercar. The cat-back system uses 2.5-inch exhaust pipes with a central muffler and twin resonators at the rear with custom stainless tips. The Hooker headers have 1-3/4-inch diameter, 26-inch long primaries with 3-inch by 8-inch collectors. They provide good spark plug clearance and the coating helps reduce underhood temperatures
A good high-torque starter is essential for any application with higher compression and localized heat in the engine compartment. The cam and compression ratio in this application generates about 170 pounds cranking compression, hence a strong battery and starter are good insurance. Both the B&M (left) and Summit units shown here do the job well. It is essential to make sure that all connections are clean and tight to ensure trouble free starting.
A final word on engine installation. After all your hard work is finished you can take further steps to ensure maximum success. A good radiator flush is often useful and the radiator should be replaced if it can't pass a pressure test. Also take the time to replace all hoses and belts and the idler pulley at this time. These are all simple things that can cause you grief at the last minute.At this point, we have driven the car and it feels very strong. Next, we are off to the dyno at Granatelli Performance to perform final tuning and get some results.
NOTESCompression ratio = 10.98, with 8.31 dynamic
The LT4 camshaft P/N 24502586 was designed to be used in many different engines. The following change may be necessary for correct engine assembly:
For LT1 and L98 engines (pre-1996) the dowel pin in the end of the camshaft must be pushed in so extension from end of cam is .30"+/- .01". For 1996 LT1 and LT4 engines, the dowel pin is in the correct position extending .620" from the end of the camshaft. This cam has a fuel pump lobe.
Many thanks to Larry Ofria at Valley Head Service, engine assembler Spike Morelli, machinists Alex and Ruben Puildo and Monty Curti and Jesse Gellis at Simi Valley Chevrolet for parts and tech support. And special thanks to Jim Bassett at Bones Fab for the assistance with installing the engine and supporting components.
VIEW PARTS LIST (All Summit Racing part numbers except where noted)
Valley Head Service
|Summit Racing||Bones Fab|
391 Dawson Dr. #3s, Camarillo, CA 93012
Simi Valley Chevrolet
|Trick Flow Specialties||Scat Enterprises|
1400 Kingsdale Ave, Redondo Beach, CA 90278