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Corvette Engine Build - The Power Principal

An Economical 383 Engine Build Anyone Can Do

Chris Petris Dec 8, 2009
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Chevrolet's Gen I small-block Chevy engines have a great track record over the last 50-plus years-powerful, simple to build, and tough as nails. When the Rochester mechanical fuel injection was introduced, we never dreamed that 1hp per cubic inch was even possible. Today 500 hp or more is easily obtainable and streetable. What an engine!

Many years ago, there was a '62 Corvette making the rounds around south Florida propelled by a 301 small-block that ran a Duntov 30-30 solid lifter camshaft that shattered the hopes of many would-be contenders on Saturday nights. That's just one of the many reasons the small-block became one of my all-time favorite engines many years ago.

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We sent the new GM block to Gerald and Charlie's Machine shop to have it bored 0.030 over by Daniel for the previously purchased Wiseco pistons. As you can see, no torque plate was used during the boring process. We are using a (green) new block that will change as it ages, and we don't feel the torque plate will make a substantial difference in this street/strip application.

For those of you not familiar with the 301 engine, it was an early 283ci cylinder block bored to 4 inches. Those early blocks had extra-thick cylinder walls that allowed opening up the cylinders. The 301 was as bad as they came until the 327 was introduced in 1962. Aftermarket small-block parts are all over the place now, from discount auto parts retailers to mega-performance suppliers. We also have many giants in the automotive industry that have taken on the small-block and built these engines to astounding horsepower-per-cubic-inch numbers.

All of this helps those of us who love the small-block and want all we can get from these lightweight engine blocks. Along with the Internet, you can find the info and parts to build any cubic-inch small-block at any horsepower level depending on your budget. The toughest parts of any small-block build are what parts to choose, and deciding whether to build it yourself or buy a complete crate engine. It's hard to beat a crate engine nowadays because, in most cases, the cost will be less for the same components. Crate engines require large production facilities and use parts in larger quantities to allow the more competitive pricing.

Our situation was somewhat different. The owner's original intent was to build the numbers-matching engine in his '85 Corvette, but the first engine build went sour and damaged the original '85's engine block. The situation then dictated using the previously purchased pieces, if possible, to recoup at least a portion of the original build costs. The original plan was to stroke the '85's engine to 383 inches to allow for a longer duration camshaft and high horsepower without sacrificing low-rpm grunt.

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Daniel goes to work honing the block, while careful to keep the correct crosshatch pattern by carefully timing the up-and-down motion of the hone and not exceed the 0.004 piston-to-cylinder clearance we decided on. There's a fine line that needs adhered to when fitting pistons. Too loose and piston slap occurs; too tight and cylinder walls are scored from the tight fit. The crosshatch pattern helps retain oil in the cylinder during the break-in period.

Our task in this 383 build is to make 450-500 hp using the parts at hand from the previous builder's pieces and follow the original concept as close as we can. Before we get too involved with the horsepower and torque numbers, rotating mass friction should be considered. The norm was to keep the crankshaft bearing clearances loose and run 20W50 oil along with STP to add more viscosity. Friction created by the high-viscosity oil costs power and fuel mileage from drag at the crankshaft main and connecting rod bearings. The added load on the oil pump also requires additional horsepower that will eventually instigate more wear on the distributor driven gear and cam gear.

When bearing clearances are kept between 0.0015 and 0.002, 10W30 oil can be used successfully even in high-rpm engines. So our first order of business is to keep the clearances tight and use Royal Purple synthetic 10W30 oil to fight heat degradation.

The rotating assembly from the first build consisted of an Eagle 3.750 stroke crankshaft and Eagle 6.0-inch connecting rods. Wiseco flat-top pistons would provide a 10.41 squeeze ratio with the Edelbrock Performer 64cc combustion chamber aluminum cylinder heads. We decided a new GM four-bolt main cylinder block was in order, but we would need a one-piece to two-piece rear main seal adapter to allow us the use the Eagle crankshaft, connecting rods, and Wiseco pistons that were previously purchased.

As we mentioned, we're locked into the short-block build of the engine due to our previously purchased parts, but we can make some changes in cam timing and ancillary pieces to boost horsepower.

We used Virtual Engine Dyno software to build our engine virtually and configure our optimum torque and horsepower numbers. Our first virtual dyno configuration horsepower numbers were 458 hp at 5,750 rpm, and our peak torque was at 4,500 rpm with 394 lb-ft of torque at 2,750 rpm. This dyno software is really cool as you can download the individual parts to make a virtual dyno run and then change them to see if the change was beneficial. Once we have the install finished, we'll see just how accurate the virtual software is.

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Now we lay the crank in position with used bearings for a rotation check. Look carefully at all crankshaft areas for interference. We weren't able to rotate our Eagle 3.750 throw crankshaft a full revolution in the new four-bolt main GM Block (PN 10105123). Out comes the crank and the grinding begins.

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This is one area of clearance concern: the block has some relief in this area already but not enough for the long rods and crank throw. We use our high-speed grinder, carefully removing just enough material in this area to allow 0.050 clearance between any rotating pieces as a rule of thumb.

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Once everything rotates, we can check the deck clearance. Our block had 0.031 piston-to-deck clearance on the odd bank and 0.029 on the even bank. We need to measure at the front and back of the block, then average the results to achieve 0.001-0.003 piston-to-deck clearance. Some blocks are quite different front to back, so it depends on how the crankshaft is lying in the main bearing saddles. (the piston shown is not a Wiseco piston.)

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Now that the crank rotates, and we know piston-to-deck clearance, another trip to the machine shop to drop off the block is necessary. Joe at Gerald and Charlie's operates the surface grinder, and he's setting up the block for surfacing. The engine block is set in place, then it's checked for level on the machine. We found that one side of our new block was not flat and the surfacing was a good thing even if we weren't concerned with the zero deck clearance.

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During each pass, Joe feels the block for any strange vibrations. Vibration means chattering, and the block surface can be in bad shape if the cutters started dancing around. Joe explained that he removed 0.004 of material each pass to prevent the chattering and leave a finely finished surface. Decking the block will ensure even compression between the cylinders banks.

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While at the machine shop, the engine block was chemically washed to remove minute particles from the decking process. The blue shop towel has brake cleaner on it, and one wipe shows just how dirty the cylinders are even though the block was cleaned. Shame on you if the engine fails from metallic particles and debris; don't expect any machine shop to supply a ready-to-assemble engine block.

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Now it's up to us to check for proper bearing clearances. The snap gauge measures the crankshaft main and rod bearing bore diameter. This tool is then measured with a dial caliper to find the inner-bore diameter. When you're looking for 0.0015-0.003 bearing clearance, accurate tool usage is important and takes some finesse. As bearing clearances increase, the oil pressure drops. Likewise, tight clearances increase oil pressure.

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Our crank journal measures 2.100 inch using the dial caliper at each main bearing journal. The main bearing bore measured 2.098, so we end up with 0.002 on No. 1 and No. 5 main bearing for clearance. The No. 2, No. 3, and No. 4 main bearing clearance was 0.0015, which is tighter; it's common to find the center bearings to be tighter. If you have a 0.003 bearing clearance, a high-volume oil pump and 15W40 oil will be necessary or low oil pressure will be the norm.

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Building any engine takes care, and when you're building a performance engine, ring endgaps are crucial for long engine life. If the rings are too loose, compression is lost. Too tight, and the rings can drag or lock in the cylinder as heat builds. Worse yet, they can break and cause piston failure. We push the ring down past midway in the cylinder and measure the gap.

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Now that we know the rings are too tight in the cylinder, our Childs & Albert precision ring filer is put to work. We use a hand-powered filer, holding the ring flat against the rotating wheel. The wheel should be rotated towards the outside edge of the ring to avoid chipping the outside edge that seals against the cylinder. This is tedious work, and care must be taken because it's easy to go too far. Once you do one ring, usually the same amount must be removed from each ring, so count the revolutions of the filer to know when you are close.

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Now we take a jeweler's file and deburr the edges of the ring so the piston isn't gouged and the cylinder wall doesn't get scratched. Don't chamfer the edges, just knock the edge off from the grinder. We talked about the possible addition of nitrous for the street/strip engine, so we would need to file the rings for more clearance to compensate for the additional cylinder heat.

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This may seem petty, but we grind each ring to fit each cylinder, then place them on their respective piston, then on the workbench as shown. Each cylinder should be the same bore size in theory, but there are variations, and every little bit helps. Having everything in its place makes the most sense when assembling components since there is less chance of forgetting something.

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The new Clevite 77 H-series bearings have a coating that we lightly scrub off with a worn Scotch-Brite pad. Clevite 77 H-series bearings are used because of their chamfer on the outside edges of the bearing shell. This allows clearance for the Eagle crankshaft's large radius at the main and rod bearing journals. The large radius prevents cracking at high rpm. We could use P-series bearings, but we would have to chamfer the bearings ourselves. Plus the H-series are race bearings that can take a pounding from nitrous if necessary.

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Finally, we can apply our Royal Purple synthetic assembly lube to the main bearings and lay the crankshaft in place. Of course, we washed the new Eagle crank in mineral spirits solvent and used shop air to blow it dry. Any grit left behind will imbed itself in the bearing and chew away at the crank so keep everything clean. Remember, all parts should be cleaned before installation, even new parts in plastic bags.

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Before we torque the main bearing caps, a dead blow urethane hammer is used to seat the crankshaft against the rear main thrust bearing. The crank is thumped from the rear and front to position the rear main cap. When we checked the clearance before and after the thumping, the clearance changed from 0.002 to 0.0045. If we neglected to position the main cap, only half of the rear thrust bearing would take the load applied by the clutch when we shift the five-speed Tremec transmission.

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It would be nice to show every step of the way, but since we can't, the four-bolt main bearing caps are torqued to specification after we apply light oil to the main-cap bolt threads. If we put the main caps back in the correct location, the crankshaft should spin easily. New engine blocks and OE engine blocks do not have the main or connecting rod cap position marked, so beware! If the caps are not put back in their respective positions, the block or connecting rods will require line boring because the crank won't turn.

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Next, the pistons can be installed with our 4.030-bore tapered sleeve. A liberal coating of Royal Purple 10W30 oil was applied to the piston and cylinder to ease piston installation and prevent dry start-up. Before the piston is installed in the sleeve for cylinder installation, the ring endgaps are positioned 120-degrees apart to lessen compression gas loss that blows into the crankcase. Remember, being conscientious and repetitive makes for a reliable engine. It may sound boring, but it is the only way to know the job is done right.

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Our Clevite 77 crankshaft protectors are placed on the connecting-rods' bolts and a coating of Royal Purple Synthetic assembly lube is applied to the rod bearing before the piston is seated on the crankshaft. Connecting rods have a bearing lock recess to prevent bearing spin. The lock recesses should always face the outside edge of the block. Connecting-rod beams are offset on the bearing saddle with the connecting rods sitting closer together at the center of each crank throw.

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The Eagle SIR connecting-rod caps are torqued to specification with a feeler gauge fitted tight between the caps to prevent bearing damage during tightening. The rod bolts can also be tightened to spec with a bolt stretch gauge and recommended on performance applications. Now's your chance to make sure the connecting rod is centered on the piston. If the rod is installed right, it will be centered, if not, the rod is installed incorrectly.

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Now we're over the top of the hill, so to speak. The Comp Cams' camshaft is now installed after a liberal coating of assembly lube. We don't use any fancy tool to install the camshaft. Once it's close to the final bearing saddles, a 5/16-inch Phillips head screwdriver works nicely. Insert the screwdriver in one of the cam gear threaded holes, and the cam can be handled quite easily.

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We line-up the timing marks on the cam, crank gear, and the Comp Cams high-tech race roller timing chain, and gear set is installed. The cam gear bolts were torqued, and the engine was rotated...oh no! The engine rotated a turn-and-a-half and came to an aburpt halt. The number-two connecting rod was hitting the camshaft. This is a common concern on stroker engines with 3.750 cranks and 6.0-inch length connecting rods and must be dealt with or catastrophic engine damage can result.

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Before we can check the cam timing, the engine has to be able to turn over two revolutions without obstructions. We removed the number-two piston and connecting-rod assembly for minor machining. The shiny spot was ground on a bench grinder, removing just enough material off the connecting rod to provide 0.050 clearance between the connecting rod and camshaft. This is not enough metal removal to be of concern regarding the engine balance unless you plan on revving past 10,000 rpm.

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Checking camshaft-to-connecting rod clearance is absolutely necessary on cylinders 1, 2, 5, and 6 on these stroked engines. We use a modified feeler gauge and fit it between the rod and cam. We had to remove all the aforementioned connecting rods and pistons to machine for proper 0.050 camshaft-to-rod clearance. Always check this clearance when assembling a stroker engine. If the cam touches the connecting rod, your stroker will become a boat anchor. In our next installment, we will finish the engine build.


Virtual Engine Dyno
Mentor, OH



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