Debate: DART SHP or Restored Stock Block?

When it comes to building a Saturday night engine, the engine budget always seems like the story lines from the Clint Eastwood spaghetti western "Dollars" trilogy: "A Fistful of Dollars," "A Few Dollars More" and the finale, "The Good, The Bad and The Ugly."

Budget engine builds don’t have to be a the typical saga of the "man with no name" digging through the junkyard for battered good, bad and ugly engine parts to refurbish. You can actually rewrite the movie by providing a quality name and title it; "A Few Dollars Less."

 

DART Machinery’s SHP (Special High Performance) engine blocks are often disregarded by the street or weekly racer in the false belief that a junkyard block will be easier on the rubber-band-tight budget.

We’re not going to pull the wool over your eyes or blow smoke up your exhaust pipe here. It’s true that an engine builder can sacrifice quality and take a lot of shortcuts with their engine build. So if you are the type that wants to reuse connecting rod bearings, this article probably isn’t for you. If you are interested in getting more quality and spending less on the foundation for your build, the engine block, then by all means… read on.

THE GOOD, THE BAD AND THE UGLY: A JUNKYARD BLOCK

Let’s keep this scenario simple and say that we want to build one of the most common engines that enthusiasts build; a small-block Chevy 350 engine. Most engine aficionados claim that SBC 350s are a dime a dozen. Perhaps, but lets consider this; Gen I SBC engines have not been in used in a production GM car for over 15 years.

Hunting around the junkyards for a Gen I SBC is going to require days of searching until you find a block that will most likely be 30 to 40-years old. You won’t know exactly what shape the block is in until you have it cleaned and checked by a machine shop – even then, there will be questions about the abuse the block has been put through by the previous owners. Remember that cast iron is a metal and all metal has a point where it fatigues. Heat cycles, loading and a host of other issues can accelerate the fatigue point of an engine block.

Assuming that you find a block in the junkyard that you are willing to chance a chance on, it will require some routine work to see if it is even salvageable. If and when the block is determined to be usable, substantial machining would be needed to make it race-worthy.

COMPARING APPLES TO APPLES

DART’s SHP line of engine blocks are not your run-of-the-mill stock engine block and a 100% side by side comparison of a stock SBC refurbished junkyard block simply cannot be achieved. There are several elements that make the SHP block more of a performance type engine block than the standard stock GM block.

DART Machinery’s Jack McInnis explained the key differences in the SHP block, "these blocks are designed for high-performance and heavy-duty applications to over 600 horsepower, but priced hundreds of dollars less than a full race block."

"The SHP block retains the small-block’s original dimensions and is compatible with stock and aftermarket stock replacement components, but it’s superior to OEM blocks because of the advanced performance features," McInnis added.

Among the performance advantages DART’s SHP block has over the Gen I junkyard block is a true priority main oiling system. In the OE production block, the main oil gallery is located above the camshaft tunnel. Pressurized oil is routed through annular grooves around the camshaft bearings before it goes to the main bearings. This OEM design causes a loss of pressure as the oil is forced through several 90-degree turns which ends up reducing oil volume as oil sprays out of the cam bearings.

The SHP block replaces this restrictive system with a main oil gallery located alongside the camshaft tunnel. Oil is routed directly from the main oil gallery to the main bearings first through drilled passages, ensuring optimum lubrication for the crankshaft at high rpm. The camshaft and valvetrain, which have lower lubrication requirements, are fed by secondary passages from the upper main bearings. This refined oil system eliminates the need for a high-volume oil pump, which requires more horsepower to drive and accelerates wear on the camshaft gear.

Some machine shops offer a conversion for the OE block to convert the internal oil system to a priority main type oil system. For comparison purposes, we are going to figure this conversion into our side by side comparison for a more accurate assessment.

The SHP block also has ductile iron main bearing caps that are the same high tensile strength material found on many race blocks. The four bolt configuration has splayed outer bolts that anchor into the strongest part of the block. If you are lucky enough to find a four-bolt main OEM block, the outer main cap bolts anchor into the bearing webbing. This area has been prone to cracking under harsh conditions like racing.

 

For our side by side comparison, we are assuming the junkyard block is a four-bolt main. A two-bolt main can be converted by some engine shops into a splayed four-bolt main, but some strength is sacrificed and the process is costly. We will disregard the two-bolt to four-bolt main conversion.

Another couple of areas where the SHP block has significant performance advantages is the thicker decks and blind-tapped head-bolt holes. These are areas that the OE junkyard block cannot be enhanced or converted. The SHP block’s minimum deck thickness of .625" provides a very rigid surface for head gasket sealing and room for surfacing on future rebuilds.

The SHP’s blind head bolt holes do not allow for the head bolts or studs to extend into the water jacket like the OEM blocks. Most engine builders use silicone sealant to prevent coolant from the water jacket migrating up the bolt threads causing a leak. Using sealant on head bolt threads makes the bolt torque less exact and uniform across the entire surface.

 

WHAT DOES IT TAKE TO REFURBISH A JUNKYARD BLOCK?

In addition to a thorough cleaning and Magnaflux or sonic testing for cracks, any block considered for racing should be line bored or line honed. Honing the main bearing and cam bearings in engine blocks restores worn out, out-of-round or damaged bores. These problems are caused by engine overheating, loss of oil pressure or a host of other conditions that you can’t tell by looking at the block in a junkyard. Without knowing the history of the engine block, the only way to give your build a chance at survival is to restore the inside diameter of these bores by line honing.

Line boring will also restore proper alignment. Engine blocks age and undergo repeated heat cycles that work on the residual stresses from the original casting process that will distort and warp the block. This warpage affects the alignment of the crankshaft and camshaft, as well as the cylinder bores. Once the engine becomes “seasoned” and stable, the camshaft and crankshaft journals develop wear patterns from the distortion that has taken place.

Any race engine builder will take advantage of the rules and build the engine to those rules that regulate the competition. Line honing and cylinder boring will align the crankshaft and camshaft to the piston and valvetrain geometry. These processes will give that extra performance edge and longevity to the engine build. Line boring or honing and cylinder boring should be considered mandatory for reconditioning a junkyard block.

RESURFACING THE BLOCK

Resurfacing an engine block for proper head gasket sealing is an essential part of engine building. Often overlooked is resurfacing the block ends where the timing cover and transmission bell housing mount. These surfaces should be reconditioned for the same reason that the main bearing and camshaft journals need line honing: warpage. Even though an engine block looks stable and nothing can twist and warp it, it happens, and it happens frequently.

 

To ensure a proper gasket mounting surface, especially if the builder is going to be using MLS or other modern head gaskets, block resurfacing also should be considered mandatory.

Most engine builders will over bore the cylinders to the extent that the rules will allow. For our side-by-side comparison, we are taking into account boring the cylinders to 0.030″ and honing the freshly cut bores with a plate attached to the engine block to simulate the stress created by cylinder head installation.

ECONOMICAL SIDE BY SIDE COMPARISON

We have already determined that DART’s SHP block has several more performance advantages for circle track race engines, so a performance comparison is not going to be fair to the refurbished junkyard block. This is not meant as a slight against the GM Gen I small blocks that were produced for passenger cars and trucks in the 60s, 70s and 80s. They were great blocks that took advantage of every piece of technology that was available and affordable at the time. In the past 40 years, technology has changed, even the materials used in the casting process has changed. Tooling has become more sophisticated and widely used. The DART SHP block takes advantage of the technology improvements and is the better performance block from which to start your engine build from. But what about cost?

We called to performance machine shops that were on par with DART Machinery’s shop to get an average of what it would cost to restore a salvaged SBC engine block to race worthy condition. The initial cost of the block is based on local wrecking yard prices which ranged from $200 to $400 depending on condition and who pulled the engine from the vehicle. We averaged that cost and set the price of a core engine block at $300.

 

CONCLUSION

To do the job correctly, by a professional engine shop, the cost of making a worn out, junk engine block into a piece that is ready to become the foundation for a race engine is greater than a new, green SHP engine block from DART Machinery. The kicker to the side-by-side comparison is technology and performance. The SHP block is less expensive, has the latest technology built in and has a higher performance level.