A Look At Summit's Impressive New Iron Small-Block Chevrolet Engine Blocks

05/05/2024

“Gee, another iron small-block Chevy block? That’s hardly news.”

If you are an aggressively jaded LS engine enthusiast, this is probably not ground-breaking or exciting information. But despite inroads by the LS family, the small-block Chevy lovers of the world are not yet ready to give up on their venerated engine. It’s no secret that despite the bajillion small-blocks that Chevrolet produced over the decades that suitable cores for the popular small-block are disappearing at a prodigious rate. Of those survivors, optimal candidates for a performance build are becoming harder to find. Try to locate an affordable standard bore, 2-bolt 400 block today. If you do, the owner will want serious coin for a crusty casting.

But now there’s another alternative. Summit Racing recognized this shortfall and along with the BluePrint engine people stepped up for brand new tooling for a series of iron blocks. Just as importantly, the quality of the casting and machine work is impressive. The partners sought out a reputable casting facility in Germany to do the heavy lifting while the CNC machine work is finished here in the USA. So yes, the blocks originate from overseas, but these castings cross the Atlantic, not the Pacific.

Summit Racing SPC small-block – Mains lubrication

Among the many welcome upgrades to the new SPC Summit block is the addition of priority lubrication to the mains. This is evidenced by the third oil galley that plumbs oil directly from the filter to the main journals instead of first oiling the lifters as with production small-block Chevy engines. This ensures plenty of oil to the engine’s rotating assembly. Photo: Jeff Smith

Enough generalities. For small-block connoisseurs, the allure is in the details. Summit labels this new block the Street, Performance, Competition (SPC). The blocks are offered with a choice of two bore diameters of 4.00- or 4.120-inches. Plus you have the option of either a traditional two-piece rear main seal or the later one-piece version. Finally, the larger bore blocks are available in either the 350 main journal diameter or the larger 400ci version. Summit is considering also offering finished honed blocks as another option.

But this new SPC piece is not merely a duplicate of an earlier factory block. Right off, all blocks are cast using a stronger Class 35 iron alloy and employ nodular iron main caps. Like their production cousins, the center three main caps are attached with four bolts with 7/16-inch inners and smaller 3/8-inch versions for the splayed outer bolts that Summit’s Brian Nutter tells us the outer bolts are there mainly to limit lateral cap movement but also add additional bulkhead strength.

A critical point is that this block has been upgraded to priority main oiling. Production small-blocks lube the mains and rods only after first feeding the lifters. The addition of a dedicated main oil galley pushes oil directly to the mains to ensure the lower end is properly lubricated.

The deck height on these new blocks is shorter at 9.00 inches mainly because most aftermarket pistons are designed around this deck height. To improve head gasket sealing, the deck thickness is an impressive 0.600-inch and all the cylinder head bolt holes are blind. This means the head bolt holes do not intrude into the water jacket.

Summit Racing SPC small-block – Main caps

The main caps for this new SPC block are of a higher strength nodular iron material. The inner main cap bolts are 7/16-inch while the outers are 3/8-inch with a lower torque value. Both are 180,000 psi fasteners that re equal to an ARP 8740 bolt. We expect that companies like ARP will soon have both main cap bolt and stud kits available. Also note the cutouts in the base of the main caps to help remove the caps from the block.Photo: Jeff Smith

Speaking of coolant flow through the block, the block designers invested significant effort into improving coolant flow. The cylinder walls are siamesed which means the cylinder walls connect at the midpoint while increasing the volume around the tops of the cylinders by pulling the lifter valley walls inboard. This can be easily spotted by the pushrod clearance radius cuts made into the lifter valley walls. There are also pipe threads cut into the all main lubrication galleys to accommodate ¼-inch NPT plugs.

The cylinder walls are also strengthened. The blocks can accommodate up to a 4.185-inch bore diameter and still maintain a minimum wall thickness of 0.220-inch especially around the thrust surfaces. The as-delivered bore size for the 4.00-inch bore versions is actually 3.995-inch while the larger bores are at 4.120-inch to allow for honing to the standard diameters for piston clearance.

Summit Racing SPC small-block -Pushrod clearancing

Note the machined reliefs in the lifter valley walls for pushrod clearance. This is because both inner walls have been moved inboard to create a larger water jacket area around the cylinders. This new block also accommodates a factory hydraulic roller cam configuration with the machined stands for the lifter spider as well as taller lifter bores for factory roller lifters. Photo: Jeff Smith

Another welcome addition is that all the blocks are fitted with provisions for a factory style hydraulic roller camshaft. Three pedestals are cast and threaded to attach the factory spider and the lifter bores are taller for use with factory hydraulic roller lifters. The camshaft height is also in the stock location so it will accept a standard single or double-roller small-bock cam drive.

These taller lifter bores do require a 0.300-inch taller roller lifter when using a mechanical or hydraulic roller, link-bar lifter and Summit notes that using these taller lifters means the heads must be removed to remove the lifters from the bores, much like an LS engine. This means that changing camshafts with taller lifters will demand removing the heads. Of course, this block can also be used with a flat tappet camshaft.

Summit Racing SPC small-block – cam limiter plate

The Summit SPC block is also machined for a factory cam limiter plate (shown here – purchased separately) that will require the use of a stepped nose camshaft just like 1986 and later factory roller cam blocks. Photo: Jeff Smith

Summit’s Mike Schmidt tells us that these blocks are all machined on high-speed Makino CNC machines which not only leaves a very smooth, final surface but with computer numerical control the orientation of lifter bores to the cam centerline, among other positions, should be exceptionally accurate. Accurate valve timing would also contribute to making more power. It’s a subtle point, but this is the same approach used to build competition engines where accuracy is critical.

Another nice addition is this Summit block is machined for the factory hydraulic roller cam retention plate. If this plate is used this also demands a stepped nose style camshaft which eliminates the hassle of setting camshaft endplay clearance.

Summit Racing SPC small-block – One-Piece Rear Main Seal

This particular block was built with a two-piece rear main seal configuration but Summit does offer versions that can use the more modern one-piece rear main seal. The one-piece adapter is purchase separately. Note the machining that leaves all the finished surfaces extremely smooth. Photo: Jeff Smith

Moving to the bottom end, the block has been factory cast with reliefs in the area just above the oil pan rail to produce clearance (depending upon connecting rod design) for up to a 3.75-inch stroke. This area is cast solid so if additional clearance is needed, there are no coolant passages in this pan rail area to worry about.

To accommodate a wide variety of production block applications, the SPC block includes the stock mechanical fuel pump mount using a stock length pushrod along with the stock spin-on oil filter location. The stock three-bolt engine mounts are logically present along with three freeze plug provisions per side with two more front and rear. Keep in mind that this block will require two more brass freeze plugs compared to a standard small-block kit. In addition, you will need nine ¼-inch NPT Allen plug for all the oil galley and water jacket plugs along with a pair of 1/8-inch NPT plugs.

Summit Racing SPC small-block – drilled oil passages

The twin 1/8-inch NPT tapped holes in this boss are there to access drilling oil passages for the front of the block to feed the lifter passages from both the front and the rear of the block. These holes must be blocked with pipe plugs during assembly.Photo: Jeff Smith

All these Summit blocks are machined for the later model, passenger side dip stick location which requires the same configuration oil pan. The engine is, of course, a wet sump design and is machined to accept the typical standard or high volume small-block or big-block Chevy oil pump.

The price of these blocks at the time of this writing is just north of $2,000, which might seem high to some. But considering that a machine shop will charge between $800 or more to clean, Magnaflux, deck the block to be parallel with the crank centerline, bore, torque plate hone, and align hone the mains. Add this to an initial used block cost of around $200 and you are halfway to the price of this brand new casting. Yes, you will still have to torque plate hone this new block but the quality of the machine work on the rest of block certainly adds significant value.

Summit Racing SPC small-block – stroke clearance

The reliefs for up to a 3.75-inch stroke crank are cast into this new block. Additionally, the inboard pan rails are solid with no water jackets hiding beneath so if additional clearance is needed, as for a 4.00-inch stroke crank, for example, there is no danger of breaking into a water jacket.Photo: Jeff Smith

This new Summit SPC block may not be the first choice for the average basic engine rebuilder. But it does fill a need for the performance builder with aspirations of big horsepower numbers. Summit says this block is more than capable of reliably delivering 700+ horsepower and there are rumors of a 1,500-hp blown application that is putting the test to this new block.

There are other blocks out there that offer some or most of these same features but they do so with a much higher price. With all the excellent features, it is certainly worthy of consideration especially if your next project calls for a stroker crank and a roller cam. There are ways to maintain the budget and still built a quality engine. That notion just moved a little closer to reality with the Summit SPC block.

Summit Racing SPC small-block – Deck Height

The Summit SPC block has a shorter deck height of 9.00 inches as opposed to the OE spec of 9.025-inches. This is because most aftermarket piston compression heights use the 9.00-inch deck height figure. All the cylinder head bolt holes are blind which means no contact with coolant passages.Photo: Jeff Smith

Summit Racing SPC small-block – Oil dipstick location

This new SPC block uses the 1981 and later passenger car side dip stick location which requires the use of the same era oil pan. The final choice of oil pan is determined by several factors including whether your specific block employs a one or two-piece rear main seal.Photo: Jeff Smith

Summit Racing SPC small-block -Oil pressure outlet feed tap

he areas just above the oil filter housing (the block is shown upside down) offers a separate drilled and tapped oil pressure outlet that could be used to feed a turbocharger or other external oil feed. The other two bolts holes are for mechanical clutch linkage. Photo: Jeff Smith

Summit Racing SPC small-block – 3rd freeze plug

This new Summit block is also fitted with a third freeze plug on each side of the block where production 350 small-blocks used only two freeze plugs. The BPE cast into the block stands for Blueprint Engines, which is partnered with Summit to produce blocks for complete engines. Summit is the only outlet for bare blocks. Photo: Jeff Smith

Rat Version of the SPC Block

Summit tells us that by mid-summer, the company will be adding a big-block Chevrolet version of the SPC block, in the MK IV configuration. These blocks will be offered in 4.500 and 4.600-inch bore sizes with either two- or one-piece rear main seals. In addition, there will be a choice of a 9.800 or 10.200-inch deck heights. Like the small-block versions, these blocks will be cast in Germany and machined in the USA. A 4.600-inch bore with a 4.250-inch stroke on a standard-deck Rat motor would produce a 565ci Rat motor. At 1.25 horsepower per cubic inch, a normally aspirated, single four-barrel combination would produce just north of 700 horsepower.