Summit Racing SPC Engine Block being measured
(Image/Jeff Smith)

It’s not quite a Chicken Little moment where the sky is falling, but the disappearance of good Gen I small block Chevy engine blocks is a major concern. If you are one of the country’s largest small-block Chevy engine builders like Blueprint Engines, then you know that usable, standard bore block cores are becoming harder to find. The ideal solution would be to build your own. That’s an expensive investment, but that’s exactly what Blueprint Engines did.

But Blueprint sells crate engines, not individual parts. That’s what Summit Racing does. So The companies made a deal: BluePrint uses the new blocks as the foundation for their engines and Summit Racing sells bare blocks to engine builders under Street, Performance, Competition (SPC) name. Either way, you win.

Available in both 4.00- and 4.125-inch bore sizes with the choice of a one- or traditional two-piece rear main seal, The Summit Racing™ SPC Engine Blocks are capable of handling 700-plus horsepower. There are rumors that a block is already out there handling 1,500 horsepower with no signs of distress.

One of the advantages of being the last to attend this ‘block party’ is that you have the opportunity to remedy all the inherent flaws of all the previous versions. This story will detail all of the important specs you’ll need to evaluate these new SPC blocks along with several third-party measurements to establish the accuracy of the machine work. The message is that a strong casting is only half of the story. If the machine work is not accurate, the more discerning engine builder is forced to spend additional money–perhaps equal to the cost of the original block–to achieve the most power and reliability out of the engine.

Measure, Measure, Measure

There are a few critical areas where proper machine work can be evaluated to determine the quality of the final product. This story was originally intended to farm out these block measurements to a professional race engine shop to carefully measure Summit Racing SPC block against GM’s own specs. But during the wait, Chris Straub of Straub Technologies in Piney Flats, Tennessee published his own independent evaluation of the block, so we chose to trust his measurements.

Straub set the stage by stating, “Out of all the aftermarket blocks we’ve have had on the machine, the Summit block was the closest to the GM (blue) print.” The machine he is referring to is a Rottler F69A. It can not only measure component locations with a wireless probe for automatic centering on items like cylinder and lifer bores, but it can perform the machine work as well. Rottler claims measurement accuracy of +/- 0.0002-inch.

Straub told us that the SPC block deck surfaces measured to within 0.002-inch on one side and 0.003-inch of true parallel on the opposite side. The cylinder bores were within 0.0015-inch for consistency within the GM-spec 4.400-inch bore spacing. Straub also reported that the main housing bores for the crankshaft were also right in the middle of the GM spec. This consistency is incredibly helpful when setting main bearing clearances.

One particular measurement point that we were interested in has to do with the position of the lifter bores relative to the camshaft. The camshaft centerline measured within 0.0015-inch of parallel with the main bearing bores. Straub also reported that each lifter bore was within 0.001-inch of true vertical relative to the camshaft center line and within 0.003-inch of horizontal. Between these two specs, the vertical is the far more critical since valve timing will suffer if the lifter bore is not “square” to the camshaft lobe.

This brings up an important monetary consideration. While this new casting is certainly more expensive than an older production block, consider the total cost of the substantial machining that must be invested in a used block to bring it into spec. Assuming the block is not cracked, it is not unusual to spend $1,000 or more to machine a block to achieve the proper specs.

This author recently spent over $2,800 in machine work to bring a late ’70s production block into spec. This included aligning the cam bearing bores and adding lifter bore bushings. The result was an older block within the specs of the Summit Racing SPC blocks. It would have been far less expensive to invest in the new block.

Modifications and Improvements

Now that we’ve established the precision machine work present in these new castings, let’s talk about block modifications and improvements. The first major change to the SPC block is the addition of priority main oiling. This is where the crankshaft receives oil directly from the oil filter as opposed to the OE path that pushes oil to the lifter bores first and then to the crankshaft.

The block deck height is slightly shorter at 9.00-inches as opposed to the OE spec of 9.025-inch because most aftermarket pistons are configured for the shorter deck height. The deck is also strengthened with a minimum 0.600-inch thickness.

One of the advantages of the tighter machining clearances is that when pre-assembling the engine to check the piston-to-deck height spec, older production blocks can vary by as much as 0.015-inch. The SPC block will likely measure closer to 0.002- to 0.003-inch in variation between all eight pistons. That eliminates the necessity of shaving the block to optimize this spec.

For the record, the SPC blocks require finish honing to establish the proper piston-to-wall clearance. Cam bearings will need to be installed before the block is ready for assembly.

Both the 4.00- and 4.125-inch bore blocks can be safely bored to a maximum size of 4.185-inch while maintaining a minimum thrust side wall thickness of 0.220-inch. For the 4.125-inch bore castings, buyers can choose the larger 400 style main journal housing size or the smaller 350 style mains. If a long-stroke combination is under consideration, be aware that 4.00-inch stroke cranks are generally ground using the larger 400 style mains for additional torsional rigidity and strength.

Summit Racing SPC Blocks all come with four-bolt mains with the outer splayed bolt holes in the smaller 3/8-inch configuration. Summit Racing’s Brian Nutter told us this is because the outer bolts’ main job is to minimize lateral cap walk and play only a very small role in vertical cap loading.

While we’re in the crankcase area, the pan rail section has been designed with a factory relief that Summit Racing says will accommodate most, if not all, 3.750-inch stroke steel rod combinations. If a longer stroke is under consideration, this area can be further relieved because the water jackets normally found in this area have been removed, making this area solid to aid in block strength.

All Summit SPC blocks are cast with siamesed cylinder liners. This means that the outer portions of the common walls between cylinders are connected. This reduces coolant contact, but this is offset by the additional strength offered with this construction technique.

Here are some smaller yet still important pieces of this small-block puzzle:

• Machined to accept a mechanical fuel pump in the OE location

• Machined to accept both the small diameter (straight across) flywheel/flexplate starter motor nose and the offset, large diameter nosepiece

• Accepts a standard small-block Chevy spin-on oil filter adapter

• Two different mechanical clutch linkage ball stud locations

These SPC blocks require a larger number of production style pipe plugs for both oil galleys and outside block drain fittings. We counted nine that will be needed to plug all the tapped holes in this block. You will also need two 1/8-inch NPT plugs for the drilled and tapped boss at the front of the lifter valley that was required to drill lubrication galleys for the priority main oiling system.

Finally, all head bolt holes are blind holes, which means they do not extend into the water jackets. This is a critical point because the length of the head bolt must be accurate to prevent damage to the block. A too-long head bolt can easily bottom out and crack the block. We’ve seen this happen to a brand new aftermarket block with blind head bolt holes. The ugly result was a serious crack in the block deck that required extensive machine work to add two cylinder sleeves to repair the damage caused by a non-attentive engine builder. So don’t be that guy.

Combine modern, CNC-machining accuracy with all the benefits of economy of scale and a high production rate and you’ve got one of the best deals on the planet for building a small-block Chevy. Let’s take a closer look.

Summit Racing SPC Engine Block Specifications

Material: Iron alloy Class 35

Weight: 181-194 pounds based on bore size

Deck Height: 9.00 inches

Deck Thickness: 0.60-inch

Bore Spacing: 4.400 inches

Maximum Bore Size: 4.185 inches

Minimum Cylinder Wall Thickness with 4.125 Inch Bore: 0.2200-inch

Main Journal Size: 2.4485 inch (350), 2.659 inch (400)

Rear Main Seal Style: Choice of 1-piece or 2-piece                                              

Main Cap Material: Nodular iron

Main Cap Bolts: 7/16-inch Inner, 3/8-inch outer

Stroke Clearance: Up to 3.750-inch

Lubrication System: Priority main

Cam Location: Stock

Cam Bearing Bore Size: 2.000-inch  +/- 0.001

Lifter Bore Size: 8.437-inch +/- 0.0003

Machined for OEM Hydraulic Roller Lifters: Yes

Oil Pan Rails: Solid (no water jackets)

Starter Motor Mounting: Drilled and tapped for both straight and offset

Mechanical Fuel Pump Provision: Yes

Dipstick Location: Passenger side

Water Jackets: Larger than OE                           

Block Coating: Black powdercoat

Parts to Complete Block Assembly   

Durabond Cam Bearings: DUR-GMP-8

Summit Racing Brass Freeze Plug Kit, 2 required: SUM-G1581                        

Pioneer 1/4-Inch Pipe Plugs, set of 25: PIO-PP-584-25        

Summit Racing Oil Filter Adapter: SES-3-60-08-900 

Fel-Pro 2-Piece Rear Main Seal, 350 main: FEL-BS40013

Fel-Pro 2-Piece Rear Main Seal, 400 main: FEL-2909 

Summit Racing Cam Limiter Plate: SUM-150-130      

Chevrolet Performance Fuel Pump Pushrod, 0.500-inch: NAL-3704817                         

Summit Racing Chrome Fuel Pump Block-Off Plate: SUM-401030

Summit Racing Oil Pressure Adapter, 1/8-inch NPT to -4 AN: SUM-220446                            

ARP Oil Pump Stud (high-volume oil pump): ARP-230-7003

ARP Oil Pump Driveshaft: ARP-134-7901

Pioneer Front Timing Cover Dowel Pins: PIO-839059                            

Chevrolet Performance Bellhousing Dowel Pins, 2 required: NAL-1453658          

Summit Racing SPC Engine Block on stand
The Summit Racing SPC block is poured using high quality cast iron in Germany, then shipped to Blueprint Engines in Kearney, Nebraska where the block is fully CNC machined. Small block fans will notice many minor changes/upgrades to a typical production block, making this casting far superior to any production casting. The quality of the machine work is top tier. (Image/Jeff Smith)
Summit Racing SPC Engine Blocks on pallet
These are as-cast blocks as they arrived at Blueprint Engines. These raw castings come already completely powdercoated so there’s no corrosion issues after the boat ride from Europe. (Image/Jeff Smith)
Summit Racing SPC Engine Block main caps
All SPC blocks feature splayed-bolt four-bolt main caps made from nodular iron. Note that the dipstick location is on the passenger side like 1981-85 Chevrolet production blocks. This dictates the use of the later model oil pan and gasket. (Image/Jeff Smith)
Summit Racing SPC Engine Block main cap closeup
The four-bolt main caps are also cast from stronger nodular iron. They use 7/16 x 14 bolts for the main vertical load and 3/8 x 16 bolts for the splayed outer holes that are mainly there to minimize cap walk. Look closely and you can see small indentations in the side of each cap. These will help you pull the caps loose from the block. (Image/Jeff Smith)
Summit Racing SPC Engine Block rear main seal
The SPC blocks are available in either one- or two-piece rear main seal configurations. This particular block is configured for use with a two-piece rear main seal crankshaft. If a one-piece rear main seal is ordered, this will require a matching 1986 and later style oil pan. If you decide you want to convert your two-piece block to one-piece, you’ll need a Chevrolet Performance Main Seal Adapter Kit. (Image/Jeff Smith)
Summit Racing SPC Engine Block front view
The casting features priority main lubrication. The main oil galleys are tapped for ¼-inch NPT pipe plugs as opposed to press-in plugs. In addition, all SPC blocks are machined for a cam limiter plate for roller cams. That eliminates the need to fuss with adjusting camshaft endplay with a cam nose button. The timing cover face is configured to accept either the original 10-bolt or the later eight-bolt style covers. (Image/Jeff Smith)
Summit Racing SPC Engine Block oil pan rail notch
All SPC blocks have this relieved portion of the oil pan rail to clear a 3.750-inch stroke and connecting rod combination. The pan rail area can be further relieved with no worry of hitting a water jacket because this portion of the rail is solid to enhance block strength. (Image/Jeff Smith)
Summit Racing SPC Engine Block lifter valley
The lifter valley is machined with taller lifter bores to accept 1987 and later-style hydraulic roller lifters. The three drilled and tapped stands in the center are for attaching the factory stamped steel retainer spider and lifter dog bone arrangement. Also note the fixture up front with the two drilled and tapped 1/8-inch NPT holes. These are drill access holes for the oil galleys and must be plugged with pipe plugs during assembly to prevent a massive internal oil leak. (Image/Jeff Smith)
Summit Racing SPC Engine Block lifter bores
It’s important to note that aftermarket tie-bar roller lifters should be checked for adequate clearance to the top of the lifter bores to prevent damage. The taller lifter bores create a more stable area but will require the head to be removed if using 0.300-inch taller lifters. (Image/Jeff Smith)
Summit Racing SPC Engine Block pushrod reliefs
These machined pushrod reliefs in the lifter valley walls are necessary because the block designers increased the size of the water jackets in this area. That required trimming to ensure plenty of pushrod clearance. (Image/Jeff Smith)
Summit Racing SPC Engine Block oil filter pad
You will need a bunch of small parts to complete an SPC block, including this spin-on oil filter adapter. We’ve included many of these parts in the accompanying Parts List. (Image/Jeff Smith)
Straub Technology’s Rottler F69A machine
This is Straub Technology’s Rottler F69A machine used to measure the SPC block purchased from Summit Racing. It uses CN technology to probe all the machined surfaces to establish how accurate these blocks are relative to GM’s original specs. The block in this photo is a used production block, not an SPC block. (Image/Jeff Smith)
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Jeff Smith, new product, small block Chevy tech
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.