|Dart Big M Block Lifter Gallery|
Big M Sportsman version (shown) comes with 4-bolt ductile iron caps on all five main bearings. Billet caps are available for power adder applications or those expected to exceed 1000 horsepower. Main caps 2, 3 and 4 incorporate splayed outer bolts to help distribute firing loads equally across the main webs.
Dart Big M Block 4-Bolt Main Caps
Dart Big M cylinder block incorporates all the important characteristics of modern race blocks in a high quality affordable casting. Available in both 9.8-inch standard deck height and 10.2-inch tall deck versions it is the perfect starting point for any serious big block Chevy racing application.
|Big M Cam Bore & Fuel Pump Boss|
Big M blocks come with standard Mark IV style front fuel pump boss and traditional front mounting bosses. Both 9.8-inch stock deck blocks and tall deck 10.2-inch blocks have standard height cam placement. All blocks feature priority main oil circuits.
|Dart Big M Block ¾ Front View|
Big M block features expanded water jackets (bulges on side of block) to optimize coolant flow. They are machined above the oil pan rail to remove weight and the oil filter pad is tapped for a dry sump pressure entry if desired.
|Dart Big M Block Front View|
Timing cover cavity is machined to accept Comp and Jesel belt drive assemblies without modification. For chain drive systems the camshaft thrust boss is tapped for a stock type cam thrust plate.
|Big M Cam Bore and Lifter Galleries|
Priority main oiling is fed directly from the main oil gallery (B) to the main bearings via a direct passage. Lifter galleries (A) are independently supplied from the front of the block as opposed to the rear in a stock block. Main oil gallery accepts a ¼-inch pipe plug both front and rear. Lifter galleries take 3/8-inch pipe plugs.
|Big M Block Inside Head Stud Boss|
Inside head stud clamping bosses are located above cylinders 3, 7, 2 and 6 on their respective banks to provide even 6-bolt (or stud) clamping force around each cylinder.
|Big M Block Cylinder Finish|
Cylinders on our block are finished to Dart recommended specs. The rough block was approximately .012 undersize. It was honed to size with 220 grit , then 3 strokes with 280 grit and 3 final strokes with 400 grit and fresh honing oil per Dart’s Pro Stock procedures.
|Big M Block Siamesed Cylinders|
This view shows the expanded cooling jacket bulges on the side of the block and the siamesed cylinder construction inside the open core holes. Note 1/2-inch pipe external oil feed to the oil filter cavity, machined scallop above oil pan rail for lightening and extra oil pan stud holes opposite each main cap to accommodate stroker applications.
|Big M Block Rear External Oil Feed|
Arrow indicates ½-inch pipe external oil feed at rear of block. Filtered dry sump oil can be input here or at the oil filter cavity. Cam tunnel accepts standard BBC 2.215-inch diameter rear cam plug.
|Big M Block Main Caps|
Note additional material removed adjacent to oil pan rail for lightening. Main caps are machined with a convenient slot on both sides for easy removal with a small pry bar. All blocks are supplied with splayed bolt caps on the three center mains and high strength bolts.
| Big M Block Stroker Clearance|
Blocks are pre-machined t accept stroker cranks up to 4.750-inch. Note extra oil pan bolt hole adjacent to main cap for stroker applications. Extended cylinder walls on stroker blocks tend to prevent the hone from sweeping all the way through the bottom of the bore. Care is required to monitor cylinder diameter at the bottom of the bore closely during honing operations. Additional short strokes near the bottom third of the bore are often required to prevent the bore from pinching in and tightening up the piston to wall clearance.
|Big M Block Right Side View|
Right side view shows many prominent features including expanded cooling jacket bulges, machined lightening scallops above the oil pan rail, standard Mark IV fuel pump boss, 4-bolt main caps and inside head stud bosses on the deck surfaces.
|Big M Block Left Side View|
Left side view displays similar features plus ½-inch pipe external filter oil feed to oil filter cavity and clutch linkage mounting bosses. Blocks accept standard BBC core plugs.
|Big M Block Rear Main Cap|
Oil pump mount on rear main cap must be plugged for dry sump oiling applications. Dart recommends .250-inch oil pump dowel pins. Many commercially available rebuilder pins are only .246-inch.
| Big M Block Priority Main Oiling|
Dart cutaway view shows passage from priority main oil gallery directly to main bearing housing. Vertical passage feeds the cam bearings from the mains. Lifter galleries are fed independently from the front of the block. Oil must pass through the entire main oil gallery and oil every main before reaching the front passage to the lifter galleries.
|Deburring a New Dart Big M block|
After a thorough inspection, deburring the block is the first step of block preparation. It’s easier than it looks, but takes some time. Break all sharp edges with a deburring tip. The purpose is fourfold. 1. To remove all sharp edges that can cause damage to other parts or personal injury during assembly. 2. To smooth and radius all potential stress locations where cracks might develop. 3. To remove excess casting flash that might break away and cause engine damage or failure. 4. To aid oil drain back by providing smoothed surfaces or re-directed paths.