632 Mountain Motor (Part 1B)


Dart's new monster big block offers a choice between 10.600" or 11.100" deck heights, a cam tunnel that's moved up 0.600" for better connecting rod clearance with stroker cranks and a choice between 4.840" or 4.900" bore spacing. The new tall-deck block offers engine builders great versatility with variable lifter locations and provisions for symmetrical or siamesed-port cylinder heads.


To avoid pump pickup cracking (due to engine shake), we opted for a very beefy billet gerotor style oil pump from Moroso, their P/N 22167. This pump features a built-in pickup incorporated into the bottom of the billet pump body, so there's no external pickup to vibrate loose. The matching oil pan to accommodate the Dart block and this pump is Moroso's billet 2-piece aluminum pan, P/N 20376.


Crane was kind enough to machine a custom-grind steel billet solid-roller stick for us. This is P/N 13R001027, Grind number R-288/5201-2S-14 SFO (Special Firing Order). Effective lift (with our raunchy 1.85:1 rocker ratio) is almost a full inch...woof! LIFT @ cam..... 0.5201" intake; 0.5001" exhaust (with our 1.85:1 rocker ratio from Jesel, valve lift should be 0.962" intake and 0.925" exhaust. If used with 1.70:1 rockers, valve lift would be 0.884" intake and 0.850" exhaust)

ADV. DURATION 317.0 deg. intake; 356.0 deg. exhaust

VALVE SETTING (hot) Intake 0.020"; Exhaust 0.022"

CAM TIMING (@ 0.020" tappet lift) Intake opens 49.5 deg.

BTDC; closes 87.5 deg. ABDC Exhaust opens 113.0 deg.

BBDC; closes 63.0 deg. ATDC CAM TIMING (@ 0.050" tappet lift) Intake opens 35.0 deg.

BTDC; closes 73.0 deg. ABDC Exhaust opens 96.0 deg.

BBDC; closes 38.0 deg.

ATDC Duration: Intake 288.0; exhaust 314.0

VALVE SPRINGS (P/N 96849 triples) Closed 352 lbs @ 2.200" Open 928 lbs @ 1.370" (minimum RPM 4700; maximum RPM 8700; valve float 9300 RPM)

NOTE: This is a special firing order (SFO) camshaft. Firing order is 1-8-7-3-6-5-4-2 As usual, we'll provide plenty of detailed information relative to all of the components as well as all machining and assembly info in the next article. As I mentioned earlier, Diamond is making our forged pistons (they have plenty of experience in designing slugs for 632 builds, so this'll work out peachy). In the next issue, I'll provide all of the custom piston specifications. As soon as Eric Simone of Diamond Racing finishes our pistons, we'll hone-fit the cylinders and file-fit our Perfect Circle rings. At that point, we'll fit-check our crank and rods for clearance. Once that's done, we'll balance the crank, rods and pistons and begin our trial-fit, degreeing the cam and measuring for pushrod length. We expect to perform a host of fitting procedures, including fine-fitting and port-matching our intake manifold-to-head fit, checking pushrod clearance and correcting as needed, etc. Oh, by the way, we plan to use a new digital cam degreeing system from Cam Logic, which we'll feature in depth. I saw this at the recent PRI show in Orlando, and it made my mouth water (I wanted to use a different analogy, but I need to watch my language). I can't wait to try it out. While we won't pursue a perfect smooth exterior block finish (remember our recent 383 Dart smallblock Chevy streetrod build?), we'll nonetheless tidy up the block exterior for enhanced appearance, eliminating any casting flash. We haven't decided on a block color yet, but I think we'll stay away from black, mainly because it's difficult to photograph (black hides too many details). Once our mutant baby is final-assembled, we'll trek up to Koffell's Place in Huron, Ohio for the dyno run, using Scott's DTS engine dyno. If all goes well, we should be able to comfortably nudge around 1200 HP out of this big-gulper.

Our Dart Big M block features a 10.2" deck height (9.8" deck is also available). Camshaft bore position matches standard big block Chevy.

Bores are slightly undersized, providing plenty of meat to hog out to achieve our 4.600" desired diameter. Minimum cylinder wall thickness is 0.300".

The steel billet main caps feature splayed outer bolts on #2, 3 and 4 (all caps are 4-bolt), and feature deep-stepped registers on each side. The main bearing bore measures 2.937-2.938", accepting standard big block Chevy main bearings.

Lifter bore diameters measure 0.8427-0.8437", accepting +0.300" longer roller lifters.

Each valley side of the block features two slotted bosses to accommodate the four head bolts that are installed on the underside of the heads.

Clearance reliefs are already provided at the bottom of the bores. Depending on the stroke, additional clearancing may be required. We'll test-fit our 4.750" stroker crank to verify.

The Dart Big Chief II alloy heads are, well, big. This is a hefty 42-lb chunk of 355T6 aluminum.

Intake flow is rated at 520 cfm @ 0.900" lift at 28 inches on a SuperFlow 600 test bench. Intake port volume is 497cc.

Our heads feature 56cc chambers (70cc also available). Intake valve diameter is a whopping 2.470", and exhaust valves are 1.800". The heads came equipped with Victory titanium valves.

Intake ports are 2.725" x 1.815" and feature a 3/4" radius.

Exhaust ports (as intakes) are CNC machined. Notice the beautiful blend radius at the valve boss.

This says it all.

Our crank is a steel unit from Lunati, with 4.75" stroke.

That's a hefty stroke in anybody's language.

Our rods are Lunati Pro Billet I-beam connecting rods, P/N LB01.

The Lunati rods feature a center to center length of 6.700".

The matching Crane set includes cam, offset roller lifters, springs, retainers and locks.

Our bumpstick is a steel billet cutie from Crane. We're also using their solid roller lifters (offset to work with the Dart heads), titanium keepers and retainers, and big-ass springs (rated for float at 9300 RPM).