We selected a set of Dart 18° Big Chief cylinder heads for this project. They are offered as cast or with your choice of Super Mod porting or Full Port CNC porting. To match our application we chose the Super Mod porting configuration. The feeling was that the full port heads might be too big for this engine size when run at Bonneville's higher altitude. 
We hoped to maintain good port energy from the Super Mod port option which essentially combines bowl porting and minor port sizing for the first half inch of the intake port along with a fully CNC prepped combustion chamber. Study the accompanying spec sheet and photos to see the Super Mod combination. With the camshaft and intake combination we are planning we still believe this engine can exceed 1000 HP.About 1.8 to 1.85 HP per cubic inch seems reasonable without resorting to an expensive dual carb tunnel ram setup, fully ported heads and the resulting need for higher engine speeds. The intent was to make good power and still maintain durability for extended high rpm runs.
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 Dart Big Chief combustion chamber |  Canted valves |
 Big Chief Super Mod Intake Port |  Big Chief Super Mod as Delivered |
 Victory titanium valves Dart Part# 18475136 I-038A
Material: 355T6 alum alloy
Combustion Chambers:100cc SS w/CNC
Intake Valve Dia: 2.400”
Intake Port volume: Super Mod (S/M), 402cc
Intake Port Dim: 1.810” x 2.525” (S/M)
Int Port Location: Raised 1.500” spread ports
Intake Gasket: Fel-Pro # 1298
Exh Valve Dia.:1.900”
Exh Port volume: 175cc (S/M)
Exhaust Port Dim: (As cast & S/M) 2.000” x 1.680”
Exh Port Location: Raised .900” Std Chevy bolt pattern
Exhaust Gasket: Mr Gasket 5914
Flow, Intake: (S/M) 444 cfm @ .800”
Flow, Exhaust: (S/M) 301 cfm @ .800”
Manifold: Dart Big Chief (opening - 1.750”x 2.350”) 8.00” tall
Milling Specs: Min. 92cc / .020” max (.006” = 1cc) Flat mill only.
Pistons: Must use pistons for Big Chief.
Push Rod length: Measurement required
Retainers: Titanium 10°
Spark Plug: .750” reach, gasketed. Autolite AR3932
Spring Cups: 1.625” - .035 cup
Spring Pockets 1.740” OD for 1.625” cup (.030” deeper max)
Springs: Dart supplied, 1.625D = 250# @ 2.000” / .790” max Vasco-Jet H-11
optional triple: 1.625T = 330# @ 2.100” / .910” max Comp 948
Valve Angles: Int - 18°, Exh - 9°, 4° cant
Valve Length: Int - 6.600” Exh - 6.450” Our assemblies w/ SS – 6.380”
Valve Stem Dia: .3415” - 11/32”
Valve Train:T&D or Jesel rocker system
Valve Guides: 1/2” OD Mag - bronze Cut for .530” PC seals (.002” press)
Valve Guide length: 3.000”
Valve Guide clearance: .0014” - .0021” (with Victory .3415 dia. valve stem)
Valve Guide Spacing: Widened for use on min. 4.375” bore
Valve Seats: Ductile Iron, .006” press
Valve Seat dim. Int. - 2.490” x 2.000” x .375” Exh - 2.000” x 1.600” x .375”
Valve Seat angles: Int = 32° - 45° - 60° - 70°-80° Exh = 37° - 45° - radius
Studs, head: Recommend Dart Big Chief stud kit PN 66120015
Titanium Valves Must use lash caps
Torque: Head Bolts = 70 ft/lb Dart’s inner head studs 3/8-7/16 = 50 ft/lb
Manifold = 35 ft/lb
Block Use: Mark IV, Gen V, Gen VI with proper head gasket
Weight: 42 lbs |
SOURCE:
Dart Machinery, Ltd.
353 Oliver Drive
Troy, MI 48084
248-362-1188
www.dartheads.com
We hoped to maintain good port energy from the Super Mod port option which essentially combines bowl porting and minor port sizing for the first half inch of the intake port along with a fully CNC prepped combustion chamber. Study the accompanying spec sheet and photos to see the Super Mod combination. With the camshaft and intake combination we are planning we still believe this engine can exceed 1000 HP.About 1.8 to 1.85 HP per cubic inch seems reasonable without resorting to an expensive dual carb tunnel ram setup, fully ported heads and the resulting need for higher engine speeds. The intent was to make good power and still maintain durability for extended high rpm runs.
