Mustang Monthly Homepage Mustang Monthly
Get Adobe Flash player

How To Build A Better Boss 302 Engine

JGM Performance Engineering Shows How To Get More Horsepower From Ford's Trans-Am Powerplant
From the June, 2007 issue of Mustang Monthly
By Jim Smart
Photography by Jim Smart
Boss 302 Build Boss 302
Boss 302 Build Oil Control
Our Boss 302's cylinder walls... 
   
  read full caption
Boss 302 Build Oil Control
Our Boss 302's cylinder walls needed finish-honing to accommodate standard-bore Speed Pro forged pistons. Jim Grubbs gave our bore a crosshatch pattern for good oil control and proper ring seating.
Boss 302 Build Hone Bores
Always hone lifter bores for... 
   
  read full caption
Boss 302 Build Hone Bores
Always hone lifter bores for the same reason you hone cylinder walls: oil control and smooth operation. At home, you can use a brake cylinder hone on lifter bores.
Boss 302 Build Chamfered
Bores are chamfered to enable... 
   
  read full caption
Boss 302 Build Chamfered
Bores are chamfered to enable smooth piston/ring installation. Our block has been line-honed and decked for perfect fit top and bottom.
Boss 302 Build Torque Plate
Does your machine shop use... 
   
  read full caption
Boss 302 Build Torque Plate
Does your machine shop use a torque plate for cylinder honing? If not, find another machine shop. Torque plates are bolted on top of the block to simulate cylinder-head installation to get cylinder bores true to what they'll be with the heads installed. Honing the bores without a torque plate is trouble because when you install the heads, cylinder bores will distort, creating ring-seating issues and abnormal wear.
Boss 302 Build Crank
Ryan sets the Scat crank with... 
   
  read full caption
Boss 302 Build Crank
Ryan sets the Scat crank with a 3-inch stroke-that's right, 302 ci. We could've stroked this Boss 302, but we wanted to retain its high-revving qualities. Ryan set the bearings and splashed on engine-assembly lube. Once the crank is set, Eric snugs the main caps. He'll torque them in thirds: No. 3 cap, No. 1 cap, No. 5 cap, then Nos. 2 and 4 caps. With each torquing, he'll check the crank for freedom of movement. He should be able to turn it with his fingers right up to final torque. If it becomes too tight, clearances are in error.
Boss 302 Build Code
We have an early Boss 302... 
   
  read full caption
Boss 302 Build Code
We have an early Boss 302 block-technically, a 302 Tunnel Port block cast December 5, 1968 and used for a production '69 Boss 302 Mustang. Based on the VIN stamped on the back of the block, 192845, it was originally produced for 9F02G192845. According to the Boss 302 Registry, the car survives in Medford, Oregon.
Boss 302 Build Block
Boss 302 blocks have screw-in... 
   
  read full caption
Boss 302 Build Block
Boss 302 blocks have screw-in core plugs, also known as freeze plugs. According to Jim, never try to remove them. Screw-in plugs coupled with four-bolt main caps are what separate a Boss 302 block from other small-block Fords.
Boss 302 Build One Piece
We're doing something sacrilegious... 
   
  read full caption
Boss 302 Build One Piece
We're doing something sacrilegious by converting an early Boss 302 block to a one-piece rear main seal. Ford used a two-piece rear main seal in all of its engines until 1982. Installed properly, it works well but eventually leaks. Ford and the rest of Detroit went to one-piece versions to eliminate that problem. Converting your small-block to a one-piece seal is easy when it's performed during a rebuild.
Boss 302 Build Seal
Going to a one-piece rear... 
   
  read full caption
Boss 302 Build Seal
Going to a one-piece rear main seal involves cutting the block with the same equipment used for boring cylinders. Jim cuts the lip out of the main cap used to retain a two-piece seal. Once the lip is cut, the No. 5 main cap will accommodate a one-piece seal. The lip must be machined off the crank as well. This is an easy task for any machine shop.

1  | 2  | 3  | 4  | Next

Ford Mustang Research
Ford Mustang Review in-depth reviews on the new Ford Mustang, featuring test drives, comparisons, options, features and more. The Mustang gets 19 mpg in the city and 30 on the highway, and has a trade in value of $20,585.00 which should come in handy when you go to shop for your next car. Other similar vehicles are the Ford Shelby GT 500 and the Ford Fusion.
Boss 302 Build Dial Indicator Boss 302 Build Tolerances
Boss 302 Build Oil Galley Plugs Boss 302 Build Deck
1970 Boss 302 Mustang
We’ve all heard the saying made popular by comedian Flip Wilson during the 1960s: "The devil made me do it." The following is a good example of where you might hear it used.... more
1970 Ford Mustang Boss 302 - Boss Lady
In a man's world, Michelle Holstein broke the rules to build a leading-edge Boss 302... more
1970 Trans Am Boss 302 - Boss Hauler
Les Werling Built A Bud Moore-Inspired Hauler To Transport His Replica Of A Trans-Am Boss 302... more
'69 Mustang Boss 302 - Destiny
A Man And Machine Relationship... more
1970 Ford Mustang BOSS 302
The Perkins Collection... more
1969 Ford Mustang Boss 302
13,800-Mile '69 Boss 302 - The Perkins Collection... more
1969-1970 Boss 302s - How-To Choose The Right Blackout Paint
A Bob Perkins Guide To '69-'70 Boss/Mach 1 Exterior Body Black-Out Detailing... more
1970 Boss 302 Trans-Am Racer - The Farewell Boss
The Last Bud Moore Boss 302 Mustang Helps Keep The Trans-Am's Glory Days Brightly Lit... more
1969 Ford Mustang Boss 302 - Future Mod Boss
Phin Stubbs Takes Restomod To A New Level With His '69 Boss 302... more
'70 Boss 302 Mustang - Resto Roundup
Concours Expert Bob Perkins Handles Your Restoration Questions... more