Right off the bat, I want to tell you that this is one of the hardest sections I have had to organize. There is so much information and it spans so many years, that much of the information changes from year to year, while other information remains static. So the information at the top will be easy to understand, but the specifications at the bottom for engine rebuilders may be a little complex. I also may have to reorganize as I add the 5.0L into the equation.
The 302 cubic inch engine was introduced in 1968 to the Mustang. Although it is a derivative of the 289 mustang, some parts are not interchangeable. In fact the block of a 289 cannot be used without some machining. Since the 302 crankshaft is larger, it requires a notched out section in the engine sidewall to allow the connecting rod end bolts to pass. If you are unsure of the parts you are using to build an engine, check tolerances carefully.
Both the engines are 90 degree V8’s. Both are built well and will run forever if you treat them right. I have put well over 500,000 miles on a 302 with minor problems and good maintenance. I have also owned a 1965, 1966 and 1967, 289 CID engine. They all pull strong and have lasted. Good maintenance as with everything is the key.
All 302 engines with the exception of the Tunnel Port and the Boss have 2 bolt mains. The Tunnel port has 4 bolt mains and the 302 Boss has 4 bolt mains and is cross bolted as well.
All 302’s drank regular gas except the Tunnel port and Boss engines, they gulped premium gas. Of all the 302 engines, only the Boss had solid adjustable lifters all others had hydraulic lifters.
On the distributor side of the equation, the Boss utilized a dual point, vacuum advance distributor with RPM limits of 5,950-6,050 in 1969 and 6,050-6,150 in 1970. The street 302’s and the Tunnel Port used a single point vacuum advance distributor.
The 302’s life cycle lasted from 1968 to 1973. In 1974 do to the normally invasive Federal government’s BS and a contrived oil shortage, Ford no longer offered the V8 powerhouse in the Mustang. However, for reasons unknown to consumers an anemic 302 was offered again in 1975 through 1978. In 1979, it was stopped and came back in 1982 with the moniker of 5.0L.
I will attempt to provide information on the birth, evolution, disappearance, resurrection and final death of the 302 (5.0L) in 1995. Very few other engines have had a life span of about 30 years. This is a testament of the quality and performance of this engine. This also explains why there is a great abundance of after market parts available at very reasonable prices.
The 302 had a late Ford blue engine block color and late Ford blue valve covers. The 5.0L engine was gray on gray. Some later 5.0L engines were simple the cast iron block color on the block and gray valve covers.
Tunnel Port 302
After winning the Manufacturers Trophy in 1966 & 1967, Ford had some stronger competition for 1968. Chevrolet was about to get involved in a very big way. Vince Piggins at Chevrolet saw the great potential for sales of Camaros by racing in the Trans Am series. He committed to SCCA that Chevrolet would support the series.
The 302 Camaros had a clear horse power advantage over the Mustangs. The ports and valves in the 289 heads were too small to produce the horsepower needed. The best head available was the high performance heads with small valves and ports. The new Ford 302 would be ideal for Trans-Am racing since it was under the 305 cid limit of class limit, but the hi-po heads would be too restrictive on the longer stroke of the 302 block. Ford started a crash development program to fix the problem at Ford Engine and Development during 1967. This effort would lead to development of the Boss 302 in 1969. It was also during this development time that the famous Ford “tunnel port head” was developed. Ford worked around the clock to increase the flow of the heads. Ford engineers developed a new head with straight intake ports and pushrod tubes running through the port instead of the conventional bend around the pushrods. The intake valves were a huge 2.12″ compared to 1.77″ for the 289. Exhaust valves were 1.54″ versus 1.44″. Each port feed an individual cylinder. These heads became known as “tunnel ports.” On paper this combination of the head design with the new 4 bolt main 302, looked unbeatable. The overhead valve pushrod engines competed for space with the intake ports. Conventional design places the pushrods along side a rectangular shaped intake port. These ports also steer around the pushrods. The Ford tunnel-port design runs the pushrod through the center of a round intake port, within a thin wall tube. The ports flow better due to their round shape and straight path. This design was first used on the 427, and then in 1968 on a special 302.
These round intake ports were 3.8 sq. in. in area at the intake manifold face. The Tunnel Port 302 cylinder heads feature 2.12″ intake and 1.54″ exhaust valves. By comparison, the 289 High Performance engine used 1.78″ intake and 1.44″ exhaust. These large valves completely filled the wedge shaped combustion chamber. The exhaust ports were larger than normal 289 & 302 heads. Two 540 cfm Holley’s sat on a high-rise aluminum manifold. Two Autolite 4300 carburetors were used on the street version.
The race version featured domed pistons, yielding a compression ratio of 12.5:1, a solid lifter camshaft and forged steel crankshaft. The nodular cast iron rocker arms were shaft mounted, similar to those used on the Y-block V-8. Lubrication for these shaft mounted rockers required a special block with revised oil passages. Also used was a special road racing style 8-quart oil pan. Some used an early transistorized ignition.
The street version used flat-top piston, for 10.5:1 compression, and a hydraulic camshaft. The engine was complete with thermactor emissions control hardware, 289 Hi-Po style exhaust manifolds, and a thermostatic clutch radiator fan. SCCA rules required 1,000 engines in production for 1968 Trans Am homologation. As used in Trans Am competition the engines produced approximately 420 bhp with an 8,500 rpm redline
You have to finish races to win them, though. The tunnel port engines just didn’t have lasting power. Engine failure after engine failure keep the Mustangs from finishing the races. Penske’s Camaros dominated the 1968 Trans-Am racing.
1968 Tunnel Port 302 Cylinder Head Casting number C8FE-6090-A
The Boss 302
After a very disappointing 1968 racing season Ford designed a new engine specifically for F.I.A. Trans Am competition in 1969, the Boss 302. The engine was introduced on April 17, 1969. About 8,600 Boss 302 engines were built.
The Boss 302 block was essentially the next generation of 289 High Performance hardware, but features a forged steel crankshaft, 4-bolt main caps, and screw-in freeze plugs. These modifications were developed as part of the 302 Tunnel Port design. Street versions used connecting rods similar to the 289 Hi-Po while the Trans Am version used heavier 7/16″ bolts.
The real magic of the Boss engines came from the canted-valve Cleveland cylinder heads. While the Boss 302 was normally considered a 302 with 351 Cleveland heads, these canted-valve heads were used first on the Boss before the rest of the Cleveland was developed. As fitted to the Boss, the heads feature steel spring seats, screw-in rocker studs, pushrod guide plates, and adjustable rocker arms. The Boss 302 and 351C-4V head casting were the same except for a minor difference in water passages. Camshafts were quite similar to the 289 Hi-Po. Due to the larger Cleveland-style heads, the Boss 302 weighs somewhat more than the normal 302, tipping the scales at 500 lbs.
The street version was conservatively rated at 290 HP @ 5800 RPM.During the ’69 Trans Am season the racing engines were putting out 470 bhp at a 9,000 rpm redline. Designed for the road racing environment, the engines featured a scraper style windage tray. This tray attached to four special main cap bolts with small threaded holes in their heads.