David Lee
Active Member
I ran across this and more on the website: LA - Chrysler small block V8 engines ,and thought it interesting for the performance engine enthusiasts here. I haven't explored the site completely, but did notice a lack of information on building a 273 engine, although I'm sure that the info supplied on the site would apply to the 273/ 273 Commando engine.
I am curious as to the option of having hardened valve seats machined into the 273 Commando would be cost effective and if so what size valves could be fit into the heads. This is a query for future reference for me.
Does anyone have advice for me regarding using a lead substitute to prolong the life of the head? As I understand the pre unleaded engines didn't have hardened valve seats and unleaded fuel in the leaded gas engines will cause premature valve seat wear. The article follows:
The first LA was the 273, with a two barrel carb, producing 180 gross hp. In 1965, a four-barrel carb and high performance cam could push that up to 235 hp; and, in 1966, a limited edition 273 with a 700 cfm carb and .500" lift cam put out 275 hp. ( From poster: Not bad pushing 300 h.p. In a stock motor! This must be the " Commando" engine?)
Engineer Pete Hagenbuch said:
The LA (for Light A) engine was developed with a wedge chamber, first as a 273 cid and then as a 318. Remember, this was the time the car lines expanded to three bodies, A, B and C. The 273 was limited to the A and B bodies with the 318 or B Engine in the C Body, which was new to Plymouth at the time.
Later came the 340 and then the 360, both with wedge chambers. And now, the one time state-of-the-art Mound Road Engine Plant is empty. And the brand that used the majority of its production has disappeared too, to join ranks with names like Packard, Hudson, Desoto, Studebaker, Nash and Willys. Next to join this group will be Oldsmobile, another of the pioneer nameplates to be tossed aside. It seems that a cherished name with a long history is not considered of value in this day and age.
1967 273 V8 273 V8
Carburetor 2 barrel 4 barrel
Manual transmissions 3 or 4 speeds 4 speeds
Gross horsepower (Valiant) 180 @ 4,200 235 @ 5,200
Torque (Valiant) 260 @ 1,600 260 @ 4,000
Bore and Stroke 3.63 x 3.31 3.63 x 3.31
Compression Ratio :1 8.8 10.5
Standard Tire/Wheel 7 x 13 (wheel 4.5) (Valiant)
The intake manifold was special hybrid single/dual plane design that incorporated two plenums, one for each side of the engine. They were joined by a specially sized rectangular passage that solved lean/rich problems that occurred with the initial, purely dual plenum design that dedicated one barrel of the BBD to each bank. This was done to reduce the overall height of the engine and allow installation in the (originally /6 designed) Valiant engine compartment. (Thanks, Jim Deane.)
Since the bolt angle on the intake changed in 1966, the 1964-65 heads and intake are unique and cannot be interchanged with other LA engines or with the later 273.
In 1968, the 273 got a hydraulic cam; the forged steel crank was replaced with a standard nodular cast iron crankshaft to save money. 1969 was the final year for the 273, its thunder having been stolen by the LA 318, which was introduced in 1967; but it still got a new manifold heat control valve (also used on the 318) with a disc-shaped counterweight.
The LA 318 was never used as a performance engine by Chrysler, unlike the 318 A-engine; the 273 four-barrel matched it in peak horsepower, and the more performance-oriented 340 was quickly released in 1968.
I am curious as to the option of having hardened valve seats machined into the 273 Commando would be cost effective and if so what size valves could be fit into the heads. This is a query for future reference for me.
Does anyone have advice for me regarding using a lead substitute to prolong the life of the head? As I understand the pre unleaded engines didn't have hardened valve seats and unleaded fuel in the leaded gas engines will cause premature valve seat wear. The article follows:
The first LA was the 273, with a two barrel carb, producing 180 gross hp. In 1965, a four-barrel carb and high performance cam could push that up to 235 hp; and, in 1966, a limited edition 273 with a 700 cfm carb and .500" lift cam put out 275 hp. ( From poster: Not bad pushing 300 h.p. In a stock motor! This must be the " Commando" engine?)
Engineer Pete Hagenbuch said:
The LA (for Light A) engine was developed with a wedge chamber, first as a 273 cid and then as a 318. Remember, this was the time the car lines expanded to three bodies, A, B and C. The 273 was limited to the A and B bodies with the 318 or B Engine in the C Body, which was new to Plymouth at the time.
Later came the 340 and then the 360, both with wedge chambers. And now, the one time state-of-the-art Mound Road Engine Plant is empty. And the brand that used the majority of its production has disappeared too, to join ranks with names like Packard, Hudson, Desoto, Studebaker, Nash and Willys. Next to join this group will be Oldsmobile, another of the pioneer nameplates to be tossed aside. It seems that a cherished name with a long history is not considered of value in this day and age.
1967 273 V8 273 V8
Carburetor 2 barrel 4 barrel
Manual transmissions 3 or 4 speeds 4 speeds
Gross horsepower (Valiant) 180 @ 4,200 235 @ 5,200
Torque (Valiant) 260 @ 1,600 260 @ 4,000
Bore and Stroke 3.63 x 3.31 3.63 x 3.31
Compression Ratio :1 8.8 10.5
Standard Tire/Wheel 7 x 13 (wheel 4.5) (Valiant)
The intake manifold was special hybrid single/dual plane design that incorporated two plenums, one for each side of the engine. They were joined by a specially sized rectangular passage that solved lean/rich problems that occurred with the initial, purely dual plenum design that dedicated one barrel of the BBD to each bank. This was done to reduce the overall height of the engine and allow installation in the (originally /6 designed) Valiant engine compartment. (Thanks, Jim Deane.)
Since the bolt angle on the intake changed in 1966, the 1964-65 heads and intake are unique and cannot be interchanged with other LA engines or with the later 273.
In 1968, the 273 got a hydraulic cam; the forged steel crank was replaced with a standard nodular cast iron crankshaft to save money. 1969 was the final year for the 273, its thunder having been stolen by the LA 318, which was introduced in 1967; but it still got a new manifold heat control valve (also used on the 318) with a disc-shaped counterweight.
The LA 318 was never used as a performance engine by Chrysler, unlike the 318 A-engine; the 273 four-barrel matched it in peak horsepower, and the more performance-oriented 340 was quickly released in 1968.
