Bronco History

History of the Ford 351M/400

By Paul (Revised 11/04/00)

The Ford 351M and 400 cubic inch V8 engines are members of the Cleveland, or 335 series family of Ford engines. The 400M was first introduced in the 1971 Full-size model cars and station wagons. It was developed as an economical, reduced emissions replacement for the larger, gas-guzzling 429/460 and the ageing 360/390/428 V8 engines. The 351M was developed in 1975 to replace the 351C for use in large passenger cars. The 351M/400 engines were used in light-duty trucks starting in the 1977 model year.


Ford Engineers developed the 400 engine in response to the new Government pollutions requirements that were to start in the 1971 model year. Ford needed a tough, “workhorse” that was small enough to meet the new Government regulations and yet rugged enough to push around a 5,000 Lb Country Squire station wagon loaded down with another 1,000 pounds of passengers and luggage for 100,000 or more miles! The FE series (360/390/428) engines were terribly outdated (13 years old by 1971), and would have never been able to meet the new pollution and gas mileage restrictions required for the 1971 automobiles. The smaller 302 and 351 Windsor engines could have done the job, however, these engines were designed for higher RPM duty in small to mid-size passenger cars. Ford needed a whole new engine to do the job.


So, Ford chose to develop a new engine based on the new, super powerhouse 351 Cleveland. Just barely a little over a year old in 1971, the 351C had already gained the reputation as one of the best Ford engines ever built. The 351C was able to produce very good low-end torque and yet it could pump out earth shattering horsepower all the way to 6,500 RPM. The 351C was light, powerful, extremely rugged, and got better gas mileage than most other engines 2/3 it’s size. This was just what the doctor ordered!


The engineers at Ford took the basic 351C block and modified it to power a whole new generation of environmentally-friendly cars and trucks. To start, Ford changed the transmission bell-housing pattern to match that of the larger 429/460 engines. This would allow Ford to continue putting the larger, heavy-duty 460 C6 transmissions with the new 400 engines. Ford also enlarged the main journal diameter from 2.75 inches to 3.0 inches allowing for a greater bearing wear area. The crankshaft stroke was also increased from 3.5 inches to 4.0 inches for a 50 cubic inch increase in engine displacement and greater low-end torque. Finally, the deck height was increased 1.09 inches in order to accommodate the 400s larger stroke. Consequently, the intake manifold had to be widened approximately one inch to accommodate the new deck height. The rest of the engine remained virtually the same. In fact all of the 351C valve train components (except for the pushrods) interchange with 351M/ 400 engines. The 351M/400 cylinder heads will also interchange with the 351C 2brl heads, although the 351M/400 heads have 78.4cc combustions chamber where as the 351C 2V heads had a 76.2cc combustions chamber.  


The year 1975 brought even tougher pollution restrictions from the Government.   


All passenger cars and light-duty trucks under 5,500 GVWR were now required to burn unleaded gasoline, to be equipped with EGR valves and catalytic converters, and to meet stricter gas mileage numbers. These new rounds of restrictions along with the discontinuation of the 351C in 1974 lead to the birth of the 351M in full-size Ford passenger cars. Ford decided to discontinue the 390 V8 in the F-100 in 1975 and to discontinue both the 360 and 390 in all light-duty trucks by 1976. Beginning in 1977 Ford decided to offer the newer 351M/400 engines in its place. Again, Ford could have used the smaller 302/351 Windsor engine since it was being offered in the F-100, however, it was decided that since all F-150, F-250, and F-350 trucks were equipped with the heavy duty 390 in the 2wd trucks and the 360 in the 4x4 trucks that the torque laden 351M/400 would make an excellent replacement. The “M”, by the way, does not stand for anything. Ford only used the “M” designation to distinguish it from the 351 W (Windsor) and the now discontinued 351C (Cleveland). The “M” designation has now become know to mean “modified” or “Michigan”, even though the 351M was produced at both the Cleveland foundry and Michigan casting center.


To develop the 351M, Ford simply shortened the “throw” of the 400’s crankshaft to the original 3.5 inches used in the 351C. The larger 3.0 inch journal diameter of the 400 was retained in the 351M. To accommodate the shorter stroke, the compression height of the 400’s pistons had to be enlarged to raise the compression ratio up to 8.0:1. So, other than the crankshaft and pistons, the 351M is exactly the same as the 400. Even the connecting rods interchange.


The year 1977 brought another set of changes to the 351M/400 engines. A new bread of trucks were about to hit the market: The new full-size Bronco. Ford decided to continue to use the 351M as the standard engine in the  F-150, 250, and 350 4x4 trucks and to use it as the standard engine in the new Bronco. Ford also decided to use the 400 as an option in both the F-Series 4x4s and Bronco as well. In fact, if you own a 1977 ½ to 1979 Bronco, then you have either a 351M or a 400, as no other engines were available in these trucks! Both the 351M and the 400 received a larger ½ inch wide 5 link timing chain and sprocket. Along with some other minor changes, this led to the 351/400 “truck” engine.


1979 was the last year the 351M/400 engines were produced in large numbers. With the continuing effects of the OPEC oil embargo and the ever-increasing pollution and gas mileage restrictions coming out of Washington, Ford decided to to use the I-6, 302, and 351W engines in the new line of light-duty trucks Ford was developing for the 1980 model year. This meant that end of the 351M/400 engine was finally carved in stone because Ford decided to phase out the production of 351M/400. Oddly enough, Ford continued to install the 351M in some early 80s model Broncos and both the 351M/400 in some of the F-250 and F-350 trucks until the last one was used in 1982.


Although the 335 engine series was only 11 years old when it was discontinued, it was scraped in favor of the lighter, cheaper-to-produce 302/351 Windsor engines. So ended the era of the great Cleveland based engines from Ford.