Pistons
In 1971, the 400 was equipped by the factory with flat top pistons that produced a 9.0:1 compression ratio, but I have not been able to find any manufacturer that reproduces this piston now. In fact, the only mass produced piston I have been able to find that is specifically designed to improve compression in the M-block engine is the TRW L2466F forged piston, and it is a 351M piston.
Other than using a healthier cam, increasing the compression ratio of an M-block engine is the most significant performance improvement you can make. Fortunately, the compression height (distance from wrist pin centerline to piston top) of 351C pistons is compatible with 400 pistons. Stock compression heights of the various 351C pistons range from 1.631" to 1.657". The compression height of the stock 400 piston is 1.650". (Remember, the 351M uses the same rod as the 400 with 0.50" less stroke, so its piston compression height is much taller than the 400 piston to make up for the different stroke with the same rod. The 351M piston compression height is 1.947".)
WARNING: Pistons are not interchangeable between the 400 and 351M. If you used 400 pistons in a 351M, the piston top would reach TDC at more than 0.3 inch below the deck surface and you would have a compression ratio of only about 5.5:1. If you use a 351M piston in a 400, it will smash into the head because it's top surface is about 0.3 inch above the deck surface.
The following table is sorted by engine application. In some cases, a single piston design can be used in more than one engine. Compression ratios are estimated by the piston manufacturers based on the average combustion chamber volume in the factory stock (unmodified) cylinder heads for each engine application. For example, the Keith Black KB148 piston is estimated to produce an 8.5:1 compression ratio when used with 351C 2V cylinder heads (average combustion chamber volume 76.2cc) and 9.8:1 compression ratio when used with early type ('70-'71) 351C 4V cylinder heads (average combustion chamber volume 62.8cc).
|
Engine Application
|
Material
|
Estimated CR
|
Brand & Part No.
|
|
351C 2V OEM-type
|
Cast
|
7.9:1
|
Sterling 425P
|
|
351C 2V
|
Forged
|
8.4:1
|
TRW L2416F
|
|
351C 2V
|
Hypereutectic
|
8.5:1
|
Keith Black KB148
|
|
351C 2V
|
Hypereutectic
|
8.8:1
|
Sterling H555P
|
|
351C 2V
|
Forged
|
8.9:1
|
TRW L2379F
|
|
351C 2V
|
Hypereutectic
|
9.5:1
|
Keith Black KB177
|
|
351C 2V 1/16-1/16-3/16
|
Hypereutectic
|
9.5:1
|
Keith Black KB108
|
|
351C 2V 1/16-1/16-1/8
|
Forged
|
10.2:1
|
TRW L2348F
|
|
351C 2V 1/16-1/16-1/8
|
Forged
|
11.4:1
|
TRW L2408F
|
|
351C 2V 1/16-1/16-3/16
|
Hypereutectic
|
10.6:1
|
Keith Black KB149
|
|
351C 4V 1970-72 (early heads)
|
Forged
|
10.2:1
|
TRW L2379F
|
|
351C 4V
|
Hypereutectic
|
9.8:1
|
Keith Black KB148
|
|
351C Boss 1971-72 with 66cc
|
Hypereutectic
|
12.1:1
|
Keith Black KB149
|
|
351C 4V 1973-74 (late heads)
|
Forged
|
9.4:1
|
TRW L2416F
|
|
351C 4V
|
Hypereutectic
|
10.1:1
|
Sterling H555P
|
|
351C 4V
|
Hypereutectic
|
11.1:1
|
Keith Black KB177
|
|
351C 4V 1/16-1/16-3/16
|
Hypereutectic
|
11.1:1
|
Keith Black KB108
|
|
351C 4V 1/16-1/16-1/8
|
Forged
|
12.0:1
|
TRW L2348F
|
|
351C 4V 1/16-1/16-3/16
|
Hypereutectic
|
12.7:1
|
Keith Black KB149
|
|
351M 1975-82 OEM-type
|
Cast
|
7.9:1
|
Sterling 451P
|
|
351M 1975-82
|
Forged
|
8.0:1
|
TRW L2436F
|
|
351M 1975-82
|
Forged
|
8.6:1
|
TRW L2466F
|
|
400 1971-82 OEM-type
|
Cast
|
7.9:1
|
Sterling 427P
|
|
400 1971-82
|
Forged
|
8.2:1
|
TRW L2414F
|
|
400 1971-82
|
|
9.5:1
|
Ohio Piston
|
Crankshaft Bearings
The 351C crankshaft has smaller main bearing journals than the M-block crankshaft. Therefore, crankshaft main bearings are unique to the M-block engine.
The following table lists crankshaft main bearings by engine application (as identified by the bearing manufacturer).
|
Engine Application
|
Main Bearing Type
|
Brand & Part No.
|
|
351M 1975-76
|
stock
|
Clevite MS981P
|
|
351M 1975-76
|
stock
|
Federal Mogul 5107M
|
|
351M 1975-76
|
stock full groove
|
TRW MS981P.std
|
|
351M 1975-76
|
competition full groove
|
Federal Mogul 123M
|
|
351M 1977-82
|
stock
|
Clevite MS1432P
|
|
351M 1977-82
|
stock
|
Federal Mogul 5078M
|
|
351M 1977-82
|
stock half groove
|
TRW MS1432P.std
|
|
351M 1977-82
|
competition half groove
|
Federal Mogul 122M
|
|
351M 1977-82
|
competition 3/4 groove
|
Federal Mogul 130M
|
|
400 1971-76
|
stock
|
Clevite MS981P
|
|
400 1971-76
|
stock
|
Federal Mogul 5107M
|
|
400 1971-76
|
stock full groove
|
TRW MS981P.std
|
|
400 1971-76
|
competition full groove
|
Federal Mogul 123M
|
|
400 1977-82
|
stock
|
Clevite MS1432P
|
|
400 1977-82
|
stock
|
Federal Mogul 5078M
|
|
400 1977-82
|
stock half groove
|
TRW MS1432P.std
|
|
400 1977-82
|
competition half groove
|
Federal Mogul 122M
|
|
400 1977-82
|
competition 3/4 groove
|
Federal Mogul 130M
|
Rod Bearings
All 335 series engine crankshafts use 2.311" rod bearing journals. The following table lists crankshaft rod bearings by bearing type (as identified by the bearing manufacturer).
