One of the oldest lines in the automotive performance field is – “there is no substitute for cubic inches.” In the early muscle car era, more cubic inches typically came as the result of an engine swap – a 440 for a 383 or a 360 for a 318. Today this approach can be expensive because you have to have two complete engines. In the 1990s, various crate engines became popular as the second engine to swap into your project vehicle. Crate engines seem to be constantly changing, but if you can find the one that fits your requirements, they were a good alternative. While crate engines were becoming popular, the aftermarket started making special long-stroke cranks called “strokers.” These new cranks were readily available and priced competitively, which meant you could get more cubic inches with a new crank. This approach opened the door to bigger, less expensive engines that required more assembly time. The main reason for the desire for more cubic inches is that the typical street performance engine makes around 1 horsepower-per-cubic-inch, which means that 20 cubic-inches more will make about 20 horsepower. 50 added inches will make 50 more horsepower. That’s a rough estimate. Additionally, added cubic inches gained by longer stroke crankshafts will also make more torque, which is very desirable in street or in dual purpose vehicles.
HEMI® Gen III Engines
Currently the new HEMI® Gen III engine available in cars and trucks is the most popular production performance engine. The two most common production versions are the 5.7L and the 6.1L. There is a bigger version of the 6.1L called the 392 (or the 6.4L sometimes) which uses a 3.795″ stroke crank – P5153578. Swapping this long stroke crank into the standard 6.1 engine (372 inches) gives you an extra 20 cubic inches. Typically these longer stroke cranks use the same rods that are in the engine, but they require a shorter piston. An engine rebuild usually requires an oversized piston (.020″ overbore is common) so you combine these two features into your new pistons – one order and two problems resolved
There have been many production 6 cylinder engines built over the last 30 years. The typical truck V6s are the truck V8s minus two cylinders. When that’s the case, upgrading to the family V8 is probably the easiest solution. The V6s used in passenger cars typically do not have a V8 relative. To increase one of these engines in cubic inches you would need to have a custom crank made – these custom cranks are generally called billet cranks. In this situation, you might want to take the old engine swap approach.
The 6-cylinder exception is the in-line 6, 4.0L engine. It is common for the Jeep engine builders to use an older 258 6-crank, shorten the nose, re-machine the threads and install it in the 4.0L engine to make a 4.6L/4.7L engine which has the torque of a small V8. The aftermarket now makes this long-stroke crank brand new – you don’t have to find an old crank, in good shape and have it re-machined. The stock 4.0L rods are used and new pistons – available at Icon.
The nickname “big blocks” is used for the 440 and 426 Gen II HEMI engines. The short blocks are closely related and can use the same basic crankshaft. The stock stroke was 3.75″ and a 4.15″ stroke crank (P5007250) was introduced for these engines in the mid-1990s. It is forged and uses the 8-bolt crank flange from the HEMI engine version (440s used 6). It is a full-radius crank for added strength.
The 440 version of the big block uses wedge cylinder heads and many common pieces with the 426 HEMI engine discussed above. There is a big-bore version of the block and the same crank can be used. Typically, these wedge engines are built with the 440 rods, which is a 6.76″ rod, so the numbers are slightly different.
The 383 (4.25″ bore) and its 400 big-bore brother (4.34″ bore) are similar engines to the big blocks discussed above except that the basic block’s deck height is about 9.98″ rather than the taller 10.72 used on 440s. This short-deck block makes these engines unique and the stock 383/400 stroke of 3.38″ makes them a candidate for more inches. For many years the popular solution was to use a stock 440 crank (3.75- stroke) with cut-down mains to the 383/400 size for a 50 cubic inch gain. This package also uses the 440 rods and shorter pistons.
Note: almost all of the engines discussed above (except the 426 Gen II and newer than 1972/3) are based on thinwall casting techniques which limit over-bores to .020″ or .030″ so the longer stroke approach is much easier and more reliable than over-boring past minimum requirements.
In the Mopar® small block engine families there are two basic groups – the A-engine (1964 thru 1992) and the Magnum engines (1992 thru 2003). The 318 and 340 A-engines and the 5.2L Magnum engines both use the same 3.31″ stroke and the popular stroker crank is the 4.00″ stroke P5007252 which is forged and has the small main bearing size used in the 318/340 engines. A ‘sleeper’ in this category is the 3.58″ stroke cast crank P5007257 with the 318 mains. In a .030″ over-bore 318 block, this makes a 349-inch engine (a poor-man’s 340 with up-graded heads). There is also a 4.00″ stroke cast crank P5007256 which has 318/340 mains. The other group of small blocks is the 360 A-engine and the 5.9L Magnum which use large main bearings. The 4.00″ stroke for the large main engines is P5007254 – forged. There is also a cast crank 4.00″ stroke version – P5007258.