General Principles to Consider:
There are two popular misconceptions about engine size that should be brought to light. The first mistake many make is in thinking that a small displacement engine will invariably give better gas mileage. This is only true if the small engine is in a lightweight, properly geared, and semi-aerodynamic vehicle. A small engine in a heavy vehicle with "tall" gears will perform poorly and give bad gas mileage. Any engine, when worked to the point where vacuum drops low enough to operate the power jets in the carburetor, or to lug, will give poor gas mileage. If too small an engine is used for the work to be done, it will operate at low vacuum for longer periods and use more gas than a larger engine that would not be working as hard. The added benefit of the larger engine is its reserve power.
The second most common error swappers make is to convert to an engine that is too large, from both size and displacement, for the vehicle. While a Small Block V8 is a great engine, there are sometimes better choices for smaller Jeeps, such as Buick and Chevrolet V6's, Ford 2000cc and 2300cc's, GM "Iron Duke" Fours and the like. Big Block V8's and heavy old I6's should hardly ever be considered in short wheelbase Jeeps! When planning a conversion into a CJ2A up through the CJ5's, remember that you are dealing with a 2500lb. vehicle. This, by all standards, is light, and that is one reason why these vehicles prove to be the most agile in the world. Adding an overburdening block of iron to smaller Jeeps will give disappointing results in terms of handling, braking and of course, breaking – of several components directly and indirectly between the block and the vehicle. Besides, fit into the engine bay is usually so poor that the work soon looks as poorly as it was thought out in such situations.
The trick is to match engine size to the load, then only use the reserve power when needed. Engine torque output is essentially related to cubic inch displacement of any engine. The RPM that maximum torque is produced at is related to the length of the stroke of any engine. A 230 c.i.d. "under-square" engine will make about the same torque as a 230 c.i.d. "over-square" engine but will do so at lower RPM due to its longer stroke. (An under-square engine has a bore that's smaller than its stroke.) Many swappers and engine enthusiasts prefer the challenge of running an optimum V6 to the power levels of V8's, and then reaping the weight and fit benefits both on and off-road.
Computers, Wiring and Fuel Injection
Many of us speak nostalgically about the days when engine electrical and fuel systems were about the simplest parts of an engine swap. Engine and vehicle management computers are now a major part of modern automotive systems, and therefore, a significant concern when doing a conversion. Some run from these issues, and others embrace them. What must be said for modern powerplants is that they are efficient, cleaner and in many cases, more powerful. What's more, many state and county emissions laws require these modern systems in modern swaps. In a word, computer controlled engines are here to stay. The neat thing is that there are good resources available to facilitate this process. We're learning a bit about these issues, and we encourage you to contact us about them. We expect to be publishing more information on modern conversion issues.
