Some motor enthusiasts say that the best way to create horsepower with a four-cylinder Jeep is to sell it and buy a V6, but Jeep's 2.5L four-cylinder is not beyond hope. It is actually a tough engine by today's standards, so an extra 30-to-80 turbocharged horsepower is at least as attainable for this powerplant as for any other.
If you are looking to buy a kit, you should know that 505 Performance makes the only one on the market and it costs $3,000 in 2010. The kit does come complete with a turbo, computer, plumbing and (almost) every piece of hardware you will need. Such an expenditure is really only justified if you need to retain the stock four-cylinder for rock crawling or competition class requirements; otherwise, you would be better off by simply trading up to a V6 Wrangler. A little smart shopping and some junkyard engineering, however, can net you a similar system for less than a quarter of what the kit would cost.
For a build-it-yourself kit, you will need a turbocharger (Ford 2.3L or Chrysler 2.2L, $250 rebuilt), the exhaust and intake plumbing, a waste gate ($150 online), turbo oil lines, an intercooler (optional, $50 from a junkyard Ford TurboCoupe or around $150 for a new unit), homemade blow-off valve ($20), homemade manual boost controller ($4 to $10) and a pressure activated fuel enrichment system (cost varies).
All told, a home-built turbo/intercooler package should run you less than $900. It should produce at least 175 to 200 horsepower on an otherwise stock engine. It will be competitive in price and power to a V6 trade-up, and lighter to boot.
The only part of 505's system that you cannot piece together for yourself is the fuel enrichment computer, but digital enrichment is only one means to that end. Hot rodders have been building pressure activated enrichment and detonation-suppression systems for the better part of a century.
You have three basic choices when it comes to enrichment--gas, propane or water/alcohol. Pressurized propane is the easiest, as it requires no pumping mechanism; you only have pressure switches, solenoids and spray-bars. Water/alcohol is the safest for you and the engine, but it is more complicated to build and more difficult to control. Gas injection can be the cheapest, but it must be engineered carefully so as not to run too rich or too lean. Proper gasoline control requires either a complicated multi-stage solenoid set-up or a digital controller, which puts you right back at square one, cost-wise.
A home-built kit will go in much the same way as any other. The turbo mounts on the up-pipe, which is connected to the exhaust manifold. The turbo's inlet is connected to the air cleaner or air box; its compressor outlet is connected to the engine's throttle body (with an intercooler in line, if desired).
Fuel enrichment installation depends on the type you are using, but throttle body-mounted nitrous spray bars are a good choice for gasoline delivery. Propane is injectable into the throttle body or turbo inlet, but water should always be injected directly into the throttle body or intake to prevent turbo impeller damage.
