2000 Jeep Wrangler 4.0L Inline 6 - Inside The Inline

A replacement exhaust was a given. On the intake side, we had the fantastic new-style intake working for us. This is an equal-length runner setup with a large plenum that appeared on the '99 WJ and on everything else in 2000. We added a larger (62mm vs. 58mm stock) Rock-It throttle body and AEM spacer (included with the AEM Brute Force cold-air kit) but we were not sure if we needed them. The stock throttle-body flow was around 450 cfm of air, according to our sources. According to the airflow monitors, our engine was using only 383 cfm at its peak rpm.

Is a stroker emissions-legal? Maybe. Is it a replacement engine or a modified engine? In those places with stringent standards, you may have a hard sell on the replacement engine part. If all the changes are internal and not visible and the engine passes the tailpipe test (many strokers do), who knows? Our sister publication, Jp magazine, built a stroker for the "Insane Inline" series back in 2005, and it passed the California test with no more than 24pph injectors and a modified timing sensor.

A larger engine, or a larger engine with a higher output, will generate more heat than stock. We addressed that two ways. First came the FlowKooler water pump idea, which has some serious flow improvements over the stock pump. It bolted up to our first block but not to the second one. Unfortunately FlowKooler doesn't offer one for the metric 4.0L block. That left us with a Northern High Performance aluminum radiator from Quadratec and a RobertShaw high-flow 180 degree thermostat.

Dyno day was exciting. The engine had been well broken-in during the tuning process. We found out early that our engine was pretty much done at 4,500 rpm. It would rev higher, but the power curve began leveling off and torque began dropping. This was our poor cam choice talking again. On the other hand, that's still well above the rpm range for 99 percent of Jeepers. Plus, it started off at 2,000 rpm with 5 lb-ft more torque than the stock 4.0L and climbed like a rocket. At 2,500, it's over 265 lb-ft where the 4.0L is only at 230. The stroker was within about 10 percent of peak torque from 2,000 to 4,500 rpm.

Even if you take out some of the higher-end additions used on this project, you can see the stroker idea has a lot of merit. It could be a very cost-effective modification if performed at rebuild time. Many of you so inclined might already have the other goodies installed on your 4.0L to enhance it, such as intake and exhaust mods. The important parts to remember are the compression and camshaft-related issues. The rest is a serious breeze, considering the results, and not expensive.

Peak Power: 225.4 hp at 4,497 rpm. Peak Torque: 280.2 lb-ft at 4,002 rpm. The UNO stroker's power and torque curves compared to a 4.0L curve. The 4.0L power curve is actually enhanced somewhat. A stock used engine was fitted with a programmable ECU and "tweaked" for optimal results-for an estimated 5-percent gain over stock. Also, this was not an SAE-rated test, with all ancillary devices, including the exhaust system, hooked up and operating. Both engines were tested to the same standard-the dyno exhaust system-no air filter and driving only the water pump. Installed power would be slightly less.

Stock Head Flow at Peak Valve Lift
Crane 753905-Intake: 208 cfm @ .456 lift
Exhaust: 143 cfm @ .484 lift

Modified Head at Peak Valve Lift
Crane 753905-Intake: 217 cfm @ .456 lift
Exhaust: 156 cfm @ .484 lift