The 4.0L bottom end is very strong especially with a good tune! I ran my truck to 220K boosted miles. Never once did it ping or detonate and we put down a healthy 450 hp and 448 lb.ft torque in its early years. The truck routinely ran 8.20's in the 1/8th (12.6-.70's for you 1/4 milers). I was actually in the process right before the wreck of rebuilding an engine with custom cams and pistons. After the wreck, I sold everything and the custom cams were shelved due to a new direction in my company. The bottom end was worked out but the cams were still a work in progress. I had two cam manufacturers which were willing custom cut grinds from billet cores. I have a couple of stock cores on the shelf to date for a pattern for the cam company.
As of January 2010 a lot has changed within my company and were are in the process of expanding so many projects have been shelved (including the above noted build) to properly align and weather the storm through the next few months. -j