Power Play
For our chassis dyno numbers we revisited The Dyno Shop in Santee, California. Owner Mark MacNeil and the rest of the gang have forgotten more about diagnosing, modifying, measuring, and extracting power from vehicles ranging from $100K turbo Porsches to carbureted dune buggies than we'll ever know. The Dyno Shop baselined our XJ back when it was stock and when we added our Gibson header and exhaust, K&N FIPK air intake, Performance Distributors Firepower Ignition Kit, Rubicon Express 62mm throttle body, and Hypertech Power Programmer (although the stroker uses factory computer calibrations).
MacNeil says our horsepower levels could be brought up quite a bit more with some computer tweaking and some leaning of the air/fuel curve. We were nervous about dinging our new engine, so we purposefully jetted our NOS nitrous system too rich. We're considering adding a larger 66mm throttle body down the road to get some more air into the engine and may tweak the computer, but for now we're happy with the added power across the entire rpm range without worrying about knocking or harming the engine.
Even though we've been experimenting with 89- and 87-octane fuel, all of our dyno testing was performed with 91-octane premium pump gas.
Test 1:
Bone Stock 4.0L
| RPM: | Power: | Torque: | Air/Fuel Ratio: |
| 3,500 | 114 | 171 | 11.9:1 |
| 3,600 | 116 | 170 | 11.9:1 |
| 3,700 | 118 | 168 | 11.8:1 |
| 3,800 | 124 | 172 | 11.7:1 |
| 3,900 | 130 | 176 | 11.7:1 |
| 4,000 | 127 | 166 | 11.8:1 |
| 4,100 | 125 | 161 | 11.8:1 |
| 4,200 | 126 | 157 | 11.7:1 |
| 4,300 | 128 | 156 | 11.7:1 |
| 4,400 | 129 | 154 | 11.6:1 |
| 4,500 | 131 | 153 | 11.4:1 |
| 4,600 | 132 | 151 | 11.4:1 |
| 4,700 | 133 | 148 | 11.5:1 |
| 4,800 | 133 | 145 | 11.4:1 |
| 4,900 | 130 | 139 | 11.3:1 |
| 5,000 | 130 | 137 | 11.2:1 |
| 5,100 | 126 | 130 | 11.1:1 |
| 5,200 | 124 | 125 | 10.9:1 |
| 5,300 | 122 | 121 | 10.8:1 |
| 5,400 | NA | NA | NA |