It's possible to have a powerful and reasonably efficient FSJ. My Wag gets right at 20 MPG if I try hard, 15 or so farting around, and can drop to 10 with very heavy towing or lots of tire smoke. It's hit 22 MPG, but not on a verifiable round-trip. I'd estimate flywheel HP at around 250-275. The basic setup:
360, .030 over, +-9.25:1 compression.
Mildly ported/cleaned-up heads w/ 3-angle.
Stock (port matched) exhaust manifold w/ very quiet single 3".
Summit K8600 cam, Crane springs.
Performer intake, GM TBI w/ custom chip.
Stock air filter housing w/ cold air hose intact, K&N element.
Stock distributor (w/ advance locked-out), TFI.
T-18a manual tranny (probably where almost all the efficiency gain was acheived), 208, 3.73s, 33s, 4" lift.
Mobil-1 0W20 in the motor, Redline synthetic in the boxes.
When the thing was stock (360/727/229/2.72s/28s, no lift) it could eke-out 13 MPG @ 75 MPH, 11-12 @ 50 MPH (torque converter loss with the tall gears & non-lockup), and 7-9 in town. Towing or tire smoke were not options.
I recently rented a Toyota Sequoia, and its performance & efficiency were both just a slight tick below those of my old Wag, and it got stuck in my driveawy.
[ April 15, 2006, 01:48 PM: Message edited by: Serious Johnson ]
360, .030-over, K8600 cam, Crane springs, ported heads, Edelbrock Performer, G.M. TBI, TFI, 3" exhaust,
T-18a/208, D44/AMC 20 w/ limited slip in both, 3.73s, 33s, BDS 4" springs, Rancho 9000 shocks, etc., etc.