Jack Roberts’ 7-Second 4.8-Liter LS

Jack Roberts' 7-Second 4.8-Liter LS

Jack Roberts, the owner of Squirrel Tuned, showed up at TX2K19 in his 1987 Mustang Fox-body ready to make some passes in the exhibition class. Unlike the majority of the race cars on the property, the engine in the Mustang is a 4.8-liter out of a wrecked 2005 Tahoe with 140,000 miles. Jack paid $700 for the complete engine with the factory ECU, harness, and a 4l60e transmission. A few changes were made to this combination before it was in fact race ready.

Jack states, ” I originally got the 4.8 engine to troll other Mustang owners. The argument from them is always, ‘Well, we have smaller cubic-inch engines.’ ” Jack reached out to John Bewley owner of Lil’ John Motorsports (LJMS), and the two devised a plan. The idea was to build a max effort stock bottom end 4.8-liter with a twin-turbo setup and hurt as many feelings as possible.  Jack states, “We did not remove a single rod or main cap. The heads are unported and we didn’t even clean them.”

The duo decided to make a few necessary changes to the engine because some of the factory parts would not live under the harsh conditions it would face. A Melling high-pressure high-volume oil pump replaced the stock unit. An IWIS timing chain was connected to the custom Lil’ John Motorsports stage 1 turbo camshaft. A set of Johnson Lifters link-bar lifters were used along with 3/8 pushrods, Brian Tooley Racing valve springs, ARP head studs, Cometic head gaskets, and a Smith Brothers trunion kit. These parts were utilized to try and make the little 4.8-liter hold together at 8,500 rpm. Other changes for the engine include a Holley oil pan, Summit Racing 25% underdrive balancer, and an Eldebrock ProFlo intake manifold.

The image in the left is a look down the head straight out of the Tahoe. The image in the right is after 35-pounds of boost and E85. Jack might not have cleaned up the 706 castings, but the engine is doing a very nice job of ridding itself of the carbon buildup.

For the turbo setup, Jack opted for two off the shelf cast Borg Warner S366S turbos with a pair of Tial wastegates per Lil’ John’s suggestion. The turbos are connected to a set of eBay turbo headers that had to be modified slightly. The Mustang also has an air-to-water intercooler with a 13-gallon ice tank with an integrated transmission cooler.

Jack bought the car as a roller that was already equipped with a mild steel 25.5 cage and coil-overs. A set of Strange Engineering single adjustable coil-overs were used on the front with Strange double adjustable unit on the rears. The transmission for the Mustang is a Performance Torque Converter (PTC) Reid case 1.80 Powerglide and a PTC 9.5-inch converter. A Mark Williams Chromoly driveshaft is connected to a braced 8.8-inch rear with strange 31-spline axles and a spool with 3.73 gears.

For the fuel system, Jack decided to run a 12-gallon fuel cell with three Walbro 465 fuel pumps to fuel the 210-pound Bosch injectors on E85. What’s comical is, the current setup is not adequate for the little 4.8. On the fastest pass of the weekend, the fuel pressure dropped to 10-pounds less than where it usually operates on an 87-percent duty cycle. Jack said, “I never expected a junkyard motor to need more than three fuel pumps and 210lb injectors.”

Other than the roller, the entire Fox-body was built and tuned by Jack. He set up the suspension, handled assembly, tunes the car, and drives it as well. Before his current setup with the Holley Performance Products Dominator, the Mustang went an impressive 8.47 elapsed time at 163mph on the stock ECU. Jack said, “I needed more map sensor and wanted to go closed loop. I went to a Holley Dominator setup which I used to set the record.” Obviously, this was a good move and paid off on the performance of the car.

This one if for the naysayers that will argue that the Fox-body doesn’t weigh 3,200-pounds. It looks like they are right since the car tips the scales with Jack at 3,260 with 50-pounds in the back for No-prep.

So how fast is the new the record? The 3,200-pound Fox-body went a 7.913 at 170.49 mph with a 1.18 sixty-foot time. The 4.8-liter stock bottom end has taken a beating so far and has cranked out a mind-blowing 1140 horsepower at the wheels while being shifted at 8,450rpm. Jack told us, “The boost on the record-setting pass peaked at 35.8-pounds during the run and went through the traps at 7960rpm.” Jack and John aren’t done yet. They are currently working on some other ideas that will make the car even faster and look to deepen the record.

Congratulations to Jack and everyone involved on this 4.8-liter record. Jack wanted to thank John Bewley of LJMS for all of the help and advise and Nikolas Brock for helping him out at TX2K19 and keeping him calm in the staging lanes. We look forward to seeing the car at the track again soon.

DragzineDragzine – Jack Roberts’ 7-Second 4.8-Liter LS

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