A few years back, while at TX2K 2019, we were on the starting line at Houston Raceway Park, where a mostly blue Foxbody Mustang had just completed a burnout. At the time, we knew nothing about the car or the owner Jack Roberts of Squirrel Tuned. But as soon as we heard that this 7-second car was powered by a stock bottom end 4.8-liter LS and held the record, we reached out to Robert’s to get the inside scoop on his Mustang. Fast forward a couple of year’s and Roberts is doing more of the same, but this time with a new car and a somewhat new combination.
Robert’s ditched the Notchback in favor of a new platform, a New Edge Mustang. The new car is lighter than the previous race car and a more capable vehicle as well. However, for the engine, Roberts decided to use the stock bottom end (SBE) straight out of the blue Mustang. “This is the original SBE 4.8-liter short block that was in my fox body the last two times I set the record,” Roberts explained. “The short block is still untouched, and I still haven’t checked the ring gap or anything even though it had 140,000 miles when I got it. I did have the reluctor wheel tacked on to the crank to make sure it doesn’t spin on me.”
Even though Roberts still hasn’t changed the stock bottom end, he certainly made some significant changes that allowed him to set a new 4.8-liter record. His first move was to scrap the stock unported 706 heads and replace them with a Wilkes Performance ported 862 with 2.02 intake and 1.57 exhaust valves. He also installed a much larger camshaft from Full Proof Performance, Brian Tooley Racing (BTR) shaft rocker kit, and a Holley Dominator to run the turbocharged combination. Roberts did stick with some of the same components, including an Ultimate RPM spring kit, 3/8 pushrods, Johnson ST2116LSR lifters, ARP head studs, and factory LS9 head gaskets.
The short block is still untouched, and I still haven’t checked the ring gap or anything even though it had 140,000 miles when I got it. – Jack Roberts
With the need for speed, Roberts also needed more fuel. The 4.8 LS is now being fed with a healthy dose of methanol thanks to 16-Bosch 210 fuel injectors and a Waterman Mini Bertha fuel pump that was set up by Robert Ette. Now you might be asking, “why does this little engine need so much fuel pump?” Well, it’s because Roberts removed the cast Borg-Warner S366S turbos and replaced them with a GTR 88mm GT55-based turbo from Forced Inductions turbocharger. Roberts said, “This turbo is commonly run in X275 and is capable of some incredible numbers, and it’s not even having to work hard on this little 4.8.” According to Roberts, the new modifications produce about 60 more horsepower than before, and that’s with 7-pounds of boost less and a conservative tune-up.
Another area that Roberts feels that he made some significant gains is the drivetrain. “The new Hughes Performance converter, dump valves, and 1.69 gear set in the trans are a massive piece of this puzzle,” explained Roberts. “This converter keeps the car in the powerband and couples smoothly without dragging the motor down. And even though it’s loose, like it needs to be down low, it still grabs the engine at high rpm, and it only slips 2-percent at 8500rpm.” In addition, even with a massive turbo, Roberts can spool the unit in as little as 4.5 seconds, thanks to the new dump valve system.
Roberts has only been testing for a couple of weeks now with the new car and is still getting the bugs worked out. However, even with a few gremlins and a soft 60-foot time of 1.19, he managed to reset the SBE 4.8-liter record with a 4.88 et in the 1/8-mile at 146mph at Xtreme Raceway Park. When asked if the Mustang had more in it, Roberts said, “The car definitely has potential, and there’s a lot of room for improvement in the 60-foot. Once I’m happy with the short time, I’ll start putting more power into it.” And we are excited to see that!