A Quick Look at a Forged 408 LS by FJ Performance


photos by: FJ Performance

We Take a Moment to Dig Up the Details on One of FJ’s Latest Performance Builds

Over the last few years, a small little tuning shop in the hills of Western Pennsylvania has been quickly growing into all-encompassing automotive facility that will not only include general bolt-on installations, but tuning, ground-up vehicle modifications and even completeĀ engine builds.

Being primarily focused on LS and GEN-V LT engines, as well as dabbling in MazdaSpeed3, Ecotec and EcoBoost tuning, FJ Performance is one of the quickest-growing shops in the Midwest. Owned and operated by Fran Johns and Matt Neubauer, they wanted to showcase one of their latest builds, which was a C5 Z06, powered by a East Coast Supercharging-blown,Ā forged 408 cubic-inch LS2.

Of course with plenty of boost and abuse in mind, only the best components will do, so FJ sourced some of the most impressive hardware available to racers today. When we spoke with Fran and Matt about the specifics, the forwarded us the complete build sheet and we passed them along to you below:


  • New OEM LS2 Block
  • Bores = Torque-plate honed to 4.0013″ (.0040″ piston to cyl)
  • Katech Billet Caps Installed with Dowel Pins
  • Block-Align Bored and Honed w/ARP Stud Kit to Nominal hsg. Diameter
  • K-1 Technologies 4″ Stroker Crank; Billet Reluctor Ring Installed and TIG-Welded
  • Crank Snout and Dampener Machined for Blower Drive Double Key
  • Heads, OEM Used Castings; Valve Bowl Port Areas Hand Worked, and Valves and Seats Machined
  • Decks Surfaced for Multi-Layer Steel (MLS) Gaskets RA13
  • Stroker Rotating Assembly, Clearance Hand-Worked Into Block
  • Rocker Arms Rebuilt w/Upgraded Trunion and Circlip Kit
  • MBC .0024-.0025″ H-series Clevite Racing 3/4 grooved
  • RBC .0017-.0019″ Coated Clevite Racing, Narrowed
  • Thrust .005″ CLRNC
  • Ring Gaps _ T .022 / 2nd .024/ Oil +.018″ Low Tension Gas-Nitrided Wiseco Piston to Cyl .0040″ Finished w/Torque Plates and ARP Stud Kit
  • Piston to Valve = @ .110″ int, .090″ ex. CLRNC. Cam centerline @ 110.5


The foundation of the boosted LS build, is an OEM GM LS2 aluminum block. Typically found in '05-07 Corvette, '06-07 CTS-V, and '05-06 GTO, among a few others,

The foundation of the boosted LS build, is an OEM GM LS2 aluminum block. Typically found in the ’05-07 Corvette, ’06-07 CTS-V and ’05-06 GTO, among a few others, they offer a large bore, aluminum alternative to the ever-so-popular and quickly dwindling number of LQ4 and LQ9 blocks that remain. Here it is, completely bare and ready for the build that would ultimately begin.



Of course, getting the LS2 from 364 cubic-inches to 408 involves enlarging the bores to a full torque-plate honed 4.0013-inch diameter. To fill the bores, low-tension, gas-nitrided forged Wiseco slugs will be connected to Clevite H-beam connecting roads and to a K1 TechnologiesĀ forged crankshaft. The deck will also be surfaced to accommodate MLS gaskets.



Before the crankshaft could be installed into the the block, the guys at FJ installed the harmonic balancer onto the crank snout, with the help of a vise. This certainly makes things easier, rather than trying to install the balancer after the fact. Both the crank snout and the harmonic balancer were also machined for a blower drive double key.



Holding the crankshaft in place, are a set of Katech billet steel main caps for increased strength and durability. Rather than the bolts used in a stock configuration, Katech’s mains are paired with 1/4-inch steel dowels.




For the top end, a set of used LS2 casting were sourced, ported, milled and generally cleaned up for improved flow characteristics and performance. The valve bowl port areas were hand worked, and valves and seats were machined.



The Roughness Average (RA) was measured in at 14.64, which most engine builders consider about as perfectĀ as it gets. Between 15 and 30 Ra is really good, and anything under 50 is considered to be acceptable, particularly with MLS gaskets.



Just prior to installing the camshaft, lifters and cylinder heads, we take a look at the the short block that will be powering this monster.



This is the assembled long block in all of its glory; including the harmonic balancer, valley cover and front and rear engine covers. You’ll also see the knock and crank sensors are in place. the rocker arms are rebuilt OEM LS2 pieces with a trunnion upgrade.



And her she is, 408 cubic-inches of forged LS2 power, motivated by an ECS blower. It’s also backed by an RPM Transmission T-56 gearbox.



With 15-psi of boost, the blown 408 was good for a peak output of 730 rwhp and 663-lb ft of torque to the rear wheels, thanks in large part to Fran’s expert-level familiarity of HP Tuners software and FJ’s in-house, in-ground Dynojet.

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