Richard Holdener
April 7, 2014

Twin-Turbo 347 Stroker
Power Numbers-NA vs. CXRacing Twin Turbo
Rising Boost Curve—Max 15.2 psi
. NA Turbo
RPM HP TQ HP TQ
3,600 NA NA 388 566
4,100 312 400 472 604
4,500 351 409 561 654
5,000 408 428 684 719
5,500 454 433 773 738
6,000 472 413 846 741
6,600 509 405 920 732
7,000 515 387 NA NA

1. The bottom end consisted of a 4340 forged crank and 5.4-inch rods. Milodon supplied the necessary main studs to allow for installation of the windage tray. It was necessary to bottom tap the main stud holes prior to installation.
2. Here is a shot of the oil pump, windage tray, and pickup installed on the short-block.
3. The Fox-chassis oil pan supplied by Milodon featured a crank scraper to remove unwanted oil that can rob power. Minor trimming of the windage tray was necessary for proper clearance.
4. Since this was a turbo stroker, we chose an appropriate profile from Crane Cams. The hydraulic roller profile offered a 0.579/0.595-lift split, a 236/244-duration split, and 114 LSA.
5. AFR supplied its new 205 Renegade heads. The heads were secured using ½-inch ARP head studs and Fel Pro 1011-2 head gaskets. The AFR heads offered exceptional airflow and a thick deck to ensure sealing under boost. Even this healthy 347 stroker could not fully utilize all that the AFR heads had to offer.
6. Thanks to CNC porting, the AFR heads offered exceptional airflow, peaking at 331 cfm on the intake and 235 cfm on the exhaust.
7. The AFR heads featured a 2.08/1.60 stainless valves and a spring package that offered sufficient rate and coil bind clearance for our sub-0.600 lift cam.
8. To maximize lift, we installed Comp 1.6-ratio Gold roller rockers.
9. Feeding the AFR Renegade heads was a single-plane, Funnel Web intake from Procomp Electronics. The intake design offered plenty of flow and pushed the effective operating speed higher in the rev range.
10. Run on the dyno with 1¾-inch Hooker headers, a Holley 950 Ultra HP carb, and MSD billet distributor, the 347-cube stroker produced 516 hp at 6,900 rpm and 434 lb-ft at 5,400 rpm.
11. After running the NA combination, off came the headers and on went the stainless turbo manifolds from CXRacing.
12. The twin-turbo kit from CXRacing came with a set of GT35-style turbos capable of supporting over 500 hp each.
13. The turbos featured water-cooled center sections, which improve longevity, but we did not hook up this feature on the dyno. Note the supplied oil feed (top) and drain (bottom) fittings.
14. The twin-turbo kit also featured a pair of 38mm wastegates. The position of the driver-side gate required use of a short oil filter.
15. Keeping things cool was an efficient air-to-air intercooler. Note the dual-in and single-out configuration of the end tanks. The kit also featured all of the necessary aluminum (polished and beaded) tubing, couplers, and clamps. Since the kit was designed for a 5.0L EFI motor, we modified a few of the tubes to create our custom carb kit.
16. The twin kit also featured dedicated 3-inch exhaust downpipes, which we configured to work on the engine dyno.
17. For turbo use, the Holley 950 Ultra HP was replaced by an 850 model modified by Carb Solutions Unlimited (CSU). Mods to the CSU carb included revised boosters, metering blocks and an adjustable, boost-referenced power valve(s). CSU also supplied the necessary carb bonnet to seal in that wonderful boost.
18. All hooked up and ready for action, the twin-turbo, carbureted 347 produced 919 hp and nearly 750 lb-ft of torque before we called it quits. The use of tight A/R turbine housings produced a rising boost curve that was climbing at a rate of 1 psi per 100 rpm at the top of the rev range. The result was a power gain of 45 hp per 100 hp, meaning there was a ton more power left in the combo had we elected to rev the motor higher.