The Build Concept

This project combined two ideas that rarely overlap: a twin-turbo system and a blow-through carburetor setup on a small-block Ford. The CXRacing twin-turbo kit is designed for fuel-injected 5.0L Fords, but carburetors remain a viable induction choice for boosted applications, offering cost savings, simplicity, and measurable charge cooling advantages. The goal was to adapt the kit for carburetor use and document the results on the dyno.

The Short-Block

The foundation was a 347 stroker built with forged internals: a 4340 forged crank, 5.4-inch rods, and JE forged flat-top pistons producing 10.8:1 static compression. That ratio is higher than typical for a dedicated turbo application, but it served the dual purpose of producing strong naturally aspirated numbers before boost was introduced.

The twin-turbo, carbureted 347 stroker on the engine dyno.

JE forged flat-top pistons at 10.8:1 static compression. Higher than ideal for dedicated boost, but effective for strong naturally aspirated baseline numbers.

The bottom end: 4340 forged crank, 5.4-inch rods, and Milodon main studs. The main stud holes required bottom tapping prior to installation.

Oil pump, windage tray, and pickup installed on the short-block.

The Milodon Fox-chassis oil pan featured a crank scraper. Minor trimming of the windage tray was required for proper clearance.

Heads, Cam, and Intake

Air Flow Research supplied CNC-ported 205 Renegade heads with flow rates exceeding 330 cfm on the intake side, enough to support over 660 naturally aspirated horsepower. The thick deck surface was well suited for sealing under boost. The heads were secured with 1/2-inch ARP head studs and Fel Pro 1011-2 gaskets.

The cam was a Crane hydraulic roller profile: 0.579/0.595 lift, 236/244 duration, 114 LSA. Effective for both naturally aspirated and boosted combinations. Crane also supplied lifters, a double-roller timing chain, and hardened pushrods. COMP 1.6-ratio Gold roller rockers maximized lift.

The intake was a Speedmaster single-plane, high-rise Funnel Web. The design pushed the effective operating range higher in the rev band, complementing the aggressive cam and high-flowing heads. A Holley 950 Ultra HP carburetor and MSD billet distributor completed the naturally aspirated configuration.

The Crane hydraulic roller cam: 0.579/0.595 lift, 236/244 duration, 114 LSA, selected for both naturally aspirated and boosted operation.

AFR 205 Renegade heads secured with 1/2-inch ARP head studs. Intake flow peaked at 331 cfm with 235 cfm on the exhaust side.

CNC porting delivered intake flow of 331 cfm and exhaust flow of 235 cfm.

The AFR heads featured 2.08/1.60 stainless valves and a spring package with sufficient rate and coil bind clearance for the sub-0.600 lift cam.

COMP 1.6-ratio Gold roller rockers installed to maximize valve lift.

The Speedmaster Funnel Web single-plane intake fed the AFR Renegade heads. The high-rise design pushed the effective operating range higher in the rev band.

Naturally Aspirated Baseline

Equipped with 1-3/4-inch Hooker headers, the Holley 950 Ultra HP, and MSD billet distributor, the 347 produced 519 hp at 6,900 rpm and 434 lb-ft at 5,400 rpm.

Naturally aspirated baseline: 519 hp at 6,900 rpm and 434 lb-ft at 5,400 rpm.

The CXRacing Twin-Turbo Kit

The kit includes stainless exhaust manifolds, GT35-style turbos rated for over 500 hp each, 38mm wastegates, an air-to-air intercooler, aluminum intake tubing, stainless exhaust tubing, all clamps and couplers, oil feed and drain fittings, and braided oil feed lines.

The exhaust manifolds accept T3 turbine housings, providing flexibility across turbo sizes. The turbos featured water-cooled center sections for longevity, though this feature was not connected on the dyno. Bulkhead fittings for the oil pan drain eliminated the need for welding.

Headers removed, stainless CXRacing turbo manifolds installed.

GT35-style turbos rated for over 500 hp each.

Water-cooled center sections on the turbos. Oil feed (top) and drain (bottom) fittings visible.

The 38mm wastegates mounted to the manifold flanges. The driver-side gate required a short oil filter for clearance.

The air-to-air intercooler with dual-in, single-out end tank configuration. The kit included polished and beaded aluminum tubing, couplers, and clamps.

Dedicated 3-inch exhaust downpipes, configured for engine dyno use.

Adapting for Carburetor Use

Since the kit was designed for the 5.0L EFI throttle body, the discharge tubing from the intercooler required modification. CXRacing offers individual turbo components, and a U-bend with a pair of 90-degree bends connected the intercooler to the carburetor bonnet.

For boosted operation, the Holley Ultra HP was replaced with a Holley HP 850 modified by Carb Solutions Unlimited (CSU). The CSU carb featured revised boosters, metering blocks, and an adjustable boost-referenced power valve. CSU also supplied the carb bonnet to seal boost pressure. A blow-off valve was included to manage the pressure surge when lifting off the throttle at high rpm.

A carb spacer with multiple vacuum fittings handled signals for the wastegates, blow-off valve, fuel pressure regulators, and dyno readout. Boost-referencing the fuel pressure regulator was critical to maintaining adequate fuel delivery under pressure.

The Holley 950 Ultra HP was replaced by a CSU-modified Holley 850 with revised boosters, metering blocks, adjustable boost-referenced power valve, and sealed bonnet.

Installation Notes

A few details observed during installation:

• The driver-side wastegate required a short oil filter for clearance, available at any auto parts store.
• The 3-inch downpipes were configured as up-pipes on the dyno for better fitment.
• A crow's foot wrench simplified exhaust manifold bolt installation.
• Oil pan drain-back holes were drilled and fitted with the supplied bulkhead fittings, eliminating the need for welding (pan removed).
• Compressor and turbine housings were oriented to align oil feed/drain fittings and compressor discharge before mounting.

Boosted Results

Static timing was reduced from 35 degrees to 23 degrees for boosted operation. At just over 15 psi, the twin-turbo carbureted 347 produced 919 hp and 747 lb-ft of torque.

The tight A/R turbine housings created a rising boost curve, gaining approximately 1 psi per 100 rpm at the top of the rev range. Power was climbing at a rate of 45 hp per 100 rpm when the engine was shut down at 6,600 rpm. A larger A/R housing, available from CXRacing, would flatten the boost curve.

The carburetor performed without issue under boost and provided additional charge cooling beyond what the intercooler delivered alone. The combination confirmed that blow-through carburetors remain a viable, effective method for forced-induction builds.

At 15 psi, the twin-turbo carbureted 347 produced 919 hp and 747 lb-ft of torque at 6,600 rpm, with power and boost still climbing.