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Ford Mustang Pro Comp Carbureted Turbo Engine
Dig Into This 1,000-Plus-Horsepower, 438-Inch Stroker Carbureted Turbo Torture Test.
Prior to adding boost, we ran the 438 stroker in normally aspirated trim. To complete the stroker, we installed a Milodon drag-race oil pan, 1 3/4-inch Hooker Super Comp headers, and an MSD billet distributor. Additional components on the normally aspirated motor included cast-aluminum valve covers, plug wires, and 28-ounce damper, all from ProComp. Also present was Lucas 5W-30 oil, a K&N oil filter, and Denso Irridium plugs (IQ27).
In normally aspirated trim, the 438 was run on pump gas with a Holley 1,000-cfm HP-series carburetor. After the break-in procedure and some minor tuning, the normally aspirated 438 pumped out 604 hp at 6,500 rpm and 568 lb-ft at 4,500 rpm.
Demonstrating the torquey nature of stroker motors was the fact that the 438 offered no less than 510 lb-ft from 3,500 rpm to 6,200 rpm. Making this all the more impressive, the power numbers came from a combination featuring a blower/turbo cam and a static compression ratio of just 9.2:1. Were we to build this motor as a dedicated normally aspirated combination, we'd up the compression with flat-top pistons (to replace the 29cc dish units), have Cam Research Corp do a wilder cam with a tighter lobe separation and more duration, and install 17/8-inch or even 2-inch step headers. Keeping the compression and cam timing at boost-friendly levels meant we were now free to install the turbo.
Since we just tested a 302 with the turbo kit from HP Performance in Roswell, New Mexico, selecting a turbo kit for the 438 stroker was as simple as pulling it off the previous test motor. The slip-fit cross-over tube allowed the turbo kit to fit both 302 and wider 351 applications. The kit from HP featured dedicated, tubular exhaust manifolds with V-band clamps, a front-mounted air-to-air intercooler, and Jet-Hot coated tubing. Though designed for a fuel-injected 5.0L (or 5.8L), the kit worked perfectly on our carbureted stroker application with just a few minor upgrades.
The first component in the line of upgrades was obviously the carburetor itself. Our blow-through (works on both supercharged and turbocharged applications) carburetor came from Carburetor Solutions Unlimited (CSU). The CSU carburetors are machined and tuned specifically for use on blow-through applications, providing precise metering under all normally aspirated and boosted conditions, including transitions.
Having had such success in the past with the CSU carburetors on supercharged motors, we were anxious to give this one a try on our turbocharged stroker. It is easy to tune a blow-through carburetor to either run well at full throttle or under cruise conditions, but CSU has mastered both. A small section of tubing was necessary to connect the discharge tube from the intercooler to the CSU carburetor bonnet.
As indicated previously, the turbo kit was originally used on a milder 302 application. Though we managed to exceed 600 hp with the supplied turbo, an upgrade was in order, but not before we swapped out the 44mm Tial wastegate. Apparently, the 44mm wastegate was too small to properly control the boost pressure supplied by the Comp Turbo-boost creep resulted in an escalating boost curve.
Coming to our rescue were the guys from Turbo Smart in the form of a 45mm Hyper-Gate. According to Turbo Smart, the 45mm Hyper-Gate offers a 20 percent increase in flow over the smaller 44mm wastegate. Installation of the Hyper-Gate cured the rising boost curve and provided complete boost control. A manual boost controller was used to bleed the pressure signal to the wastegate, thus allowing us to adjust the boost pressure from 7 psi (the wastegate spring setting) to over 15 psi (or more with a spring upgrade).
The final upgrade was the turbo itself. Comp Turbo supplied a 74mm turbo for our stroker. The 74mm was a slick piece of equipment, featuring a billet center section plumbed for water-cooling, though we didn't run it in this configuration. Externally, it didn't look much bigger than the 60mm run on our 600hp 302, but boy did it flow like a bigger unit. Using the 74mm turbo, we were able to exceed 950 hp, but it wasn't quite large enough to reach 1,000 hp. A quick phone call and trip to Comp Turbo resulted in an upgrade to an 80mm impeller and housing. Using this new configuration, we were able to not only reach 1,000 hp, but exceed it by producing peak numbers of 1,037 hp at 6,000 rpm and 957 lb-ft of torque at 5,100 rpm. Torque production actually exceeded 900 lb-ft from 4,500 rpm to 6,000 rpm.
With minor jetting, the CSU carburetor provided a safe air/fuel mixture below 12.0:1, while the total timing was kept conservative at just 21 degrees. Combining the air-to-air intercooler and cooling from the fuel supplied by the carburetor resulted in an ultra safe combination that could easily run on pump gas (we ran ours on race fuel to be safe).
Despite the stress, the ProComp block, rotating assembly, and heads impressed us with the ability to support these extreme power levels.