Additional goodies employed...
Additional goodies employed on the 438 included a Milodon oil pan, MSD distributor, and 1,000-cfm Holley HP series carburetor. Though a tad on the small side for this application, the stroker exhaled through a set of 1 3/4-inch Hooker Super Comp headers to the tune of 605 hp at 6,500 rpm and 568 lb-ft at 4,500 rpm. Now it was time for some boost.
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.
Running boost required swapping...
Running boost required swapping out the 1,000-cfm Holley for a dedicated forced-induction carburetor. Having had such success in the past with this CSU carburetor on blow-through supercharged applications, we were anxious to try it on a turbo motor.
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.
Feeding the CSU carburetor...
Feeding the CSU carburetor was a CSU carb bonnet. We liked the fact that this bonnet was not directional and could be mounted in any orientation. This was important as our turbo kit from HP Performance was originally designed for a 5.0L fuelie application. A small section of tubing was all that was needed to connect the discharge tube to the bonnet.
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.
The kit from HP Performance...
The kit from HP Performance featured complete Jet-Hot coating and was the very same one we used on the 302 test run previously for MM&FF. Running a smaller turbo and low boost pushed that smaller 302 over 620 hp, but this same kit would work equally well on this 1,000hp application.
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).
To minimize the charge temperature,...
To minimize the charge temperature, the turbo kit from HP Performance featured an efficient air-to-air intercooler. Airflow through the core was supplied by a dedicated fan during testing.
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.
The 44mm Tial wastegate supplied...
The 44mm Tial wastegate supplied with the turbo kit was unable to control the boost, so we swapped over to a 45mm Hyper-Gate from Turbo Smart. According to Turbo Smart, its 45mm wastegate offers a 20 percent increase in flow. Boost creep was no longer an issue with the larger wastegate.
The standard Fox-chassis turbo...
The standard Fox-chassis turbo kit from HP Performance comes with a 60mm turbo, but upgrades are available for increased boost and power potential. To reach the 1,000hp mark, we installed this 80mm turbo from Comp Turbo in San Dimas, California. After just missing 1,000 hp with the smaller 74mm turbo, they quickly upgraded the impeller to the 80mm version, and we were instantly rewarded with over 1,000 hp.
ProComp 438-NA vs. Turbo (12.8...
ProComp 438-NA vs. Turbo (12.8 psi)
This 438 stroker was powerful both in normally aspirated and turbocharged trim. Despite a static compression ratio of just 9.2:1, it produced 604 hp and 568 lb-ft of torque. In fact, torque production exceeded 510 lb-ft from 3,500 rpm to 6,200 rpm, making this one impressive street stroker. Adding boost with the 80mm turbo from Comp Turbo resulted in serious ponies. The combination topped the 1,000hp mark by posting peak numbers of 1,037 hp at 6,000 rpm and 957 lb-ft at 5,100 rpm. Torque production exceeded 900 lb-ft from 4,500 rpm to 6,000 rpm. The wastegate upgrade from Turbo Smart controlled the boost perfectly, and given the use of the air-to-air intercooler and CSU carburetor, we see no reason why this combination wouldn't run safely on pump gas.
To improve strength and reduce...
To improve strength and reduce weight, the 80mm (ball bearing) turbo from Comp Turbo features a trick billet center section set up to receive water cooling.
Run on the engine dyno at...
Run on the engine dyno at 12.8 psi, the turbocharged 438 stroker produced peak numbers of 1,037 hp and 957 lb-ft of torque. Stressed to impress, the ProComp block easily shrugged off power and torque numbers that would have split a production block right in half.