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1993 Big Block Ford Mustang - Hybrid DriveIn Its Quest For A Dance Partner, Our 775hp Big-Block Ford Mates With A Turbo 400 Trans. From the September, 2009 issue of Popular Hot Rodding By Stephen Kim Photography by Stephen Kim
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While standard magazine protocol involves pulling the handle on the dyno, patting yourself on the back, and calling it a day, readers want more than just engine buildups destined to languish idly as pricey garage decorations. To make amends for these pathetic wastes of horsepower, back in the June issue we chronicled the build of a 532ci big-block Ford that spit out 775 hp and 673 lb-ft on pump gas. This big lump was conceived with an actual purpose in mind-go figure-and that's to drop it on a full-weight '93 Mustang notchback, run solid 9s on drag radials and a stock-style suspension, and survive the 200-mile roundtrip trek to the dragstrip while maintaining street legality. With the key ingredient in the powertrain complete, the next step is selecting a trans capable of surviving the harsh demands of a dual-purpose street/strip role. Given our needs, it only makes sense to go hybrid. Although our decision to run a GM TH400 will surely bunch up some Blue Oval panties, it's been the benchmark heavy-duty drag automatic for decades. Not only have countless Ford and Mopar buffs put brand loyalty aside and bolted them into their project cars, but the TH400's legendary reputation for durability has infiltrated the hallowed turf of Euro elitists as well. Despite their superior technical aptitude-at least that's what they try to tell us-prestigious marques such as Ferrari, Rolls-Royce, Bentley, and Jaguar have all used TH400s in their past rides. Likewise, U.S. troops abroad rely on trusty TH400-equipped Humvees while evading the bad guys' bullets and IEDs. Granted, a Ford C6 can be built to handle our intended application, we opted for the TH400 due to its lower mass, superior efficiency, smaller dimensions, and more readily available parts. Furthermore, adapting a Turbo 400 to fit behind a Ford mill is very straightforward Thoroughly impressed with the fine work he performed on Project Talladega's 700-R4, we once again turned to Greg Ducato of Phoenix Transmissions. He set us up with one of his company's PT400SX-model Turbo 400s, which can easily handle 900 hp. To improve upon what's already a rugged trans from the factory, Phoenix's bag of tricks include high-capacity clutch packs, a 300M billet steel input shaft, a five-pinion rear planetary, a billet clutch hub, a Kevlar band, and a 34-element sprag. This is surely one stout piece, but in the walk of performance transmission rebuilds, it required very little work to elevate the TH400's durability to such impressive levels. "If you want a gnarly brute of a no-compromise transmission and need dead nuts reliability, you need to go with a Turbo 400. You can take a lighter-duty trans like the TH350 and bring it up to the same level as a TH400, but that requires a ton of trick parts," Greg explains. "At the end of the day, you'll have a TH350 that costs more than a TH400 that's still an inherently weaker design. The only downside to a Turbo 400 is that its rotating mass is greater-which equates to more parasitic loss-but if you're making huge power to begin with, it's a small price to pay for the added durability. The few hundredths of a second you might pick up at the track with a TH350 may be important if you're racing in an extremely competitive class, but the average guy on the street will never feel the difference." Since it was quite obvious who the real expert was, we let Greg do all the dirty work, and documented the intricacies of building a bulletproof Turbo 400.  With a PML deep cast pan,...  With a PML deep cast pan, slick case finish, and beefy J.W. bellhousing, the Phoenix PT400SX TH400 certainly looks the part of a beastly automatic. Rated at 900 hp, its $1,645 list price-which includes a custom converter and a two-year, 24,000-mile warranty-is a raging bargain.  There are several methods...  There are several methods of adapting a GM TH400 to a big-block Ford, but the most practical for a track-oriented application is with an Ultrabell bellhousing from J.W. Performance Transmissions. It features the Ford bellhousing bolt pattern on one side, and attaches to the TH400's front cover on the other side. Of course, this requires cutting off the factory bellhousing using a template included in the J.W. kit. With the measurements scribed on the case, the old bellhousing was hacked off with a plasma cutter. Afterward, final shaping was performed using a hand file to ensure a close fit to the trans case.  After cutting off the stock...  After cutting off the stock bellhousing, the TH400 case is cleaned and prepped in a proprietary process that not only yields a brilliant finish, but also closes up porosity for added strength. The seven-step procedure involves bead blasting, steam cleaning, flat filing, casting flash removal, and a bath in a tub full of vibrating ceramic alloy media and brightening solution.  High-quality OE-style frictions...  High-quality OE-style frictions (brown) work great for most buildups, but for extreme-duty applications, such as in our project Mustang, Phoenix prefers using semi-metallic, waffle-pattern (gray) clutches. The extra grooving in the clutch face helps displace fluid when the clutches apply, which promotes positive engagement and heat dissipation.  For no-compromise durability,...  For no-compromise durability, Phoenix's TH400 utilizes a straight-cut sun gear, and front and rear planetaries. While the ratios remain unchanged from stock, the straight-cut gears substantially reduce thrust loads at the expense of gear whine. The added noise is most noticeable in lower gears, but it's a small price to pay in a heavy-duty drag application.  The long shelf life of the...  The long shelf life of the TH400 means that it can benefit from revisions made to its successors. For instance, this five-pinion rear planetary assembly out of a 4L85E is substantially stronger than the TH400's four-pinion unit, as it distributes torque over a greater surface area. Note the straight-cut gears.  Whether you're building a...  Whether you're building a motor or a trans, it's the little things that distinguish the studs from the duds. The later-style Torrington bearing set (top) features a greater number of rollers than its stock counterparts, which beefs up load capacity.  The low-reverse band is subject...  The low-reverse band is subject to tremendous loads under heavy throttle, as it holds the heavy reaction carrier in manual-low and reverse. Likewise, increased line pressures exert additional stress on the band as it engages. Compared to the stock band (left), the aftermarket unit (right) has wider contact points for the lugs, and carbon-blended lining material.  Heavy-duty low-reverse sprags...  Heavy-duty low-reverse sprags (bottom) are equipped with larger springs and a reinforced cage design. This provides a more stable contact area for the sprag rollers, which must support the loads exerted on them by the reaction carrier assembly.  The stock stamped steel intermediate...  The stock stamped steel intermediate apply piston (right) is prone to deflection in high-hp applications. Not only is the cast aftermarket piston stronger, it features additional clutch contact area for increased holding capacity.  It doesn't look like much,...  It doesn't look like much, but aftermarket Teflon rings (bottom) are preferred over factory cast iron rings in high-performance TH400 builds. At high rpm, iron rings will stick, bind, and wear into the clutch drums. Teflon rings offer far better sealing ability under high rpm and increased line pressure. Furthermore, the stock plastic thrust washers were replaced with steel and bronze units for enhanced durability.  The TH400's claim to fame...  The TH400's claim to fame is its integrated center support. Its large center bushing cradles both the gear train and clutch packs, which provides excellent internal stability. The center support is critical to overall durability and longevity, since heavy-duty transmissions like the TH400 pack lots of rotating mass. Neither the Ford C6 or Chrysler 727 transmissions have a center support which, according to Phoenix, gives the TH400 a definite edge in strength.  Through the years, TH400s...  Through the years, TH400s have been equipped with three different types of intermediate sprags, which are responsible for bringing the heavy direct drum to a halt on the 1-2 shift. The super strong 34-element unit (top) is far more durable under high torque loads than the early- (center) and late-model (bottom) sprags.  Opting for a 34-element sprag...  Opting for a 34-element sprag mandates the use of an early model drum (left). The difference in the sprag race design is quite evident between it and the '72-and-up unit.  The stock steel clutch apply...  The stock steel clutch apply piston (bottom) is the weakest link in the TH400 design, and has just a narrow band of surface area to engage the clutches. The aftermarket aluminum piston (top) is a step up, but will only allow loading five clutches in the drum. The aluminum piston (right) used in our build is the best alternative, as it provides additional strength and accepts six frictions.  The front band is only applied...  The front band is only applied when Second gear is selected in manual mode. The heavy-duty aftermarket piece (bottom) features a heat-resistant Kevlar composite lining, and a weld-reinforced end.  When loading the high clutch...  When loading the high clutch drum into the case, careful attention must be paid to prevent binding. Rotating the assembly back and forth ensures that the drum engages both the intermediate clutches and the sun gear.  To accommodate the larger-diameter...  To accommodate the larger-diameter 300M billet input shaft (right), the spline area of the forward drum has been enlarged. This dramatically reduces the likelihood of the shaft breaking or twisting the splines in the cast drum.  Compared to the stock input...  Compared to the stock input shaft, the 300M piece is larger in the drum area and features longer splines. In metallurgical terms, 300M is basically 4340 steel with higher silicon, carbon, molybdenum, and vanadium content. The stock shaft is very stout, but Phoenix suggests upgrading to a 300M unit at the 650hp mark for added insurance.  The factory cast iron forward...  The factory cast iron forward clutch hub (right) is a rugged piece in its own right, but high-load drag applications call for a billet steel hub to avert spline failure. Phoenix uses billet hubs in all of its ST- and SX-model TH400 transmissions.  A big bonus of using the patented...  A big bonus of using the patented cast aluminum J.W. bellhousing (PN: 92454-A) over a cut-to-fit adapter is that it's 600 times stronger than stock, and doubles as an SFI-approved flexplate shield. Throw in the fact that it costs just a smidgen more than a flexplate shield at $300, and the decision is a no-brainer. With over 40 different Ultrabells in its catalog, J.W. probably makes something for whatever motor/trans hybrid combo you can dream up.  To complete the TH400-to-BBF...  To complete the TH400-to-BBF adaptation, J.W. also offers a matching flexplate (part No. 93001) and crank spacer (part No. 80002-1) to ensure proper torque converter alignment on the input shaft. Essentially a BBF flexplate with a TH400 converter bolt-pattern, this J.W. piece is SFI certified and boasts a replaceable ring gear. It's offered in both standard- and lightweight trim, but for our straight-line application, we went with the heavier model.  After loading the forward...  After loading the forward clutch drum and input shaft into the case, it's time to bolt up the J.W. Ultrabell. This ingenious design bolts through the pump body and into the case using longer-than-stock bolts. TH400s were produced in both six- and eight-bolt front cover configurations, and the J.W. bellhousing will work with either case design.  Proper line pressure is critical...  Proper line pressure is critical in order to reliably engage the clutches and bands in a performance transmission. The orange pressure regulator spring used in our build provides just the right amount of tension for our application.  The primary objective of our...  The primary objective of our TH400 is to endure the rigors of track abuse, but it will also need to be friendly enough for the 200-mile roundtrip to and from the strip. Consequently, Phoenix installed a forward-pattern semi-automatic valvebody. This enables manual shifting capability at the track, but will also shift itself on the street with the gear selector in Drive. Opting for a transbrake would have required a less-street-friendly full-manual valvebody and a reverse-pattern shifter.  Phoenix includes a custom-matched...  Phoenix includes a custom-matched and balanced torque converter as part of its transmission packages. It optioned our converter with a heavy-duty one-piece front cover, reinforced fins, a machined billet hub center, bronze support bushings, Torrington bearings, extra long input shaft splines, a hardened pump drive, anti-balloon plates, and beefier springs and sprags. Since our project Mustang will be fitted with relatively small 275/60R15 drag radials, we had Phoenix set the stall speed at 2,000-2,500 rpm. While that may seem a bit tight, our big-block Ford kicks out 673 lb-ft of torque, and we'd rather take a conservative approach while dialing in the chassis to prevent blowing off the tires. If the car hooks hard and needs more grunt out of the hole, we'll have Phoenix loosen the converter up in the future.
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