FLYWHEEL TECH. BULLETIN
FLYWHEEL SELECTION FOR HIGH COMPRESSION ENGINE APPLICATIONS AND RING GEAR FAILURE.
During recent years, the use of engines having compression ratios upward of 18:1 has pushed the envelopes of many materials. In the case of flywheels, in some instances, stresses on ring gears have exceeded material strength. A worst-case example is a high compression engine that uses a small diameter, 130-tooth flywheel.
Although ring gear failure may occur at any time, the cause of the failure most often is generated during startup. Consider the forces to which the ring gear teeth are exposed:
During startup, inertia and high compression must be overcome to bring the rotating assembly up to cranking speed. Ignition timing then enters the equation. Advanced timing is very likely to cause engine “kick-backs” thereby introducing substantial additional pressure on the ring gear.
Although the use of ignition retard devices is helpful, it is wise to consider the fact that during startup, the engine must rotate a few degrees before the timing is actually retarded. During that time, the ignition is at its advanced setting. Should ignition occur during those few degrees of rotation, the force on the ring gear is dramatically increased.
During the period when ring gear force is maximized, tooth failure may occur. In addition, very minor cracks may be created in the area between the teeth. Some are detectable under close visual inspection while others may only be seen under a microscope. Cracking to any degree demands flywheel replacement prior to further operation.
Once cracking begins, it is only a matter of time until the crack travels completely through the ring gear (i.e. Crack Propagation). At that time, centrifugal force begins to separate the ring gear from the flywheel. As the ring gear separation increases, so doe’s centrifugal force. Usually, the ring gear separates from the point of the crack to the next weld area. At times, the force is sufficient to cause the entire ring gear to separate from the flywheel. Close inspection of failed flywheels revealed the fact that much of the ring gear remained attached to the weld, clearly indicating the fact that the forces had exceeded the strength of the ring gear material.
As a note of interest, larger diameter flywheels are exposed to a higher centrifugal force, yet their failures are substantially less frequent. The reason? Larger diameter flywheels provide more leverage and are therefore subject to less stress during cranking.
To reduce flywheel stress, many racers use ignition switches in addition to retard devices. Until the engine reaches cranking speed, the ignition switch is turned off. When the switch is turned on, the engine benefits from the same inertia force that was previously a deterrent and “kickbacks” are less likely to occur. JW highly recommends that ignition timing management be used in all applications at and above 12:1 compression ratios. While this is not a “cure-all”, it contributes to flywheel stress reduction.
Most every manufacturer of ring gears use 1045, 1050 or comparable materials. While these materials easily accommodate OEM and most high performance applications, they are unsuitable for some applications such as super-high compression alcohol engines. Critical applications require much higher strength gear material such as 4130-chrome moly. Ring gears made from that material are difficult to obtain thereby leading racers to one-piece, billet flywheels. While higher strength, one-piece flywheels may be expensive; their cost is far less than that which results from vehicle damage and potential personal injury. Carefully consider your application before you select your flywheel.
If you have any questions, we invite you to give us a call. JW Performance Products, Inc. has been serving the race industry since 1976. We would be happy to share our knowledge and experience.
Those who have R & D concerns or product concerns should contact Ken Frederick at 321-632-6205 or e-mail to firstname.lastname@example.org.
New JW Ultra-Bell Brings Strength And Rigidity To 700-R4 Trans!
Rockledge, Florida – JW Performance Transmissions introduces a new Ultra-Bell, high-strength, one-piece, racing bellhousing for the GM 700-R4. Part No. 92450-700 is a one-piece design engineered to be both super stiff as well as super strong, for serious drag racing use. Increased rigidity in the critical bellhousing area means more accurate alignment between the engine’s crankshaft flange and the transmission input shaft. This reduces or eliminates side-loading, and that delivers more power to the rear wheels, for quicker ET’s and more MPH. The increased strength and rigidity also reduces component failures due to mis-alignment that is common in extreme-torque drag racing applications.
The JW Ultra-Bell also designed installs under stock floorboards, and is SFI certified and NHRA/IHRA approved.
Installing the new JW 700-R4 Ultra-Bell is easy. Just remove the stock bellhousing (easily cut in a garage band saw) and then bolting the Ultra-Bell to the transmission’s front pump. JW even provides Grade 8 fasteners to complete the job.
JW’s new Ultra-Bell, one-piece, aluminum alloy bellhousing for the GM 700-R4 transmission, Part No. 92450-700, and other fine JW products are available by calling the tech help folks at JW Performance Transmissions, 1829 Baldwin Street, Rockledge, FL 32955, (321) 632-6205, or visit their website at: www.racewithjw.com
New JW Trans-Brake Brings Quicker Launches,
More Consistency And Greater Reliability To TH-400!
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Story By Jim Hill
When it comes to race performance, there’s a “holy trinity” of automatic transmissions produced by General Motors and used by their various divisions. These three most popular transmissions are the Powerglide, a two-speed automatic that first appeared as a cast-iron unit available in 1955 Chevrolets; The Turbo-Hydramatic 350 (TH-350), first offered for the V-8 ’68 Camaro; and The Turbo-Hydramatic 400 (TH-400), for high torque engines such as the big-block Chevy 396-427. The TH-350 and TH-400 units both offer three forward speeds and have two sets of planetary gears. All three are known for their basic simplicity and reliability.
Of the three units the Turbo-Hydramatic 400 is the strongest. Like the TH-350, the Turbo-400 offers three forward speeds plus reverse, neutral and park, and is especially favored by racers running heavier full-bodied cars, high-torque, big-block engines or those running “power enhancers” such as superchargers, turbochargers or Nitrous-Oxide. Turbo 400’s are also rules-required for some NHRA and IHRA Super Stock and Stock Eliminator classes in which the 400 was offered as the production transmission for specific big-block engine options. Those very famous and now rare L-72 C.O.P.O. option, 427-425 HP ’69 Camaros and LS-5/LS-6 454 Chevelles and Corvettes came with the TH-400 as did big-block powered Chevy and GMC trucks.
Because the Turbo 400 is a bigger, beefier version of the GM TH-350, this added strength comes with increased rotating weight and mass of its gears and internal components. As all good racers know, weight and mass absorbs horsepower produced by the engine, and those stronger, wider gears increase what the engineers refer to as “parasitic loss”, due to greater friction. Just how much power is sacrificed to a TH-400 over, say, an aftermarket design, two-speed Powerglide varies by application. Despite this shortcoming, when power and torque exceed the capability of an automatic transmission to resist component failure, the answer is often found in a Turbo 400. It’s also still reasonably easy to locate a used Turbo 400 transmission core as a starting point, and the cost of a racing rebuild is also still attractive.
To compliment their inherent strength, the Turbo 400 can be readily improved with upgrades, courtesy of the very innovative performance and racing aftermarket. Improvements such as numerically higher, first-gear sets, improved clutches, steel separators, bands and other components render this already robust transmission even stronger. When high HP engine output or heavy-car issues are at hand, this added strength is obviously welcome.
The next obvious improvement to the TH-400 has to be the addition of a reliable, electronically activated Trans-Brake, to allow more precise driver launch control and to raise starting line engine RPM. JW Performance Transmission, the same Florida folks who created the Ultra-Bell replacement bellhousing and “The Wheel”, steel flexplate flywheels for serious drag racing, now offers a brand new, precision manufactured, JW Trans-Brake for Turbo 400’s.
JW’s new Trans-Brake brings the instant engagement capabilities of a Trans-Brake to the proven strength of the TH-400. This combination of brute strength plus consistent, accurate engagement means more consistent starting line launches, quicker 60’ short times and lower reaction times when correctly matched with the right torque converter stall speed, cam profile and traction availability. When these items are properly matched the result is more round wins with less breakage, something any serious racer is seeking.
JW’s new TH-400 Trans-Brake is available as Valve Body Part No. 30218-RN, or Trans-Brake Part No. 30550-BRN. The JW Trans-Brake is a Reverse-Only manual brake design, and allows you to take greater advantage of the stall speed of the selected torque converter by increasing the engine speed (rpm) at which the car leaves the starting line.
While it’s not the same as a Pro/Stock, sky-high launch, a properly set up, brake-equipped automatic transmission and tuned suspension system offers a tremendous upgrade in performance potential and launch consistency.
A specific advantage to this new Trans-Brake, according to JW President and founder, John Winter, is it operates with lower line pressure while in Park or Neutral, but provides increased line pressure when in 1-2-3. The new JW design valve body is CNC machined from T-6 aluminum alloy material. CNC machining is significantly more accurate than the casting processes used by other manufacturers, and allows dimensions in all fluid passages to be tightly controlled. This machining accuracy translates into improved response, quicker release and quicker, more precise upshifts.
Each JW TH-400 Trans-Brake is carefully assembled by master racing transmission technicians, and then each unit is in-house tested for both performance and reliability on JW’s own transmission dynamometer. John Winter’s dedication to quality is commendable, but he is quick to explain that it’s the only way he can guarantee a 100% fail-safe unit going to racers. John’s oversight and insistence on this quality is something he championed when he began JW Performance Transmissions 30+ years ago, and this credo continues throughout the company’s product line. In drag strip field tests of the new JW TH-400 Trans-Brakes all those who tried the new brakes reported complete satisfaction with the new units, and more importantly, zero failures!
GM’s Turbo 400 units were installed in several hundred thousand, big-block powered Chevy cars and trucks, but in spite of those OE numbers, Chevy TH-400 units still have the lowest total GM production numbers. These carried a Chevy bolt pattern bellhousing. Considerably more TH-400’s were installed in “B-O-P” (Buick-Oldsmobile-Pontiac) vehicles, but these vehicles used a different B-O-P bellhousing bolt pattern. TH-400 Chevy units are more difficult to locate, and of course, are more pricey than B-O-P 400’s. But, the hot rodder inspired, performance aftermarket now offers a viable solution, a sturdy, reengineered, aftermarket bellhousing that carries the more desirable Chevy bolt pattern.
One such example is JW Performance Transmission’s “Ultra-Bell” unit. These require careful band saw removal of the stock bellhousing so the 400 transmission case can be used with the aftermarket housing, but this also allows use of the less expensive B-O-P Turbo 400 transmission. Taking a saw to an aluminum case transmission may make you nervous, but the folks at JW tell us this is merely minor surgery, and the “patient” is well served by this procedure. After this it’s a fairly straightforward job to adapt a B-O-P unit for easy bolt-on to a Chevy simply by using a JW Ultra-Bell. This modification also yields a TH-400 unit that is significantly stronger, due to the race-inspired, structurally improved design of the Ultra-Bell housing. Reducing or eliminating trans case flex insures that internal components remain in place, retain their alignment and reduce more of that pesky parasitic power loss due to side-loading of gears when a stock case does the “hootchy-cootchy” while being torqued by a big-inch, big-torque, big-block engine. It’s a classic case of a situation where being completely inflexible is a drag racing attribute!
The new JW TH-400 Trans-Brake is a perfect addition to a JW race transmission system. This includes the new JW Trans-Brake, a JW Ultra-Bell one-piece racing bellhousing, a JW “The Wheel” flywheel and a complete JW built racing transmission for a driveline package that’s not only stronger and more reliable, but quicker and more consistent. And that’s what drag racers everywhere are seeking!
The new JW TH-400 Trans-Brake Valve Body, Part No. 30218-RN, or Trans-Brake, Part No. 30550-BRN, and other fine JW products are available by calling JW’s performance/racing drivetrain tech help experts at JW Performance Transmissions, 1829 Baldwin Street, Rockledge, FL 32955, (321) 632-6205, or their website at: www.racewithjw.com