A conversation with Eric Holliday, General Manager of Next Gen Performance Center.
When people shop for a performance Turbo 400, the conversation usually starts with horsepower: "How much power will it hold?"
That's obviously an important question, but there's a lot more that goes into building a TH400 for a serious racing application than installing a collection of billet parts and putting a horsepower rating on it.
Hard-part selection matters. But so do line pressure, converter charge pressure, converter exhaust, fluid volume and, ultimately, how the transmission and torque converter work together as a complete system.
For us, that's especially important because so many of our combinations are behind Ford Modular and Coyote engines, where taking care of the engine's thrust system is something we pay very close attention to.
How do you determine the horsepower rating of a TH400?
When we're building a Turbo 400 for a specific power range, parts selection is a key component.
If I tell a customer that I expect a transmission to support 1,500 horsepower, we're going to select and install components that we realistically believe will support north of 1,500 horsepower. There needs to be some cushion built into that number.
Nobody wants to buy a transmission rated for 1,500 horsepower and find out that its actual limit is 1,501.
But once we've established that the hard parts are capable of supporting the intended power level, there's another side of the transmission that becomes extremely important: the hydraulic system.
Why is converter fluid flow so important in a high-horsepower TH400?
One of the next things we address is fluid flow to and from the torque converter.
A large percentage of the applications we deal with are Modular Ford and Coyote combinations. These engines have a relatively sensitive thrust system, so we don't want the transmission unnecessarily pushing forward on the torque converter and ultimately loading the crankshaft thrust bearing.
That means we pay very close attention to:
- Line pressure
- The converter-feed circuit
- Pressure regulation
- The rate at which we're supplying oil to the converter
The goal isn't simply to reduce converter pressure. The goal is to supply the converter with the amount of oil it actually requires to operate correctly while controlling the pressure within the system.
That's also one of the reasons we offer our split-circuit setup. Instead of simply relying on the traditional internal circuit, we can create a system that gives us considerably more control over how the converter is supplied with oil, based on what that particular converter requires.
What happens when you put too much oil into a torque converter?
There are actually two sides to this problem. You can overfeed the converter, or you can under-exhaust the converter. They're different problems, but they can produce essentially the same result.
If we're putting too much oil into the converter, not allowing enough oil to leave it, or some combination of the two, pressure builds inside the converter. That pressure can physically force the converter forward toward the engine, and now we're applying forward force against the crankshaft and its thrust bearing.
Historically, converter ballooning could also be part of the problem. We don't see that nearly as often with today's quality performance converters, thanks to anti-ballooning plates and improvements in converter construction, but excessive internal pressure still isn't something we want.
And engine thrust damage isn't the only concern. A converter that's being overfed, or can't adequately exhaust, isn't necessarily going to operate the way it was designed to operate.
That's why we don't look at converter charge by itself. We look at the complete circuit.
Isn't cooler-line pressure the same thing as converter charge?
This is an area where I think people can get overly focused on one measurement.
On a Turbo 400, people tend to put a lot of emphasis on what they see at the cooler line because it's easily accessible. But we're interested in the entire system: what's going into the converter as well as what's coming out of it.
Over the years we've spent a lot of time looking at how much fluid different converter combinations actually require. We've tested things, documented the results, compared combinations and continually refined what works and what doesn't.
That's an area where I believe we've really excelled with Coyote combinations. Instead of treating every converter exactly the same, we're trying to understand what that particular converter needs.
Does converter size change its fluid requirements?
Absolutely.
We have combinations that we use repeatedly, and with those packages we already have a very good understanding of where we need to start.
If you buy a complete transmission and torque-converter package from us, chances are it's a combination we've worked with over and over again. We know the converter, and we know the transmission.
Ready to build your TH400 combination?
Whether you're swapping a Coyote Mustang to a Turbo 400 or stepping up to a higher power level, we'll help you put together a transmission and converter package that works as a complete system.
- Shop TH400 Swap Kits & Parts
- Shop Torque Converters
- Questions? Call us at 410-729-0005 or contact us.