Regulations can be good.
"This entry is part of a Special Series on the S54 GrandAm Forged Steel Flywheel.
My previous experience with an S54 single mass flywheels was atrocious. If a flywheel will make the cut for my build, it might be this one.
In this entry, I take a brief detour into the BMW GTR, GrandAm and its regulations. I then unbox and document what makes this GrandAm flywheel special and my expectations for street car."
- Matt
American Lemans, and the infamous GTR.
The E46 M3 racing pedigree is most often associated with the infamous E46 M3 GTR race car in American LeMans Racing and its unique V8 engine: the P60. Its 4.0 V8 is perceived as a predecessor to the S85/S65 pair of engines that followed in 2005 and 2007.
On the surface, it makes sense: the P60 had an oversquare engine design with a 94mm bore to a 72mm stroke in a complete aluminum engine. It sported a quad cams, 32 valves head with a flat plane crankshaft, making 444hp at 7,500 RPM.
Specs that are awfully similar to the S65/S85. Yet there is no direct, immediate lineage between the P60 and S65/P65 street & race engine configurations.
The S65 is instead directly related to the S85, and its F1 heritage.
GrandAm, and the less famous GTR.
The E46 M3 GTR also raced in the Rolex Grand-Am by a privateer team owned by Tom Milner. The Prototype Technology Group (PTG) to compete with the Porsche 911s in the Grand-Am Rolex Sports Car Series back in the early 1990s.
PTG built 5 cars for the series: 3x chassis were given the dry sump'ed S54/P54B32 and the last 2x chassis were given a dry sump'ed S62B50.
GrandAm attracted various racing teams that have become household names in the BMW industry today: Turner Motorsport and BimmerWorld.
The GrandAm regulations.
The Rolex Grand-Am Series was founded as a Sports Car series first, introducing prototypes racing later in the series' evolution. The Grand-Am races were known for a lot of action, with over 50 cars on the track at any given time.
The series's popularity was in large part due to the ease of use and low cost of the cars in all classes. This was derived from the regulations draw up by the Grand American Road Racing Association.
GrandAm merged with ALMS in 2013 to form IMSA.
The flywheel regulations.
Relevant to this entry are the regulations surround the flywheels, GrandAm mandated a maximum weight reduction of 20% to the flywheels versus the original manufacturer component. The flywheels could be single mass, eliminating the dual mass flywheel mechanisms of street cars.
The rationale was around cost management: lighter flywheels have higher risks related to engine and transmission failure, and dual mass flywheels are more expensive to replace.
TTV Racing's centralized mass design.
TTV Racing designed a flywheel back in the 2000s to meet GrandAm regulations specific to the S54 race engines and 420G transmission. They came up with a clever design that focused on superior material selection and optimized machining to reduce rotational inertia where it matters most.
As a very niche product, this flywheel was made to order on my request. It took a few weeks and I received it on Jan 9th 2024.
I filmed and edited a reel with voiceover commentary here.
The theory.
I previously documented the science related to flywheels in my V10 experiments in "It's science bro!". I didn't deep dive into rotational inertia itself, here, it is a critical component highlighting TTV's design brilliance.
The dynamics of the theory are relatively simple: weight that is further out of a flywheel requires more engine power to rotate. If regulations would limit maximum weight reduction, where do you try to remove most weight to optimize for performance? Further out of the circle!
This is exemplified in TTV's S65/S85 Clubsport's Transmission Package. The flywheel is machined down from 240mm diameter to 215mm and paired with a smaller clutch.
The real world application.
The S54 flywheel is designed to fit with original clutch diameters as mandated by GrandAm. As such, the clutch facing side of the flywheel is very similar to OEM as the friction surface remains the same.
There is no additional pocketing by the crankshaft to further reduce weight, nor can the flywheel's diameter be reduced.
As a hint of the centralized mass design, you may notice some concentric machining lines towards the crankshaft bolt holes.
The engine facing side of the flywheel is usually where the dual mass mechanism of the original flywheel would be. It's entirely deleted in this design, making it a single mass flywheel.
The crankshaft mounting points is where there is the most mass remains. Zooming in, this is where TTV optimized the central mass design.
A key enabler of this design is the material selection. The carbon forged steel used by TTV is of higher density than aluminum. It allows the central mass design to be optimized within a smaller, centralized diameter section of the flywheel.
At 8.8 kg / 19.4 lbs - I do not consider this is a lightweight flywheel.
The GrandAm flywheel is machined to be compatible with Genuine BMW clutches or equivalent replacement units. It has the needed threaded mounting points and dowel pins.
The flywheels are dynamically balanced in-house. With only a 20% weight reduction, this was the lowest count of machined balancing holes I've seen on any TTV Racing flywheels.
There were 3x in total.
The crankshaft bolt holes are machined to fit with Genuine BMW hardware (SKU: 11227805885). One of the hole is further machined to indicate starter alignment.
The outer diameter is precisely machined to fit with the engine starter.
My previous S54 flywheel experiences.
I bought the Phoenix with a VF Supercharger bolted to my S54 paired with a Turner Motorsport lightweight flywheel and Sachs HD clutch. The sprung single plate clutch was excessively heavy, and the flywheel was, by far, the loudest sack of bolts dropped into a transmission I have ever heard.
It made driving the car insufferable in any conditions but long drives.
The Turner flywheel was 7.5 kg / 16.55 lbs and made from chromoly steel.
Why this matters to me.
TTV Racing's centralized mass design has the potential to be what I consider the ideal sweet spot for a street driven S54.
- Light enough to improve engine and drivetrain response.
- Smartly removed weight to enhance the driving experience and not sacrifice daily drivability.
- Compatible with OEM clutches or equivalent.
One question remains: will it be as loud as my previous Turner unit?
Up next: I document the installation of this flywheel, and later on, my driving impressions.
I can source the GrandAm flywheel for your S54 project year long here.
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