Why Get a Lightweight Flywheel?

By Matthew Eddy - 2018-07-20

First, Ill explain why a lightweight flywheel is beneficial. Obviously, any racer knows, that reducing the weight of the vehicle is always good. In fact, nothing improves a car more than reducing weight because you can accelerate faster, stop quicker and turn harder. Basically it checks all the boxes when it comes to improving performance, so just on weight reduction alone it provides some advantage. Additionally, there is another benefit when it comes to what is called “parasitic power loss.” What this means is the engine uses some of its power to move internal components (pistons, crankshaft, etc) and driveline parts (driveshaft(s). A lot of this is unavoidable, but some of it can be reduced be eliminating as much mass in the system as possible.

They flywheel is one of the heaviest single component in the drivetrain – depending on the vehicle. It serves a few purposes such as helps to start the car, stores energy to smooth out the engine, and ease shifting by keeping the RPMs from dropping quickly (or at least that is some peoples opinion). Essentially, its to make the driving experience more pleasant. However, for a more race/performance centric car this is less of a concern and instead the focus is on speed and power. So taking this heavy flywheel out (for perspective the one in my E36 BMW weighs about 24lbs) and replacing it with a lighter one will reduce the overall weight of the car and more importantly reduce the amount of mass the engine has to turn and that means more power to the wheels.

There are a few different lightweight options available depending on the application. For lower power cars such as my stock BMW that produces 190hp, a good option is an aluminum flywheel. As I mentioned above, the stock flywheel weights 24lbs, the aluminum flywheel is only 10lbs. Now, an aluminum flywheel is not 100% aluminum, the ring gear that the starter engages will be steel, and the face the clutch will grab will be a hardened steel plate riveted or bolted on because the aluminum will just get torn up. You can see the pictures of the flywheel I just purchased for my BMW below for reference. Another claimed benefit is for some cars with dual mass flywheels, the single piece lightweight flywheel improves reliability since the dual mass flywheels can fail when you ham-fist your shifts during some spirited driving.

There is a steel plate bolted to the face of the flywheel where the clutch engages

Other side of the flywheel

Now aluminum is great but some engines produce a lot of horse power and the aluminum may not be able to stand up to it. You choose to go with something that is a bit stronger such as one made from chromoly. The weight savings are not as good but it’s still fairly significant. One for my car would be 11-14lbs (depending on brand) which is a 10-13lb weight savings over stock but still 1-4lbs heavier than the aluminum one. What is chromoly? It’s a particularly high strength steel alloy with relatively high amounts of chrome and molybdenum. It’s from Chrome and Molybdenum that the term chro-moly comes from and is designated as 4140 steel. Most flywheels are made from cast iron which isn’t particularly strong but its cheaper to make. Using high strength steel the weight savings come from the flywheel being a lot thinner and holes are added to remove additional material as well. I am not going to tell you which is best to go with, you may have to do research on your particular car and what makes the most sense for your application. Fidanza has an interesting article that you might light to read for some additional information.

https://fidanza.com/aluminum-vs-steel/


What is 6061 T6 aluminum? 

There are multiple alloys of aluminum out there but the most common “billet” type is 6061 T6. The 6061 designates the alloy, and the T6 is a reference to how it was heat treated. This allow also comes in tubes, bars, sheets etc. So pretty much any aluminum flywheel will be made with 6061 T6, but its also a very good alloy of aluminum. Billet simply means it was made from one big chunk of metal. There really is not any other way to make a flywheel, but it sounds cool to say “6061-T6 billet aluminum flywheel.”   

OK Cool But How Much POWER do I Gain?

This may vary significantly per engine and how much of a weight savings you are gaining over the stock flywheel but if the test done below is any indicator – it may be 1-2% gain in peak horse power and 2-3% gain in peak torques at the wheels. This may not seem like a lot, and its hard to say that this directly correlates, but if we say this could translate to 1-2% reduction in lap times that’s not too shabby.

http://www.superchevy.com/how-to/engines-drivetrain/1502-how-to-add-hp-with-a-lighter-flywheel-why-weight/

Why I Won't Buy A GT-R!

They haven't built a new car here, they've built a new yard stick. 

-Jeremy Clarkson, Top Gear, season 11, ep 4

Would I buy a GT-R?

There is a whole sack full of words that can be used to describe this car; words like awesome, brilliant, superb, cool.  It is most certainly a very competent car that is amazing not just for its driving capabilities but also the price.  There is only one other car that I would classify as a super car that wasn’t also super priced, and that was the early generations of the Dodge Viper.  Of course, affordable is a relative term, but in this regard I mean that this car is within the grasp of the middle class, of which I belong.  So if I returned by bottles and cans, and stopped eating out so much, I could buy one.  One huge benefit of the GT-R over the Viper is that with all of its gee-whiz gadgets, and magical traction control, it won’t kill you if you make a mistake.  It is almost like the Mitsubishi EVO 10, except better looking, a ton more power, and electronically controlled suspension.  The concepts between the two are the same; take a car with an extra helping of horsepower, plop it onto an all wheel drive power train, then tie it together with sensors and computers and then turn it loose.  For the driver, the car offers thrills that are hardly matched since you can push the cars right up to the very edge of their limits and then dance there all day long.  Not that you can’t exceed its’ capabilities, I have seen to many Youtube videos of EVO drivers stuffing their cars into walls. But to wreck the car they committed some very grievous errors.  Compare this to the Viper, all you have to do it look at the corner wrong, and the car will punish you.  It is to easy to give the engine just a little to much air coming out of a turn and suddenly the wheels spin, the car spins and your head spins just before you hit the wall.  Don’t misunderstand me, I am not criticizing the Viper, and I am exaggerating a bit, but the Viper requires more from the driver and because of that, a driver, especially a less experienced one, would be more timid to explore the cars limits. 

If you haven’t heard the specs by now, then you have been living in a cave, and if you have been living in a cave here is a quick summary of its stats.  This car is strapping a hand assembled 3.8L six shooter, with twin turbos that push a minimum of 480 horses to all four wheels.  I say minimum because the engine is hand assembled and there is some variation among the cars; some testing at well over 500 from the factory.  0-60 time is around 3.5 seconds, and with the new launch control (the first iteration of the launch control would apparently destroy transmissions after 5 or 6 launches) it may even do it as quickly as 3.1 seconds.  Large 6-piston Brembo calipers are ready to grab the 15” two piece drilled and slotted rotors, and bring the stout 3800 lb car to a stop in 104 feet when traveling at 60 mph. The transmission is a 6 speed semi-auto paddle shifter deal with dual clutches, feeding the 50/50 power to the front and rear wheels when at low speeds or accelerating hard, but normally it will feed 70% of the power or more to the rear wheels.  This is all well and good but the stats I am more interested in are lap times.  Nissan claims a lap time of 7:26 around “the Ring” (Nurburgring, if you don’t know what it is, look it up) on stock tires, which is very impressive.  On the Top Gear test track, the car posted a time of 1:19.7 which is .7 seconds slower than an Enzo and in front of the likes of the Carrera GT, C6 ZR-1, and the Audi V10 R8; all cars that are priced well above $100,000.

Quick List; 4 Reason to Buy the Car:

One, the car is stupid fast.  480 horse power!  0-60 in 3.5 seconds!  Come on!

Two, you can drive the car quite tamely on the street as a daily driver.  The leg room in the back isn’t enormous, but it is functional.  It also has a trunk you can put groceries into.  It is all wheel drive, so in snow, wet weather or other low traction scenarios the car will be fun; I mean safer.  Four wheel power slides in a parking lot covered in fresh snow is one of my favorites!  So, getting back on subject, you could buy the car to drive to work and on weekends take to the track to play.

Three, for the weekend warrior, this car offers a lot of thrills.  You don’t have to be a Mario Andretti or Lewis Hamilton to be able to drive the car at 9/10ths it capability since all these little computers and sensors will help keep you pointed in the right direction even if you try to take a corner too fast. 

Four, it is not a common car.  Here in Michigan it would be more common to see a Ferrari Modena then a GT-R.  Many people may not agree with me on this, but I want a car that is at least some what unique. 

What it comes down to, is the car worth it?  With a price tag of $80,000 USD, car far surpasses anything else out there in terms of speed, corning capability, practicality and thrill, so it seems like the car is perfect.  Now that I have sung the cars praises and given you four reasons to buy is there any reason NOT to buy it?  I thought it would be interesting to contrast the four reasons to buy the car with 4 reasons not to buy the car but I could only think of one; it is not a driver’s car.  It is a fun car on the track and it is definitely a new yard stick in performance and price, but the car is too good!  Really, too good?  Does that just sounds like the words of an irrational hater?  What I mean is that it doesn’t challenge the driver.  When I was at an open track day (in NASA speak, I was at an HPDE), the running joke was that you can just program in your lap time and then hit the “go” button.  A car that is “too good” is a car that does all the hard thinking for you.  Miss the braking point and turn into the corner carrying a little extra speed and the car steps in to figure out how to save your sorry butt.  The novice drive continues on down the track thinking he is godly as he passes the Vette and the Ferrari not realizing that if he did that in any other car he would have spun or taken an off-roading adventure.  If you like the thrill of the track and you want something fast that won’t try to kill you, this is the perfect car.  If you a very experienced driver and are looking for something you can drive to the track, spank Porsches and Ferraris, then this car is for you.  But, if you are a road racing beginner and you want to become the best driver you can then DO NOT buy this car.  It won’t teach you.  You would eventually get to the point where you could drive this car close to its limits, but once you got into something with more teeth, you will find yourself wrapped around a tree or in the wall.  A Miata, Solstice/Sky (non turbo), RX-7 (non turbo), an old E30 (mid-late eighties BMW 3-series) or anything comparable, would be a far better teacher, and much cheaper.  The GT-R is an amazing car, and I would love to own one, but only if I can also have a good drivers car.