As most of you know, the 2.0t FSI engine is equipped with balance shafts; two shafts that have weights strategically placed to cancel out the engine's secondary order vibration when spun at 2x the crankshaft speed.
Some of the big turbo build guys have picked up on the danger of running these balance shafts at high RPM's. It's seen much more frequently in the VW world than on our Audi's probably because we aren't as high performance or as fast to adopt builds as the VW guys. But you can imagine someone who builds their engine spends a pretty penny on gaining the ability to rev past the stock limited, some may even want to go past 8,000 RPM's, which means the balance shafts are working at over 16,000 RPM's when they aren't designed to exceed 14,000 RPM's. The only thing holding the balance shafts to the crankshaft is a very small gear that shares a chain with the oil pump and is affixed the the crankshaft oil sprocket. Shearing of this gear and the bolt that holds it is not something uncommon in the VW builds, and something we are starting to see in the Audi builds.
How do you prevent shearing?
1.Don't rev so high.....hah but I just spent all my money on nice valves and springs, of course I'm going to rev higher.
2.Delete the whole balance shaft assembly which includes the oil pump that is cast into the balance shaft housing.....that means delete everything inside your oil pan and convert to the 1.8t oil system, new oil pump, new crankshaft gear, new oil filter housing...lots of money. Even worse this adds quite a lot of vibration to the cabin, even more than the 1.8t already has with aftermarket mounts, because as engine size increases in a four cylinder inline application, the worse the vibrations get.
3. Perhaps some sort of dowel pin solution we haven't seen yet or a reinforced bolt and gear, basically an upgrade and revamp to the balance shafts to make them compatible at 8,000 RPM's.
One misconception I had was that balancing the engine before it's run would help. So I spent some money to have my machinist assembly my crankshaft from tip to tip, meaning from the crankshaft main bolt that holds the harmonic balancer, the timing gear, all the way back to the pressure plate. He "dynamically balanced" the crankshaft which meant he spun the crankshaft noticed where the imbalances where and drilled some holes out of the crankshaft counter-weights to balance its rotation. Don't get me wrong this is a great idea, I can't imagine what my car would be like without it, but this in combination with a fluidampr is no replacement for the balance shafts. If it were as simple as a machining process and a better harmonic balancer then Audi would not have spent so much time and money toward implementing balance shafts into their 2.0t FSI engine.
If you've ever looked at the balance shafts you can see that they rotate counter to each other, meaning their inertia is cancelled out in the horizontal plane, but they add force in the vertical plane at exactly a 180* frequency delay from the secondary order vibrations, and much like sound waves they cancel out. Meaning there is no replacement for the balance shafts, they are beneficial for the engine when you are trying to build a comfortable and reliable engine. That is not the purpose for most big turbo builds.
Most guys who build their engine's always talk about daily drivability, not ending up with a gt35, or any comparable turbo that provides power only at 5,000+ RPM's. Deleting the balance shafts is definitely the thing to do when you are going for power over any soft of comfort. You will get harsh vibrations, but you will be able to rev higher, at least to the extent that the HPFP doesn't float, and let's not forget it free's up some power by reducing the rotational mass of the engine probably somewhere around 5-8% of the engine's power.
This has all been information that has been around for a while, deleting that bulky housing and replacing it with the 1.8t oil pump will allow you to run more oil, gain some power back, and rev out, but no one has ever looked at fueling, we have extremely small injector windows and while this is still a relatively unadopted procedure, we don't know how it affects combustion.
I have 500 miles on my rebuilt engine with the balance shaft delete, and I have hit a wall, I have oil pressure that drops as my car warms up until it reaches 0 psi. I've swapped in two different 1.8t oil filter brackets, as well as the stock 2.0t oil filter bracket, ran three different oil weights, and the final thing left on the checklist is to replace the oil pump. There is a valve which I assume is a pressure relief valve in the balance shaft housing which I think will fix my issue.
I hope to have some updates soon, and I hope we can continue this balance shaft conversation so that we can become better at troubleshooting an area that is somewhat unknown to most FSI owners.
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Originally Posted by Scotty@Advanced
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