Originally Posted by Jonmartin
No one really knows the true drivetrain loss every dyno reads different, doesn't nesscessarily mean drivetrain loss its just measured differently. i.e. Average Dyno Dynamic will read 310whp or so with a stock M3 that would be about 33% difference from the claimed crank hp. On a dynojet the stop whp number will be between 335-350whp depending on the machine. That could me a 18% difference neither one means that the M3 is really losing the power its just measured differently.
Based on my experience nothing beats a custom tune. What might work for my car might not make the same power for your car why who knows. But fact is every car is different when modded and exhaust from company A doesn't just mean company B's exhaust will make the same or more power it could make less and that can be enough to require a different tune. But even if all the cars are the same with the same stuff certain cars just react differently when they're broken in differently different fuel all kinds of stuff but I have yet to see a OTS tune make the same or more then a Custom tune.
Unless you are running a full catless exhaust system there is 0 need for a custom tune. The engine management system in this car eliminates the need for custom tuning it actually wont let you custom tune it like the old days. With multiple input signals this engine management system calculates corrections on its own, you simply tell it what AFR targets you want and it will execute the corrections to achieve it. Where you can gain a little power on this stock motor is by setting ideal timing / AFR targets, adjusting the cylinder noise levels and adjusting VANOS controls. These targets are the same for ALL
stock cars. How a motor was broken in or how it was put together makes no difference.
When you run a full catless exhaust you can set custom targets to take advantage of the less restrictive exhaust and remap the VANOS control to correct for overlapping due to loss of back pressure. This is done by collecting data on the exhaust system with several dyno runs, comparing them to the original baseline and making corrections based on how that particular design is affecting performance and where there is room for improvement. This process when done correctly takes time.