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Old 08-15-2011, 10:48 AM
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chilliwilli chilliwilli is offline
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Impressive data indeed...

However, can't help but wonder that while all tunes carry potential risk of user/manufacturer error, i'd prefer the less worrisome if error were to ever present itself.

I found the below regarding dyno accuracy to be interesting...

Quote:
Originally Posted by Stive Dinan
By far the most significant criticism I have for many dyno facilities is the use of fans that are simply too small for the job at hand. The fan size is so significant that we employ a very large unit that was actually designed for ventilation systems installed in high rise buildings! This powerful fan produces 38,000 cfm of air flow @ 75 MPH, which is still less than the 150 MPH air that a modern BMW might see at redline in 5th gear, but it certainly provides a closer to real-world scenario than the more common fans I have seen used in dyno facilities. It should be noted that 5th gear is used for our dyno testing because it is one to one, meaning that the input and output shafts are connected, reducing power losses and transmission wear. I have seen many examples of dyno facilities where low flow fans obtained from the local hardware store are employed, and even situations where there was no fan at all. A minimum of 15,000 cfm and preferably 40,000 cfm of air flow is required for proper heat exchanging. This type of fan will produce a 40-80 mph air discharge velocity.

A lack of air-flow during dyno testing will almost always alter the fuel mixture in the rich direction as the radiator cannot exchange enough heat, resulting in the computer compensating by retarding timing and richening the fuel mixture to prevent the engine from overheating and detonating. In addition, the intake air sensor will read substantially higher temperatures than that seen on the road with proper airflow. This issue is particularly important to address when testing high output cars like the M5 or M3, and even more so on forced induction cars with intercoolers as the heat exchanger is not able to cool as efficiently because of the reduced air flow. The engine compartment is normally flushed with air driving down the road, particularly at speed, cooling the manifolds and other associated engine components. Cooler engine components and lower air intake temperatures will result in a leaner air/fuel mixture and ignition timing will be advanced, invariably resulting in greater power on the road than on the dyno. In simpler terms, accurate measurements can only be achieved when the dyno tests are conducted in a manner that simulates the car driving down the road, in as much as is possible.
From 13:00 mark:
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