I tend to disagree with this statement and this is why. Years ago cars were only making 300 HP and the rear ends and drivetrain parts needed to support that level of power were small. Look at the Dana 36 or the 7-5/8 rear end in the 4th gen Camaro, they were small and light duty. The power to drive these rear ends was low and the frictional losses from these rear ends due to oil drag and bearing friction was low. Step up to todays 650 HP cars and take a look at the E-Differential in vette. That is one impressive piece but it is large to handle all the power those cars put out. Large gears, large bearings, heavy duty half shafts, all good things to have but there will be more frictional losses with these items when compared to older smaller rear ends.

I have done a few back to back dyno tests of the small 7-5/8 ring gear in the 4-gen Camaro when compared to aftermarket rear ends like the strange S60 or the chevy 12 bolt and in those cases depending on the power output of the car I have seen the larger rear ends with the same gear ratio drop 12 to 15 HP with no other changes. It takes power to spin the larger larger rear ends, more losses from frictional drag of the oil and frictional drag from the bearings.

 

WAT R UR MoD5

 

So all these posts make me wonder who or how the new cars get dynoded from the factory. I know viper does their own. I wonder If they need really good tuners or what they look for in a standard for a tune, since they can be improved after purchase.

 

For sure the factory doesn't dyno every car. They dyno the engine during development when the production design is finalized. They dyno at the flywheel, with the engine set up like it will be in the car with everything installed - air intake, exhaust, accessories (AC not operating, as you might have guessed), emissions equipment. This is known as "net flywheel HP", which all manufacturers are required to use when advertising power numbers.

Not that they don't do chassis dyno testing. A former co-worker went to work for the GM Proving Grounds in Michigan back in the early 90's and sent us a picture of him standing next to NASCAR #3 on the chassis dyno - his comment: "This one was loud."

 

There are margins built in for production tolerances, but not nearly as much as there used to be. These days, onboard ECMs are sophisticated and fast, so they are programmed to sense knock and stay just inside the safe zone, for example. There aren't big gains to be had on a new car, and those that get some gains are flirting with the safety margins. The days of safely picking up 30hp with just a tune or chip are gone.

ETA: That is not to say that if you make mechanical mods, such as long-tube headers, on a new car there isn't power to be picked up from reprogramming. That's a different story.

 

Many an amateur has found out the hard way with these and others (S/C stangs esp) that its just best to leave them alone