Can't wait to see the "after" dyno Happy moddin' Jon

 

Thanks guys

Yeah i will be starting the modding in the New Year. Not masses of things planned, but will hopefully see a decent gain from the 3 i'm doing first engine wise.

 

Is there a standard correction factor for the Maha dyno? I'm confused how the crank hp is so high. Gabe?

 

Crank numbers are always a guestimate unless you pull the engine out and measure it on an engine dyno.

Even pulling the engine out, doing an engine dyno for a baseline, putting it back in the car, hopping on the chassis dyno, and figuring out the correction factor won't give you an exact number once you start modifying. Why? Drivetrain losses vary according to power. Once you start modifying the car, that correction factor will change. This way will give you the most accurate estimate, but even then, it'll remain an estimate.

Really, the best thing to do is to pick a good dyno facility, with an honest, competent operator with good attention to detail, powerful fan, fair pricing, and good availability. Start with them for a baseline, then stick with them. Furthermore, always get the "to the wheel" horsepower, torque, and (if you're picky) a/f ratio. This way, you'll always know if the part you just installed really gives you power, or gives you the shaft(tm).

As calibrated/sensitive as we each think our butt/ear dyno is, it never really quite compares to the real thing.

 

From Lincolnshire Jon, thankfully I have a really good and trusted RR within a couple of miles from me, which is ideal as I will be getting lots of runs done as will be testing various tuning boxes then a ECU remap to compare.......

IIRC the average MANUAL BMW drivetrain loss is reccond to be in the region of 23 - 28% ????

Doesnt an inertia RR measure the down run so you can accurately guestimate the drivetrain loss btw ?

 

Yes, in theory what happens is you run the vehicle up to a certain speed on the dyno, and depress the clutch. As the rollers slow down, the dyno measures the losses, assuming losses are linear with respect to speed. It gives you a negative horsepower number (basically the HP loss) at a given speed. You take that speed and you calculate (or look up) your RPM at that speed in that gear, which you then divide by the horsepower at that RPM.

In practice, that's in no way accurate. Drivetrain loss varies according to RPM, speed, transmission fluid temperature, coolant temperature, tire pressure, and a host of other things.

Do not be fooled by companies giving you guestimated crank numbers. Insist on getting the real wheel numbers.

 

I always go by RWHP anyways, its the only true reading

 

Thanks guys.

Also in regards to the Maha road that PS use. The drag figure is double that of what it would be on a Dyno Dynamics road because the wheel sits in between the 2 rollers so there are 2 contact patches on each tire thus providing twice as much drag so, drag figure is 66.2 BHP which makes the wheel figure 467.5 BHP

 

Sorry, this is not correct. DynoDynamics and Mustang Dynos both use two rollers, just like tha Maha. None of this changes the drag figure nor the wheel numbers. Furthermore, I have not seen a Dyno Dynamics dyno show a stock M5 at more than about 405 hp to the wheels unless some multiplier was applied.

 

Ok, well i'm only going on what i've been told by the people who run the RR at Powerstation. Either way, i can't imagine i'm loosing 120hp from fly to wheels.