Dyno'ing an AWD on a FWD Dyno.

[PieEyedPiper]

In this thread:
http://www.dsmtuners.com/forums/showthread.php?t=226325

People are barking back and forth about this subject. No one came up with much of an argument, it was more or less, "no, it won't" or "yes, it will".

Personally, I believe there is an almost identical benefit to dyno'ing an AWD on an AWD dyno and dyno'ing an AWD on a FWD dyno.
My reasoning is we're not tunning the engines ability to turn the drivetrain parts, we're tunning the engine for the most efficient air to fuel ratios. End result? More HP and more torque.
I believe that it would make sense that if you dyno'ed an AWD on a FWD dyno, you'd end up with the same gains you achieved in FWD mode as AWD mode, becuase all we've done is optimise the air/fuel ratio so that the engine can better, or more efficiently, perform it's function. Drivetrain loss/traction will not effect the tune of the engine to any degree I can concieve on my own.

I will, however, admit that it is most likely possile to have a SLIGHTLY more accurate tune by tunning based on the exact kind of loads that particular vehicle will see (running in AWD mode, of course).
But I also believe the difference would be merely an ethereal item that would never have any real-world impact.

I know there are a few nay sayers out there, and I'd be interested in a supported rebuttle.

agreeing or disagreeing, please post back.

 

[JayRolla]

I agree with you. I think you would beable to tune the car just as well. It may be minimal difference from the load you would get on the motor with 4 tires instead of two. So I agree with yea.

 

[92awddsm]

Mine has been tuned on a fwd dyno and worked perfectly in awd. The closest awd dyno to me is about 45 miles. The closes fwd dyno is about 10 miles. Why would I travel the extra difference for the same service? Im not worried about how much power I made, Im more worried about my tune.

 

[kenamond]

The problem is that you can't dyno test an AWD on an FWD dyno. The rear wheels want to turn, but there aren't any rollers connected to the dyno for them to sit on.

That was part of the point of that previous thread; if you had the option of disengaging the rear wheels, then you COULD dyno test an AWD car on an FWD dyno by switching to FWD mode.

And I agree that dyno tuning has nothing to do with the drivetrain unless you're trying to evaluate drivetrain changes, losses, rotational inertia during acceleration, "will it break at Xwhp?", etc. If you had the luxury, you'd do all of your engine tuning on a stand-alone motor bolted to a dyno without the car (or drivetrain) being involved at all. That way, you can swap out parts without them being buried in the engine compartment, you can submerge your IC in a vat of room-temperature (or hotter) water to dodge heatsoak or to emulate a particular IC efficiency, you can put a pressure gauge on your ex. mani and run it however you want, etc. If you're tuning the motor, you can do it FWD or AWD.

But if you have an AWD, you can't use it on an FWD dyno, so what's the point.

 

[kenamond]

Mine has been tuned on a fwd dyno and worked perfectly in awd. The closest awd dyno to me is about 45 miles. The closes fwd dyno is about 10 miles. Why would I travel the extra difference for the same service? Im not worried about how much power I made, Im more worried about my tune.

How did you dyno your AWD on an FWD dyno?

 

[ALLBoostAWD]

For tuning purposes it is completly fine to use an FWD dyno with an AWD vehicle. When tuning you are comparing HP/TQ/AF numbers with changes to the Air,Fuel, timing, boost etc. HP and TQ will rise and fall with these adjustments regardless of the drivetrain.

If you want numbers for HP and TQ they wont be correct but you can get an idea.

A FWD vehicle usually losses 15% of the Rated Flywheel HP going to the wheel. meaning a car rated at 200HP will put down about 170 HP to the wheels.

An AWD vehicle roughly losses 25-30% of flywheel HP to the Wheels, so if your going to dyno the front wheels in an AWD then subtract about 10-15% from the number you get at the front wheel.

should be ended.

 

[ALLBoostAWD]

The problem is that you can't dyno test an AWD on an FWD dyno. The rear wheels want to turn, but there aren't any rollers connected to the dyno for them to sit on.

That was part of the point of that previous thread; if you had the option of disengaging the rear wheels, then you COULD dyno test an AWD car on an FWD dyno by switching to FWD mode.

.

I disagree. This can be done, custom modifications have to be done to the transfer case and drive shaft but this is possible, I have seen it.

 

[PieEyedPiper]

How did you dyno your AWD on an FWD dyno?

You can alter your drivetrain, fairly quickly actually, and turn your car into a FWD for the duration of the dyno'ing.

 

[JayRolla]

The problem is that you can't dyno test an AWD on an FWD dyno. The rear wheels want to turn, but there aren't any rollers connected to the dyno for them to sit on.

That was part of the point of that previous thread; if you had the option of disengaging the rear wheels, then you COULD dyno test an AWD car on an FWD dyno by switching to FWD mode.

And I agree that dyno tuning has nothing to do with the drivetrain unless you're trying to evaluate drivetrain changes, losses, rotational inertia during acceleration, "will it break at Xwhp?", etc. If you had the luxury, you'd do all of your engine tuning on a stand-alone motor bolted to a dyno without the car (or drivetrain) being involved at all. That way, you can swap out parts without them being buried in the engine compartment, you can submerge your IC in a vat of room-temperature (or hotter) water to dodge heatsoak or to emulate a particular IC efficiency, you can put a pressure gauge on your ex. mani and run it however you want, etc. If you're tuning the motor, you can do it FWD or AWD


But if you have an AWD, you can't use it on an FWD dyno, so what's the point.

Yes AWD car can dyno on a 2wd dyno. I think slowboy sells something you put in the t-case to make it FWD. It has been done many of times, but since there is so many AWD dynos now you dont hear much about it. So the point is valid.

 

[92awddsm]

How did you dyno your AWD on an FWD dyno?

I have a vce installed in my tranny. All I have to do is drop the tc and driveshaft to drive or dyno in fwd. By the way, I feel sorry for fwd people that have 400+ fwhp. In fwd, my car drives worse on dry pavement than it does on wet pavement with awd.

EDIT: I usually just drag race with very little street driving so I leave my vce in at all times. If I were to swap out the vce for the vicious coupler, it takes about 30 minutes.