Again, another question from the peanut gallery. I saw in the thread about the car competition they would be disconnecting the drive shaft for the HP test on a 2WD dyno.

The question is: when Porsche quotes HP figures for the Turbo and the Carrera4, they give figures (I would assume) that they got from a 4WD dyno. Or if they did it at the crank, what was there conversion factor? Do I get a different reading with a 2WD with the drive shaft disconnected vs. a 4WD? Is there another conversion factor for that? Just curious. How do we level the playing field so we know what all these different numbers mean?

I'm trying to get to Meridian this week to baseline my car where it is before trying 100 octane just to see what the delta is. Then move up to ball bearing turbos and see what that gives me.

 

Ken,

Porsche uses an engine dyno. The 2wd and 4wd chassis dyno's have different conversion factors due to the fact they have different drive train losses. The 4wd dyno will have more drive train loss. The engine dyno has no drive train loss.

Even given the above, you must ask if the readings are SAE J1349 or "Standard Corrected." There is a difference. The "Standard Corrected" makes the numbers "appear" alot better.

 

Perfect. I appreciate the answer - like you said, the "correction" factors make a difference.

As long as I bench mark each time on the same type of dyno, at least I'll get a relative difference

Thanks

 

Chad,

When trying to dyno a Turbo or GT2, shouldn't the dyno have fans that blow on the car to simulate driving or does it not matter. I am talking about 2 or 4 wheel drive dynos not engine hp. Thanks

-Lou

 

approx 10-15% greater wheel numbers with a dynojet vs Mustang

 

The fans are used for cooling purposes only.

I posted this before...but here you go...

"The Mustang Dyno MD250 dyno is a true loading dyno, because it uses an inertia weight as well as an eddy current motor that is attached to the rollers. This eddy current motor creates a drag on the shaft by way of electricity that causes a magnetic field to try and overcome the torque going through the roller shafts. This current is controlled by software that is always trying to simulate load as if the car is driving in real world conditions. The real benefit from the loading dyno is the ability to maintain a load that allows a tuner to properly go through a fuel map or ignition map and tune the chip for optimum horsepower and torque. It has the ability to also simulate the IM240 emissions test as required in some states. It can check 1/4 mile times as well as times for 0-60 MPH and 0-100 MPH. It can also be used for road testing and simulation for drivability problems. As a result of the loading capability, the dyno numbers from a mustang dyno will come out lower than the inertia (dynojet) dyno.

The Dynojet 248C is actually an accelerometer whereby it uses a 3000-3200 pound drum that is used to create an inertia load on the vehicle being tested. The vehicle's horsepower (HP) and torque try to overcome the weight/inertia of the drum to accelerate it. As a result the software and electronics try to measure the horsepower and torque that the vehicle is developing to overcome the drum's weight and inertia. The resulting horsepower and torque will be higher than a true loading dyno because once the drum starts rolling not as much power is needed to keep it going. Example -- When pushing a car on a flat road, once the car starts moving not as much power (effort) is needed to keep it going. The software does not ask for vehicle weight or anything like horsepower needed to maintain 50 MPH (a number that is actually put out by E.P.A. and N.H.T.S.A.). "

 

Thanks alot. The reason for my question was that I heard there is one place that has a dyno that is close to me, but, they do not have any fans! I believe the dyno is a 4 wheel dynojet, not sure which model. Will this damage the car since fans are not used?
-Lou

 

If they dont have fans, what do they use for cooling?

If they dont offer any sort of cooling mechanism, I wouldnt do it at all.

 

Thanks,

It seems the boneheads bought a 4 wheel dyno, but didn't buy fams or the fans they have are not sufficient for TT or GT2's

-Lou