Flat spot

[Janner_Sy]

FWIW my car made the same figures as JKM on 3 separate DD rollers.  Also judging by the rolling road days on here surrey rolling road gives the same results as JKM as well.

What is it in your opinion that makes JKM read so low?

The reason i asked about the rail pressure, is you thought the issue with the OP sounded like fuel cut, which on a stage 1 car is not a regular occurrence.  in fact that s pretty much un heard of now.  It did happen when the tuners first got their hands on the TFSI and started finding the limits of it, but not anymore

[PDT]

The car should be run so that the wheel leaves the rear roller, this eliminates the risk of over tight straps, once the rear idler roller isnt in contact with the tyre the strapping tension wont have any effect on the power output, if the tyre stays in contact with the rear roller then the car coukd be trapped too tight. The only way to ensure every car is tested in the same way is to use this method, this is the way we have been trained by DynoDynamics on 2 occasions, today DynoDynamics were at our London outlet installing and training the staff there on the new 2wd system they have just bought, they were trained to use the exact same method.

Heres an extract from an Unofficial DD guide written by a highly regarded dyno operator:

The Climbing Effect and Strapping

How hard a car is strapped down will have an effect on all dyno's including the Dyno Dynamics.

If a car is strapped down hard on a base run and then 'looser' on the one after a small-medium difference will be shown in the output.

The problem here is that a car may be totally non-moving on a dyno and this can be done without you ever knowing the strap tension. How are you going to know how hard a car is strapped if it's not moving around?? No way of telling!

The Solution is simple and we use it.

Allow the car to mount the front roller completely leaving the rear one. Once the car has mounted the front roller, it doesn't matter where it sits on it because the reading will be the same.

So not scare the hell out of customers we just allow them to leave the rear roller by about an inch.

The overall benefit is that you achieve maximum grip and strap tension doesn't come into it. All the dyno operator has to do is hold the car back once it's moved forward a very small amount.

You totally cancel out the effects of strap tension!

With all of the above you should have no issues. There are no other hidden secrets other than the obvious ones:

- not pressing the throttle all the way down on the base line run (difficult to deal with!)

- Applying the brakes lightly on the base line run (Stand at the rear of the car if it's safe)

- Changing the ramp rate between runs - will be displayed on your print outs.

If anyone has any questions please do not hesitate to ask.


  

[PDT]

The reason i asked about the rail pressure, is you thought the issue with the OP sounded like fuel cut, which on a stage 1 car is not a regular occurrence.  in fact that s pretty much un heard of now.  It did happen when the tuners first got their hands on the TFSI and started finding the limits of it, but not anymore

We will run as much boost as possible before requested boost excessively exceeds the airflow that the engine can produce, the requested fuel is then mapped to give a safe AFR. The fuel cut problem will occur if airflow is increased by improving the intake, then as a safety precaution the ECU will reduce timing and/or boost as the fuel system cant supply enough fuel, the map can either be altered to avoid this by reducing requested boost levels or improving fuel supply. This is where a device such as the sps switch from revo is usefull as you can reduce boost slightly to compensate for the increased airflow, however people usually add intakes to imorove power, not lose it by removing boost to compensate for the lack of fuel. hence the popularity of the HPFP upgrades.

I think people are getting a little hung up on the whole 'stage' tuning thing, we tune for each individual car, not by a pre determined stage to dictate peak boost and other factors.       

[vRS Carl]

The car should be run so that the wheel leaves the rear roller, this eliminates the risk of over tight straps, once the rear idler roller isnt in contact with the tyre the strapping tension wont have any effect on the power output, if the tyre stays in contact with the rear roller then the car coukd be trapped too tight. The only way to ensure every car is tested in the same way is to use this method, this is the way we have been trained by DynoDynamics on 2 occasions, today DynoDynamics were at our London outlet installing and training the staff there on the new 2wd system they have just bought, they were trained to use the exact same method.

Heres an extract from the DD guide:

The Climbing Effect and Strapping

How hard a car is strapped down will have an effect on all dyno's including the Dyno Dynamics.

If a car is strapped down hard on a base run and then 'looser' on the one after a small-medium difference will be shown in the output.

The problem here is that a car may be totally non-moving on a dyno and this can be done without you ever knowing the strap tension. How are you going to know how hard a car is strapped if it's not moving around?? No way of telling!

The Solution is simple and we use it.

Allow the car to mount the front roller completely leaving the rear one. Once the car has mounted the front roller, it doesn't matter where it sits on it because the reading will be the same.

So not scare the hell out of customers we just allow them to leave the rear roller by about an inch.

The overall benefit is that you achieve maximum grip and strap tension doesn't come into it. All the dyno operator has to do is hold the car back once it's moved forward a very small amount.

You totally cancel out the effects of strap tension!

With all of the above you should have no issues. There are no other hidden secrets other than the obvious ones:

- not pressing the throttle all the way down on the base line run (difficult to deal with!)

- Applying the brakes lightly on the base line run (Stand at the rear of the car if it's safe)

- Changing the ramp rate between runs - will be displayed on your print outs.

If anyone has any questions please do not hesitate to ask.


  

That's not from DD but from a BMW Tuner who uses the DD rollers

http://www.mk5golfgti.co.uk/forum/index.php/topic,10198.0.html

Whereas JKM Say:

http://www.jkm.org.uk/performance/dynotesting.htm

[Janner_Sy]

 

[PDT]

It was re-posted by a bmw tuner. Its posted on hundreds of websites, but is factually correct and is how DD train their operators to run a car. It was part of a guide that we were emailed in 2005.

[PDT]

Well if thats how JKM strap the cars its certainly not how DD train you to do so, but strapping methods are down to the individual operators not the manufacturers of the dyno.

The problem with strapping so that the wheel doesnt move away from the idler roller is that the car can be strapped too tight without knowing it and the rear roller adds extra losses to the end result as the idler roller is just that, a roller designed to be in contact with the tyre when the car is idle.


Edit:

To settle the argument on strapping methods once and for all, I have sent a link to this post to DynoDynamics Uk's tech support guy, he also trains all of the DynoDynamics operators accross europe when they buy a DD system, so if anyone can give a definitive answer as to which method is correct, he can.

[vRS Carl]

So if strapping methods are down to the Operator why would DD train you to do it that way but say "hey fellas strap it how you like"??

[vRS Carl]

Also in this official DD video why are the cars not being allowed to rise up ??

[PDT]

They dont carl, but once DynoDynamics leaves the premises after training the operator to use the correct method, the dyno operator can strap how they like, wether its how they were shown during training is another matter. But if the individual operator feels they want to use a different strapping method, thats their decision.

[Janner_Sy]

If the 'correct' way to run them was to allow them to run up the front roller, then why would they design in the rear roller when they could have just used the 1

[Top Cat]

                               


Guys i hope this thread is going to stay friendly.    Sy and Carl i can see why you are dubious about the figures from Dave's map, but we all know how rolling roads will throw up all sorts of results, DD roller's or not. But this thread is starting to look like a bit of a witch hunt. Cant see it going down a constructive route at this point. 

[Janner_Sy]

   not meant in that way.  Im genuinely intrigued about the dyno setup though. 

[vRS Carl]

It's not a Witch Hunt TC.

I'm just curious as to why their are different methods of strapping being employed utilising the same Dyno.

[PDT]

Here is a great video showing 2 cars being strapped and tested by the owner of DynoDynamics Europe (Mike Gurney) who also trains every dyno operator how to use one of their dynos.

 http://video.google.co.uk/videoplay?docid=6576817030959103698&q=vroom+vroom#

the first car tested (the morgan) doesnt show the climbing effect too clearly, but watch the BMW. Clearly shows that DD themselfes allow a car to leave the rear roller during power testing.

As for the question of 'why have 2 rollers then? '   its very hard to park a car right on top of one roller and strap it and test it effectively, also having 2 sets of rollers makes it far easier to load the car on and set it all up. Then theres the safety aspect, 2 rollers effectively traps the car if it decides to go sideways, I am sure you have all seen the video of the EVO on a single roller dyno when the strap snaps, nothing to stop it going wherever it wants. If a strap lets go on a dual roller dyno, as it drops back inbetween the dyno rollers it pulls the steering straight 


As for a witchhunt, dont feel that at all, if people dont ask questions about a subject they have no knowledge of (other than what they read on the web) then they wont find out the facts, or the opinions of the people that use a dyno every day as part of their job. The truth is that unless you get to use a dyno for a prolonged period of time you simply wont understand how they work, how the ramp rate or load is applied to the roller and how the estimated horsepower is calculated so ask any questions you like lads, I have owned a DD dyno for nearly 6 years now and have had 2 seperate training courses but still learn something new every day.