GTR Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
1,757 Posts
Discussion Starter · #1 ·
All.
Got meself to Gforce yesterday.

Very impressed with the set up and big thanks to Chris and the other guy who kept making me chuckle. What happened to the eye dude?.

Execellent facilities and anyone that manages Porsche racing teams for their bread and butter has to know what they are doing. The GT1 race car and the 953 Kramers really done it for me!! Basically the largest air capacity rollers in th world and capable of shitfing a shit load of hot air after runs to return to normal air temps. A safe environment to run in.

OK so they have the Dyno Dynamics rollers which is basically the new way of mesuring the forces exerted by a car. ALL the top drag and racing teams do it this way and I know that Mario uses these rollers as do the RalliArt and Subaru rally teams.

A very different measurement system and it measures the power at the wheels and does not measure or confuse the issue with drivetrain losses which can be maipulated by the operator. Also the systems used guarantees to be within sth like 0.5 percent of the final figures.

The system has the ability to compensate for air temps diffs aafter a run, as well as humidity changes and so on. So after each run, this is a new setting and takes into account any changes. SO you get a TRUE reading.

So I got 324.6 BHP AT THE WHEELS. After speaking to Mark at Abbey the drag factor included this is roughly about 470-475 BHP at the Flywheel if I was to run this at TJ. PMJ had a drag factor of 130 BHP loss and that is with 17" wheels. With the 18s and wider tyres then there will be more loss due to more drag.

I am chuffed to bits with that as this is a TURE reading of the cars capabiliteis and what the engine is making and transferring down to the ROAD.

I am now going for the bigger cooler and hard pipe kit to increase stability of air temp and slight improvements. I have another run planned after this so see what it comes back with. after the mods.

Take a look for yourself: www.g-force-motorsport.co.uk
Link to 4 wheel drive dyno and it will tell you about the accuracy of the dyno. Speak to chris.

I suggest we get some cars down there for a whole day as Chris would like to accomodate this to compare and conquer. Would be interesting to see what the true readings are at the wheels and what is going down on the black stuff.

TTFN, NLW.
 

·
Registered
Joined
·
2,061 Posts
Rollers

Nick,

Sounds like a very good setup there, glad you were pleased with the results.

Just one comment, the T-J rollers also measure power at the wheels, as per the GForce rollers, they just add the drivetrain losses as well as an extra calculation.

If you look at the graphs from T-J, there is a graph for power-at-wheels as well as power at engine.

It would be interesting to compare what the readings for power at wheels are on both dynos. What gear was your car run in, as that makes a big difference in the ratio of power at wheels vs drivetrain loss.

Guy
 

·
Registered
Joined
·
1,757 Posts
Discussion Starter · #3 ·
exactly right big guy.

I compared my results with PMJ's from TJ and he did lose about 130 through the drivetrain losses and I guess I would lose more.

But this does seem to be a LOT of loss as industry standards for 4wd CARS should be around 22-24% max. And that is perma 4wd aka Evo, Scooby. AS thr skyline is rwd until loss of traction surely the loss should be less??

The rollers at Gforce only measure at the wheels and then they can take different drag coefficient into place if you want to work out power at the flywheel.

But they mainly deal with race cars so all the outputs at the flywheel are done on engine dynos which is the best way to do it.
Then the race engines are mapped and finished off at the rollers as the conditions under load are different to the engine dyno.

The test was taken in 3rd gear like with tj I think. Car was run up to 7200 with the max delivery around the 6900 mark.

Maybe one for the future.
Nick
 

·
Registered
Joined
·
2,061 Posts
Rollers

TJ Runs are done in 4th for R33 and 5th for R34, so would give lower power at wheels figures, but higher transmission losses.

The GTR runs in 4wd on the rollers, since when the rear wheels start turning, the computer senses that the fronts aren't, assumes it is wheelspin and sends power to the front wheels.

Thats why both rollers turn, since power is going to both rollers.

Guy
 

·
Registered
Joined
·
3,636 Posts
I always wondered about that.

When the car is on the rollers, does ATTESSA just believe that the car is stationary with the rear wheels spinning furiously? (and thus transferring power to the front?) It's quite a hard concept to grasp since the wheels are turning as they should, and the speed increments as it would do were it on a normal road.

ie. It's not as if in normal wheelspinning conditions the car is not travelling as fast as the wheels/RPM/gear would suggest.

Or am I just overcomplicating it? :)
 

·
Registered
Joined
·
1,757 Posts
Discussion Starter · #6 ·
the system can have

some adverse effect on the behaviour onthe rollers.
we witnessed a rocking effect at high RPM and this is where the ECU is sensing movement but not in a STRAIGHT line. So the G meter kicks in as it thinks the car is sliding and then starts to move the power around accoridngly.
So this means you are not getting a true and linear power delivery as the car thinks it is not going totally forwards and all the clever bits kick in.
If you can get the car to rear wheel drive only then you can get lees in the transmission losses but you need to get the power down effectively.
I have got the HKS torque controller in mine but it would not play ball and was still sending a minute amount of power to the front wheels. So I guess this will always happen as this is what is meant to happen: traction on the rear, off it goes to the front in little bits.

so overall: Car too bloody clever for its own good!!!
 

·
Registered
Joined
·
335 Posts
test

I cant wait to test the rollers.
A guy on the lancer forum with a 7 reckons that his stock car with airfilter/exhaust change ran 258 at the wheels.
Velly interlesting.
That would make the car approx 320/325 @ flywheel at least considering I lost 101 to the transmission at TJ?
We will seeeeeeee.
 

·
Registered
Joined
·
2,949 Posts
power at dynos

i would like to know why at dyno day 3

Mikes R33 was down about 40 BHP from when
it was on the same dyno only weeks before
he had his big wheels fitted to his car, i thought the dyno was able to work out the drag and it did not matter what size of wheel are fitted to the car,it then works out the power at the flywheel ????????????????????????????

star in scotland had a almost std EVO 7 on the dyno they done a few runs
with it and found out that when the dyno was reading the drag
at the end of the run they seen allmost the same power at the wheels but could get the drag to read funny figures that gave
the EVO 7 anything from 300 BHP to 370 BHP so that goes to show if the clutch is dragging or the operator is reving the engine this will play tricks on the drag and may give you a bigger power at the flywheel figure ?????????????????????.

Mike if you can please let me know what your
BHP figures at the wheels on your 2 dyno sheets are.

thanks keith

keith
 
1 - 8 of 8 Posts
Top