Strapping The Car Down On A Dyno Influence The Results

[CEF11E]

Hi All.

I have just finished tuning my car and have come up with some curious results. firstly let me say i really don't care what the number is but it would be interesting to find out what the story is here.

previously my car made 254rwkw and 420nm of torque on a dynodynamics machine when i first built the engine on a conservative tune

since then i have retuned it and it is a lot faster and has a lot mor torque. this time it was done on a dynodynamics and it made a max of 220rwkw but it made 65onm of torque.

the setup is an RB30det with hiflow, the tune was done in normal ramp mode not shoot6, tyre pressure was the same. temp probe was hanging it the air like normal,

the dyno just reads 20% less than before, boost is now 18psi and before it was 16. i have added more timing and it runs 12:1 dead flat once it reaches full boost.

the car is substantially faster and gtech time is 0.3 0 to 100 faster. so it is not my imagination.

the only difference is that the car was heavily stralled down during the runs. this is because it was trying to climb off the dyno and the operator rightly doing the safe thing.

anyone else have any experience with this?

[gtst25]

Yep - have been told that the best way to dyno is to strap the car so it climbs up on the front roller during the power run. This was from a guy who strapped the horsepower heroes cars at summernats - over 1000 rwkw!

And yes generally you'll get a lower power output reading if strapped down hard between the rollers - I got a reading of 260rwkw and the bloke who dynoed it said it would have read another 15rwkw at the tyres if strapped to sit on the front roller. I've had my car strapped both ways and I like the front roller idea - there was no wheel spin - the day it was strapped between the rollers the tyres copped it.

Cheers

[VB-]

seen its heaps of times, when it isnt strapped down tight enough, it will climb off the rear roller and make it read higher as all that force is going straight through one roller instead of two, although i think the resistance is apllied through that one roller, it still seems to make quite a difference. that said, you should be making more than 220 IMO (yes i know every dyno is different and they are a tuning tool not a yard stick, it should still read higher than 220)

[WARLORD]

seen its heaps of times, when it isnt strapped down tight enough, it will climb off the rear roller and make it read higher as all that force is going straight through one roller instead of two, although i think the resistance is apllied through that one roller, it still seems to make quite a difference. that said, you should be making more than 220 IMO (yes i know every dyno is different and they are a tuning tool not a yard stick, it should still read higher than 220)

true..!!

[Kranker]

Post up the graphs so we can have a look

More torque at same revs = more power..... no two ways about it

So yeh, bit of a funny result

[GeeTR]

DD units have the retarder unit in the front roller only I believe. 80% of cars i see tuned rise up onto the single, front roller anyway when strapped. Soft tires with low pressure are "supposed" to sap power, but 35+ rwkw's? Hrrrrm... mystery

[kevind]

was it the same dyno

[rob82]

There is alot of power to be had in correct strapping. My opinion is that the straps should be almost verticle pulling directly towards the ground. The attatchment point should be forward of the axle towards the front of the car so that as the car torque's up it puts more of a moment in pulling th tyre into the roller.

The problem I've seen with letting the car creep up on the front roller is that most cars esspecially turboed cars only situp on the front roller as they come through peak torque and then they sit back down on the rear roller, which causes a huge drop in power as it has to accellerate the rear roller back up to the current wheel speed. So essentially you will inflate the torque figure while reducing the peak horsepower figure.

The other thing to consider is the tyre compound - cause if your producing over 7000N of tractive effort then you could be giving away power through the adhisive forces that some tyres can produce.

And as for tyre choice - I've seen an rb30DET making 310rwkw on street slicks go to 368rwkw on normal hard compound tyres with no change in anything but tyre choice. This car wsa producing over 8000N of tractive effort.

Edited June 29, 2008 by rob82

[CEF11E]

yep. i have done some more reading about it and have found the same results.

the car was making 6500 tractive effort with dips and bumps in the curve that look like wheelspin. the cae was tied down HARD and you could feel it trying to walk forward. the rear cradle was point of anchor and the wheels were between the rollers.

Also I thougnt a car making that sort of tractive effort at 4000odd rpm would be making atleast another 50rwkw,

sheets to come later