Dyno's - Why?

[Zebbie]

I was looking through the ls1.com.au forums the other day (from a link on here)

- They were talking about Dyno'ing, and the fact that they got different results from how tightly the car was strapped down.

Is there a specific tightness etc? - I'd guess you need to strap her down to get traction, but can you tighten too much?

IIRC, they lost power from stapping down a car too much!!!!?

(I could see if they didn't strap it down enough, but....)

I'd link to the post, but the forums on ls1 doesn't have a search function I can find... It was a post talking about test results from supercharging/turbocharging a V8 engine.

Thoughts?

To Quote from the LS1's Forums :

We have done back-to-back testing between our dyno and 3 others (CSV, Autotechnique, G & D) and found there to be excellent consistancy between all 4 dyno's +/- 5rwkw @ ~300rwkw. All done on the same day, same tune. We run ours in DIN certification, which just happens to reduce the observed numbers by about the same as the traction-slip encountered.

We participated in some testing by the author of the DynoLogic software (Andrew E) to try and establish what is "lost" through tyres and roller inertia and it was VERY interesting. As a "rule of thumb" we found that 10 to 25rwkw could be sacrificed by varying tyre pressures and vehicle retention (strapping down).

This was again verified recently at the F1 Performance dyno day when our Monaro was run ... the 1st run was 317rwkw and showing a bit of wheelspin, so I asked it to be pulled down tighter ... the next 2 runs were about 300rwkw. My fault, but it indicates the method of strapping can have a significant effect.

http://www.ls1.com.au/forum/showthread.php...89&page=2&pp=15

[paulr33]

I've heard this too and the rear weight can affect how much power it makes, also the ramp rate set on the dyno can alter it too

[rob82]

In dyno dynamics shootout mode the ramp rate is fixed for 4,6,8cyl and 4,6,8 cyl forced induction plus a few others 2R 3R 4X4 ect ect. The reason that strapping is essential in comparing graphs is that if the car is allowed to torque up onto the front roller it is therefore not spinning the rear roller hence faster acceleration rates; hence more power and torque.

A properly designed strapping system should force the tyre into the roller more and more as the torque increases rather than just forcing the tyres down.

[Freddy Kruger]

yeah, if you want to know the performance of your car, take it to the track. a dyno is just a guide pretty much, dynos werent exactly designed specifically for power runs, more the tuning etc side. i think the dyno (dynamics ?) site they go into a bit of detail.

if you think your car suck, just loosen the straps, ive heard of a gain of 17kw doing that! cheapest power mod ever...

[Zebbie]

Yep.. I can imagine my local guy's face when i tell him to keep loosening the straps until I see the 'Tension Release boost mod' :-D