Dyno info?

Quadcams · 09-02-2005, 11:57 AM

if you car is putting out around 230rwkw's, should it be strapped down to stop posible wheel spin- loss of power? I've noticed some people on here have mentioned that there cars have been strapped down and were putting out similar power to me.
Also the guy said that the dyno had a limiter at 200km so therefore he had to use 3rd gear not 4th gear, the dyno was a MDX dyno

Also does anyone know were to tap in to get rpm on the dyno graph, I have a MKII XR8 ute as the guys that dynoed my car diddn't know.
I'm dont think I have faith in there practices and a bit suss on my figures, going to have to track down nearest Dyno Dynamics dyno seem the most accurate dyno's

Much apreciated for any onfo.

Casper · 09-02-2005, 12:00 PM

If the car is not strapped down it will usually give a slightly false HIGHER reading. I cant remember why now.

XA-Coupe · 09-02-2005, 01:22 PM

because it rides high on the front roller .. how that works I dunno but that's how it was explained and demonstrated at the APS day.
I think it has something to do with the outting a higher load on the front roller and making it think it's working harder ... just from my frazzled brain so don't quote me !

tickford2001 · 09-02-2005, 01:35 PM

Quote:

Originally Posted by Lowride260

I'm dont think I have faith in there practices and a bit suss on my figures, going to have to track down nearest Dyno Dynamics dyno seem the most accurate dyno's

just remember that dynos are a TUNING TOOL, they are designed to have a car put on it and tuned throughout the rev range without having to strap yourself to the bonnet and get a mate to drive you up the street!

they are not designed to give you an accurate power figure that can be used for **** factor down the pub or on a forum like this...there are too many variable for them to be the same from one to the next. If you want a more accurate comparison between two cars, you need to run them one after the other in shootout mode, and it may be different your previous read out on another machine, but you can see where the two cars are at

anyway, back onto the topic of strapping the car down, XA is on the money im pretty sure. Maybe peter (aps), rob (herrods) or barry (bpt could get on here and give us a run down??

Kev_BLNXR8_Ute · 09-02-2005, 05:27 PM

Every one seems to be pretty spot on. From what I understand not strapping the car down tight alowes the car to ride up on the front rollers of the machine which puts less enertia, load ( I cant spell but Im sure u can work it out) on the drive of the car and therefore alows a higher reading on the machine.
I know G&D were I get all my work done have a Dyno Dynamics machine. They are in Cranbourne if that helps you at all.

Cheers..........Kev

rodderz · 09-02-2005, 07:01 PM

Thats the way I would interet it too....The tighter your car is strapped down to the dyno at the back the power figure will drop

Big Mick's APS Stage II XR6T got a rwkw figure of around 260rwkw or so, and someone asked him to loosen the straps relieving pressure on the back of the car and the power run went up 10rwkw's, and the car was close to jumping off the rollers too....

There are a few tricks that some people use to get higher figures also, pays to go to a reputable tuning shop that has frequent servicing of their dyno to get consistant and accurate results

Quadcams · 09-02-2005, 11:51 PM

Quote:

Originally Posted by rodderz

, pays to go to a reputable tuning shop that has frequent servicing of their dyno to get consistant and accurate results

I think thats the best answer, going to try out a more reputable place.
Maybe the last place was correct but its alway good to know between wright and wrong.

Thanks for the comments guys.

G&D PERFORMANCE · 10-02-2005, 01:19 AM

The MDX from what I've seen will read higher than Dyno Dynamics,that doesn't mean that there is anything wrong with that style of dyno,it's just calibrated differently,different roller diameters,software etc.We must remember that a dyno is a tuning tool & must be used as a before & after comparison for mods using the same dyno or just plain tuning for max performance.The ultimate is an engine dyno measuring power at the flywheel requiring the engine to be removed from the car which unfortunately is just not practical for most.

A chassis dyno measures power at the tyre so many factors come into the equation such as tyres pressure,tyre size,gearing(torque readings),drivetrain mass and so on.The more you pull (strap) the car down the more friction it creates between the tyre & the dyno rollers reducing the power output reading at the dyno.Also if the car isn't strapped down in any way it will in 99% of cases give you a misleading high power figure as the car is then allowed to climb up onto the front roller & off the rear roller therefore reducing the amount of power robbing friction on the tyre to only one roller contacting it instead of two.At G&D we always tie each vehicle down to identical tension unless of course it's making big horsepower 500RWHP upwards,then they require more tension on the straps to reduce wheelspin.

So for all you guys out there getting mods,make sure your tuner straps your car down for a true figure.I'ts not uncommon to see 10 plus RWKW's from a car that climbs up on the front roller.I'll try to post something educational up in the near future such as dyno graphs etc to demonstrate how people can be mislead in this way & what to watch out for whilst having your car dynoed.

Regards Glenn

NZ · 10-02-2005, 11:20 AM

G&D can you tell us how the dyno actually works, are the rollers resistant to turning? do they have some sore of geared system? What type of maths is involved to get to a power figure? how to they work out a torque figure from the wheel speed etc? Im just one of those curious people who likes to know shit lol If you share some knowledge that would be awesome.

G&D PERFORMANCE · 10-02-2005, 06:20 PM

Although I've used dyno's for years & enjoyed every minute of it I've never actually delved right into the scientifics of dyno operation to the endth degree but I'll try my best to describe it for you anyway.Most chassis dyno's have a set of driven rollers connected via a split retarder that is power via an electrical 3 phase power supply.As the rollers are driven via the rear wheels this retarder does as it's name states,using magnetic forces acting on a central disc sandwitched between it's 2 halves it attempts to retard forward motion creating a percentage of resistance between the roller/1st retarder halve & the fixed retarder half.This resistance is measured internally via some form of electrical load sensing device which connects to the roller/1st retarder half which translates back to the dyno computor.The computor then relies on it's complex software to combine torque & speed to calculate the overall torque & horsepower readings that the end user see's on the screen.I'm sure we could find some more indepth info via the net & intake temp correction info etc,this should give you the basic idea.Hope this helps.

Regards Glenn

XplosiveR6 · 10-02-2005, 06:43 PM

isn't it dangerous not strapping down the car? I would have thaught the car might jump off the rollers and come off if it had enough power

xdc351 · 10-02-2005, 07:23 PM

Quote:

Originally Posted by EF_Dave

isn't it dangerous not strapping down the car? I would have thaught the car might jump off the rollers and come off if it had enough power

I've heard a few urban ledgends about that but none verified. Same as the legend about the apprentice that didn't take the lock pin out of the rollers and the car, apparently, went straight off the dyno into a hoist and knocked a car off it.... sounds fair enough until you ask yourself how anyone driving the car failed to realise what was going on as soon as they started accelerating!