spotv6 Posted May 21, 2011 Report Share Posted May 21, 2011 just wanted to see what peoples opinions are and if we could all benefit from some informed choices when it comes to the infamous dyno results from different dynos. as those who drunkenly paricipated :rolleyes: in the infamous dyno runs at rising sun show will tell you the operators were using an etch a sketch to plot whatever results they thought apropriate :rolleyes: mick baileys results were ridiculously low compared to when he had his car set up my torque figures were just plain ridiculous and sj ended up with 2 completely different torque graphs for the same run! so leaving behind the flywheel versus wheels debate i think we should try and find the most accurate dynos and if we are going to arrange dyno days in the future lets try and use the same type of dyno once we get the definitive answer on what that type may be i cut and pasted this article for our perusal because it seems to give the clearest explanation of the different types of dyno available . the mustang dyno at raceshack in tewkesbury is where i had my standalone link set up but for referance only gives the actual wheel horsepower figures but i believe that the hub dyno or the dynanometer also give an accurate flywheel figure. so lets have our opinions pick out the best type of dyno and see where they are in the country. heres the article.... There are 2 main types of dyno, retarder dynos and inertia dynos. Inertia dynos use heavy rollers of a known mass. The wheel power of the car is used to accelerate the rollers as fast as possible. Given that the mass of the rollers is known, force = mass x acceleration allows you measure the rate of acceleration an thus calculate the force. The 2nd type of dyno is a retarder dyno. A retarder dyno uses a non contact eddy current brake to retard a light roller with little inertia. The dyno system allows the rollers to accelerate at a fixed rate when the power of the car is applied to them. This means if you dyno a 100bhp car, or a 1000bhp car, the acceleration rate is constant. A retarder dyno uses a load cell to calculate the tractive effort at the roller surface. Personally i much prefer retarder dynos. Dyno Dynamics, Mustang (new ones- old skool are inertia iirc), Mainline dyno log, and Land and Sea etc are retarder dynos. Maha, Hoffman, Dynojet etc are inertia. An inertia dyno is very dependant upon gear ratio. You need to run the car as close to 1:1 a possible. If you dont and say you run the car with a mechanical gearing advantage, say in like 2nd gear, the car will accelerate very fast, the rollers will accelerate very quickly due to the mechanical advantage of the gearing, and a huge power figure will be read. This means that the power number can be 'frigged' up or down by gear selection. Additionally, most inertia dynos calculate transmission loss via a coast down method. Lets say the test has been conducted in as close as 1:1 gear as possible, so the 'wheels' figure is as realistic as possible, however, then it can all get a bit sketchy. Irrespective of any debate about accuracy of coast down method, what happens if the operator does the coast down with the handbrake applied, or even the foot brake? You get a mahoosive flywheel number. Retarder dynos use direct measurement (via the load cell) and a controlled acceleration rate and most use modelling to transfer from wheel power to flywheel power, as opposed to coast down. I'll be 100% honest and tell you i have a dyno dynamics 4wd dyno- so of course i am gonna say its the best one- which of course i believe it is, but it is nearly double the price of some others. If you are gonna go and spend your money- you buy the best one there is. No point on getting one for less money that doesnt do the job as well. Irrespective of that though, i believe retarder type dynos are much superior to inertia. I regularly see cars coming in with dyno numbers from other types of machines. I saw one recently, dyno'd on one machine at 225bhp, dyno'd on mine at 160 ish (Flywheel). The customer commented that the guy at the first dyno then ran the car again (maybe in another gear) and generated 280bhp! Conversely i also see very similar results from other DD machines. I saw a golf with a supercharge conversion, dynod on another DD at 229BHP (fly) the operator had told him it went lean at high rpm, so matey had fitted a fuel reg and turned the base pressure up to 'fix' it. (I know, i know!) Dyno'd at 224BHP Fly on mine. AFR was pegged at 10 on both dyno sheets, but jumped to 16 at 5500rpm on the first one, and very slightly higher on the one i did. Cheers, Ben. Link to comment Share on other sites More sharing options...
mbailey Posted May 21, 2011 Report Share Posted May 21, 2011 Interesting reading there spot. I can confirm that it turns out i did have a problem and was not running on full boost, it was peaking around 5/6psi. Now i have sorted it out its at 7/8psi. It may not seem a lot but there is a mahoosive diverence Comparing my graphs i have they were very closely matched untill the boost started to flat line. Had it increased as normal i 'guess' i would have been somewhere close to what we were expecting. When its retuned next month (yes ive ripped it apart again before a show ) im going to see if i can have results and graphs in flywheel power and wheel power and see the difference Link to comment Share on other sites More sharing options...
hyper-wrap Posted May 21, 2011 Report Share Posted May 21, 2011 How do car manufaturers do their bhp figures? As whatever that is...would surely be the most accurate? Link to comment Share on other sites More sharing options...
stevenc1603 Posted May 21, 2011 Report Share Posted May 21, 2011 at a guess I would say on an engine dyno with the engine not in the car. Link to comment Share on other sites More sharing options...
hyper-wrap Posted May 21, 2011 Report Share Posted May 21, 2011 Ah, didn't know they existed...learn something new everyday! Link to comment Share on other sites More sharing options...
izzzzythedog Posted May 21, 2011 Report Share Posted May 21, 2011 yep the engine is strapped into a frame , a water brake is then attached ( not listed above strangely ) and the engine is run , there is a known amount of power created based on the compression , volume of fuel , type of fuel and swept volume , an engine is then stripped of its components gradually to work out lost power , then going on the frigidity of the components some are kept and some are not , it may be interesting to some that heat accounts for a 33% loss of all potential power from an engine as someone whos car lost torque not made more when revved based on a dyno i think the only place dynos really have are to create a base figure from which to tune your car , if you go into buying a run expecting impeccable service plus toyota and the dyno to be accurate your in for not a nice surprise , manufacturers bullshit the public , dynos read differently depending on vrs factors would be nice to have some sort of standardization Link to comment Share on other sites More sharing options...
Recommended Posts