MattJ Forum Contributor
Last Online: 26-07-2009 05:37 PM
Member Since: Dec 2001
Location: I dont know any more...
Current Ride: VX SS M6, BF Typhoon A6
Dyno Mythbuster...
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I have touched on my despair of dyno figures and the importance most people put on the numbers at the top of the dyno sheet in a few posts over the years. I just thought I’d start a dyno Mythbusters post and pass on some of my findings over the years. This is something I have wanted to write for years as in my position of performance sales manager I have to deal with this sort of thing countless times a day. Not everyone will be happy reading this as a lot of people here and on other forums hold the dyno sheet close to the ego.
Also, I can see how some shops feel that they have to provide big numbers as the customer demands the same figure as his mate or some guy on the forum with similar mods. But in the end, it starts and finishes with the performance dyno shops.
I bought a BF Typhoon about 2 months ago, the previous owner had the car tuned with injectors and a cat mod. He was given a dyno sheet stating 315rwkw. I did not buy the car because of the stated power nor am I for a second suggesting the previous owner pulled a shifty, but when I got the car back home, and without touching a thing, it made 279rwkw on the HP-F dyno. Where the missing 35rwkw fits into the list below, I don’t know. But this is the sort of thing that can make a customer think that one shop is shit and another the kings.
No dyno reads exactly the same! HP-F have two dyno’s, they read different. A dyno is not a ruler where 30cm is always 30cm wherever it’s measured. Every dyno company and just about every shop will say theirs reads more accurate or more repeatable which is great, but the simple fact is that every dyno reads different and comparing one to another is folly. The difference between one run and the next on the same dyno is what you need to keep in mind.
There is more than one way to dyno a car! HP-F have had the privilege to be able to build and tune some of the tuffest dyno cars in the country, the dyno HP-F use to tune the big bangers is set up to make 1700+hp turn the rollers with minimal slip and when Dyno Dynamics wants there latest technology tested they come to us. Utilising this latest technology gives us no choice but to follow the rules when strapping down a car. The Dyno Dynamics dyno is calibrated to have the rear rollers stay in constant contact with the wheels all the way through the run, if they come off, the power number will be inaccurate and read higher than it should. Strapping down of the car on the dyno has a huge effect on the final reading, a car with loose straps will ride up on the front roller for most of the run and then normally just after peak power the car will sit back in onto both rollers, you can see on the graph when this happens as the power line drops, looking something like (and often confused with) faulty valve springs.
The dyno is only as good as its operator! There is quite a few other ways for the dyno to read inaccurately, the incorrect placement of the intake air temp probe is a beauty and incorrectly typing in Barometer reading will have a real effect. All these things are easy to avoid for the alert operator and easy to tamper with for the dishonest. Calibration and regular service can also help maintain constant, reliable numbers.
Different tyres will read different power! We once had a car make a lot less power then what we thought it should for the given mods, we got the car up on the hoist, searched high and low, checked compression, double checked the tune, dropped the exhaust, changed intakes, you name it we tried it. Nothing doing. One of the guys took a backward step, had a look at the car and suggested we should try different tyres. The ones on the car were brand new but what did we have to loose? We pulled a couple of wheels of Rob’s ute and bung ‘em on. The car picked up the lost power, and some… 25rwkw from a tyre change!! Tell me, how do you compare one car to another?
Each engine is different! Two cars with the same mods rarely make the same power, even in standard form most cars make different power on the dyno. Or what about auto or manual? High stall torque converters? These thing all effect the power readings. Again, how do you compare one car to another?
A tune for the dyno and a tune for the road! Simple really, a lot of times the final run on the dyno needs to be trimmed up to stop the odd ping found on the road test, big problem with XR6-Turbo’s. The main issue with this is that you pick up your car with X-power figure on the dyno graph and a few days later you dyno the car somewhere else and it reads low or, your mate expects what your makes. What about a race cam in a road car, you want to replace valve springs every 20,000 kays or do you want to flycut the pistons to fit it in?? Nothing wrong with either of these two options if your prepared to go through it, but to base you figures for a ‘cam only’ upgrade on custom shop set up’s is folly.
And Finally…
Don’t let the facts get in the way of a good story! How the car was run up on the dyno is another thing. Race fuel? Shhssh don’t tell anyone. The problem with that is that one day your going to have to repeat it and one day the car might be out of your hands and the questions will start. Disclosure of the facts is important as anything else if you want to be taken seriously and not live a life where everyone now doubts your every move. So how can you tell? Simply, you probably cant, but like life, if it is seems too good to be true, it most probably is.
Ultimately, the car makes what the car makes, its fine to have goals but the basis of these goals has to be reality. Sorry for the long post...