A 5ēC inaccuracy in air temperature can lead to a 0.9 per cent change in power figures. A 3mB (normal range 900 to 1050mB) inaccuracy in barometric pressure gives a 1 per cent change in power.

One of the things that I really hate about the tuning industry is this:-

Whoever quotes the least money in return for the biggest number of Horsepower; no matter how unrealistic either of those numbers, will get the job. The worst of it is that many companies have absolutely no intent whatsoever of delivering either that power figure, or for that number of pounds. This comes about either through ignorance, or through a deliberate attempt to blag the customer.

When its ignorance, for example, not realising that you need fuel injectors and an ecu to reach a certain horsepower target on a certain car, the tuner will try one of two things:-

1. Increase the price.
In order to deliver what you want, the tuner will have to increase the price. He cant fund your ecu and injectors out of the profit in selling and fitting a turbo. Trust me, the margin isn’t there! Now you are not gonna be paying the amount you thought you were in the first place, so the whole basis of the purchase decision is gone.

2. Fake the results.
Seriously, that’s what they do. They have told you Ŗx, they figure out they have underquoted and they need more stuff to make the car do the power they promised. They cant go back to you and tell you that you need x,y or z because it makes them look like they don’t know what they are talking about. Their pride prevents them from admitting they were wrong. So they fake the dyno results.

The true blaggers.
These guys are out there and they are not uncommon. I could name a list of tuners who do this. Its morally wrong, its dishonest and it gets the industry a bad name. But trust me on this, it isn’t uncommon. They have no care or idea if they will get the results that they told you for the Ŗ they have told you. None! They just take your money, say the right things, and then give you the results they told you they would. But since they cant truly deliver the results for the Ŗ that you have agreed, they simply cheat on the Dyno. For a long time I did not believe the extent to which you can fudge a dyno, but after seeing a bone stock Impreza make 14,410 BHP, then I know that it can and is done.

While I’m on the subject of numbers, be wary of any tuner who confidently asserts you will get a certain horsepower number. You cannot ever know. Every car is different. The tuner hasn’t even seen your car. How do you, let alone he, know what its power output is now. And so how can he say you will get 400bhp for sure for the Ŗ200 you are going to spend without even clapping eyes on your car! Tuners who are more honest will couch their language, they will say ‘it should make’ or ‘in the region of’ or ‘ those mods normally see an increase of’.

Defending yourself against being ripped off.
There is nothing I can do to stop the guys who deliberately quote low to get the job, and then ‘add stuff’ to the price afterwards. It isn’t a straightforward way of doing business, its certainly sharp practice, but there is little I can do to stop it. My only advice is, if it sounds too good to be true, it is.

But the guys who cheat the dyno, that I can help with. The more people who understand how a dyno works, the more people can defend themselves from being blagged by unscrupulous or dubious tuners. The more you understand, then the better protected you are, and the more you will understand about the tuning process.

FACT
The process of tuning a petrol engine, any engine, is the same. It is a process through which you isolate variables, and test different combinations to deliver the best torque for a given operating condition. Most proper professional tuners, the people who know and use this process will get within 5% of each other in terms of out and out power output. So you know what? When someone claims to be able to get more power than anyone else, or who consistently gets higher numbers than anyone else, then its bull. Walk away. If they already worked on your car, then get it checked somewhere else.


So how do you spot a dodgy dyno graph? Lets have a look at a pucker one.




Dyno Mode
First of all, dynos have multiple modes. Pretty much every dyno will have a power test mode. For Dyno Dynamics, which is more or less industry standard now, its called Shootout. In Shootout mode, the ramp rate, and inertia of the dyno are fixed. Changing these variables- particularly the inertia will dramatically change the power output which is calculated. So you want to make sure that the dyno graph shows the shootout mode that the car was run in. If its not there, then the dyno wasn’t in shoot out, and so the reading is bull.

On the digital dynos, the mode is shown in the data box. Its also shown in the run summary at the bottom of the page. Here is a data box for you. See it shows the Shoot out mode as shoot-4



On the older dynos, the same data is printed at the bottom of the page.

Dyno Dynamic Shoot Out Modes
Shoot-4 4 cylinder Normally Aspirated
Shoot-6 6 cylinder Normally Aspirated
Shoot-8 8 cylinder Normally Aspirated
Shoot-4F 4 cylinder Forced Induction
Shoot-6F 6 cylinder Forced Induction
Shoot-8F 8 cylinder Forced Induction
Shoot-44 All 4 wheel drive NA and Forced Induction
Shoot-2R Twin Rotary
Shoot-3R Tripple Rotary

So if you cant see the shootout mode displayed- start calling bull. If the data box is not there, then the data on your print out is useless. The databox only comes out as a check when the dyno is in shootout mode.

It’s a reasonable question to ask though, why do dynos have multiple modes at all if it simply introduces the possibility of a fudge taking place? The answer is that in order to remap a car, you have to put it through all the load cells in the map. In order to isolate a load cell, you need to hold the car at a certain load and certain speed. This lets you sit in that load cell and then optimise the parameters for it, before moving on to the next. This part of the tuning process is called steady state. The dyno needs a different mode to do this speed and load holding, and you need variable inertia to cope with heavy or light drive trains. You also need variable ramp rates to stress test an engine under the most arduous conditions it can face to ensure it is safe for your customers to use in those conditions.

While I mention steady state, here is something to consider. If you don’t see your tuner doing steady state, or at least checking the car in steady state, then you need to walk away too. Its lazy tuning, it’s the recognition by unscrupulous tuners that a customer will accept a car that drives like a bag of nuts as long as the full power delivery is okay and the number is big. A properly mapped car will drive nicely and even with pretty wild mods can be made to behave in a civilised manner. But only if the tuner can be bothered.


Atmospherics
When a dyno gives a power reading- any dyno- it’s a reading that its corrected for standard conditions. That means standard temperature and pressure. That’s why a decent dyno will have a weather station on it. When it has a weather station, the dyno measures barometric pressure, relative humidity, air intake temperature and ambient temperature and it uses these to give a reading that is corrected to standard temperature and pressure.

So when you read a dyno graph, you need to look at the atmospheric data. Is it reasonable? On a day when the pressure is high, the air is denser and so the car makes more power. The dyno will compensate this out, to give a number that’s corrected for standard temperature and pressure. An unscrupulous tuner will use this to his advantage. By turning the weather station off and altering the atmospheric data, or on older dynos, by simply entering false data, the operator can generate a power output that is greater than the actual. So say it’s a high pressure day, but the dyno operator enters a baro pressure that is low, the dyno correction will increase in a positive direction, and so the power number that is generated will be artificially high.

Conversely, if he wants to show you how poor the last guys map was, he will enter a barometric pressure that is higher than it actually is, so as to generate a negative compensation and artificially lower the power number. He’ll then remap it, flip the barro reading down to invert the correction fudge again, and hey presto, a ‘mapping god’ who has just got 50bhp out of your car for zero work. The customer will drive off happy having had hundreds of pounds removed from them for nothing.

The same thing happens with intake temperature, but to a lesser degree. The higher the IT goes, the greater the atmospheric correction applied. If the intake temperature is 30 degrees c, but the dyno operator wraps the probe round the exhaust, then the recorded intake temperature will be much higher than the actual. This will give a false high power number. This happens because as air temperature increases, its density reduces something like 3% for every 10 degrees. The dyno compensates for temperature and pressure when it gives its result, so entering a false high IT will give a false positive correction.

Be careful however. Under bonnet temperatures can get very very hot, particularly on turbo cars. So when you call BS on a high intake number, be aware that you can easily see +30 or +40 degrees over ambient temperature on an intake temp. What you need to look for is consistency. If the intake temp was 5 degrees above ambient on the before run, but yet it was 35 degrees above on the after, then that’s BS. If the number variance is consistant, then that’s fine. Many tuners are also aware that since a high IT is visible and commonly known about, they don’t fudge the results this way. Its easier to run outside shoot out mode, or fudge the barro.

Lets take a look at the data box again.



The first line is labelled BP, barometric pressure. In this box its 970pa. That would be a pretty low pressure day. So the day this was done on would have to be a nasty poor weather day. The RH, relative humidity, is also high, which tends to support it’s a wet dull nasty day. If it was bright and sunny that day, its time to call horse poop!

The third line is AT, ambient temperature. 13 seems reasonable given that it was a wet, nasty day. IT is intake temperature. Its 17 degrees c. That’s a 4 degree variance. I’d be expecting that this graph was generated from a naturally aspirated car with a cold air intake with a short pipe run under the bonnet.

Loose Strapping
When you buy a dyno, they teach you how to strap a car down. The straps are there for the safety of the car, the dyno and anyone else in the area. They hold the car to the dyno and then ensure proper grip at the tyres.

Loose strapping is when the straps are set very loose- so loose that the car is physically climbing out of the dyno bed. When this happens, the car will climb the rollers. When its doing that, not only is the force of the cars wheels turning the rollers, but gravity is having an effect too. This can introduce a variance of up to 10%. It’s a favourite with your sketchy tuner, because you cant see it in a dyno graph. When your car is strapped correctly, it will move slightly on the rollers, not a lot. If its moving around a lot, then the straps are too slack and someone is trying to pull something on you.