Knowledge Boost: Dynos Explained
Dyno 101

If you’re building a performance street car or race car, at some point you’re probably going to need to use a dyno if you want to get the most out of all your shiny expensive parts. It wasn’t too many years ago that dynos were almost the exclusive realm of well-funded race teams. They were expensive, rare and difficult to use, so that really limited their usefulness in the street performance market. These days though, the dyno market is bustling, and as tuners we have access to a wide range of quality, accurate dyno equipment at a fraction of what it cost back in the early to mid 2000s.


Dynos have an unenviable reputation – just search ‘Dyno Fail’ on YouTube and you’ll get the idea. For some they are the source of bragging rights, but for others they are the destroyer of hopes, dreams and engines. Before blaming the dyno though, let’s get a better understanding of what you’re dealing with. This post will sort some fact from fiction and give you the information you need to know before heading to a dyno shop.

Let’s start with what a dyno actually is…

A dyno, or dynamometer as it’s also known, is a device that we can use to apply a load to an engine to simulate how the engine operates when we drive on the road or track. Think of it like this – if we jacked the drive wheels of a car off the ground and tried to drive the car, there would be no resistance on the engine and even a moderate amount of throttle would have the engine sitting on the rev limit. The dyno provides a load to control the engine RPM, so you could think of it like a big brake.


Being able to apply an accurately controlled load is important, but at the same time a dyno will log data while we’re running the engine. RPM, torque, air/fuel ratio and boost pressure are some of the key channels we want to monitor, although the options are almost unlimited. This lets us perform a ramp run on the dyno, check the engine’s performance, and make decisions about tuning changes based on the logged data.

From the tuner’s perspective, it’s all about quantifying the results of a change. This might be a tuning change such as altering the fuel, ignition timing or boost, or it may be measuring the result of changing a part like a manifold, camshaft or exhaust. Either way, we need accurate data so that we know if the change we made was an improvement or a disaster.


Dynos can be broken down into two main types: engine dynos and chassis dynos. Engine dynos require the engine to be removed from the car and fitted to a dyno fixture for tuning. A chassis dyno on the other hand is what we are probably more familiar with these days, where the engine is tuned while it’s still fitted to the car.

An engine dyno is often a better option for development work as it’s very easy to work around the engine and parts can be quickly swapped and tested. This is why engine dynos are the dyno of choice for professional race teams, engine builders and OEMs. For street and amateur level motorsport though, the chassis dyno is a much more convenient and cost effective option. It’s the development in chassis dynos particularly that has made dyno tuning an accessible and affordable option for those of us on the street.


A rolling road dyno is probably what most people have in their mind when they think of a chassis dyno. These are still by far the most common, however manufacturers such as DynapackMainline and Rototest also produce hub dynos where the wheels are removed from the car and the car is physically bolted to the dyno. The advantage of a hub dyno over a rolling road is that wheel spin is eliminated, which is handy for very high-powered engines.


The most common methods used by the dyno to apply load or braking force, include eddy current retarders, a water brake or a hydraulic brake – often referred to as power absorbers. Dynos incorporating a power absorber can accurately control and vary the load allowing the engine to be tuned in ‘steady state’. This is where the dyno holds the RPM steady regardless of the throttle position – something essential for properly mapping an aftermarket ECU.

These braked dynos that I’ve just mentioned shouldn’t be confused with an inertia dyno which uses no brake or power absorber. Inertia dynos use a single roller with a large mass, and knowing the mass, the diameter of the roller, and the rate it is accelerated at, allows the power to be calculated. Since this type of dyno has no brake though, it’s only really useful for tuning at wide-open throttle. So, great for a drag car but less useful for circuit or street cars.

The Truth About Dynos

Most people assume that the dyno is there to measure engine power but this isn’t quite the case. The dyno doesn’t measure power, it calculates it, and to do this the dyno needs to know the amount of torque being produced as well as rpm. A dyno will often measure torque using a load cell as pictured. Once the dyno knows the torque and rpm, it can calculate the power.

Since there is so much misunderstanding around dynos, so here are a few more common misconceptions I’ll clear up:


Dynos Blow Up Engines

This is probably the most common myth I’ve heard in 15 years as a professional engine tuner. Many years ago there may have even been some truth in this as dyno technology and control systems weren’t as advanced, but these days though a modern dyno can perform a full ramp test through an engine’s RPM range in as little as 8-10 seconds. Following this, the engine will then be brought back to idle while the data is analysed and decisions are made.

There is no more load or stress placed on the engine than if you were to drive it at full throttle on the road. In fact, with all of the engine’s parameters being monitored, usually it’s much safer.


Power Figures

Everyone loves power figures and when it comes to dyno sheets, the bigger the better. There will always be a steady stream of keyboard warriors stroking their ego on various forums by posting up their latest dyno sheet, and next comes the inevitable battle about which dyno reads high or low, and how does that compare to ‘X’ brand of dyno. The reality is that every brand of dyno will produce a different reading.

The dyno should be considered as a comparative tool only. Personally, I don’t care if a dyno reads in killowatts, horsepower or mega-ponies. What I’m interested in is how much power I had when I started and what I ended up with when I was finished. This is the true value of a dyno from a tuner’s perspective and trying to compare numbers between different dynos is pointless. This also means when you are developing or modifying your car, you always want to do your testing on the same dyno.


Flywheel vs Wheel Power

A couple of decades back, if you wanted to run your engine on a dyno, an engine dyno was your only option and these dynos return a reading of flywheel power. These days though, we are more likely to use a chassis dyno which measures power at the drive wheels. With a gearbox, differential and perhaps a transfer case between the flywheel and the wheels, the wheel power value will always be lower than the flywheel figure.

Since everyone wants bigger numbers, the question always is: ‘What’s it make at the flywheel?’ This is harder to answer than you’d think. First of all it will depend on the drivetrain. An automatic transmission is a little more power-hungry than a manual, and a four-wheel drive will tend to sap more power than a two-wheel drive. Secondly, we need to think about how this power loss is dealt with. Is the power loss constant, or is it a percentage? And what happens to the power loss when you increase the engine power?

In reality the answer doesn’t matter – the only way to get a true answer is to remove the engine and run it on an engine dyno. Beyond that, forget about bragging rights and use the dyno as it was meant to be used: a comparative tool.


The Dyno Is The Only Way To Tune An Engine

The dyno is an important tool for any tuner as it gives us feedback about the tuning changes we are making. It’s also important to understand its limitations though. For example, it’s hard to replicate the sort of airflow on the dyno that we could expect at 200km/h. Since we don’t drive or race cars on a dyno, what really matters is the engine’s performance on the road or track, and this is why I’m a big advocate of checking and confirming the tune out in the real world.

Getting The Most From Your Dyno Session

I’ve spent a good chunk of my life on various dynos around the world and the problems I see are always the same. Dyno time is expensive so you want everything to go as smoothly as possible. This will ensure you get the best results out of your dyno session and it will help with your tuner’s sanity. Here’s my five top tips for your next trip to the dyno:

1. Turn up with a full tank of fuel

Pretty straightforward, yet I’ve lost count of the number of cars delivered for tuning with the low fuel light on. Tuning isn’t magic and to properly tune your engine, it’s going to need fuel. A tune could consume anything from 20 litres through to 80 litres or more depending on how long the car spends on the dyno, so give yourself the best chance with a full tank. This is even more important if you’re running some exotic and hard to find race fuel.


2. Make sure your engine is dyno-ready

Dyno tuning is going to put your engine under the same sort of stress you can expect on a race track. You wouldn’t head to the track without making sure your fluids are topped up and the same applies to a dyno session. At a minimum you want to check your fluid levels and also check the condition of your spark plugs. If your car has a manual gearbox you’re also going to need a clutch that’s in good health and not slipping.


3. Don’t bring a grenade to the dyno

While a dyno isn’t going to place any more stress on your engine than driving it at full throttle on the road, if your engine is using oil, smoking heavily out the exhaust, pushing water out or generally in poor health, your dyno session probably isn’t going to end well. If you know your engine isn’t healthy it will be cheaper to fix it before you end up with a hole in your block!

4. Fix your oil leaks

Cleaning up the dyno bay isn’t fun and if you want to keep your tuner smiling and minimise your bill, stopping your car from messing up the floor is a great place to start. If your engine resembles some kind of internal combustion sprinkler system, get it fixed before heading to the dyno.


5. Make sure your expectations are realistic

Remember that bit about dynos blowing up engines? Well, sometimes despite the best efforts by everyone involved, things can go wrong. So who’s to blame? This is an awkward question that unfortunately comes up from time to time and it’s important to have your expectations clear from the start.

You should be able to expect a professional tuner to provide the correct air/fuel ratio and ignition advance to keep your engine safe. If you’re chasing huge power numbers that are well beyond the factory limits though, even the best tuner in the world can exceed the mechanical strength of a part. Also, if your engine is just plain worn out or already damaged then things can end badly.

If you are trying to break world records (or pump up your Instagram game), then you need to accept that things can go wrong. If on the other hand, if breaking your engine would ruin your day or your bank account, then let your tuner know so they can tune with an appropriate safety margin.

So there you have it – I hope that’s cleared up some of the misunderstanding surrounding dynos and given you some valuable info for your next tuning session. If you want to see a dyno in action, check out the video above, or click here if you can’t see it.

If you think I’ve missed something or you have more dyno-related questions, ask away in the comments section below and I’ll do my best to answer them.

Andre Simon
Instagram: hpa101

Images by Ben Silcock



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Great morning read for me ..
Thanks a lot

Can`t wait for the next knowledge boost :)


What happens if a dyno breaks during a run? Who is responsible? And if that car is damaged as a result would it be covered by the shops insurance?


ChrisKutcher I'm glad that helped you get through the morning :)


@Ash If the dyno breaks and damages the car most workshops would cover this damage and it should be covered under their insurance. If you are concerned though it's always best to have the discussion with your tuner first though about these sort of liabilities. That way everyone knows where they stand and there are no surprises.

I'll add that this is a VERY unusual situation though and probably much less likely than most people think.


Keep doing this please. Forever. And thank you!


Andre Simon Thanks for the reply, I figured that would be the case. I guess it is probably a good idea to check before hand if they have insurance or not for that sort of thing.

Gianluca FairladyZ

This... Is very good!

The old brick

Awesome article. Thank you for this information and please, keep up the good work.


How is the load cell linked to the rotating parts? Is it just on the end of a simple brace with a known distance from the centre of rotation? Or are there different types of setups between hub (& engine) dyno's and rolling roads?


What exactly are some ways a dyno could break? The only way I can think of is possibly exceeding the power limit time after time.


tunerguy21 Had a case on a 4WD where the brake only worked on the front roller and not the back. So it rapidly slowed down the front wheels, without slowing the rear. It broke the rear diff.


Off topic, I want to know more about that tube frame thing in the first photo.


@Kenny As a formed (and some times current) weighing scales technician I'm also curious on how exactly the load is routed to the loadcell. I don't mind if you don't want to write up a full explanation, but a link or article I could flick through would be handy, I may be missing out on some interesting business here... haha.


DanielMikels search: engineered to slide / drift hilux,  they did a 5 part coverage of the guy's amazing build 2 years ago


This was a great article, I didn't know a whole lot about dynos and I thought this was really interesting. Good job you guys are awesome!


Great article, broadened my mind on Dyno's a lot more. And that Evo near the beginning looks insane!


LukeEVOVIII Thanks for the feedback. The EVO near the beginning held the late model 4WD 1/4 mile record until STM Tuned recently took the crown. It went 8.34 @169.7 mph and made 1001 whp at 42 psi on Q16 :)


DanielMikels as JoshuaFallet1 mentioned, Nigel's 'Engineered to Slide' build has been covered on Speedhunters. You can also check it out here -


@Kenny in the case of our Mainline dyno the load cell is attached to the eddy current absorber via the arm pictured. This places the load cell at a known distance from the centre of rotation and as the absorber applies load, the resulting torque is transferred through the arm to the load cell where it can be measured.

Sorry Robo_No1 I don't have any other resources I can point you towards on the subject.


tunerguy21 on a rolling road dyno the most likely scenario would be a strap breaking rather than the actual dyno. This can result in the car jumping off the dyno which usually doesn't end well. To be honest even if a car does come off a rolling road at speed the result usually isn't as spectacular as you would think.


I enjoyed the article, a good read. I have to ask though looking at out scene here in NZ and the numerous options for dyno tuning around the north island. If different tuners ( say your top 5 tuners in this country, would love to know who you rate in NZ for tuning cars) used the same dyno at a single venue and were instructed to go for maximum safe as possible power on the same car do you think the results would vary greatly? Just to add the car in question would have the same basic tune for each tuner when they started.


RussClarke you ask a great question. This was summed up perfectly by Shane T a while back so I'll borrow his reply:

Tuners don't 'make' power. The amount of power a certain combination can make is the result of the parts chosen and the amount of air the engine can consume. If a tuner does their job right, the engine will make the power it was designed to. Anything less is either a conscious decision to help ensure engine reliability or a lack of talent on the part of the tuner.

With this in mind, and to answer your question, if you gave the same car to 5 competent tuners, the results you would get should be very similar. When choosing a tuner, I'd suggest talking to a few of their customers about the experiences they had. Peak power isn't your only consideration either - Consider idle quality, cold start performance, general driveability and economy as well. These aspects are often more important unless you have a dedicated race car.


Andre Simon RussClarke  Thanks for the reply, I do have a dedicated race car and my tune was basically for reliability over maximum power and things like idle, cold start etc. I certainly don't get the huge turbo on a 2.0 liter motor just to say I have x amount of power. I looked for useable power over a wide as possible rev range.

I hope then in this country that the well known tuners (i.e feature in nzpc etc) deserve their reputation and results between them given the above scenario would not be all that different.


Great article ,nothing expected from you and keep up the good work you n speedhunters ....


DanielMikels You can have a read through Nigel's build posts here on Speedhunters too:

The average guy

Good read:) how does a chassis dyno calculate engine power, i guess it uses different methods for different drivetrains? I mean how does it know the power loss margin of the different drivetrains? Is it precalculated, or is a known fact that for example Subaru 4wd uses 20% of total power, Merc rwd uses 14%, etc?


Nice read Andre.

Some dyno's use twin rollers where the wheel goes in the middle and others use a bigger single roller. Is there any advantage/disadvantage to these different designs? I would guess the twin rollers are easier to set the car up on as it can't roll back or forward.

I've noticed that on full power ramp runs the wheels lift off the rear roller anyway on the twin setups so it seems sort of pointless and according to my tuner it actually has better traction if you set the straps up to enable it to do this?


The average guy I don't remember exactly, but they use the spin down to calculate the inefficiencies and find your crank HP.


The average guy  The dyno I use is actually built using a generator from a German WW2 submarine (mounted on a rotating frame with a load sensor to measure the torque). This has a gearbox built in which can effectively turn the generator into a electric motor. We can use this motor to spin the hubs which will in turn spin the wheels of the car (while its in neutral of course). When we measure the force needed to spin the wheels we then have a correction force that accounts for all losses in the drivetrain.
There might be other ways of doing it, but this way is simple and pretty accurate


That video is a good watch, nice to see the tuning story from start to finish with everything explained.


Great article - I cannot stress enough that customers make sure their car is ready to go on a dyno before it does. You could not imagine how many cars come in with no oil on their dipsticks, no air in their tires, no fuel, or coolant already pouring out of the overflow. And I can spot a slipping clutch from a mile away - usually just while driving the car on the dyno if it's catching high enough. It's very frustrating.


Ian Cormack it really comes down to the dyno manufacturer's preference as much as anything. Having used both types of dyno I can tell you it's much easier to strap a car down on a twin roller design as you don't have to precariously balance the car on top of a single roller.

As you say, under power the car will tend to climb onto the front roller anyway.


Judau Agreed. The slipping clutch is particularly frustrating. If the clutch won't hold on the street then there is little chance for it on a dyno!


The average guy it does depend on the dyno. Some don't make any attempt to calculate flywheel power at all. Others will allow the dyno operator to enter a percentage loss so the flywheel figure can be calculated back from that but obviously the result is at the discretion of the operator and the loss percentage they choose to enter.

Some dynos such as the dyno jet inertia dyno perform a calculation as the dyno ramps down to work out the drive train loss. I've never had the opportunity to compare the numbers with those taken from the same engine on an actual engine dyno. Without seeing this I'd still be a little sceptical of the ultimate accuracy. As I said in the article though, use the numbers for what they are - a comparison only. If you do this then the flywheel number really doesn't matter.


Andre Simon The problem is sometimes the clutch will be fine at lower power, then they'll add on a larger turbo, E85, etc. and the new mods will overload that clutch that has been barely holding on for the last year. At that point it just comes to research before the appointment and swapping it out if you have any concerns so it doesn't cost you dyno time and your tuner's time to come back for another visit.


Awesome article Andre, thanks for sharing your knowledge with us!

One question i do have is why does there seem to be a big difference in dyno results or numbers between the guys in the USA and the rest of the world?
For example a modified car here down under would make 260kw ( 349hp ) at the wheels and the same car in the US with the same modifications on a similar dyno would make 280kw ( 375hp ) at the wheels. 

I see this a lot of this in the different car forums i visit and i cant work out why? 

Is it the tuner? Better fuel? Different dyno type / make / model? is it the way power is calculated in the different regions?

It's something that has always made me wonder.



I do a lot of dyno r&d in motorcycles. So the answer will be no different from a car. Im simple words..Two dynos will never give the same reading to the same well as two engines of the same make model tunning with the same parts will give you different readings, the ideal scenario will be to have similar and or close readings but not the same reading. In my personal opinion is more of a mechanical thing on the engine and the dyno that will gave you different readings. Also we have to take in consideration where the dyno is located, altitude above or below sea level, ambient temp, the weather, the maintenance that the dyno receive the maintenance that the car has etc etc etc...there's a lot of factors of the why....
But all that it should not be a issue. Again a dyno is just a tool for you to know where you stand towards your goal.
The bottom line is no matter how much time you spend in the dyno or making simulations...
Nothing absolutely nothing beats testing on real live environment like the track or the street.
Making big hp numbers on the dyno is not a big deal and today is easy.
Power is nothing without control.
Just my humble opinion


How does one become an engine tuner anyways? It has been a career path I've often thought about as I continue my quest to learn about all things in the automotive trades...


Go and enroll in a mechanic institute or credited school most of them will have a specific racing tunning course where you even get dyno certified and learn anything from chassis building, suspension, to turbos and nitrous, flow benches electronics etc... once you past all the theory and basic courses, if really serious about it mix it with a mechanical engineering degree...and star like all of us messing and braking our own stuff.


AndrewCinch the tuning industry is an interesting one as there is currently no industry recognised certification process that will make you an 'engine tuner'. Most tuners get started by tinkering on their own cars and beginning to build up experience. Alternatively maybe they had enough money to buy a dyno and automatically they can open for business tuning cars. 

There are hands-on training facilities that specialise in teaching EFI tuning such as EFI University in the US or you could consider an online option such as the training school I run - High Performance Academy. Options like these will fast track your learning and ensure that you understand the fundamentals of EFI tuning. This will also sort fact from fiction and deliver you with accurate and reliable information.


D1style There can be multiple reasons for this. Obviously first we need to consider the type of dyno. As stated in the article, there is no point trying to compare dyno results between different brands of dyno. This probably makes up for a large percentage of the differences you're likely to see. 

Fuel is another contributing factor. The pump fuel we see here in NZ for example is quite low octane compared to some countries. This can effect how aggressively we can tune the engine while retaining safety.


EliThanos your comment echoes what I've said in the article - The dyno needs to be considered as a comparison tool. 

While track or street testing is critical, I still consider the dyno to be the best place for development work as we have immediate feedback as to how our modifications are working - We don't get to see this on the street or track.

I am however a big advocate of always confirming the tune on the road or track after an engine has been tuned on a dyno. As I mentioned in the story, we don't drive or race our cars on dynos, and it's common to see slight discrepancies in AFR for example between the road and dyno.


Indeed mate you article was spot on. I for instance that are more familiar with motorcycle tunning have use the dyno countless of time for troubleshooting problems instead of actual tunning to extrac more hp.
The dyno is a great tool when use properly.


Andre Simon Your online course sounds more interesting and achievable for me as I live in Canada; I'm not really willing to transplant myself into the US for only one course. At the moment I'm just trying to sample a bunch of things to find the best fit for my specific skills. It may sound unrealistic, but I'd like to become skilled in almost all things automotive related.


I recently heard my son and his friends talking about a dynamometer, and that they wanted one to check out their cars. Now, after reading I finally understand what a dynamometer is used for. I'll see if I can't find one to buy for them, so they can check the torque and other stats of their cars.


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