Rolling Road

We operate the Rolling Road dynamometer that has full data capture to give you full printouts of engine horsepower, torque, emissions and boost pressures (where applicable). We test all vehicles (except 4-wheel drive) for both road and competition, with the expertise to diagnose faults on all systems whether it is on engine management functions or for good old carburetors and distributor operation.

To some people putting their car on the rolling road may seem expensive, especially if they're the sort of person who carries out all their own mechanics, it will however be the best value for money that they or you have ever spent, as no matter how technically skilled you are it is not possible to set an engine by ear or by road test, plus it is also a lot quicker. Why spend thousands on special parts or hours of preparation time only to get less than the full horsepower you built into the unit. In all our 30 years of experience we never seen an engine set up manually that we have not been able to increase the power on by adjustment of the equipment already fitted.


This section is required reading for all accept for the real expert. Rolling Roads or Rolling Road Dynamometers, to give the their full title, are a method of calculating the horsepower delivered to the wheels of the vehicle. The word dynamometer means a testing facility for measuring power. You can also have the engine dynamometers or dyno's for short, that the engine is mounted on to calculate the power. Technically any engine dyno is probably better than Rolling Road, particularly if you are going to try out a lot of modifications, and is more accessible to work on. On the other hand when the engine is in the car you can make a better judgment of how the package works especially regarding cooling, due to bodywork reducing airflow etc. The one disappointing aspect of Rolling Road dyno's is the power figure they give in comparison to engine dyno's, due to the power losses through the vehicles transmission. The power losses on most vehicles are between 18% and 27%, so that an engine measured on an engine dyno giving a 100 horsepower will only show 73 to 82 on the Rolling Road. This factor is often a great source of disappointment to an owner of vehicle as his manufacturers hand book says his standard cars has 100 horsepower and cannot understand why it has suddenly lost 25 horsepower.

The main components of Rolling Road dyno consist of two free running rollers that the driving wheels of the car on test sit on, along with a host of electrical equipment to give the horsepower readout. The car is then started and put through the gears, the power from the wheels turning the rollers. When normal operating temperature is reached the test is conducted in fourth or fifth gear and a load is applied to the rollers gradually, which tend to slow the engine and with combination of throttle openings and load applied you gradually get to full throttle and the particular RPM you wish to check the horsepower. The load applied to the rollers is transferred from a mechanical load to an electrical signal that gives horsepower reading on the console. Sounds simple and foolproof doesn't it! Read on.

There is more bullshit talked about horsepower than anything else, whether it is in the pub about a road car or in the pit lane about a racecar. Although one would think the machine couldn't lie, it can be operated to do just that.

The first piece of advice is that you should not necessarily believe the horsepower figure the machine reads as these machines need calibrating and due to the cost of this, most are not checked often enough. Even more importantly a lot are deliberately set to read higher than true figures, to boost the ego of the customer or more importantly to prove how much horsepower the tuner has built into your engine.

Secondly, if it is possible, have your engine tested before you have any conversion done to the engine. Every car manufacturer prints horsepower figures so you should know what you should have to start with. The most important part about any conversion is how much extra power you have achieved and the only realistic measurement is a percentage increase, not what horsepower is registered on the dyno. One word of warning however going back to calibration, it is possible for the calibration to be altered between the first test and the second. Turning a simple adjusting knob or screw, that can be very accessible, sets the calibration. Time to change it, about three seconds.

Make sure that when a test is being done that the same gear is always used. This is probably the most important factor to remember, especially if you are having a before and after conversion test. The reason this is so important is down to the basic physics of gear ratios. Why does a car accelerate faster in first gear than top gear, after all the engine is still the delivering the same power? The answer lies in the gear ratio. If your first gear has ratio of 4 to 1 and top gear is 1 to 1 it will accelerate (theoretically, but not in practice due to extra friction in lower gears) 4 times as quickly because the effect is to give your engine 4 times the power. This ratio difference has the same effect on the horsepower registered on the dyno. It is normal to a test a car on a dyno in as near as a 1 to 1 ratio as possible so you get the truest horsepower reading you can. This is often difficult with modern cars as no gear is a straight 1 to 1. Most 5 speed gearboxes have a 4th gear at say 1.3 to 1 and 5th gear at .93 to 1, meaning that in 4th gear it will overstate the horsepower and 5th understate it. If we take this to it's logical conclusion a car first tested in 5th gear and giving a 100 horsepower at the wheels with a .93 to ratio is really 107 BHP whereas if the vehicle is then tested in 4th gear with a 1.3 to 1 ratio the horsepower reading will be 100x1.3 = 130 BHP. These are hypothetical figures, as the friction, and hence horsepower losses, in the gearbox are greater the further you go way from 1 to 1, but the principle is still the same. So be quite sure that every time your car is on the dyno the same gear is always used.

The above are some other reasons that cars with supposedly different dyno horsepower figures can perform the same on the road. One other factor not discussed in relation to horsepower and performance, is the diff or final drive ratio. Whilst altering this will not affect horsepower the engine delivers in relation to the different gears, it will affect the acceleration of the vehicle to extent that the car appears to have more horsepower. If you reduce the final drive ratio by 30% the car will accelerate as if the vehicle has 30% more power.

Is a rolling road test so necessary? The answers are many. Firstly you are dealing in factual results not impressions like you are when road testing a vehicle. If you try to tune an engine by road or track testing the amount of variables are too great to make it possible to get the best set up. Lets assume you are testing on a track you know well and race on all year-round, the variables are as followers.

1) Are you feeling in the same mood?
2) Can you make a judgment of 2% to 5% better or worse acceleration?
3) Is the track as quick as when you last were on it, the difference of even an hour and a change of weather can make all the difference?
4) Is the inlet air temperature the same as last time, if it is cooler the car will seem more powerful.
5) Have many modifications being done to the suspension or are the tyres the same as before, as any variances in these will slow or speed up a lap time, without any engine modifications.

Apart from the above there is the time it takes to prove or disprove an adjustment, even assuming you can make a 100% correct judgment. Is only takes about five minutes maximum to test horsepower on an engine on the dyno whereas road testing it will take 3 or 4 times as long, minimum, to get a true feel.

Let's also consider the simple, easily adjusted, but vitally important things that can be done whilst the car is running on a dyno, that is impossible otherwise. You can adjust the richness of the mixture and ignition timing, the two main causes of power increase or decrease. To give a perfect example of personal track feelings against a dyno, we built our 1294 cc AX racer with a really wild camshaft and it produced 151 BHP at 8250 RPM and it sounded like a Ferrari, music to the ear. Our previous engine was 147 BHP at 7800 RPM and sounded a lot less powerful but yet went round the track 2 seconds quicker even though driving it you would have said it was the opposite. The real answer lay in the fact the less powerful engine had a much broader band of horsepower and torque and so accelerated more quickly out of the corners. If we had been on a track with few corners and mile long straits it may have been a different story. It just goes to show how driver perception can be misplaced.

This also goes to show that if you are buying a highly tuned engine getting the maximum power figures are perhaps not the most important thing, you need to know the horsepower all the way through the rev range so you can calculate the usability for your purpose. The only way you can do this is to get the engine or vehicle dyno tested. So remember this is the most important part of your tuning program not as some people judge it as an unnecessary expense or just to prove what horsepower you have. It is a means of getting the best out of what has been built into it. The only time I use a dyno to prove the horsepower is as a means to find if a previously tested engine had gone off song and needed attention or when buying a car the owner says has a certain horsepower figure. The last scenario is very worthwhile considering if you are buying a so-called tuned engine, as it is expected that you will pay a premium for the extra horsepower; the higher the power above standard, the higher the price premium. The majority of quoted horsepower figures are, especially by sellers, pure fantasy. Even if you can see the engine has had a lot of special parts fitted to it, it does not follow that it delivers what it should, as it could be badly put together or just not set right.

One notable vehicle in this category of overstated horsepower was a series of Citroen Saxo VTS that was sold by company as having a 160 BHP or 40 BHP more than standard, which is a dramatic increase when one considers the standard car has 120 BHP from 1600 cc, which is very good to start with. This vehicle was tested in Max Power magazine as being a rocket ship, which naturally took our interest. I contacted the company marketing it, pretending to be a private individual and asked what they did to the engine to make it so much better. The answer was very hazy and very uninspiring for sales patter to get someone to buy one. It went like this. Oh! Well we polish the head a bit alter the ECU and a few other bits and pieces, which would cost about £1000 to do on your car. I could not believe that by such minor alteration such an increase in power was possible and remained very skeptical. As luck would have it the owner of the car tested in Max Power contacted ourselves and told us how disappointed he was in the cars performance in comparison to his friends standard Saxo VTS and asked for us to do a dyno test on it. Naturally we jumped at this chance and duly tested it. Our standard VTS produces 94 BHP at the wheels and yet this vehicle with supposedly 40 more BHP than standard gave only 7bhp more, not surprisingly the customer was disappointed. The only answer must have been that the transmission had absorbed the extra BHP.

So whatever you want from a fully programmable ignition and injection system re-map, a re-jet on a carburetor or just a test on a road car, this could be the best money you have ever spent. Whatever you want give us a call to discuss your needs.


Prices for rolling roadwork are based on a cost per hour for the vehicle being tested. Normal garage labour rates for doing simple servicing can be substantially more than the cost of using the Rolling Road. All the work under taken on the rolling road is done by one of our race team mechanics or development engineers. A normal power run check with the production of graphs will be done within an hour and are normally available on a days notice. Remember you must make sure the engine is running at its best if you want a quick on and off with meaningful results and a minimum of time spent. If in doubt lets do a tune up at our normal £35 per hour to prevent costly dyno time being wasted.

If you have an annoying fault that is difficult to replicate standing still or on the road by all means put it on the dyno as this is one of the machines strengths, to fault find. Remember a dyno test is the best money you can spend, as it is a factual test of the true performance of the engine as it eliminates all feelings and judgments, especially bullshit.

£40 Per Hour

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