Rolling Road Tuning
Introduction
For every make and model of car, whatever its age, size and level of sophistication there are numerous companies offering products that will improve its power and performance.
One principle which applies to all engines is the need to provide the correct balance of air, fuel and ignition advance to ensure it will produce the optimum power output for the modifications made. The other thing which is common to almost all tuned cars is that this is a crucial part of the tuning process and is the one thing that is usually neglected, often resulting in disappointing power levels for the amount of money spent, and in the worst cases an engine that self destructs the first time it is driven in anger.
When a manufacturer designs a production engine, many factors such as reliability, economy, driveability, emissions and cost have to be taken into account. All these factors mean that the end result is a compromise aimed at providing good all round performance. As part of the design process, the manufacturer will spend a great amount of time developing a system to provide the right amount of fuel and ignition for all driving conditions, again taking into account the need for good cold start performance, economy and reliable power.
As soon as any modifications to the engine are made the original calibration of fuel and ignition will no longer be exactly correct and therefore the optimum performance available from the modifications may not be achieved. Simple mods like performance air filters or free flow exhausts may not affect the manufacturers calibration sufficiently to adversely affect driveability. However, anything more fundamental such as a high lift cam or big valve head must be accompanied by a recalibration of fuel and ignition to achieve the best results.
How Dynometers work
The only way to accurately recalibrate fuel and ignition for a modified engine is to simulate the load imposed on the engine when driving, both throughout the rev range and at all throttle positions. This is done using a Dynamometer, which imposes a braking load on the engine and measures the torque reaction at the same time. There are two types of dyno’s, the engine dyno and the chassis dyno, which is commonly known as a rolling road.
As the name would suggest an engine dyno requires the engine to be removed from the car and bolted to a purpose made rig, which is housed in a sound proofed cell and fed with cooling air and water. The fuel and ignition system as used on the car is also fitted to recreate the installed package as closely as possible.
The advantages of this set up are that torque is measured very accurately as the flywheel is physically bolted to the unit providing the braking force, hence the term flywheel power. Engine dyno's are particularly good for engines producing very high power outputs or where specific and highly repeatable tests are required. With twin roller dyno's (cradle type) like our old Sun ram 12 it was also difficult to control wheelspin on engine's with high torque or on very lightweight cars. Our new Superflow dyno is the single roller type and can handle up to 1200 bhp. We have already run a turbocharged front wheel drive car which made 558 bhp at the flywheel (502) at the wheels and 438 ft/lbs of torque with no wheelspin at all.
 
The main drawbacks of an engine dyno is the cost of using one, usually at least £800 - £1000 as it takes up to between 3 to 4 hours just to install the engine on the dyno, never mind tune it. Although the engine will normally run on the fuel and ignition system used in the car, the engine will usually produce a better figure on an engine dyno due to optimum intake air temperature, better cooling and exhaust gas flow, as only the cars exhaust manifold will be used not the whole system. There is also no load on the alternator as all electrical power rquired to run the ignition or injectors and ecu is provided by the dyno.
The chassis dyno or rolling road is a much more accessible method of tuning a modified car. The car is simply placed on the rolling road with the driven wheels on top of the rollers. It is then strapped securly from the front, rear and sides so that it cannot move even when running at full power and high speed. As with the engine dyno the rollers are attached to a retarder unit which imposes a braking load to the wheels and measures the torque reaction caused. As with all dyno's torque is measured by the rollers and horsepower is calculated using a set formula which is Horsepower equals torque X 5252/RPM.
 
 
What to expect from a session on the Rolling Road
The first thing to be done before starting to tune a car is to establish what modifications have been made to the engine, what is a safe rev limit and what is the recent history of the engine. The last factor is more important than you might think as we have had some customers who travelled a long way to get their car tuned only to find out the engine has only run for a few minutes after a full rebuild. All engines, even race units need a period of running in before full power runs can be conducted. For a race/rally unit that will be rebuilt reasonably frequently, between 30 minutes to an hour of running in is perfectly adequate. For a road engine we would recommend around 200 to 300 miles before conducting a full tuning session. With a race/rally unit we can run the car in for you on the rollers although this obviously adds to the expense. With a road engine we would recommend tuning the car to around 4,000 rpm on a light to medium throttle to allow the car to be run in on the road and then returning at a later date for a full session.
Assuming the engine is run in we would first carry out a visual inspection of the engine for any potential problems and also check oil and water before commencing any tuning work. At this point, I think it worth a mention that a rolling road is no more stressful for an engine than being driven on the road or track. Providing temperatures are monitored carefully a rolling road session is no worse than a good blast down the road. It is also a controlled environment in which a new installation can be tested with less risk of damage than simply driving on the road or track.
Once the condition of the engine is established the driven wheels are placed on the rollers and the car strapped front and rear, it is then driven at slow speed to centralise the wheels on the rollers. This ensures the tyres have got an even contact patch on the rollers and stops the car moving about and placing unnecessary strain on the straps. The car will then be strapped down further to ensure it cannot move on the rollers. This used to be particularly important with front wheel drive cars and light cars such as single seaters and Westfield or Caterhams etc, but as the tyres now sit on top of the roller rather than in the cradle formed by two rollers the cars are much more stable.
Providing the engine is running reasonably well we would normally do an initial power run at this point to establish a starting point for torque and power and to highlight any problem areas. Where possible, we conduct power runs in 4th gear as this gives the best results when the dyno software calculates flywheel figures based on transmission losses. Runs can be done in any gear (if you have a stock car with only two gears we can accommodate you). The rollers simulate the inertia of a 600kg vehicle so it is possible to do power runs by accelerating the engine against the inertia of the rollers. For high power or cars with very low gearing we can add a percentage of retarder load to slow the rate of acceleration. Before the dyno leaves the Superflow factory it is calibrated for windage and parasitic losses so it is very accurate. Using the versatile software we can compensate for drivetrain inertia to further refine the accuracy of the data aquired. This makes the dyno a superp tool for ongoing development. Once calibrated the dyno software can graph power and torque against rpm very accurately. We can also overlay fueling, speed, boost, transmission losses plus lots more.
If you bring a memory stick with you we can save all your data into a datapack and you can view, print and replay your runs at your leisure.
The tuning process can now be started and will include compression tests, ignition system condition, performance, carb balance, fuel pressure and finally recalibration of fuelling and ignition under various load and rpm stages. For calibrating fuel, the rolling road is used in steady state mode where the operator will dial in a road speed which the rolling road will not exceed, regardless of throttle position and power out put. By staying in the chosen gear this means that every rpm increment and throttle position can be accessed and the fuel and ignition calibration checked and adjusted. This process is particularly important when mapping engine management systems with hundreds of load and rpm sites that can be calibrated. Exhaust emissions are measured by either a Sun diagnostic 4 gas analyser, or more commonly with our Etas wide band Lambda reader which reacts to fuel changes within 200 milliseconds. Lambda bosses can be fitted by us before we start tuning or can be despatched in advance of your appointment if you want to fit it yourself. We can also use a special exhaust pipe attachment which has its own sensor to provide equally fast and accurate exhaust gas measurement.
We carry in stock a full range of Weber and Dellorto jets as well as some Solex jets. Also stocked are a wide range of SU and Stromberg needles and jets, although there are so many variables available we cannot guarantee to have your exact requirement on the day.
We are Omex and Weber Alpha engine management dealers and can also calibrate DTA, MBE, Emerald, Race Tech, Motec etc. If your system is not listed give us a call as with the software and comms lead we can usually map most systems.
After having fully tuned your engine, final power runs are carried out to check that the adjustments made have translated into improvements in power, torque and driveability. The dyno and its Wyndin Software is so accurate it will easily detect small gains or losses and will also show misfires or flat spots. By using successive power runs at the end of a session, fine changes to ignition or cam timing will show on the plot and the best calibration decided upon. Finally, the customer is provided with print outs confirming power, torque and a summary of the detailed data gathered by the rolling road software.
Of course, whilst all this is going on, our two cooling fans rated at 30 and 70 MPH keep everything cool and our exhaust extraction keeps the tuning bay safe.
Costs
Every car is different and as a result it is impossible to give exact quotes for tuning. Our rolling road rate is £85.00 per hour plus VAT and generally a normal session would take between 2 - 3 hours. This can vary, particularly if we have to spend time sorting simple problems, or if you want us to try different choke sizes in DCOE carburettors for example.
As a guide for engine management mapping, ignition systems generally take 3 to 3.5 hours whilst full engine management will usually take 4 to 4.5 hours to map from scratch. With engine management, please bear in mind that we WILL map all the sites necessary to get the best possible driveability and power from your system, not just full throttle as many other tuners may do. This means that you will get the full benefit of the system you have bought and can enjoy good idle and low rpm driveability even from the most radically tuned engines.
FAQ's
Can the Rolling Road damage my engine?
No, the rollers cannot stress your engine any more than you can when driving on the road or track. We will always stick to the rev limit you give us and will carefully monitor coolant and oil temperatures. Remember your car is in a closed environment where the noise and vibration are amplified by the surroundings.
Will the rollers damage my tyres?
Tyres do work hard on the rollers but the single roller design is much kinder to tyres than the old twin roller system. Whilst the dyno will not damage tyres, if you have a pair of older tyres on rims we will be happy to swap them before and after the session for you. Some of our regular customers will always run their cars on the same rubber every time the car is tuned to help maintain consistency between runs. If you have a rally car it is better to run on tarmac tyres than forest rubber as these tend to get hotter and absorb more power.
How does temperature affect the results?
The Wyndin software records the actual measured torque and power but has the facility to enter the ambient temperature and barometric pressure and will calculate a corrected figure. This allows us to make accurate comparisons between a session carried out in the summer and one carried out in mid winter.
What fuel should I use and how much do I need?
Try to make sure you use the same fuel you would normally run when we tune the car, but above all ensure there is plenty of it. Rolling Road work uses more than you would think and we regularly get cars running out of fuel during a tuning session.
How much power can the rollers handle?
Our rolling road is rated at 900 horse power at the wheels under static load and 1200 horse power on a transient power run. It is also rated to 225 mph which means we can run the gearbox in whichever gear gives the most accurate results. This is usually 4th in most standard gearboxes. Some dyno's are limited to as low as 120 mph which means many cars need to be run in third. Our dyno is a two wheel drive rolling road so unless your 4 X 4 is switchable, i.e. a Vauxhall Calibra, then unfortunately we can't help.
How long will it take?
Obviously this depends on the engine and its state of tune, but remember when working at full power, or when mapping we will have to stop periodically to let the car cool down. If you plan to wait, be prepared to spend at least half a day with us.
Preparing for a Rolling Road session
Ensure you have plenty of oil and water and preferably give the engine an oil and filter change beforehand. Please also ensure your cooling system is in good order otherwise we will have to keep stopping to let things cool down.
Check the basics, i.e. spark plugs, leads, distributor cap, rotor arm and coil. Again, any faults in these areas will show up during the session and we can sort them if you wish, but there is a charge for the diagnostic time.
Ensure that the carbs or throttle bodies are getting full throttle. This is a common fault especially on DCOE carbs as getting a throttle linkage set up is fiddly and time consuming so you will save some money if you get this right before coming to us.
Again, with DCOE carbs on a four cylinder engine make sure the carbs are not bolted up solidly to your inlet manifold, as this will froth the fuel in the float chamber at high rpm.
Click here for a rolling road demo
If there are any questions we have not answered, or if you have a specific question relating to your car, let us know via the site email and we will get back to you as soon as possible.
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