the TVR SEAC pages
Following Jack Acres letter in last month's issue of Sprint, I feel that a few myths about ECUs and power outputs need to be dispelled before they fester into "facts".
The following notes appertain to Rover based engines using the 14 CUX fuel injection system. as used by all later TVR Rover V8 models.

1. Large power increases can be achieved by modifying the ECUs for most modern turbo charged engines. This is possible because the boost pressure is controlled electronically, and to put it simply more boost equals more power. Obviously this is not possible with a normally aspirated engine, all that you can alter is the quantity of fuel injected and the ignition timing. So there is very little scope for power increasing. To make matters worse only the quantity of fuel injected is controlled by the ECU on the Rover V8. The ignition timing, which is more critical, is controlled by the traditional distributor.

2. No TVR left the factory with a standard Range Rover ECU. The amount of modification depended on the state of tune and intended application. Most had the following modifications:

Removal of the speed limiter which prevents range Rovers exceeding their tyre speed rating of 112mph.
Increasing of the rev limiter in line with the camshaft and valve train capabilities
Adjusting the idle speed control to achieve the best compromise of emission levels and smooth running.
Re-calibration of the main fuel maps (including cold start and accel/decel maps) to achieve the best power output, fuel economy and smooth running consistent with low exhaust emissions.
Modification of the closed loop control strategies and overrun fuel cut-off for improved drivability and emissions performance (cat cars only).
Re-calibration of the air flow meter input to cope with high air flows (5 litre engines only).

3. No TVR thinks that is an automatic. There is an input on pin 34 of the ECU consisting of a 510 ohm resistor connected to ground to enable manual mode. If this is not present idle speed may be low or erratic.

4. If your engine is unmodified, running the correct ECU, and everything is working correctly, it will not be short of fuel at high rpm. If you suspect that your engine is running lean then check the following:

Idle speed mixture: Adjust to give 1.5% CO (2.0%.will give better throttle response but poorer fuel economy). Non cat cars only.

Full throttle operation: The throttle must be hard up against the stop to enable full throttle enrichment, corresponding to a voltage 4.6V on the throttle potentiometer, otherwise the engine will run lean by 5-10% depending on RPM. NB. A few engines were produced, or converted to run with large throttle diameters (usually 4.3 to 5.OL). It is very important that these engines run the correct ECU which will enable full load enrichment at 3.6V
Tune resistor: The ECU contains several "tunes" for different applications. It is essential that you are using the correct tune resistor for your engine. TVR only use two tunes, one of 470 ohms for non cat cars and one of 3k9 ohms for cat cars. If the tune resistor is missing then the ECU will run in default mode.

Fuel supply and pressure: Cheek that the correct fuel pressure is maintained under full load conditions. If it is low, check: regulator, fuel pipes for damage or kinks and both fuel filters (before and after the fuel pump).

Road speed input: This is required for correct idle speed control on all cars and it enables full load enrichment on cat cars. (Check with an oscilloscope on pin 6 of ECU).

Improvements were made on a continuous basis. Serpentine engines benefited from improved idle speed control. Late model 400s , V8S, early Griffiths. and Chimaeras may benefit from this change.

All TVR ECUs have a socketed EPROM holder to allow the chip to be changed easily. Standard Range Rover ECUs do not.

Ignition, Horsepower, and Detonation
Most TVR Rover V8 engines give maximum horsepower with an ignition timing of 30 to 33 deg. total advance. However due to the gradual decline in fuel octane ratings many early cars can no longer run on their optimum settings due to detonation. In order to prevent detonation and consequential serious engine damage, the ignition timing will need to be retarded a few degrees. This can be minimised by the following:

Ensure your engine is running the correct fuel mixture as above.

Ensure your engine is drawing the coldest air possible. High air inlet temperatures are a major contributing factor to power loss and detonation.

Check that your engine has an 82 deg. thermostat with a large orifice (This is a standard TVR part but is not commonly available from other outlets).

Check that the heater matrix bypass hose has not been removed. This is necessary to ensure correct coolant flow around the cylinder heads when the heater is turned off.

Use the later retracted nose spark plugs.

Use the latest distributor which has a more suitable advance curve for lower octane fuels, or better still find someone who can re-tailor your distributor to give less mid range advance but 33 deg total advance. (A mapped ignition system would be the best but most expensive solution).

Do not use an engine oil with a relatively high phosphorous content as this leaves combustion chamber deposits that can promote detonation.

Use a high quality fuel and alternate between four star and super unleaded if you have a non cat car.

Avoid chip tuning companies unless you are 100% confident they know what they are doing. Chip changes are only necessary if you have modified your engine.

Unless done correctly, chip changes will be diagnosed as faults on TVR or Rover diagnostic equipment. Genuine TVR chips are available for all TVR engine variants for £16.37+vat from the factory.

Rolling Road tuning
If your car is unmodified, has been correctly serviced and is in good condition a rolling road tune will achieve little other than relieve you of a large amount of cash. If you have modified your car it is well worth your while in order to get the best from your modifications unless your engine has been set up on a bench dynamometer.
A bench dyno is the most accurate, repeatable and safe way to test and develop a high output engine. It is probably also the most cost effective in the long run. Points to bear in mind if you take your car to a rolling road:

How good is the operator. The most expensive high tech equipment is worse than useless unless the guy using it really knows what he is doing.

Be very careful not to overheat your engine as very few rolling roads can keep water, oil and air temperatures stable to those you actually see on the road. This is essential if any meaningful data is to be gathered and to prevent engine damage. Inertia type dynos are better in this respect as they only load the engine for a short time. Watch out for wheelspin which is sometimes difficult to detect.

Wheelspin can overheat your tyres so can strapping down too hard to prevent it. It is quite possible to wreck a good set of tyres!

Ensure copious cooling air flows around the engine and exhaust to prevent bodywork from overheating, removing the bonnet often helps.

Who pays if something goes wrong its usually YOU

Don't waste your time and money if you think you have more than 300bhp. Use a bench dyno.

When was the rolling road last calibrated? And by whom?

What is the output given as?
Actual measured horse power (at the wheels) horse power at the flywheel
std corrected horsepower
SAE corrected horsepower
DIN corrected horsepower
ISO corrected horsepower

You may be forgiven for thinking that all of the above would be the same. They are not! The first is the easiest to understand as it is the power in bhp which is actually measured at the rollers as you do the test. This power will be considerably less than you have at the flywheel and it is what is left to drive your car forward after you have removed all the losses due to friction in the whole of the drive line including the tyres. If you have measured the power whilst accelerating the engine you will have additional losses as power is required to accelerate the engine internals, the whole of the drive line and the rollers.

Some dynos estimate flywheel horsepower by performing a coast-down run which attempt to measure the drive line frictional and inertia losses. These power losses can then be added to the measured power to give you an estimate of the flywheel horsepower. This is much nearer to your engine's real horsepower but still does not account for the power used to accelerate the engine itself or the difference in friction between a lightly loaded transmission in a coast down and that of a lightly loaded one during a power run.

The other four corrected horsepowers are an estimate of what the power would be if it were measured at the temperature, pressure and humidity required by the relevant SAE, DIN or ISO standard. All of which are different, thus give quite different power figures! This correction process is fraught with assumptions and inaccuracies. The only accurate way to obtain values of DIN or SAE horsepower is to measure it on a bench dyno at the required air temperature humidity and pressure. This is both difficult and expensive.

This may lead you to believe that actual measured horse power is the only meaningful number obtained from the rolling road; well think again as this number will change as the air temperature, pressure and humidity changes. "Your power output literally changes with the weather!"

I hope that this has demonstrated some of the difficulties in measuring and quoting (or misquoting) horsepowers.

However the actual number is not important unless you are a very sad individual, all that matters is how well your car actually performs.

John Ravenscroft TVR Engineering Ltd

More on Fuel Injection Tuning and Rolling Roads by Mark Adams

Having read Jack Acres' letter "Rolling Roads" in the February 1997 issue of Sprint, I felt it necessary to write and clarify a few of the points raised in his letter. Hopefully this will help TVR owners understand what TVR do to modify their cars, and also remove any unrealistic expectations that people may have about the benefits of tuning and modification of the Fuel Injection system.

Firstly, let me make my own position clear in this, for those who do not know me. I have been a specialist purely in Rover V8 Fuel Injection and Ignition systems for approximately six years - I do not deal with any other engines.

My work centres around modified cars, and those with particularly difficult injection problems. Over the years I have modified and fixed over three hundred vehicles. The work covers a large range of variants from Rover Vitesse, Range Rover, TVR, Morgan, and assorted competition and other specials. I can modify, test, and diagnose all Lucas systems from the 4CU flap type injection system, through 14CUX "Hotwire" to the latest Range Rover GEMS management system. My background is in High Performance Real Time Aerospace computing found on Tornado and Eurofighter aircraft. The Lucas systems are simple by comparison, but the lack of processing power presents its own special challenges.

Generally I work with specialists such as John Eales (JE Developments 01203 639 647 - NOT to be confused with JE Engineering), V8 Developments (formerly Rovertec 01 16 240 4344), Power Engineering (01895 255 699), and Wedge Automotive (0114 281 7507). I also have good relationships with many TVR and Land Rover dealers. I do not work with TVR themselves, for the simple reason that they are doing perfectly well without my help! My service is complementary to, and not a replacement for, the engineering work they do.

Jack Acres is a very active and enthusiastic member of the TVR Car Club, owner of one of the most beautiful and carefully maintained 400SE wedges you're ever likely to see, and a jolly nice chap too! However upon reading Jack's letter, it is open to misinterpretation - one possible view is that 14CUX Hotwire cars are fitted with bog standard Range Rover ECUs. This is definitely not the case and I'm certain that Jack (and TVR for that matter) would wish me to set the record straight. My failure to do this would malign the effort that TVR put into engineering their cars, as they always use the best and most innovative current technology available.

When any Hotwire car is presented for a rolling road session, the first step is always to plug in the Laptop PC and perform full diagnostics on the Injection system - the software I use allows me to check those parts of the system beyond the reach of the more normal Fault Code Reader. There's no point in proceeding with a faulty car.

It soon became apparent that Jack's car had a fault. The 14CUX ECU contains several different tune options to cope with different end markets for the host vehicle, and this includes Cat or Non-Cat, Automatic, Manual, and Air Conditioned models to name but a few! The ECU works out that it is in a Manual gearbox vehicle by looking for a particular resistor (which TVR mount below the Fuse Box). In Jack's case this was broken, however I have seen other vehicles where it has been missing altogether (although it certainly left the factory with one there). This causes a fault code to be set in the ECU because it cannot determine the type of transmission fitted, and this in turn affects idle speed behaviour. As standard, a TVR does not think it is an automatic Range Rover.

Having fixed the fault and done some power runs, it soon became apparent that Jack's car was not standard. This showed up as massive under fuelling. Also the profile of the torque and power curves was quite unlike that of many other 400s I have cared for. Since the fuel pressure was not dropping off then the ECU needed attention.
Tailoring the ignition timing, fuel map and overall fuelling level released the 41BHP quoted in Jack's letter, together with a massive increase in mid range torque.

Two points need to be made here. The first is that unless your car is modified, there is no way you will see such a massive gain on a standard car by tailoring the fuelling. However, it was believed that Jack's car was indeed standard - the truth was only revealed by the rolling road test. He may never have known otherwise. Several non-standard cars have been revealed in this way. A rolling road session will soon show up any problems, and if the car is standard and well maintained then it will not require a new chip unless there is something else you wish to alter.

The power and torque figures for the bulk of the cars I have run on this dyno are stored on the computer. This makes it very easy to determine the results of any modifications, and also to compare the results for similar cars to see whether they are on the pace or not.

When TVR modify the ECU they pay attention to many areas of its behaviour. Just some of these things are removal of the road speed limit (oh yes!), a sensible rev limit, idle speed, etc. As time moved on they made continuous improvements which affected other areas such as warm-up fuel, acceleration fuel, etc. Larger engined models (450 and above, and latterly 430HC models) received further modifications including scaling of the airflow meter input which is vital to achieving good driveability, overrun engine braking, full throttle enrichment point, etc. As later versions of the software and ECU itself became available they used those too. The best technology is seen in their latest Serpentine Cat cars.

All of the above things I can alter as required to suit modified engines. Standard cars can be tailored to suit the owners preferences and to accommodate the inevitable slight variations between production engines. Any power increase here will be limited to no more than 10-15BHP at best, but may be nothing. This is your decision as the owner. Obviously early cars derive benefit from being upgraded to the latest compatible software with all the latest modifications. Please note that I do not lift the rev limit set by the engine builder for obvious reasons.

On the subject of rev limits, did you know that Land Rover use two settings - for Cat cars it is 5200RPM, and for Non Cat they use the incredible figure of 8500RPM! If any standard Range Rover has ever achieved this then I expect the pistons are still orbiting Pluto!

It is important not to set too much store by the actual value of the power figures obtained from any dyno - chassis (in car) or engine (out of car). Both types of dyno feature advantages and disadvantages, but at least with a chassis dyno you don't have to take the engine out of the car. There are so many different ways of calibrating and compensating for the figures obtained, that actual figures may vary between dynos by as much as 30BHP in this power class.

Personally I always use John Eales for Engine dyno, and Power Engineering for Chassis dyno work. Both these use calibrated dynos, both give realistic figures, and both largely agree with each other. However what is important is the differences obtained by any modification process which is one reason why I always use the same installations.

Power Engineering are best known for their work as Cosworth and Ford RS specialists (excellent people to talk to if you have Ford V6 power). They regularly feature in leading magazines, and build many championship winning vehicles (Vecta Ford, Eurosaloons, etc) - the list is too long to put down here. Their facility is a fully computerised, regularly calibrated, state of the art rolling road. This means that a brief single pass is all that is required to record full load figures. This is kinder to the engine, transmission, and tyres, and is unlikely to provoke overheating. It is able to read power at the wheels and also estimate flywheel figures.

One major point comes across from the standard TVR engines I have tested. The absolute power figures do not actually reveal the best part of the story. If there is one thing that marks out a quality engine build, it is consistency. As an example, all the STANDARD 390 engines, and 400 engines, I have tested have produced the same power to within plus or minus 2BHP - which is a spectacular achievement. Also they all serve up a more than generous wad of mid range torque, which after all is what gives you your acceleration. TVR do not promote these two outstanding features enough, although it is difficult since most people like to blah about BHP instead!
I hope this clarifies things. Happy TVRing!

Mark Adams