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Custom Tuning

Custom tuning is a very interesting field to work in but it can be confusing. To make this easier we’ve split this information into two sections, firstly how much to you know about tuning?

I Know a Little

What is Custom Tuning?


Custom tuning is where the software provided for a remap is written specifically for your vehicle, taking into account your driving style, the condition of the vehicle and any modifications that may be fitted to the car.


It’s different to other forms of tuning (i.e. chip tuning or driveway tuning) in that we’ve written it for you and not bought it from somewhere else that may only take into account how the vehicle is supposed to perform based on the dealer level spec.


Why use the Rolling Road?


Our rolling road facilities are 4WD compatible, fully embedded into the ground for security, and installed directly by the manufacturer directly in our premises. This means that it’s accurately set up to give you a true reading of the power output of your vehicle and that it will be correctly dyno’d because it’s tied down from all load points.


Using the rolling road to check the before and after power output also allows us to accurately check through any files we’ve written for you throughout the entire rev. range for safety and reliability.


What do you mean by Safe Limits?


At Big Fish we’re only interested in increasing the power output within the safe limits of the vehicle. What we mean by that is we don’t want to reduce the overall lifespan of certain component parts on the vehicle and if we have concerns over any parts, your clutch for example, we will let you know at the time of tuning.


Why the Pre-Tuning Health Check?


We do a rolling road run and a pre-tuning general health check before any tuning begins to ensure that the vehicle is in a good condition to be tuned (i.e. your alignment is good, you have no issues with your clutch or any sensors) and proceed from there.


This means that we can be sure that your vehicle is in a good condition to be tuned and that custom tuning won’t highlight or exacerbate any underlying issues.


If we do find anything which gives us a cause for concern we’ll discuss it with you and we can either adapt our tuning to work around the issue (if it’s minor) giving you the chance to take the vehicle away, fix the issue and bring it back later for a tweak OR if the issue is one where we’ll advise you not to proceed there will be a minimum charge of £150 per half day slot for the rolling road run and diagnostics.


OBD or ECU Out?


OBD means that the tuning can be done via the diagnostics port and your ECU does not need to be removed from the vehicle. This is the case with most modern VAG and BMW cars.


If your ECU does need to come out for the vehicle to be tuned this is done at no extra cost and we have an ECU clean room where the ECU can be correctly and safely opened for custom tuning. The ECU is then resealed using a waterproof sealant and refitted securely and accurately to the vehicle.




This is one of the questions we are asked most frequently; ‘Should I inform my insurance provider?’ and the answer we will always give you is ‘yes’. If you’re over 25 with a good driving history you’ll likely encounter no issues with your insurance provider and if you phone them in advance they may even tell you a specific power increase percentage (i.e 25% more bhp and torque) which we can make sure our tuning stays within to avoid any changes to your monthly/yearly payment.


I Know a Lot

Chip tuning is the original terms of what is now known as ECU Remapping. Chip tuning requires the removal of the Eprom from the ECU and the software is programmed to the chip on the bench with a dedicated programmer. Once the maps are extracted from the chips, the files are identified, altered and loaded back onto the chips. This process is know as the remapping. In most cars due to the introduction of software updates by dealers, we can use the same communication method to introduce a custom version of the maps. This is done by the OBD diagnostic port as found on most cars. As manufacturers have tried to prevent this method of remapping the ECUs has developed to use processors known as Tricore. At this present time these processors do not allow remapping through the OBD port without removal of the ECU first to alter the boot loader of the ECU. This is less intrusive as all security bolts are replaced and special tools designed by Big Fish to prevent any soldering onto the board using special probes and spring loaded arms.


We work on all ages of ECU from the early EDCs requiring chip tuning right the way through to modern MEDC17 locked tricore processor ECUs with tuner protection. 


We use all the latest tools from CMD Technologies, Alientech, EVC, VCPowerTeam, Byteshooter, Piasini and others.


We also have various OEM level diagnostic level tools including Renault CAN Clip, Opel/Vauxhall Tech2, Porsche PIWIS, Bosch KTS, Peugeot Planet, BMW GT1, Mercedes STAR, Citroen Lexia, Fiat Examiner, Ford/Mazda/Land Rover IDS, Volkswagen/Audi/Seat/Skoda VAS 5054 & VCDS.

All our remaps are written in-house and all ensure the key following points (Though not limited to):


Air Fuel Ratios (AFRs) It is important to ensure optimum AFR is achieved in order to ensure the stoichiometric mixture. This in basic terms means that the engine isn’t running lean or rich fuel mixture. This is also important in ensuring that your engine is MOT compliant.

Boost Pressure It is important that correct boost pressure control is achieved to ensure that no spikes or dips occur to ensure maintained life of the turbo charger. A spike in the boost delivery can cause over-boosting which pressurises the compressor to a level beyond its tolerance.

Exhaust Gas Temperatures (EGT)

When increasing the fuelling and boost pressures of an engine it naturally increases the EGT. It is important to log the EGT of an engine as there is a crucial limit which shouldn’t be surpassed to ensure maintained longevity. This is a good tool in monitoring the efficiency of uprated intercoolers etc.

Injector Duty Cycles (IDC)

This is crucial to know the fuelling limitation of the injector. On some modern cars we are seeing injectors with 100% IDC from standard meaning there is no room for further modification without upgrading the injectors (this is rare however). If it was a turbo application, and the boost pressure was raised, due to there being no additional fuel available, it would cause the engine to run lean and potentially melt your pistons. As a result of fine monitoring and adjustment to our remaps, we are able to provide safe and reliable tuning solutions to our customers. We will not operate outside of the engines capabilities on standard components as your vehicles reliability is as important to us.


Contactless Service Available

Here at Big Fish the safety of our staff and our customers is very important to us. We love what we do but sadly we can’t do it from home as our state of the art 4WD rolling road, vehicle support equipment, and vast array of tuning and diagnostic tooling aren’t portable. That is why we have introduced new safety measures for the foreseeable future.


You can book your appointment by clicking here or alternatively by contacting us directly on 01642 039111.


Once you have booked your appointment you will be provided with a link to pay your deposit as well as a link to our online sign in system. This must be completed prior to your appointment as it is where you’ll provide us with details of your vehicle and your driving style. Also in our online sign in process you’ll find details of our on-site safety measures that you’ll need to read and acknowledge.


On the day of your appointment please park your car in one of the allocated spaces outside the Big Fish compound gates. Once your all parked up please call the office on 01642 039111 to let us know that you have arrived. Someone from Big Fish will then meet you outside, remember to keep a safe distance which should be no less than 2 (two) meters apart. Place your keys on the rear window or another safe place on or in the vehicle. We will talk to you from a safe distance and if anything else is needed we will call or text you for more information. Please remember to arrive with plenty of fuel for your tuning session – Big Fish will not fill your car for you.


To maintain social distancing our waiting room and on-site facilities will be closed to customers, this means that you cannot stay on site during your appointment so please do make alternative arrangements. Big Fish will then wipe down the steering wheel, gear lever, and use steering wheel covers and seat protectors whilst we’re in your car. Weather permitting windows will be put down and then it will be moved into our workshop.


As well as this we have upped our available on-site sanitation facilities to keep our staff throughout the day. We’re happy to video/record your vehicle whilst it is in our care but please let us know in advance to ensure that we can accommodate this. For all video/photographs we will fit and remove our Big Fish plates to preserve your privacy.


As always we will treat your vehicle with the upmost care, including securing your vehicle with multiple straps and also ensure that the vehicle is supported and cooled throughout. Once the vehicle has been tuned the vehicle contact points will once again be cleaned as well as the dyno cell itself. We will then park your vehicle in one of the allocated bays to await collection. All footage, graphs, and receipts will be emailed to you to minimise contact.


Big Fish will contact you to let you know that your vehicle is ready to collect.


Keeping you safe, and keeping us safe is our priority.

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