GM B20DTH Tuning

"All you need to know about performance tuning the GM B20DTH engine!"

One engine that keeps cropping up in emails and questions we get sent, is the B20DTH, and what modifications work best on it. So we've put together this page which covers our go to modifications that you should tune and outline which modifications we feel are the best.

The GM B20DTH make a good tuning project and with the ultimate upgrades like ECU maps, turbo improvements and camshafts you will enhance your driving enjoyment.

In this article we examine B20DTH tuning and show the best modifications.

History of the B20DTH Engine

This turbo diesel engine part of the GM Medium Diesel family of engines, it offers good power and response, but is crying out for a few more mods.

  • 1.6 136hp @4000rpm 320nm @2100rpm

The B20DTH was fitted in the following vehicles.

  • Opel Astra J 1.6 CDTI 136 HP 5p 05/2014-08/2015
  • Opel Astra J 1.6 CDTI 136 HP Sedan, Sports Tourer e GTC 05/2014-11/2018
  • Opel Astra K 1.6 CDTI 136 HP 07/2015-06/2018
  • Opel Insignia A 1.6 CDTI 136 HP 08/2015-02/2017
  • Opel Insignia B 1.6 CDTI 136 HP 02/2017-02/2020
  • Opel Meriva 1.6 CDTI 136 HP 02/2014-05/2017
  • Opel Zafira Tourer 1.6 CDTI 136 HP 06/2013-07/2019
  • Opel Mokka 1.6 CDTI (136 HP) 04/2015-08/2016
  • Opel Mokka X 1.6 CDTI (136 HP)09/2016-06/2019

Tuning the GM B20DTH and best B20DTH performance parts.

Best B20DTH upgrades

Just because particular tuning parts are popular with B20DTH owners it doesn't mean you should fit it, instead we'll concentrate on the best tuning parts that will give your B20DTH the best power gain for you money.

Performance camshafts helps you to boost top end power so are more suited to petrol engines, than diesel ones. You will usually get a peak power increases through performance camshafts on most engines.

So altering your B20DTH cam will make a difference to the engine power band. Choosing a higher performance cam profile raises the power power range accordingly.

Fast road camshafts commonly boost the bhp and torque over the rpm band, you could drop a little bottom end torque but top end will be higher.

Motorsport and race camshafts, boost the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Race camshaft is not great on the daily commute.

You should ideally optimize your engines power to your driving style so for a road car stick with a mild fast road B20DTH camshaft

B20DTH Camshaft Upgrades

Different B20DTH engines respond differently primarily due to the airflow when camshafts are fitted depending on the camshaft being more aggressive camshaft durations and cam profile as unique due to manufacturing tolerances and quality variations|so set your engine up on a rolling road|check your engine on a rolling road.

The ECU mapping and fuel pump and injectors also have an effect on the power gains you'll hit.

Longer valve durations can adjust the power band, and on most engines there are some advantages to extending the intake or exhaust durations and valve lift.

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Best Engine Mods for your car

  1. Mapping - remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.
  6. Typical stage 1 mods often include: Intake headers, Drilled & smoothed airbox, Sports exhaust manifold, Panel air filters, Fast road camshaft, Remaps/piggy back ECU.

    Typical stage 2 mods often include: induction kit, fuel pump upgrades, Fast road cam, high flow fuel injectors, Ported and polished head, Sports catalyst & performance exhaust.

    Typical stage 3 mods often include: Twin charging conversions, Adding or Upgrading forced induction (turbo/supercharger), Internal engine upgrades (head flowing porting/bigger valves), Competition cam, Crank and Piston upgrades to alter compression, Engine balancing & blueprinting.

    The B20DTH engines make great tuning projects and we're finding that there are increasing numbers of upgrades and tuning parts out there.

    ECU Mapping Improvements for the B20DTH

    Remaps will help fully realize the full potential of all the upgrades you've done to your B20DTH.

    (Sometimes flashing the ECU is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but check it has knock protection and that you get it correctly setup.) It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but the end result may rely on the upgrades you've done and the condition of your engine.

    Air Flow improvements on the B20DTH

    It is the main goal to any car tuning project to shove more air and fuel into each cylinder

    The intake plenum take the air during the suck phase from the filter and allow it to be fed into the engine cylinders with fuel for the squish phase.

    Design and rate of flow of the Intake manifold can make a substantial improvement to fuel engine efficiency on the B20DTH.

    I usually find air intake manifolds are in desperate need of aftermarket tuning parts, although some OEM provide reasonably well designed air intake manifolds.

    Larger B20DTH valves, carrying out port matching and head flowing will also raise bhp and torque, and more importantly will permit a greater bhp and torque increase on other tuning mods.

    B20DTH Turbo upgrades

    The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes significant power gains.

    There are common areas of failure for every engine, with some being incredibly solid and some only just able to handle stock power. It is important to find these restrictions and fit higher quality components to cope with the power.

    There are many car owners spending a lot of money on turbo charger upgrades on the B20DTH only to experience the whole thing literally blow up when it's first rolling road session.

    Larger capacity turbos often experience low end lag, and little turbos spool up really quickly but do not have the high rpm bhp gains.

    Thanks to progress the selection of turbos is always moving on and we commonly find variable vane turbos, allowing the vane profile is altered according to speed to lower lag and increase top end bhp.

    Twin scroll turbos divert the exhaust gases into 2 channels and flow these at differently profiled vanes in the turbo. They also help the scavenging effect of the engine.

    It is not unusual that there is a limit in the air flow sensor AFM/MAF on the B20DTH when loads more air is being fed into the engine.

    Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting torque at a much lower level.

    Adding a supercharger or additional turbo will make large performance gains, although more difficult to get working. We have this article covering twinchargers if you want to read more.

    B20DTH Fuelling Upgrades

    When you increase the torque you will need to uprate to the fuel system.

    More torque needs more fuel. Performance fuel pressure regulators can provide a better throttle response.

    It is important to over specify your injectors flow rate.

    The accepted safe increase is to add 20% when specifying an injector, this allows for injector deterioration and affords you some spare capacity should the engine need more fuel.

    We think this one is common sense, but you'll need to match your fuel injector to the type of fuel your car uses as well.

    B20DTH Performance Exhausts

    You should look to replace your exhaust if the existing exhaust is creating a flow problem.

    On most factory exhausts you should find that the flow rate is fine even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

    Please don't run with the widest exhaust you can find this will reduce the exhaust flow rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

    For road going cars mods such as a sports catalyst pretty much remove this restriction, thanks to it's larger size and surface area, and will effectively raise the performance to levels you would expect without having a catalyst installed.

    This keeps the car road legal and will flow much better due to its higher internal surface area and design. The alternative decat or cat removal should be considered an off-road-only mod, as removing a catalyst is illegal in most territories and regions for road registered cars (and in some you can't even replace a working catalyst).

    Weak spots, Issues & problem areas on the B20DTH

    The B20DTH engines are fairly reliable as long as they are regularly serviced and maintained.

    Regular oil changes are essential on the B20DTH, especially when tuned, and will help ensure the reliability of the engine.

    Keep an eye on the cambelt/timing chains, a failure of these can be catastrophic. The first symptom is generally a rattling sound at startup.

    Keep an eye out for carbon buildup, a loss of power or poor running may indicate the start of this issue and an intake clean is the solution, using a propriety cleaning injection system, walnut blast or removal of the intake and manual clean. This is common on all direct injection cars, especially those that only do short journeys.

    If you want to know more, or just get tips on Tuning your B20DTH engine please join us in our friendly forum where you can discuss B20DTH tuning options in more detail with our B20DTH owners. It would also be worth reading our unbiased GM tuning articles to get insights into each modification and how effective they will be.

    Please help us improve these tips by sending us your feedback in the comments box below.

    We love hearing what our visitors have got up to and which parts work best for them on each model of car. Comments are used to improve the accuracy of these B20DTH articles which are continually updated.

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