Hot chips - too good to be true?

First published 1998.
Last modified 24-Dec-2012.


The car companies are ripping you off. With the simple little chip swap for your car's electronic control unit (ECU, the engine management computer), you can get considerably more power at only a small fuel economy cost. The true tyre-smoking grunt of your car's engine is hobbled by incompetently written software. It's all a conspiracy.

The above view is what the makers of aftermarket ECU upgrade chips want you to believe. And many people do. But that doesn't make it true. Review after review in hot-car magazines has stated that new chips for stock engines typically do not much of anything - and, when particularly mismatched with a given engine, have been known to reduce power. But this doesn't stop people buying the things.

What they are

The "chips" we're talking about here are erasable programmable read-only memories (EPROMs), which contain the data used by the ECU to manage the engine functions. The exact type of upgrade hardware varies from make to make and often also model to model, but whatever vehicle you have, you'll spend at least a few hundred dollars and possibly more than a thousand for a new chip. So what are you getting?

Upgrade chips change the way the ECU performs its two functions - ignition timing and fuel delivery. On older cars, the distributor and carburettor do these jobs, and can be tweaked in any home garage, by rotating the former and changing the jets in the latter. But computers aren't that simple.

The standard, factory ECU settings aim to achieve decent fuel economy, pass exhaust emissions regulations, handle low-octane budget-priced fuel, and give the engine a good chance of survival even if the car goes much longer between services than it's meant to. And, logically, people who are willing to take better care of their cars than the average and don't mind using a bit more petrol and spewing a bit more pollution can get better performance by optimising the settings.

But the operative word here is "can". Not "will". Upgrade chip makers are fond of phrases like "up to 10% more power". Buyers should bear in mind that "up to 10%" includes "0%".

Hot chips advance the ignition timing - applying the spark earlier in the piston stroke. This adds a bit of power, but the earlier your ignition is, the more strain you put on the piston, connecting rod and crankshaft. If you ignite the fuel-air mixture only a moment after the piston has passed top-dead-centre, the almost-vertical connecting rod is going to do its level best to bend the crankshaft.

Worse yet is "pinging" or detonation, which happens when the fuel-air mix is ignited long enough before the piston makes it to top dead centre that a high combustion pressure occurs when the piston is still on the way up, or stopped at the very top of its travel. It's normal for a petrol engine's ignition timing to fire the spark before the piston makes it to top dead centre, but that's only because combustion doesn't happen instantly. If the spark fires too early, you're trying to push the crank round in the wrong direction, which is very bad for numerous components.

Detonation can happen because you actually managed to set the ignition timing that way, or it can happen if of one or more cylinders gets hot enough that your engine becomes an impromptu diesel - the extra heat created in the fuel-air mixture as it's compressed, plus the heat from the hot spots in the cylinder, is sufficient to cause the mixture to spontaneously ignite before the spark happens.

This spontaneous ignition can be particularly bad because the fuel-air mixture will explode, rather than burning out in a relatively smooth flame front from the spark plug (or plugs, in twin-spark engines).

The explosion means that the pressure change in the cylinder is much too rapid. The resultant shock wave can hit the piston much harder than it expects and thereby damage the engine even if the piston is past top-dead-centre. It can also blast the protective air-and-oil "boundary layer" right off the inside of the cylinder. This can lead to a variety of other unfortunate events, not least of which is yet more heating of the cylinder, which makes the problem worse and worse.

You can reduce the chance of pinging by using higher octane "premium" petrol. Engines with "knock sensors" can deal with it, too; they detect pinging and correct the ignition timing in response. They may also turn off the spark to knocking cylinders completely, to let them cool. But this just makes a very bad thing a bit better. You don't actually want pinging to happen even once in a while.

It's possible to advance the "base" ignition timing of modern cars manually anyway, without changing anything in the computer, for much the same effect. Chip upgrades can alter the timing according to the throttle setting, which does the job better than just tweaking the base timing by hand, but the difference is a small one.

Hot chips also change the "fuel mapping", which determines the amount of fuel that's squirted into the cylinders at a given throttle setting. Adding a little more fuel (running richer) gives a bit more power, and a bit less efficiency, and slightly increases pollution emissions. (Adding a lot more fuel can do more exciting things, like blowing flames out of the exhaust and burning out your expensive catalytic converter.)

On turbocharged engines, hot chips can also increase the manufacturer's boost limit settings, so the turbo boost can be cranked up. This can give hefty performance increases, especially on turbo-diesel vehicles that are more conservatively tuned by default.

Of course, overpumping your turbo can also wreck it, and more cylinder pressure is yet another thing that encourages pinging. And you can gain a large portion of this performance gain more cheaply, by leaving your ECU as it is and simply installing a T-piece in the pressure line running to the turbo wastegate, so it opens later. Well, you can do that as long as you've got an older, dumber car, and/or you're brave; see this page for more discussion.

Doing it properly

An aftermarket engine management ROM upgrade is a much more useful addition for people who've already upgraded their engine. Once you've got new cams, a new exhaust system, a better air filter, a new flywheel and whatever other upgrades take your fancy - like, for example, a turbocharger - a new chip is a wise addition. Actually, an engine with any serious modifications probably won't work properly at all unless you re-chip the ECU.

You can get chips pre-programmed for particular engines with particular modifications, or you can get one custom-programmed for the particular characteristics of your engine's setup. A proper custom chip may actually be cheaper than the rather audaciously priced chips for stock motors.

The next step up is to completely change the whole ECU. Here in Australia, this usually means buying a MoTeC computer, because MoTeC make the only aftermarket ECUs that are legal for Aussie street use. The new computer adds lots more diagnostic and adjustment options for people who've seen engine telemetry displays in Formula One pits and liked the look of them. You can, for example, hook up a laptop for real-time display of all the stats and easy modification of computer settings, and data logging lets you download everything that happened on the last few laps to see what needs fixing. Replacement computers work with standard sensors and injectors, so you don't need to rework everything in sight to fit one, but you still won't get much change from $2500 for even a basic MoTeC setup.

Rice-boys ahoy!

If you drive an automobile with suspension so low you bottom out on a white line, spray-on low-profile tyres, a muffler that adds 1% more power and makes an obnoxious noise, a wing the size of a surfboard that does nothing at less than 150 km/h and may actually be on a front-wheel-drive car, patches of carbon fibre that may be real or may just be stick-on laminate, stickers advertising Japanese "racing teams" with odd names, a stereo the size of Tasmania that requires eight extra batteries and gives the car the performance of a 1962 Beetle, neon illumination of random componentry, a gigantic fluffy thing dangling from the rear vision mirror, and unwarranted logos, emblems and other accoutrements transplanted from the top-of-the-range version of your base-model car, then an after-market upgrade chip for your stock motor is another fine wank for your collection.

If you don't, a plain chip-swap is lousy value for money.


Powerchip - Australian maker of engine management chip upgrades

MoTeC - only manufacturer of replacement car computers street legal in Australia

Give Dan some money!
(and no-one gets hurt)