12/22/2010

12-22-10 - Obscure issues with modern car electronics

It would be nice if there was a car review site that actually gave you the real dirty information about cars, things like will the brakes overheat in one lap of a track, is it dialed for understeer, can you turn traction control completely off, etc. Instead we get the same shite all the time, stories about how great it felt on their favorite back road and useless 0-60 times and so on. The annoying this is there's just nowhere to look to actually get good information on a car; what cars really can handle track abuse? what cars really give you full manual control with no limitations? what cars really have properly sorted chassis that don't have inherent understeer or snap oversteer or high speed instability?

Some things you may not know that you may want to watch out for :

Just about every car made now is on e-gas (electronic throttle). Mostly this is an improvement, because it ensures that you get a good idle throttle level, and because it means you actually get a fully open throttle for the range of your pedal movements, which often was not the case with old cable-actuated cars. However, there are problems with e-gas that the enthusiast should be aware of :

1 : One is brake throttle override. This mean that pressing the brake sends a signal that cuts the throttle. The idea of this is as a fail-safe if something goes wrong in the electronic throttle, you can still brake. Many e-gas cars already have this (all VW,Audi,Porsches do for example), and it will be even more common because of the Toyota bullshit. (in fact I think it is required for 2012+ cars). In normal driving of course this is no big deal, but it is a big problem if you are trying to left-foot brake, or keep on throttle during braking to spool your turbos, or brake and throttle at the same time to control a spin, etc.

2 : Another problem is that the egas signal is often smoothed by the ECU. Basically they run a low-pass filter on the signal. This is usually done to improve emissions because sudden throttle changes lead to lots of inefficient ignition cycles which are highly polluting. In some cases manufacturers have put smoothing in the throttle to reduce driveline noise and lash. In a non-filtered car, if you are coasting along and then you suddenly slap on the throttle, you will get some clunks and grinding sounds as the driveline goes from unloaded to loaded and lots of little bits of slack gears and such knock together. In order to give cars a false feeling of "solidity" the ECU smooths out the throttle so that it very gently engages pressure on the driveline before ramping up.

Smoothing the throttle is not the worst thing in the world, because for track or daily driving you actually should be smooth on the throttle anyway. But if you're trying to kick the throttle to start a power-on oversteer drift, it's annoying.

3 : Electronic Stability Control is already in most cars, and will be mandatory in all cars in the future. Mostly it's a good thing, but when you want to play around with your car (eg. whipping the tail to do hairpin 180's), it becomes a big negative. Performance cars generally have an "off" for ESC, but it rarely actually turns it all the way off, it just puts it into "minimal" mode. For example, a lot of cars now (G37, 135, etc) use the ESC as a type of electronic LSD. That is, they have an open diff, and the ESC brakes the spinning wheel, which is the only way power is transferred to the wheel with traction. This stays on even when you turn ESC "off". Furthermore, most cars will still kick in ESC when you are braking and the car is sliding, for example Porsches (PSM) and Nissans (VDC) will both kick in the ESC even when it is "off" when you touch the brakes. Because of the "electronic LSD" and other issues, it's probably not even desirable to turn ESC completely off on most cars - they are designed to work only with ESC on.

4 : Most cars are set up to understeer. This is done for safety/liability, and it actually affects the famous oversteering brands the most, such as BMW and Porsche. Because they were so renowned for dangerous oversteer, they are now sold in just the opposite way - understeering plowing beasts. This is done through alignment settings (too much toe), suspension (too soft in the rear usually), and tire staggers. Non-cognoscenti see big tire staggers (wider rear tires than front) and think "muscle", but in reality the excess of rear grip and surfeit of front grip also means understeer.

5 : Your "track ready car" is probably not actually safe to drive on the track. It's sort of pathetic that manufacturers get away with this. They sell cars with "competition package" and talk about how great they are on the track, but the vast majority of "track ready" cars are not track ready, and quite a few are downright unsafe. You need to do research on your exact car to determine what the problems are, but some common ones are : insufficient oil cooling (sends car into limp mode; affects many cars with HPFP's), insufficient brake cooling (very dangerous! affects some M3's and Nissans), cheapo brake pads, cheap lug nuts (for example Dodge SRT's are known to lose wheels), oil sloshing / oil pan starvation ; lots of cars have this problem if you put on R-comps or slicks (because of the increased cornering forces), but most are okay if you are on road tires ; there are exceptions though, for example I know the Pontiac/Holden G8 will slosh all its oil out and you'll be bathed in a cloud of blue smoke.

And of course, there's also the problem that manufacturers will deny warranty claims if you track the car, even with cars like the Dodge Viper ACR or a Porsche GT3 RS which are clearly intended as track weapons, and even when the problem is clearly manufacturing defects and not abuse. But this is totally off the electronics topic, so back to that -

There are some solutions :

1 : On most cars this can be defeated by snipping a wire that goes from the brakes to the ECU. You have to be careful about how you do this on your exact car, because you presumably still want ABS and brake lights and such. The smoothest way to do this is to find the right wire and splice in a switch, so you can turn it on and off. ( some info on Porsche EGas throttle cut )

2 : On most cars you can defeat this with an ECU flash (aka a "tune"). Most of the claims of "tunes" are nonsense (on non-turbo cars; on turbo cars they can of course up the boost and help you blow up your WRX engine) but getting rid of throttle low-pass filtering is something they can do.

3 : Similar to 1, on most cars you can defeat this by finding the right wire and splicing in a switch. On Porsches the most elegant way is to disable the yaw sensor. Put it on a switch and you now have a true "PSM off". Looks like there's a similar trick on Nissans . On Mercs there's a secret code .

4 : It's reasonably easy to undo most of this, but you do have to do some research. The obvious answer is to remove the tire stagger. The details for your car are important, you need to find an expert who knows your suspension and how it all works together. I know that for Boxster/Caymen, and for M3's (E46 in particular), going to a "square" (non-staggered) setup works very well. I wrote before about alignment a bit; and you can get stiffer rear / softer front sways. But depending on the car, you may not be able to dial out the understeer in a nice way and actually get a good handling result - if you just do it by decreasing rear grip that's not very cool.

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old rants