[onfireX5]

[QUOTE=Knifeedge2k1;26596786]Posted this on the G30 forums mainly regarding softens between jb4 v flash tune but focus it would still be relevant here

The TLDR: JB4 and RACECHIP increase power with the exact same mechanism (tricking your ecu by manipulating map and boost sensor data) but the JB4 is a better product in that it monitors the effect of its changes (via obd2/CANBUS) and its ultimately able to make bigger/better changes because of this. The Racechip does the same "thing" as the JB4 but because it is running blind (can't monitor anything) the designers couldn't push the boundaries as much as JB4 (with no mods a B48/B58 can run +6psi boost vs stock while racechip GTS Black tops out at stock +3psi,which is equivalent to "map1 on JB4). For the almost the same price the JB4 is objectively better in every way because the JB4 has potential to grow with your car (by operating as a WMI controller or boost controller) whereas the Racechip has no purpose once you start going beyond your first few mods.


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Main difference between a JB4 and a tune is the JB4 can only affect boost in a semi direct manner and a/f ratios / ignition timing in an extremely indirect manner (no matter what the dealers tell you).

A real tune can change everything that is "changeable" by an ecu (ignition timing, boost, a/f ratio, vanos which is cam timing and lift, throttle opening... all vanos engines still have a physical butterfly valve throttle, exhaust butterfly valves if you have it, etc.) it doesn't mean that you NEED to change these things and if you have a bad tune it can be worse than stock but assuming everything is done properly, you would rather have the ability to change these things than not, the stock ecu tune was optimized for a certain set of conditions that by definition you are stealing away from when you modify the car.

What any ecu does is take a bunch of inputs of sensors, compare them against a table of (what should I do if I see air temps here, rpm here, engine load here, driver pedal position here, etc ....) then do some things it looks up from a table "the tune " ( command a certain level of boost via the electronic waste gate, inject this much fuel, change ignition timing to this, use this vanos setting) while observing from other sensors whether things are safe and ok (measured air fuel ratio, exhaust temperature, boost measured, knock sensors, etc)

What the jb4 does is intercept the manifold air pressure and boost pressure sensor inputs into the ecu and tell them they are lower than they actually are so the stock ecu does not send a command to the waste gate to back off on the boost until much later than it otherwise would normally. That's it. That's how the jb4 makes power, full stop.

The problem is that ignition timing settings and to a certain extent vanos settings used by the ecu are now the settings that were optimized from the factory for 10psi of boost but in reality the boost level is 16psi or something. In the bad case scenario this is going to lead to knock (which the STOCK ECU will detect and retard timing). The best case scenario is you simply run suboptimal ignition timing and vanos which could be either (both) less smooth, less efficient (less power).


Air fuel ratio is a bit of a special case which I didn't include in the above because most modern engines run on closed loop cycle nearly all the time (it aims for 14.7 AFR nearly all the time and constantly checks the oxygen sensor to adjust the fueling to attain this) even when under load in high horsepower /throttle scenarios. In the old days turbo engines would just run rich in high throttle high boost situations (by operating open loop and commanding AFR of 9 or something) as the extra fuel being atomized in the intake charge would cool the intake charge and help prevent knocking. There's nothing about modern engines that would make this strategy not work, it's just bad for the environment so OEMs are highly disincentivized to go down this road in tuning strategy (something an aftermarket tuner has no issue with)

The JB4 hooks up to the obd2 and canbus so it had the ability to (listen) to the same sensors that the ecu is listening to but the jb4 has no way of actually changing AFR or ignition timing or vanos settings directly. In the above example of jb4 adding 6psi, let's say the ignition timing should be retarded 3 degrees or something compared to the stock timing in the same scenario the jb4 can't do this. It simply can't. The JB4 IS safer than other boost controllers that don't observe these settings because the JB4 can observe when things go wrong (it sees the stock ecu and "undo/back off" it's adjustments to the TMAP and boost sensors so the engine returns to "stock" conditions. This is a REACTIVE system not a PROTECTIVE one. I would also find it extremely dubious if someone claimed that the JB4 could predict the preconditions to knock occurring better than factory engineers (this would be the holy grail of tuning, to predict knock before it occurs, you wouldn't need a knock sensor now would u).

One might then ask, if the JB4 doesn't actually back off its adjustments until something bad actually occurs, and relies on the stock ecu to do so, how is it better than something like race chip which doesn't have this obd2/CANBUS listening system. Well consider the scenario where both systems are running the same setting (eg 6psi above stock boost) setting. When knock is detected the ecu will immediately back off timing for both cars. But it doesn't do it forever, knock is a rare thing for stock engines. The ecu will after a set amount of time return to its original programming. But we know the precursor to knock is highly likely to be because of the uprated boost conditions (in conjunctions with environmental factors that day, let's say it is really hot and dry day). As soon as the factory ecu returns to initial settings, knock occurs again. The jb4 can see (oh shit, knock is happening a lot in a short interval, maybe we should back off a bit, save this data in the logging file and let our user know, maybe only command +4psi instead), while the race chip will be happilly unaware and continue chugging along ignorantly. That's the reason why race chip doesn't add as much boost as jb4, racechip and jb4 does the same thing (manipulate what TMAP and boost sensor data the ecu "sees") but the jb4 is able to check its work whereas racechip cannot, so racechip engineers must specify a lower amount of excess boost it's system can "safely" provide.

An aftermarket tune is both better and worse than the jb4 in that factory engineers coded for a lot of those corner cases that took millions of dollars of development to find (those 1/100,0is
00 scenarios). A JB4 "keeps" these settings intact but a custom tune wipes it out. At the end of the day, what's more important to you, that's something only you can decide for yourself.

“A JB4 "keeps" these settings intact but a custom tune wipes it out”.

A sophisticated custom tune can keep safety settings. Some can actually add safety protocols not available from the factory.

Biggest problem with custom tunes, is they are now easily detected and are warranty busters.