Re: .205\'s or Upsolute?
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Pysslan:
TDI Believer
Why should it cause trouble when you use Chip + Injectors + Tuning Box??<hr></blockquote>
OK...I didn't say the combination of Chip + Injectors + Tuning Box WILL cause trouble, I implied it COULD cause trouble.
First, let's agree that it is possible to push these engines too far. Let's also agree that optimum combustion in a TDI occurs within a 36-degree window of crank rotation, between 15-degress BTDC and 21-degrees ATDC (according to papers provided to me by SkyPup, this is correct). Fuel quantity for injection is controlled (by the ECU) by varying the length (in time) of the injection pulse. At WOT the injection pulse is the longest. If the injection pulse lasts beyond 21-degrees ATDC, energy from combusion begins to convert to heat instead of work. Mileage goes down and exhaust temps go up. The turbo operates by converting heat from the exhaust to work (driving the compressor). With these things in mind, let's look at what the three fueling mods do.
FAT INJECTORS: The fat injectors cause more fuel to be injected into the engine for any given injection pulse length. With the injectors therefore, it is possible to inject more fuel into the engine without lengthening the injection pulse duration. The injection pulse stays within the optimum 36-degree angle of crank rotation. This is a great mod! A larger injection pump will have the same effect.
CHIP: The chip advances the injection timing, increases turbo boost (by about 5psi), and extends the limits for injection pulse duration beyond the factory limits. At WOT, the injection pulse duration is likely near or beyond 21-degrees ATDC, causing exhaust temps to rise a bit and mileage to drop. If the engine has fat injectors, the effect is amplified somewhat because there is more fuel available at the end of the injection pulse to be converted to heat. Keep in mind this heat acts on the turbo to produce boost. There is more stress on the engine and the turbo. As long as this stress doesn't exceed the design limits, you're OK. To my knowledge, no one has destroyed an engine running chip and injectors yet.
TUNING BOX: The single-pot tuning boxes allow you to adjust fuel quantity (injection pulse duration) even beyond what the chip will give. Three-pot boxes also allow you to adjust injection timing. There is a limit to how much the ECU will allow you to lengthen the injection pulse. When this limit is reached, the dreaded Warp Field Collapse occurs - the engine takes the fuel pedal away from you and you end up kissing the windshield until the engine speed drops near idle. This is a very abrupt event.
Now keep in mind, with all three mods (together) you are lengthening the injection pulse to maximum while injecting more fuel than the ECU knows about (because of the fat injectors). At WOT, you will be creating very high exhaust temps.
With all of that said, the safest way to increase power on the TDI is to do whatever you can to increase fueling without exceeding the 36-degree window of crank rotation by too much. This will help ensure that all that fuel is converted to work instead of heat. Fat injectors and bigger injection pumps will work for this.
Also keep in mind that when you add more fuel, you need more air to burn it. Turbo upgrade anyone?
And lastly, the stock clutch on the A4 is only up to one fueling mod. Two and it will slip. Three and it will fry. Stock differentials have been known to fail (ask BG) from too much power in extreme situations (like popping the clutch). There are aftermarket alternatives from Quaife and Peloquin.
Whew!