So much boost for so much fuel?

[Johnny Cetane]

Well, from what I can gather, stock TDI's dont smoke very much (Gripe: They wouldn't at all if we had better fuel). TDI's running .205's smoke more, but to acceptable degrees and .216's, well, they smoke like chimney stacks. The problem quite simply sounds like a lack of air in the cylinders to compensate for the added fuel. So, how much boost is needed (in order to add more air to the cylinders) to make .216's smoke like .205's? More than the stock turbo 18 psi can handle? Is lowered compression mandatory?

Oh, out of curiosity, I was told that adding .205's and a chip would be bad because the engine would 'never get enough air to handle the fuel'. Can anybody explain to me why? Does the chip increase the pulse width significantly or something?

Thanks!

 

[GoFaster]

Chip adds more fuel by lengthening the duration of each fuel injection period. Bigger injectors add more fuel by squirting it in at a higher flow rate in the same number of crank degrees. First method is easier. Second method is more expensive but is theoretically capable of striking a better balance between minimizing peak cylinder pressure (you want start-of-injection as little advanced as you can get away with) while minimizing smoke and exhaust gas temperature (you want the injection period to FINISH before something like 20 degrees after TDC).

here's the progression that I have gone through:

0.184 injectors, stock chip, stock 12 psi boost, EGR on or off doesn't matter: OK smoke-wise, not OK power-wise.

0.184 injectors, Ups chip, Ups 15 psi boost, EGR off: OK smoke-wise and power-wise. I had to use water injection to keep it smoke-free in the summer. (not enough intercooling)

0.216 injectors, Ups chip, faked sensors for 20 psi boost (too much for stock turbo), EGR off, lots of power (too much for the clutch), lots of smoke, lots of shudder (very unpleasant driveability): No good. Too much power for long term durability, too much smoke, too poor driveability.

0.216 injectors, stock chip, faked sensors for 17 psi boost, EGR on but reduced to minimum, power slightly greater than Upsolute, minimal smoke: OK. (This is my current setup, it works GREAT and I'm not planning to change it.)

I know of another vehicle (A3 Jetta) that has this:

0.205 injectors, Ups chip, Ups 15 psi boost, EGR on but reduced to minimum, nutty power, lots of smoke but not near as bad as 0.216/upsolute. This arrangement will probably be tolerable (but I doubt if smoke-free) if set for around 18 psi boost pressure.

I highly recommend a mechanical boost pressure controller as a backup for the OEM solenoid (connected in parallel) for these highly tuned tweaks. I don't trust the electronics, and the mechanical one will completely eliminate boost pressure spikes and fluctuations at full load. www.dawesdevices.com has a simple one that works well enough for me.

 

[MacGuy]

GoFaster,
Will this mechanical boost pressure controller
( Dawes, right?) work on my Y2K Golf (no wastegate!). I have boost pressure spikes up to 25 psi !!! Trying to aid that as much as I can but sometimes goes up. I have 0.250' injectors and UPsolute. Since long lasting "slow down shudder" problem is finally gone I was hoping to find solution for this. Any suggestions? Thanks.

Golf GLS, Y2K, 5 speed
UPsolute, 0.205's,, PiperX panel

 

[Johnny Cetane]

GoFaster, do you have any dyno numbers for your current setup? I'm very interested.

 

[GoFaster]

Mechanical boost controller hasn't been tried on a VNT as far as I know, but it should work (remember to solder the very small vent hole closed, you don't need it and you don't want the vacuum leak). You're on your own beyond that.

No dyno results, only an uphill 100-to-120 km/h test that's relevant to my driving patterns. It's "sufficient"

 

[96Wagon]

GoFaster. Why, disregarding the environmental factors, did you hook up your EGR again? Do you feel more power or do you just like being Green? This question is not a joke.

 

[GoFaster]

The EGR is connected because I found that having a very slight amount of EGR makes the engine run smoother and quieter at light engine load with the current arrangement, and it helped to eliminate a problem I was having with "limp mode" under certain speed/load conditions.

 

[nuke]

Johnny,

Since you live in California, you are getting fuel that is high in cetane and low in sulphur and similar in most respects to european fuel.

Market average california fuel is cetane number 53 and sulfur 130ppm - which is pretty good anywhere on the globe.

More fuel = more smoke.

Bigger injectors = more fuel and less atomization of the fuel when it sprays in = more smoke.