2.0T boost level - vs. Gear and RPM

[B8_Jim]

I finally got a chance to do some data logging. First on my car (stock) then one with APR stage 1 running the 93 program.

Full details over at AW (sorry) but I wanted ask a question here about the turbo spooling behavior.

FYI - AW post is here : http://forums.audiworld.com/showthread.php?p=23956755

For the APR 93 car, we logged some WOT runs from low RPM up to the speed limit in each gear.

On my old B5 I did some acceleration measurement long ago and it looked like the 1.8T didn't produce full torque in 1st or 2nd gears. I wondered if the quick increase in engine RPM - which meant a quick increase in airflow required - outpaced the turbo's ability to spool? These measurements were done to perhaps answer the same question on the B8.

The plot below shows much quicker ramp-up in boost pressure in the higher gears. Similar to the backed out torque curves I got from the B5 acceleration data. Looks like the B8 2.0T isn't producing it's claimed 258 ft-lbs at 1500 RPM in anything but 6th gear driving up hill :-)

- 1st gear never gets to full boost (of course my car, stock, likely would have - 13 ish psi - I'll have to log that sometime...)
- 2nd gear reaches full boost at about 3800 rpm - just before starting down
- 3rd gear - full boost at about 2500 rpm

Of course this all kind of depends on what you call "full" boost for the APR 93. The 6th gear pull kind of makes me wonder if the target isn't 21.26 as in the 3rd gear pull data from above and the bumps to 22.5 are overshoots? I didn't log "specified" for this set to try to get the sample rate up - 1st gear was sparse even logging only boost and RPM - got about 4 samples/sec, or 2 RPM and 2 boost readings per sec.

If that's the case "full" APR boost is reached :
- 1st Gear = never
- 2nd Gear = 3500 rpm
- 3rd Gear = 2500 rpm
- 4th Gear = 2350 rpm
- 5th Gear = 2230 rpm
- 6th Gear = 2000 rpm

If I assume that stock is something like 13.5 psi (see above, the specified value for stock is kind of all over vs. APR which has a nice plateau at 21.26) and the ramp-up is similar (it seemed to be above) full stock boost would be reached :

- 1st Gear = 3300 rpm
- 2nd Gear = 2650 rpm
- 3rd Gear = 2075 rpm
- 4th Gear = 1950 rpm
- 5th Gear = 1850 rpm
- 6th Gear = 1750 rpm

Torque will be directly related to boost pressure right? So any 0-60 run suffers from a loss of torque relative to the published "max" in first gear? For a stock car would revving to 3300 RPM before dropping the clutch allow the engine to produce full boost or do you need 3300 RPM and the extra exhaust gas WOT would create vs 3300 with no load (low relative throttle setting) ? Naturally aspirated engines like the 3.2 V6 would not suffer so much at low RPM with fast increasing revs?

Thanks,

Jim

[eboosted]

Nice post Jim.

You should log requested boost as well, so you can see what APR is requesting. It could be overboosting in higher gears but that would be the MAP value at the IC not the boost at the intake manifold after ther throttle plate, so take this value with a grain of salt, nevertheless APR should have a better boost control strategy to avoid overboost and mess with the turbo lifespan, maybe control overshooting with N75 duty cycle.

On any turbocharged car, full boost won't be reached in first gear, unless it has a tiny underpowered one, max torque should be reached higher in the RPM range in lower gears because of lack of exhaust gases, that's why 3rd gear ussually reach full boost.

Remember that torque has a lot to do with boost but timing plays an important role on the ecuation, with that being said max boost and max torque doesn't always match.

[ItsDubC]

Is overboost a common occurrence in turbo-charged engines? I suppose like you said it would not be the exact value at the intake manifold but I would imagine there'd be a way to infer the actual boost amount at this location based on the value taken at the IC sensor.

[B8_Jim]

Nice post Jim.

You should log requested boost as well, so you can see what APR is requesting.

I did for the 3rd gear pull (see the AW post I quote above) - but eliminated everything except RPM and actual boost for these logs to try to get the data rate up - I knew the 1st gear stuff would happen quickly, and 2hz wouldn't cut it. I still only got about 4 hz.

I suppose I could have added specified after the 1st or second gear run, but this was done during one drive trying to find gaps in traffic to get a 1500 rpm to 60 ish MPH run.