2.0T power drop off at high rpms
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Some of it is the tuning. If the tune isn't producing a sold gain above 6000 rpm, there's a deficiency in the tune.
If there is a gain, but torque drops off in the higher rpms, that's a function of the motor. A tune can produce a 20% gain from 3000 rpm to 6800 rpm, yet your butt dyno will still notice the drop off, despite the gain up top.
Some tuners focused on the midrange more than the top end.
If there is a gain, but torque drops off in the higher rpms, that's a function of the motor. A tune can produce a 20% gain from 3000 rpm to 6800 rpm, yet your butt dyno will still notice the drop off, despite the gain up top.
Some tuners focused on the midrange more than the top end.
Technically speaking, redline does not mean the optimal shift point but a maximum safe RPM. The best shift point is the RPM where the torque curve in one gear crosses the torque curve in the next gear or redline, whichever comes first. I haven't plotted the curves to see where they cross but would not be surprised if in some gears they cross before redline and therefore the optimum shift point would be lower than redline.
Those are 2 separate items. One is an assumption and one is a question.
What is the basis for saying the turbo can't keep up? It can hold the its HP from 5500 to 6800 rpm, so it definitely can flow more more air above 6000 rpm. With a tune it can run more boost at 6800 rpm than the turbo achieves under the factory tune at any rpm. It's just that as rpm increases TQ is falling. GM could have put a turbo on the car with less low end response and the same top end, and it would feel like its keeping up. Don't get me wrong, I'd like a bigger turbo, or at least a different compressor map biased towards the higher rpm. It's just that the car is designed for a lot of midrange TQ and to spool quickly at low rpms to overcome the fact there's only 2l of displacement to respond to heavy power demands.
As to the shift points, GM has them set at 6600 rpm and this is below redline. As HD described, the the torque can drop a lot on the top end before the next gear results in more TQ to the wheels. This is because the gear ratio are spaced around a 30% drop off. You'll feel a drop off in torque of 20%, so your butt dyno is correct that acceleration is slowing on the top end; its just not slower than the next gear. Also gear changes are violent events at WOT, so they feel bigger than they really are. The car is accelerating; then for part of second, the car isn't accelerating (or is barely accelerating) and then boom the car is back at full TQ or even slightly above due to a TQ spike of boost.
Beating on your motor passed max HP and/or TQ is self defeating. Now when you toss in a turbo with an electronic waste gate you have a whole new set of issues. Lastly, IMHO, your exhaust has big part in how the turbo reacts. Just look at the junk in the way.... catalytic converter, 2nd cat, mini muffler and one huge resonator. With some exhaust work and Diablo tuner you can firm up the shifts if you want to and change your rev limiter and speed limiter. But, remember your are now putting new pressures on the engine and trans that push it to or pass design specs. Also you have to consider VVT, cam phasers and cams etc.
Example - My 5.7L Hemi has a 5,800 rpm rev limiter and that is just about max hp. I set the rev limiter to 6,000 and shift at 5,800 or so. With a Tremec 6 speed you really can't power shift it like an Muncie 4 speed.
Lastly a well built auto trans will always out shift a manual... Many drag racers are running built 2 speed Power Glides. My buddy is running a turbo 400 on his 392 twin turbo Challenger, which ran over 200 mph at the Texas Mile and runs in the low 10's in the quarter.
Example - My 5.7L Hemi has a 5,800 rpm rev limiter and that is just about max hp. I set the rev limiter to 6,000 and shift at 5,800 or so. With a Tremec 6 speed you really can't power shift it like an Muncie 4 speed.
Lastly a well built auto trans will always out shift a manual... Many drag racers are running built 2 speed Power Glides. My buddy is running a turbo 400 on his 392 twin turbo Challenger, which ran over 200 mph at the Texas Mile and runs in the low 10's in the quarter.
Are there dyno's of the 2.0T holding its hp from 5500 to 6800? I thought they all show it dropping (tuned or not tuned).
I bought a Diablo tune, and it did pull much stronger in the top end than stock. However, I ended up only running the tune for a total of 1,500 miles. This tune was very in consistent in my car. Sometimes it would pull strong, other times the acceleration was lumpy, and about 50% of the time, the power was very diminished, almost as if the car had no turbo at all. I tried multiple different brands of gas with the same result. Who knows. The stock tune is very smooth in my car, but I do miss the extra power (when it worked). At some point, I might do the Vermont tuning kit with upgraded turbo internals, catless dp, intake, and tune. We'll see...
We're actually doing some consistency testing as I type this....
Smaller trim turbos are great for low end power delivery but run out of steam. You'd have to change to a turbo with a higher flow to keep enough air moving at higher RPMs. The best you can do is try to flatten it as much as possible through tuning. This is 99% of OEM turbos these days.
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