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Turbo feels laggy at high rpms

3K views 13 replies 8 participants last post by  Philster 
#1 ·
Evening all!

First post, absolutely loving the car!

I’m a bit inexperienced with turbos! So this might just be me being a bit silly!

Went on a lovely drive today, but noticed if I short shift into third the turbo feels like it’s spooling up multiple times, is this normal? Sounds like it’s dumping then spooling, dumping spooling repeat!

Is this to do with short shifting? No lights or anything on the dash!

All help welcome!

Cheers,

Jamie
 
#2 · (Edited)
Mileage?
Driving mode DNA?
RPM you consider a ''short shift?"

How is 4th... 2nd? Load and RPM don't care about what gear your in. The gear impacts, based on overall road and speed limit and traffic conditions, whether you can do X rpm with Y load. Still, turbo should be independent of gear.

I know the throttle pedal is kind of loose, so foot movement can make the engine seem like surge/off/surge/off as the road fluctuations and bumps drive the 'drive-by-wire' throttle crazy. My foot has a hard time not going down/up on the pedal.

At speed (which might explain issue in 3rd) it gets worse because speed makes the road fluctuations and bumps worse, and if you're trying to settle the speed down (esp in D or R), then it could feel surge-ish. Short shifting would suggest you're taking your foot out of it, so to speak, and now wanting to tame it, the throttle pedal (via your foot) is fluctuating up/down.

Just a thought and wild guess, based on info provided.

Welcome! WE. LIKE. DETAILS. :)

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#4 ·
You're saying that turbo feels laggy at high rpm, but if you have shortshifted you couldn't have been in high rpm actually. Did you shortshift or did you downshift?


I have noticed that in a particular cases, when the I was downshifting at relative high RPM, let's say from 3rd to 4th and the revs landed at about 4.5k rpm and I floored it, it took quite a while for the turbo to spool and it felt similiar like you're describing.
 
#6 ·
Thanks for the replies!

Sorry should have made things clearer! I short shift from 2nd to 3rd, and then go through to redline and it’s choppy at high rpms. Maybe laggy isn’t the right word, it’s definitely spool slight dump spool
Slight dump as if revs through!

Going to take the car out quickly and get a better response!

This is in dynamic mode and manual shifting
I’ll see if it’s just pedal movement or something I am doing
 
#8 ·
Okay, after a nice spirited drive I think I’ve managed to get it down!

So low rpm 3rd gear, floor it.

Then it’s lag, watch boost build as normal, when at max boost sounds as if it’s releasing some pressure then building it back up in very quick cycles! Guessing this is normal and me being paranoid! Doesn’t feel like it’s losing any power or anything!

Thanks for all the help! Guess I should go and introduce myself now ?
 
#12 · (Edited)
OP: Given that third is a taller gear and you're getting into it a lower RPM, you're making it slightly longer, so you actually have time to feel and observe what is going on as it pulls from low RPM to redline. In 1 and 2, it's a blur.

Redline shifting, in addition to being chosen because power has peaked or mechanicals are at risk, is also designed to drop the engine into a power band (in the next gear) that let's it pull in such a way that boost and power curve and other considerations give the engine the best pull in that gear. Momentum, power curve and boost are timed via redline and gear ratios/spacing.

Short shifting isn't helping anything. Redline shift if you're making full throttle pulls, so the engine, trans and turbo are all jiving with the RPM you wind up at after the redline shift.

(Note: Manual trans are great, but the hidden advantage of an automated manual working with a turbo engine is how the boost stays on when shifting, if done right. The whole package is tuned to keep pulling. Outthinking yourself via weird shift points when you want max accel just un-syncs everything.)
 
#13 ·
Switch through the display options in Dynamic until you're on the oil-temp and boost display and you can watch that and compare what you're feeling--might get some better data correlation that way. Next I'd consider connecting an OBDII scanner and watching something like "load" , https://mechanics.stackexchange.com/questions/17537/how-is-engine-load-determined , maybe graph it if your scanner sw has that option.
 
#14 ·
Put it in auto-shift mode; stomp the go pedal and let it run to redline for a few gears.

I think the driver is introducing variables with shift habits. Eliminate all variables. Let the trans shift for you and simply stomp it.

Report back.

Given how this thread got started and confusing high-rpm issue and confusing short shifting (in one gear), I prefer the trans do the shifting and we see how the turbo behaves (or feels).

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