New to Turbochargers

[JBRecording]

I poked around a bit online, and haven't really found a good video or article talking about the driving experience difference between a standard non-turbo engine and turbo engine. I've heard of turbo lag but don't quite understand what it is. I found a video explaining how turbos work, but it seemed to be a dive into the engineering behind it, which lost me after a minute or so.

My basic question is...driving-wise, how is driving a turbo car different than a non-turbo car? As far as acceleration, is it like, normal then the turbo kicks in and gives you a boost then turbo dies down and has to "re-spool" ?

[gstrouse]

With todays use of smaller turbo's, the "lag" is much less than in days of old. Many of the newer cars if you weren't told it was a turbo, you'd never know. They have been designed to give a much more linear power delivery. The biggest thing is that most turbo engines require premium fuel. This is mainly due to the higher temp of the intake air. Even with an intercooler to cool the compressed air going into the combustion chamber, it is still higher. So there is the concern with pre-ignition. And since all new turbos are oil cooled, you will or should use synthetic oil to keep the oil for breaking down to the high temps in the turbo.

[compu_85]

The lag on the new Passat is basically no existent... it's not like an old MB Diesel where you press the pedal and several moments later the turbo comes up. Mine seems to be spooled up by 1700 rpm!

-J

[JennyDriscoll]

It's my understanding the "turbo" in TDI is not the same as the traditional/typical/standard application of turbo technology performance boosting related to a gas engine. As always, I could be wrong but that's my understanding and just as always if I'm wrong, someone will correct me LOL!

[compu_85]

TDI's since 1999 have had variable nozzle turbos... makes for even quicker spooling



-J

[JBRecording]

Is the turbo "always on" in that it's always functioning, or does it only work for a few seconds then it has to spool up again? That's one thing I've never quite understood.

[compu_85]

The turbo is always on. If you lift off the go pedal then re-apply the turbo does have to respool, but it happens so quick you won't notice. Once the turbo has spooled up it will continue to make boost as long as there is exhaust energy to make it spin.

-J

[turboDSG]

I owned both a wrx and GLI so I have experianced both and they are night and day. The Subaru uses a much larger turbo that does not spool to peak boost until about 3k rpm at which point it is crazy power and was mush below that. Especially with the 2.0 vs the newer 2.5. The 2.0 tsi vw is much differnt. It drives more like a smooth v8. The lag is almost non existent since from the factory it is full boost and torque around 1700 rpm. It lacks the all out blast of power you get from big turbos like the wrx but it is nice and smooth and just feels like a much bigger engine than it is.

[MasVW11]

Is the turbo "always on" in that it's always functioning, or does it only work for a few seconds then it has to spool up again? That's one thing I've never quite understood.

It's got a valve called a waste gate that changes how much air goes through the turbine....at speed, when you're not trying to accelerate, the gate opens and the air goes straight to the exhaust and you get the fuel economy of the smaller 2.0 engine....it's only when you ask for power that the gate closes and the air is directed through the turbo....Invented by Saab in the late 1970's

Having driven Saab turbos for 10 years, I'd say the lag is noticeable, but not in 2nd gear at 30-90 mph....there it's a rocket. It's from 0-30 that you notice the lag, and the NA engines have more oomph. My 2.5 is better from 0-25 than either of my Saabs were, but they blasted up to the ticket danger zone once I got to 25-30 mph.

[turboDSG]

^^ that lag is esentially gone on the 2.0 TSI on the newer VW's.. Have never driven a TDI but I'm sure it's quite similar with even more torque down low.

From a standstill it starts spooling just above idle and it is fully boosted by 1700 ish rpm which is the blink of an eye. quite an engine I miss very much.. but I can promise the na 2.5 does not have more oomph at at point in the power band.

[compu_85]

Normally wastegates are closed, and opened to relieve excess pressure. The tdi does not have a wastegate, it had a vnt like I posted a picture of.


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[MasVW11]

Normally wastegates are closed, and opened to relieve excess pressure. The tdi does not have a wastegate, it had a vnt like I posted a picture of.


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Sure they're closed under load when you've got the pedal down. The wastegate bypasses the turbine, but it's more than just a relief valve. When you release the gas pedal, the boost pressure drops rapidly ( at least in both my 9-3's it did), and the wastegate has a solenoid actuator that is controlled by the ECU (trionic in a Saab)....so the wastegate spills the pressure charge and reduces the boost when it's not needed. And I think under moderate loads it regulates the precise boost pressure going to the turbine.

Don't know how this design is different in the TSI or the TDI, but the OP was asking about turbos in general.

5 cylinder engines have overlapping power strokes compared with a 4 cylinder that doesn't (even more ovelap with 6 or 8 cylinders). And I can tell the difference at low speeds between my 2006 2.0T and my Passat. No matter what the specs say. The Saab was a rocket with torque once you were rolling, but not from line. If the TSI eliminates this effect by charging the turbo earlier, then I imagine I'd like the TSI better.

[turboDSG]

yes, you should go test drive a TSI sometime just to see what it's all about. You will be quite impressed. My wife had a 2007 9-3 2.0T Aero 3 years that I drove quite often along with my WRX and it is about as night and day between the two as between the TSI and WRX. The saab has more linear power than the WRX but had substantially more lag then the VW.

It's really quite hard to speak of turbos in general because pretty much every setup is unique from engine to engine system to system. Even the FSI compared to the TSI is slightly different in overall boost characteristics.

A lot of things mitigate lag on modern turbos including twin scroll setups.

The TSI to me is the most perfect daily driver setup.. again in drives like the V8 in the 4runner truck I use for work sometimes.. It is just smooth with plenty of power and torque on hand. It is not a fast car like the WRX and does not have blistering acceleration even under peak boost. Just strong lag-less and consistent.

the 2.5 is ok but I am very eager to get back to the 2.0 TSI after this lease is up. the driving experience is 100% improvement with loads of additional potential.

[coffeemade]

Tdi is like night and day from tsi and fsi. I went from a 2.0fsi to a 2.0tdi. I modded my last 2 turbo cars and when I got the tdi I just recently learned on a tdi the system it doesn't have vacuum they have a vacuum pump for the stuff like the brake booster.

On a tdi full boost is very low rpm but I love it and my gas mileage is awesome. I would do it all over gain except I think I might get a golf.....I miss my GTI but I still love my new passat

[Andy@Ross-Tech.com]

I've done a good bit of logging requested and actual boost while driving and the CR 2.0 TDI does have some turbo lag. It's not awful but you can watch (and feel) a second or two between pressing the accelerator and reaching full boost in 6th gear at highway speeds. Without the turbocharger, this just isn't a very powerful engine at all so there isn't that much energy to get the turbocharger spinning fast enough to deliver the quite high (22-23 psig) boost.

[turboDSG]

wow did not realize the TDI had 22-23 PSI. That is quite a bit, stock I rarely ever saw past 10 on the TSI. I always knew the TDI was much weaker on the top end than the low end but that is surprising it is pushing so much boost on a 2.0 engine and getting such little power compared to 2.0T petrol engines. I have ridden in many 2.0 WRX's with the same amount of boost pushing close to 300 CHP which the TDI has less than half.