Engines- Throttle Response Vs Turbo Lag

[jozeff]

Hi all,

Just wanted to ask a few questions. I currently own a BMW 130i with a glorious NA straight six but have always craved more power. My prayers were answered when news of the BMW M35i arrived.

Basically the questions that I would like to get peoples opinions about circle around NA vs Turbo and throttle response vs lag.

1. Is turbo lag defined as the time taken for the turbo to reach max torque? I.e in an STI it would be about 3500rpm and in an N55 it would be about 1300rpm??

2. Once a turbocharged car has overcome its lag, does this mean that its throttle response will be similar to that of an NA car? i.e I notice that with my N52 i can 'tap' the pedal anywhere in the rev range and the engine will jump up and down instantly in response to my foot. Now in an N55 once the turbo is fully spooled, does it mean tapping the accelerator the engine will respond as an NA car?


Before you ask, yes i have owned 2 turbocharged cars previously. I had a Mazda 3 MPS and now a Golf GTI.... however i'm hoping the engineering in an N55 makes the engine more NA like......

[Superdaws]

Originally Posted by jozeff

Hi all,

Just wanted to ask a few questions. I currently own a BMW 130i with a glorious NA straight six but have always craved more power. My prayers were answered when news of the BMW M35i arrived.

Basically the questions that I would like to get peoples opinions about circle around NA vs Turbo and throttle response vs lag.

1. Is turbo lag defined as the time taken for the turbo to reach max torque? I.e in an STI it would be about 3500rpm and in an N55 it would be about 1300rpm??

2. Once a turbocharged car has overcome its lag, does this mean that its throttle response will be similar to that of an NA car? i.e I notice that with my N52 i can 'tap' the pedal anywhere in the rev range and the engine will jump up and down instantly in response to my foot. Now in an N55 once the turbo is fully spooled, does it mean tapping the accelerator the engine will respond as an NA car?


Before you ask, yes i have owned 2 turbocharged cars previously. I had a Mazda 3 MPS and now a Golf GTI.... however i'm hoping the engineering in an N55 makes the engine more NA like......

1. Turbo lag refers to the time it takes for the exhaust gases to flow over the turbine to create compression and then the time it takes for the compressed air to get into the combustion. Its not RPM specific, the fact the N54/55 reaches its max torque early is just how the engine/technology is engineered.

2. Refer 1. If you take your foot off the gas, then the turbos arent working at max effiency and therefore in theory have to start building up again on the next accell depress, but there is alot more to it than that. You wont see the resposnse you get from your N52... You will however find epic torque!

In reference to the other comparison cars, compared to a 3 MPS and GTI, the n54/55 has much better response IMO.

Im sure others can add more.

[Dackelone]

For me... Turbo lag refers to the time it takes from when you step on the throttle and the time you start to feel the engine respond and make more power. There is very little "lag" on my N54. I think on the M135i (N55) it would be even less. (only one turbo on that engine and it makes peak Tq(Nm) a few hundred rpms sooner than a N54).

You should drive one in order to make up your mind. I think you will like it.

Dackel

[BBK]

In real world terms, when a car has a lot of turbo lag, it means it takes a while for the car to produce high torque like you said. So the lower the power kicks in, the low the 'lag'. High power turbo cars like modified Supra's etc have huge lag because they use massive turbos.

Response as you also said, is the time it takes for you to put your foot down and then the engine to respond to that input, irrespective of rpm or power coming out of it.

[flinchy]

The rpm boost starts building is called the 'boost threshold' not lag

Lag is as said above, how responsive it is regardless of rpm

[Jeef Beef]

Yep, lag is not related to RPM. Smaller turbos take a shorter time for the exhaust gases to spin up the turbine compared to larger turbos. When you step on the accelerator, you'll hear and feel the engine start revving, and then after a bit feel the turbos kick in. The time between these two events is turbo lag. On N54/55s, this period is very very small.

[flinchy]

Originally Posted by Jeef Beef

Yep, lag is not related to RPM. Smaller turbos take a shorter time for the exhaust gases to spin up the turbine compared to larger turbos. When you step on the accelerator, you'll hear and feel the engine start revving, and then after a bit feel the turbos kick in. The time between these two events is turbo lag. On N54/55s, this period is very very small.

Yup! Lightweight turbine materials, super low friction bearings, and efficient wastegate/inlet manifold design, as well as.. Aren't the n54 twins vgt? Or just twinpower? Both of those would contribute to lower lag.

[Superdaws]

Originally Posted by flinchy

Yup! Lightweight turbine materials, super low friction bearings, and efficient wastegate/inlet manifold design, as well as.. Aren't the n54 twins vgt? Or just twinpower? Both of those would contribute to lower lag.

From memory the n54's turbos are not variable geometry

[Jeef Beef]

Originally Posted by flinchy

Yup! Lightweight turbine materials, super low friction bearings, and efficient wastegate/inlet manifold design, as well as.. Aren't the n54 twins vgt? Or just twinpower? Both of those would contribute to lower lag.

Originally Posted by Superdaws

Yep from memory the n54's turbos are variable geometry

I thought only the single turbo N55 had variable geometry and the N54 didn't? Just twin small parallel chargers to eliminate lag.

EDIT: my bad, I was thinking of N55 being twin-scroll. The N54 is single scroll, but not sure about VGT.

[Jeef Beef]

Originally Posted by Superdaws

From memory the n54's turbos are not variable geometry

Did I just get ninja edited? Looks different from what's quoted in my previous post

But yes, confirmed. Our N54s do NOT have VG

Originally Posted by shiv@vishnu

Unfortunately, we don't have a variable geometry turbos in the N54 engine.

shiv

And for those who know what's going on here, a picture.

[Superdaws]

Originally Posted by Jeef Beef

Did I just get ninja edited? Looks different from what's quoted in my previous post

But yes, confirmed. Our N54s do NOT have VG

Yep ninja edited sry, realised what i had typed immediately after hitting post ;P

least we are both on the same wavelength...

[flinchy]

Ahh ok, so n54 is neither vgt OR twin scroll? Wow surprisingly basic, unlike the n55 it seems lol

[MrBlonde]

Originally Posted by jozeff

Hi all,

Just wanted to ask a few questions. I currently own a BMW 130i with a glorious NA straight six but have always craved more power. My prayers were answered when news of the BMW M35i arrived.

Basically the questions that I would like to get peoples opinions about circle around NA vs Turbo and throttle response vs lag.

1. Is turbo lag defined as the time taken for the turbo to reach max torque? I.e in an STI it would be about 3500rpm and in an N55 it would be about 1300rpm??

2. Once a turbocharged car has overcome its lag, does this mean that its throttle response will be similar to that of an NA car? i.e I notice that with my N52 i can 'tap' the pedal anywhere in the rev range and the engine will jump up and down instantly in response to my foot. Now in an N55 once the turbo is fully spooled, does it mean tapping the accelerator the engine will respond as an NA car?


Before you ask, yes i have owned 2 turbocharged cars previously. I had a Mazda 3 MPS and now a Golf GTI.... however i'm hoping the engineering in an N55 makes the engine more NA like......

Turbo cars make a shit ton of power. If you want no lag and linear response get a big block v8. But the turbo will still make more power and beat you ;-)

[Dackelone]

Originally Posted by Jeef Beef

I thought only the single turbo N55 had variable geometry and the N54 didn't? Just twin small parallel chargers to eliminate lag.

EDIT: my bad, I was thinking of N55 being twin-scroll. The N54 is single scroll, but not sure about VGT.

No BMW turbo engine has variable geometry for the turbo blades.

N55 has one turbo and dual scrolls. N54 has two turbos and single scroll(snails).


Porsche has been one of the few manufactures to go that route. I think Chrysler was the first with their GLH-S back in the day.

[Jeef Beef]

Originally Posted by Dackelone

No BMW turbo engine has variable geometry for the turbo blades.

N55 has one turbo and dual scrolls. N54 has two turbos and single scroll(snails).


Porsche has been one of the few manufactures to go that route. I think Chrysler was the first with their GLH-S back in the day.

Yep, that was my conclusion.

However, I read that the 330d has variable geometry turbos.

[Dackelone]

Originally Posted by Jeef Beef

Yep, that was my conclusion.

However, I read that the 330d has variable geometry turbos.

Yes, but I thought we were talking about gas engines.

VAG has also been using VGT's on some of their TDi's as well. I guess BMW must be getting away from VGT's on diesel's bc the new M550 has three turbos, two small and one large for high end ommph!

[flinchy]

Ahh from my quick google, it's very posssible the new m3 getting the n55 (based engine) with twin vgt's or something to that effect - probably where i confused myself

Ed: just watched a video on the m550 (have seen before) regardless of being diesel, that's an amazing car..

Take into account the smoothness and the crazy torque, the fact it's diesel.. Mm.. The video first-second gear looks totally neck snapping and no traction issues

[Jeef Beef]

Originally Posted by flinchy

Ahh from my quick google, it's very posssible the new m3 getting the n55 (based engine) with twin vgt's or something to that effect - probably where i confused myself

Ed: just watched a video on the m550 (have seen before) regardless of being diesel, that's an amazing car..

Take into account the smoothness and the crazy torque, the fact it's diesel.. Mm.. The video first-second gear looks totally neck snapping and no traction issues

Yeh the car is ridiculous, 4.7s 0-100, and I'm guessing high 12s for 400m, all with 6.2L/100km.

A diesel is still a diesel, but this one is amazing.

[sparoz]

Does anyone know the specs on the n54 turbos? I know they are Mitshubishi TD03 but can't find turbine and compressor size. I know the smallest size Garett's and Borg Warner's around the 48mm for the higher end products with ball bearing centre section. Wonder if we can fit two of those in our engine bay . Wonder how good/bad these turbo are compare to what's available.

Wonder what you need to have 18psi sustained to 7200rpm or even 7500rpm whilst maintaining response.

[1q2w3e4r]

Mitsubishi- TD03L-10T