Turbo vs NA

[Skurge]

Iv never driver a turbocharged car before, but I hear people saying they are easier to overtake with than NA cars with similar power figures. It seems to me that Turbo engines have more torque, but I always thought they had narrow power-bands.

So what I'm really asking is, what are the different characteristics of Turbo vs NA engines given similar power figures.

 

[DivideBYZero]

Most modern turbo charged cars have (artificially) flat torque curves so the power band is very wide. Others have twin turbos, twin scroll units or variable vane technology.

Typically you'll get more torque down low in the rev band with a turbo car, but as with anything this is completely dependent upon the engine, as there are plenty of high torque NA motors that pull hard at low revs and plenty of high revving turbo cars.

 

[Skurge]

Most modern turbo charged cars have (artificially) flat torque curves so the power band is very wide. Others have twin turbos, twin scroll units or variable vane technology.

Typically you'll get more torque down low in the rev band with a turbo car, but as with anything this is completely dependent upon the engine, as there are plenty of high torque NA motors that pull hard at low revs and plenty of high revving turbo cars.

How do they artificially create flat torque curves?

 

[amdhunter]

I miss the turbo in my GLi.
Boost is addicting.

 

[coxmaster]

How do they artificially create flat torque curves?

They tune them specifically to cause that.

I miss the turbo in my GLi.
Boost is addicting.

You should have gotten a tune, it opens it up even more :thumbsup:

 

[exdeath]

How do they artificially create flat torque curves?

You design and tune the engine so it had 200 lb-ft @ 2000 RPM and 450 lb-ft peak between 6500 and 7000 RPM. Then you restrict the tune to chop off the peak so you can advertise that it's 200 lb-ft flat from 2000 to 7000 RPM.

Since you market it as a 200 lb-ft engine you can claim it has a flat torque curve. If you left it uncrippled it would really be 450 lb-ft peak engine but then people would point out the turbo lag since it doesn't hit that until 6500 RPM.

In other words it's trickery. They aren't actually able to increase the low end to actually make up for the turbo spool, they are chopping off the peak higher up to hide it and make the curve look flat like people want. If you look at any of those types of "flat torque curve" turbo engines like the Ecoboost with a tune, you'll see that all the power gained is mostly in the upper RPMs, eg: removing the peak restriction and unflattening the curve. But then to the casual Joe this looks like "turbo lag" and is not effective marketing even though it's still faster.

 

[EightySix Four]

You design and tune the engine so it had 200 lb-ft @ 2000 RPM and 450 lb-ft peak between 6500 and 7000 RPM. Then you restrict the tune to chop off the peak so you can advertise that it's 200 lb-ft flat from 2000 to 7000 RPM.

Since you market it as a 200 lb-ft engine you can claim it has a flat torque curve. If you left it uncrippled it would really be 450 lb-ft peak engine but then people would point out the turbo lag since it doesn't hit that until 6500 RPM.

In other words it's trickery. They aren't actually able to increase the low end to actually make up for the turbo spool, they are chopping off the peak higher up to hide it and make the curve look flat like people want. If you look at any of those types of "flat torque curve" turbo engines like the Ecoboost with a tune, you'll see that all the power gained is mostly in the upper RPMs, eg: removing the peak restriction and unflattening the curve. But then to the casual Joe this looks like "turbo lag" and is not effective marketing.

Actually they usually don't do that to hide the lag, quite the opposite. They do it to hide the come down at the end. My car made huge boost and tons of torque from 3k rpm through 6000rpm or so, but once the turbo ran out of breath it was like hitting a brick wall.

If you look at where the gains are usually made, it's in the mid-range, not the peak. Of course this early peak happens because they use small turbos to minimize lag to begin with, but that's not the point

 

[exdeath]

Yup either way, seen both. Either using small turbos and clipping the peak in the mid range to hide the drop off at the upper RPM and the spool time at the start, or clip off the peak at the end and hold torque constant for the entire pull so it doesn't look like it's it's gaining and therefore not obvious it wasn't full power yet.

Really just marketing for people that don't understand how turbo cars work and want to see "the flat torque of a V8".

Oh well, leaves more on the table for us tuners, I'm ok with that

 

[punjabiplaya]

Yup either way, seen both. Either using small turbos and clipping the peak in the mid range to hide the drop off at the upper RPM and the spool time at the start, or clip off the peak at the end and hold torque constant for the entire pull so it doesn't look like it's it's gaining and therefore not obvious it wasn't full power yet.

Really just marketing for people that don't understand how turbo cars work and want to see "the flat torque of a V8".

Oh well, leaves more on the table for us tuners, I'm ok with that

rgr that. tune the turbo to it's max without pushing past the efficiency, or pull it out and put a better turbo in

look at how flat the GT2 RS's torque curve is...

 

[the DRIZZLE]

Yup either way, seen both. Either using small turbos and clipping the peak in the mid range to hide the drop off at the upper RPM and the spool time at the start, or clip off the peak at the end and hold torque constant for the entire pull so it doesn't look like it's it's gaining and therefore not obvious it wasn't full power yet.

Really just marketing for people that don't understand how turbo cars work and want to see "the flat torque of a V8".

Oh well, leaves more on the table for us tuners, I'm ok with that

I wouldn't call it marketing. There's nothing wrong with putting a smaller turbo and giving up some top end for better response down low. It's a legitimate design trade off.

 

[zerocool84]

It's usually easier to get more power out of a turbo/supercharged car compared to a fairly equal NA car. Exhaust+tune easily makes good power on forced induction.

 

[HarryLui]

How do they artificially create flat torque curves?

Limit the amount of positive pressure (boost) at certain RPM.

 

[thedarkwolf]

They also limit the torque for drive ability and to save the trans. My old ass 89 dodge caravan turbo from the factory limited the boost to 5psi bellow 4k rpms and 9psi after and spooled it up fairly slow. Hooked up to a manual boost controller still limited to 9psi and it would hit 9psi at 1800rpms and rip the steering wheel out of grandmas hands while the front tires spun all over the place.

Given the same power numbers I'd take a NA engine. No lag.

 

[exdeath]

I wouldn't call it marketing. There's nothing wrong with putting a smaller turbo and giving up some top end for better response down low. It's a legitimate design trade off.

Talking about tuning to make a flat curve by limiting power and boost, not turbo sizing or anything physical.

Except that an engine that does 200 ft-lb on the left side and 350 ft-lb on the right side would be the better engine than one that does 200-ft-lb all the way across.

Yet if people see the 350 ft-lb on the high and only 200 on the low, they cry "ew turbo lag no flat torque curve" but if you lop off that 150 that ramps up toward the high end and market it as a 200 ft-lb engine, people will look at it and say "oh yay torque peak of 200 at 1500 RPM and flat all the way to 7000 RPM"

 

[Zap]

My car made huge boost and tons of torque from 3k rpm through 6000rpm or so, but once the turbo ran out of breath it was like hitting a brick wall.

My mostly stock Mazdaspeed 6 is kind of like that. It runs out of breath about 500-1000RPM before redline. Adding a CAI maybe gave it another couple hundred RPM. My wife's stock WRX feels like it pulls to redline, but doesn't have that midrange hump mine does. Both are 4 cylinder turbos and they feel totally different.

My wife's previous Mazda 3s also felt quite different from a Toyota Corolla XRS that we test drove, and they were both NA 4 cylinder. The Mazda felt totally easier to drive with a nice midrange while the Corolla XRS was pretty peaky, feeling anemic until revved past 4000-5000 RPM.

I guess my point is that an engine feels how it is tuned to feel.

 

[punjabiplaya]

My mostly stock Mazdaspeed 6 is kind of like that. It runs out of breath about 500-1000RPM before redline. Adding a CAI maybe gave it another couple hundred RPM. My wife's stock WRX feels like it pulls to redline, but doesn't have that midrange hump mine does. Both are 4 cylinder turbos and they feel totally different.

My wife's previous Mazda 3s also felt quite different from a Toyota Corolla XRS that we test drove, and they were both NA 4 cylinder. The Mazda felt totally easier to drive with a nice midrange while the Corolla XRS was pretty peaky, feeling anemic until revved past 4000-5000 RPM.

I guess my point is that an engine feels how it is tuned to feel.

yep, the k04 runs out of steam on stock tune after 5500 rpm. It can be pushed further, but it's past its efficiency after 6k rpm. IIRC the throttle plate starts to close around 5800 rpm (at least on the speed3s, I don't see why it would be diff for the 6) so you get that huge loss of power without a tune.

Mazda's been going with longer stroke engines so there's a lot of midrange power, but no high rpm vtec yo type power. So it depends on what the engine engineering team is aiming for/designing too. Of course the tuning will just further complement what the motor is designed for.

edit: I see a lot of other manufacturers doing this too, BMW, etc... turbo-ing up and losing the high revving engines

 

[vshah]

edit: I see a lot of other manufacturers doing this too, BMW, etc... turbo-ing up and losing the high revving engines

yup, i will miss the m3's v8, that was a sweet engine

 

[PricklyPete]

yup, i will miss the m3's v8, that was a sweet engine

You mean the same V8 everyone complained about because it was not an inline 6?

Part of me hates seeing high-revving N/A engines coming to an end...but driving a well tuned FI engine is quite exhilarating with all the torque available.

 

[satyajitmenon]

You mean the same V8 everyone complained about because it was not an inline 6?

Part of me hates seeing high-revving N/A engines coming to an end...but driving a well tuned FI engine is quite exhilarating with all the torque available.

Right up to the point the Fuel Pump fails.

 

[Zap]

yep, the k04 runs out of steam on stock tune after 5500 rpm. It can be pushed further, but it's past its efficiency after 6k rpm. IIRC the throttle plate starts to close around 5800 rpm (at least on the speed3s, I don't see why it would be diff for the 6) so you get that huge loss of power without a tune.

I guess that's the technical explanation of what I feel sitting in the driver's seat. :hmm:

"Without a tune..." do these respond well to just a chip/ECU?

 

[PricklyPete]

Right up to the point the Fuel Pump fails.

That's just BMW's way of reminding you what you've got. Just like going back to tapes after getting used to CD's...you didn't realize how good the CD until you played a gimped tape again and remembered what you would squirm through just to hear you're beloved Van Halen.

 

[punjabiplaya]

I guess that's the technical explanation of what I feel sitting in the driver's seat. :hmm:

"Without a tune..." do these respond well to just a chip/ECU?

Not insanely well, but an AP and a pro-tune will make a world of a difference.

 

[exdeath]

Narrow power bands are when you use big turbos on tiny engines and want to make decent power.

In terms of driveability, throttle response, linear power, etc it goes like this:

tiny engine < tiny engine with turbo <~=> big engine < big engine with turbo

 

[ShawnD1]

You design and tune the engine so it had 200 lb-ft @ 2000 RPM and 450 lb-ft peak between 6500 and 7000 RPM. Then you restrict the tune to chop off the peak so you can advertise that it's 200 lb-ft flat from 2000 to 7000 RPM.

Since you market it as a 200 lb-ft engine you can claim it has a flat torque curve. If you left it uncrippled it would really be 450 lb-ft peak engine but then people would point out the turbo lag since it doesn't hit that until 6500 RPM.

If the engine put out 450 instead of 200, that would make the drivetrain hella expensive. Tranny and everything else connected to it would need to be a lot stronger.



In any event, NA cars are flat as well. first google image result for a honda civic torque curve. The second spike is the vtec kickin in, yo

Also, I started a thread like this a while ago. Turbo is better than NA because high compression NA is high compression all the time. Turbo is more dynamic. It can run at low compression or it can spin up and run high compression. That range gives a lot of flexibility.

 

[PlasmaBomb]

If the engine put out 450 instead of 200, that would make the drivetrain hella expensive. Tranny and everything else connected to it would need to be a lot stronger.



In any event, NA cars are flat as well. first google image result for a honda civic torque curve. The second spike is the vtec kickin in, yo

Also, I started a thread like this a while ago. Turbo is better than NA because high compression NA is high compression all the time. Turbo is more dynamic. It can run at low compression or it can spin up and run high compression. That range gives a lot of flexibility.

The range of boost gives flexibility rather than the range of compression - high compression improves thermodynamic efficiency.