Turbo vs NA

[ShawnD1]

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

In the turbo thread I asked why they don't run the turbo full power all the time. The answer was something about running too lean destroys the cylinder heads or it fails some emission thing or something. Running super lean creates a lot of nitric oxides and that's a direct cause of acid rain.
Don't quote me on that though. I just repeat stuff I hear at the beauty salon ()

 

[jlee]

In the turbo thread I asked why they don't run the turbo full power all the time. The answer was something about running too lean destroys the cylinder heads or it fails some emission thing or something. Running super lean creates a lot of nitric oxides and that's a direct cause of acid rain.
Don't quote me on that though. I just repeat stuff I hear at the beauty salon ()

Clearly they are automotive geniuses.

 

[ShawnD1]

Clearly they are automotive geniuses.

Clearly.


Wiki says something interesting about this.
http://en.wikipedia.org/wiki/Air-fuel_ratio_meter

Lean mixtures improve the fuel economy but also cause sharp rises in the amount of nitrogen oxides (NOX). If the mixture becomes too lean, the engine may fail to ignite, causing misfire and a large increase in unburned hydrocarbon (HC) emissions. Lean mixtures burn hotter and may cause rough idle, hard starting and stalling, and can even damage the catalytic converter, or burn valves in the engine. The risk of spark knock/engine knocking (detonation) is also increased when the engine is under load.

So full boost all the time would make it burn like dog shit to the point where it doesn't burn all of the fuel and starts throwing unburned fuel out the exhaust

 

[Skurge]

Clearly.


Wiki says something interesting about this.
http://en.wikipedia.org/wiki/Air-fuel_ratio_meter



So full boost all the time would make it burn like dog shit to the point where it doesn't burn all of the fuel and starts throwing unburned fuel out the exhaust

Like the flames you see with race cars and the thick black smoke and rough start in this video?
http://www.youtube.com/watch?v=VQ7gFfWZKWU

 

[ShawnD1]

Like the flames you see with race cars and the thick black smoke and rough start in this video?
http://www.youtube.com/watch?v=VQ7gFfWZKWU

I can't view youtube at work, but flames out the back means rich burning. Super duper rich fuel mixture.

 

[Skurge]

I can't view youtube at work, but flames out the back means rich burning. Super duper rich fuel mixture.

That shows a 2L turbocharged 4cylinder, Every time he goes on the throttle, theirs thick black smoke coming out the exhaust.

 

[ShawnD1]

That shows a 2L turbocharged 4cylinder, Every time he goes on the throttle, theirs thick black smoke coming out the exhaust.

Is it a Chrysler? :awe:

 

[Skurge]

Is it a Chrysler? :awe:

LOL

No, one of those Pikes Peak rally cars.

 

[jlee]

Clearly.


Wiki says something interesting about this.
http://en.wikipedia.org/wiki/Air-fuel_ratio_meter



So full boost all the time would make it burn like dog shit to the point where it doesn't burn all of the fuel and starts throwing unburned fuel out the exhaust

No.

 

[exdeath]

It doesn't do that all the time, that's the accelerator pump shot or TPS enrichment commanded by a sudden increase in throttle position. Its to protect the engine on sudden acceleration because air flow changes hit the ports faster than fuel adjustments can be made and it takes a second for air flow readings to stabilize. Its not unusual to see a dip to rich in AFR on the low end on the hit that works its way back up to hold flat for the rest of the pull.

Ideal AFR for boosted cars is around 11.5-12 and that alone is not going to produce black smoke. Any more than that at WOT and your turbo motor becomes a flex fuel hybrid that also burns aluminum.

Black smoke like that on a turbo race car is usually due to antilag systems more than the engine mixture.

 

[DivideBYZero]

Abandon the thread, ShawnD1 has posted...

 

[PlasmaBomb]

Wiki says something interesting about this.
http://en.wikipedia.org/wiki/Air-fuel_ratio_meter

So full boost all the time would make it burn like dog shit to the point where it doesn't burn all of the fuel and starts throwing unburned fuel out the exhaust

Great... now you are confusing AFR with Compression.

 

[PlasmaBomb]

It doesn't do that all the time, that's the accelerator pump shot or TPS enrichment commanded by a sudden increase in throttle position. Its to protect the engine on sudden acceleration because air flow changes hit the ports faster than fuel adjustments can be made and it takes a second for air flow readings to stabilize. Its not unusual to see a dip to rich in AFR on the low end on the hit that works its way back up to hold flat for the rest of the pull.

Ideal AFR for boosted cars is around 11.5-12 and that alone is not going to produce black smoke. Any more than that (AFR >12:1) at WOT and your turbo motor becomes a flex fuel hybrid that also burns aluminum.

Black smoke like that on a turbo race car is usually due to antilag systems more than the engine mixture.

Pre-emptive clarification.

That's what you mean isn't it Ex?

Doesn't running rich normally just foul your plugs, kill your cat, and cause a loss of power?

Edit: Bar running stupid rich and washing off oil and destroying the lubrication or causing hydrolock...

 

[JCH13]

Turbos aren't at peak boost all of the time because it is stupid to do that. A turbo is, generally, for making more power. Essentially a given engine at a given MAP and RPM can make a certain amount of power. 95% of the time a vehicle's power requirement is pretty low, i.e. simply maintaining speed, and the required MAP to make the required power is below 1ATM and no boost is needed.

Abandon the thread, ShawnDerp1 has posted...

FTFY

 

[JCH13]

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.

The turbo motor (or any FI engine for that matter), of similar power output, will generally be lighter and more efficient that the equivalent NA motor.

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.

This. My speed hits noticable boost at 2krpm, and peak boost by 3krpm, very torquey and very nice for street driving, just gobs of smooth torque. My Miata, on the other hand, hits peak boost around 4500-5000 rpm and has a very 'peaky' power band. When the boost hits it's like flipping a switch from "cute convertible" to "fury of Satan." Both are fun to drive, IMO, and have some sort of FI is almost a vehicle requirement for me (and the rest of my family) at this point.

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

This is really annoying. The MZR engine w/ K04 (especially a reworked K04) is still pretty potent up to red line without that throttle closing, though it is putting out less torque.

 

[punjabiplaya]

Turbos aren't at peak boost all of the time because it is stupid to do that. A turbo is, generally, for making more power. Essentially a given engine at a given MAP and RPM can make a certain amount of power. 95% of the time a vehicle's power requirement is pretty low, i.e. simply maintaining speed, and the required MAP to make the required power is below 1ATM and no boost is needed.

Haha, can you think of a turbo running at peak all the time? Holy hell (see what I did there?). There's a reason most cars run load based tuning for boost.

 

[Chrono]

Never driven turbo? Time to try it... power is cheap... torque is an addiction... equip that with AWD and you got yourself one fun ride (STI/EVO). However, there are some other good cars out there that are not AWD but with turbo and are pretty darned good too.

 

[ShawnD1]

Ideal AFR for boosted cars is around 11.5-12 and that alone is not going to produce black smoke. Any more than that at WOT and your turbo motor becomes a flex fuel hybrid that also burns aluminum..

Oh noes, not my aluminums!
Good to know :thumbsup:

Great... now you are confusing AFR with Compression.

I don't know if you're aware of this, but forcing a bunch of high pressure air into the system without increasing the amount of fuel injected changes the air fuel ratio.

Grade 2 math, it's amazing

 

[alkemyst]

You really can't say turbo vs NA...you need to be more specific. All any forced induction does in general is to make a smaller engine displace what a larger one does.

Everything else gets more specific.

 

[exdeath]

I don't know if you're aware of this, but forcing a bunch of high pressure air into the system without increasing the amount of fuel injected changes the air fuel ratio.

And this will never happen unless you suck at tuning or just enjoy killing engines.

 

[punjabiplaya]

And this will never happen unless you suck at tuning or just enjoy killing engines.

perhaps he really likes knock knock jokes?

 

[ShawnD1]

And this will never happen unless you suck at tuning or just enjoy killing engines.

That was the question originally asked though. Why not run the engine super hardcore lean all the time. It might have been you who said in that other thread: it destroys the engine.

 

[exdeath]

That was the question originally asked though. Why not run the engine super hardcore lean all the time. It might have been you who said in that other thread: it destroys the engine.

Lean = more oxygen than fuel.

Hot oxygen under high pressure needs to react with something.

If there is not enough fuel for it to react with, the materials in the head, block, values and pistons become the fuel.

 

[Howard]

I don't think the metal actually oxidizes, but I could be wrong. In any case, combustion temps increase significantly (and dangerously) as AFR goes toward stoichiometric.

 

[JCH13]

Oh noes, not my aluminums!
Good to know :thumbsup:



I don't know if you're aware of this, but forcing a bunch of high pressure air into the system without increasing the amount of fuel injected changes the air fuel ratio.

Grade 2 math, it's amazing

Cearly you have no idea that cars determine fueling based on either the amount of air going into the intake (MAF) or the air pressure in the intake manifold (MAP) so unless the ultimate fueling capacity of the system is exceeded, it won't go lean.

Lean = more oxygen than fuel.

Hot oxygen under high pressure needs to react with something.

If there is not enough fuel for it to react with, the materials in the head, block, values and pistons become the fuel.

This. Burning aluminum/iron/titanium etc makes a crap-ton of energy. You basically turn the inside of your engine into a thermal lance, which is why the engine gets so freakin' hot.

I don't think the metal actually oxidizes, but I could be wrong. In any case, combustion temps increase significantly (and dangerously) as AFR goes toward stoichiometric.

Like this:

But temperature is not exactly what's dangerous, it's the amount of heat that's dangerous. Idling or even moderate loads burning at stoich are fine. While the combustion is hot, there is not a lot of heat or thermal energy. However, if you tried to burn stoich at maximum power there would be too much thermal energy for the engine to dissipate and bad things would happen, like melting pistons.