Why NA? Because it might be a thing of the past..

[strat61caster]

Originally Posted by rice_classic

It's too bad that the trend is for small displacement engines with turbos as opposed to superchargers. Clearly people who like FI, like both options for a wide variety of reasons.

It makes sense, turbos are thermodynamically more efficient because they're powered by waste heat, superchargers create a parasitic drag on the motor, when the goal is fuel efficiency the turbo wins every time.

[serialk11r]

Originally Posted by strat61caster

It makes sense, turbos are thermodynamically more efficient because they're powered by waste heat, superchargers create a parasitic drag on the motor, when the goal is fuel efficiency the turbo wins every time.

Common misconception, turbos are not powered by waste heat. That would only be the case if you isolated each cylinder's exhaust and injected water or something after the valve closes. They are powered by a combination of increased static pressure in the exhaust system upstream of the turbine (aka, backpressure, energy supplied by the piston), and the momentum transferred to the turbine from the waves produced by blowdown when the exhaust valve opens (this is free energy).

They are typically more efficient under boost than a supercharger, but we're talking low single digits in terms of total engine power. A big supercharger say in a ZR1 might suck 40hp, a similar turbo might sap only 20-30hp through increased backpressure, on a 600hp motor (you can run some quick numbers yourself to see that the numbers I threw out are pretty reasonable). This is why Audi is using a supercharger on its 3.0L V6s; better response for a small loss in on boost efficiency.

Normally people don't think of it this way, but there's a continuum of response vs efficiency of sorts with FI; You could have a huge turbine that creates almost no backpressure that would be extremely efficient but the throttle would feel like a helicopter or jet plane where you have to sit there and wait for for several seconds. You could have a tiny turbine housing like most OEM setups that has good response but gives up a lot of efficiency under boost because the way it creates good response is by creating more backpressure and thus tapping into the engine's power to increase the boost level faster. Then you have the supercharger that is 100% powered by the engine and thus has great response.

One thing you can do to leverage the response characteristics of the supercharger is to do something like the Mazda KJ-ZEM, instead of try to collect waste energy in the exhaust with a turbine, simply cut the waste, trading engine power for efficiency, and then get the power back with a supercharger.

[strat61caster]

Originally Posted by serialk11r

Common misconception, turbos are not powered by waste heat.

Paragraph 1: I don't know what you're point is, yes your statement is more accurate but it does not discount my statement. I think I may be quoting my textbooks depending on your response to my post.

Paragraph 2: The first part of the paragraph agrees with me, the second is random numbers pulled out your ass on hypothetical cars, the third is about throttle response which has nothing to do with efficiency.

Paragraph 3: Talk of response, not sure how this is relevant to my post, I agree with what's posted here, this jives with what I know. I guess you're saying energy efficient turbos have poor response? That's nice.

Paragraph 4: Optimizing an engine to have minimal waste heat and make up the power with a supercharger? Um that works I guess. Oh wait looked it up, that's working off the Miller cycle, essentially having a longer intake stroke than compression in an attempt to raise compression ratio and reduce pumping losses.

[ame="http://en.wikipedia.org/wiki/Miller_cycle"]Miller cycle - Wikipedia, the free encyclopedia[/ame]


I guess you're saying that there are alternatives to turbos? That's true, but as of right now turbos are the obvious solution to increasing efficiency. It's well developed technology that is relatively well understood and has been implemented reliably in consumer vehicles.

[serialk11r]

Originally Posted by strat61caster

Paragraph 2: The first part of the paragraph agrees with me, the second is random numbers pulled out your ass on hypothetical cars, the third is about throttle response which has nothing to do with efficiency.

I guess you're saying that there are alternatives to turbos? That's true, but as of right now turbos are the obvious solution to increasing efficiency. It's well developed technology that is relatively well understood and has been implemented reliably in consumer vehicles.

They're not pulled out of my ass, the supercharger on a ZR1 uses ~40hp at peak power, and 6.2L*6500rpm/2=335L/s, so every bar of backpressure added uses 33.5kW=45hp up. The ZR1 runs 0.7 bar boost, and a well designed turbo system might have somewhere from 0.5 to 0.7 bar backpressure in this scenario.

That's not important though. What I'm saying is that turbo is not *the* obvious solution. You don't need different length compression and expansion stroke to make a Miller cycle engine, no one does that. It's called keep the intake valve open longer and have some of the charge pushed back out. Tons of cars do this. That's still not the point. Even without Miller cycle, a Roots supercharger lets you downsize the engine just as much, has very low parasitic drag when not on boost, and the better throttle response compared to a turbo system gives you flexibility to configure the engine for more efficiency as Mazda did, because the fact is throttle response does matter to some degree, and it matters a lot in performance car applications.

[strat61caster]

Originally Posted by serialk11r

They're not pulled out of my ass

Source? If you don't mind?

The idea of leaving the intake valve open longer IS part of the miller cycle, you're shortening the compression stroke to reduce losses, when you look up the Mazda motor you mentioned the Miller cycle is linked. Valves stay open beyond the bottom of the stroke because air is fluid, it doesn't fill the chamber 100% and better volumetric efficiency is achieved by leaving the valve open longer, I think you might be confusing the two?

http://en.wikipedia.org/wiki/Mazda_K_engine#KJ-ZEM

In any case, you can argue that the supercharger is better but there's companies putting billions of dollars into turbos: Fiat (Chrysler), Ford, Hyundai, that's probably the majority of all auto manufacturing taking place.

On a personal level, I agree that throttle response is king, given the choice I would take a supercharger over a turbo any day. I think (and most agree) that tubos will be the next widespread engine technology (like fuel injection and variable valve timing), outnumbering superchargers and naturally aspirated engines by a wide margin.

[serialk11r]

Originally Posted by strat61caster

Source? If you don't mind?

I'm really bored, so I'll work this out.

Calculated based off Eaton's charts, it's an estimate. Owners report 10.5 psi boost, and the engine specs are 638hp@6500rpm vs 430hp@5900rpm (the respective torque output is 35% higher) and 819Nm peak torque vs 575Nm peak torque (42% higher, though the torque peak is earlier), so the supercharger is increasing volumetric efficiency by something like 45%. Adiabatic compression of air 1.45 times yields absolute pressure of about 1.6 bar, or 10psi barometric. The intercooling on the ZR1 probably isn't that great, which is why you see 10.5psi boost.

At 100% volumetric efficiency the LS3 engine breathes 335L or 0.335 m^3 per second as I calculated before, at 80% this is 0.268 m^3/s. It's likely not below 80% as Ferrari had to use all kinds of tricks to squeeze 125Nm/L from the 458 and the LS3 makes only slightly under 100Nm/L. Take 145% of these 2 numbers to get a range of 0.388 to 0.486 m^3/s. Oops, gotta convert to m^3/hour, those are 1397 and 1750. Looking at Eaton's map for the R2300, these 2 points fall on the 70% and 65% efficiency islands respectively.

The amount of energy it takes the ideal compressor to compress air is 1/(gamma-1)(P1V1)((V2/V1)^(1-gamma)-1) where P1 is starting pressure, V1 is starting volume, V2 is final volume, gamma is heat ratio. In this case, it's 2.5*(100kPa*388L)((1.45)^0.4-1)=0.4*38.8kJ=15.52kJ, and this is the amount of air we're compressing each second so that's just 15.52kW. At the upper end, it's 19.4kW or 26hp. This is the ideal scenario, with the non-ideal compressor we get something like 21hp/0.7=30hp or 26hp/0.65=40hp. Due to the efficiency penalty of having a supercharger you need to pump more air so I think 40hp is closer to the real number. The belt drive and gears are like 95% efficient or something which adds on like another 2hp if you like.



...ANYWAYS
Eaton is making a pretty good case with their TVS chargers, and Audi is actually using them on a lot of cars, and so does Toyota on some of their special TRD and GRMN models. It'll be interesting seeing how this plays out with the turbo competition, I hope SC wins. You can boost a small 4 cylinder engine with a TVS charger that weighs only 7 pounds, and the next generation is going to be even better.

[Rayme]

High pressure Direct injection technology isn't "new". It's been used in diesels since forever and since those engines already have high compression and works on knock principle, it should be quite reliable.

When honda/toyota (and most japanese care actually) went from carb to port injection in the late 80's - early 90's those provided many of the companies most reliable vehicles ever since.

DI is too good to be hated on, let's embrace it with open arms and bring Mr. turbo to the love fest.

Originally Posted by regal

First the industry is being forced into Direct Injection due to upcoming emission and efficiency regs.

If you haven't noticed an NA DI engine have "issues." The addition of a turbo gives a wider window to meet durability, performance, economy, and emission targets. So the entire industry is slowly moving to DIT for new 4 cylinder designs. Even a $15 Chevy Sonic can be bought with a DIT 4 cylinder. Even Honda is working on their first turbo 4 cylinder.

Personally I and most reviewers think Toyota dropped the ball by not allowing Subaru to use the FA20DIT in the twins.