dwightlooi

NO! The whole point of the thread to the explain that! (1) Gasoline engines are throttled by being choked of airflow (except at Wide Open Throttle); if they are not making the maximum output at any rpm it is because the throttle plate is adding pumping losses to prevent it from doing so. (2) Whether it is the throttle, a dirty filter or a dead rat in the intake thats doing the choking, the effect on the engine is identical if the net resulting airflow is the same. (3) This is a main reason why gasoline engine are less efficient than Diesel Engines; Diesel Engines have no throttle plate and always run with the intake Wide Open, relying solely on fueling to control engine output. Therefore Diesel Engines have lower pumping losses at all scenarios except WOT where both are about the same. (4) This is also why DOHC 4V heads, or any measure to make the engine breathe better, has ZERO effect on fuel efficiency. At anything but WOT (or pretty darn near WOT anyway) the throttle plate is adding all the pumping losses needed to meter engine output to the driver's needs.

(1) As much as is necessary to produce the desired acceleration based on his arse? Nobody measure the throttle position in percentages, degrees or inches. They depress the throttle until they feel the desired acceleration that meets their driving habits. With a dirty filter more throttle will be applied. With a clean filter, less will be applied. But at the same acceleration, the net airflow to the engine and hence the net fuel flow will be identical. At WOT the engine will simply make less power and use less fuel with a dirty filter. (2) I meant to say EXACTLY THAT. A net reduction in mass airflow to the engine of the same amount has fundamentally the same effect. Whether it is caused by a dirty filter, a smaller throttle opening or dead rat in the intake is irrelevant. The fuel use and engine output will be exactly the same, if the airflow is identical.

(1) DC Motors are not better (or worse) than AC motors. They have different characteristics. DC motors have a linearly decreasing torque curve which starts at peak torque and falls to zero. AC motors start at part torque but reaches its peak output in the upper middle of its operating range. The problem with DC motors is that in order to have a usable output throughout the vehicle's operating speed range, it will be necessary to "over spec" the motor to have a wider operating rpm range and torque such that you'll still have usable torque at the mid and upper end. You will then artificially cap the torque output at low rpms to manage traction and/or protect the gear set. This "over specing" often negates, or reverses, the power density advantage of the DC Permanent Magnet Motor (PMM). (2) Another issue with DC PMMs -- particularly large and powerful ones -- is that they are hard to assemble since you need to work against powerful magnetic forces to set the magnets in place. AC Induction motors are very easy to assemble as there are no magnetic forces to contend with until it is turned on. (3) Economically, the PMM is reliant on Rare Earth metals for which the USA is not currently a major producer due to environmental and economic reasons. 80% of Rare Earth metals is produced by China today due to silly "Free Trade" and "unequal Trade" policies of successive US and western governments. It is for reasons (2) and (3) that military and maritime applications have thus far shunned DC PMMs in favor of AIMs. Making small motors for RC cars is one thing; making 48,000 shp drive motors for a navy vessel is another.

You seem to be having a hard time understanding basic operating principles. So, let's try again... (1) In the REAL WORLD, the driver will open the throttle more to compensate for the dirty filter because his car feels slower to get it to accelerate at his desired pace. (2) But, despite him opening the throttle more, the dirty filter causes in the same amount of air mass actually flow into the engine as would have if the filter is clean and he opened the throttle less. (3) Because fuel is metered based on the measurement of Mass Air Flow, the amount of fuel used is the same, as is engine power and acceleration. (4) The added restriction of the filter is no different from placing a limiter on the throttle opening; it absolutely reduces maximum power of the engine but has no effect on fuel economy. BTW, Mass Air Flow is NEVER measured in CFM. CFM (Cubic Feet per Minute) is a measurement of Volume per unit time. Mass Air Flow -- by definition -- is always measured as Mass per unit time. Saying 40 cu-ft of air entered the engine does not tell you how many air molecules are in the cylinders, hence how much fuel should be burned in them. 40 cu-ft at 14.7 psi (sea level pressure) has more air molecues than 40 cu-ft at 12 psi (Denver; 1 mile altitude) and less than 40 cu-ft at 30 psi (under turbo or supercharger boost). That is why Mass Air Flow is measured in kg/sec or lbs/min or some ther unit of mass over time. The alternative is a Speed-Density estimation of airflow whereby the CFM (Flow Speed) is read off a table based on the known corresponding volumetric efficiency of the engine at a particular RPM. An Manifold Absolute Pressure (MAP) sensor is then used to accurately determine the Pressure of the air actually entering the engine, whilst a Temperature also read off another sensor. Density is calculated as a function of Pressure and Density. Remember pV=nRT? The throttle does not affect the CFM. Neither a dirty air filter nor turbo boost affects the CFM either. However, these ALL affect the pressure of the air in the manifold. Mass Air Flow is then calculated by the ECU as Flow x Density. I hope you get it now, because I am trying VERY HARD to explain it to you...

An engine on a test stand has zero mpg, but it still has measurable fuel economy in form of Brake Specific Fuel Consumption (BSFC). The MAF sensor generally reads out as a voltage. The ECU converts that to the appropriate mass air flow value in mass per unit time. This can be pounds per minute, kilograms per second or whatever unit of measure the programming prefers to work with. The instantaneous reading of the MAF sensor while the vehicle is being driven is what determines the fuel injector cycle and hence fuel flow. The gas pedal itself has no direct bearing on fuel flow, it merely regulates the intake restriction via the throttle body with a mechanical cable or with electrical signals to a actuator motor. A dirty filter is no different from an intake restrictor and no different from a small throttle opening. Saying that a dirty filter reduces fuel economy is like saying driving your car gently like Grandma does reduces fuel economy. It's bogus. Airflow to a gasoline engine governed by the throttle body, the idle air duct, the air filter and every geometric restriction in the intake plumbing. These things collectively limit the air flow to the engine, collectively affects the reading of the MAF sensor and consequently fuel supply. The important thing you need to understand is that NONE of these things affect fuel economy. All they do is throttle the engine no differently that the throttle body does. A gasoline engine, by design and operational principle, is ALWAYS running choked up. This is one of the priniple reason why it is less efficient than a Diesel Engine which is always running at the equivalent of Wide Open Throttle (because it doesn't have a throttle body at all).

I am talking about EXACTLY THAT -- dirty air filter(s) will not affect fuel economy when you drive your car in the real world (or on a test stand for that matter). Because, while it increases how much throttle you need to achieve the same acceleration, or to maintain the same cruising speed, that increase in throttle opening DOES NOT change the amount of fuel the engine uses. This is so because net Mass Air Flow ALONE determines fuel supply. How that net Mass Air Flow came about is irrelevant.

Right, and that is 100% due to the change in the mass air flow measured subsequent to the motion of the gas pedal, not due to reading the position of the gas pedal. Fueling is determined by net airflow measured. How much of that comes from the throttle plate, or other restrictions in the intake system, makes ZERO DIFFERENCE to the determination of fueling or fuel economy. ZERO.

Let me put it in a simple way so it's easy to understand. There is NO CONNECTION between the fuel injection system and the "gas pedal". All you are doing when you step on the gas is reduce the breathing resistance to the engine. This in turn increases mass airflow, which is measured and used to determine the amount of fuel the engine receives. Where, or how, this restriction comes about is irrelevant. A Gasoline engine is NOT throttled by fuel supply; fuel is measured to match air supply. A Diesel engine is throttled by fuel, but that is a different story for a different thread. The air filter, when clean, has a much larger porous area than the throttle body and should have a negligible effect on airflow. When it gets clogged enough though, it will start to act like a second, partially open, throttle plate upstream of the throttle. Or, like an intake restrictor on a race car if you will. This will absolutely limit maximum horsepower, but it will have no effect on fuel economy. If the filter is totally occluded -- if you dip it in cement and let it dry -- it'll be like a throttle body that is totally closed with no idle air duct or valve. The engine will not run at all. A carburetor's ability to squirt fuel on a cranking or stationary engine is not an extension of it's normal operation and purpose. It is a work around for the fat that it won;t work at cranking speeds and too low an airflow level. The fuel metered by "squirting" is invariably the wrong amount -- either too rich or lean. Sometimes it is so wrong that the engine still won't start. This is why carburetors have a "Choke" to limit airflow to match! This is also why no carbureted engine will ever pass modern start up emissions standards.

Vacuum and flow restriction is one and the same. The former is what you experience when the latter is present. How deeply you step on the gas pedal DOES NOT determine the amount of fuel the engine receives. The amount of throttle induced vacuum (by itself) DOES NOT determine the amount of fuel injected either. Your gas pedal DOES NOT determine fuel flow! If it did, your engine will be injecting fuel when you floor the pedal while the engine is not running. If it did, it'll inject the same amount when the engine is at 800 rpm and when it is at 8000 rpm as long as your foot is depressing the pedal the same amount! The ONLY thing that determines fuel flow is Mass Air Flow across the MAF sensor (or in a Speed Density engine a mapped or calculated function of the vacuum in the intake manifold and the engine RPM). The intake displacement of the piston will normally draw that amount of air. Vacuum created by the throttle plate and the filter restrictions collectively reduce the pressure of the air going into the engine. Mass airflow = Volume x pressure (of air). Mass air flow is measured and used to determine fuel flow. -- As I said previously, a 50% throttle opening and a clean filter is no different from a 65% throttle opening and a dirty filter if both generate the same mass airflow into the engine. To accelerate at the same rate you will burn the same amount of fuel in both cases. If you have 10 layers of dirty filter (which causes a 90% restriction), it'll be like driving around with no filter but with the gas pedal restricted to 10% of its normal travel. Your car will be VERY SLOW, but it'll be just as economical as a car with no air filter but driven at no more than 10% throttle all the time. Get it? -- Of course racers remove air filters. Who wants to race with their throttle limited to 90% or even 99%?

The simple way to put it is that a carburetor has a finite range of airflow under which it can operate and meter fuel. It's like an airbrush or a paint sprayer in principle; try breathing over the tip and see if any paint comes out (I don;t think so). When you are starting the engine, it is cranking at a speed which does not provide enough airflow for the carb to work. The whole pumping the pedal nonsense is not necessary at all if you can crank the engine at 1000 rpm or relatively fast speeds. Unfortunately, that isn't the case with the typical starter.

Again, I find it hard to excuse that GM's flagship engine -- the Blackwing 4.2 -- does not have dual injection and does not have the cam-switching Tri-power valvetrain.

Let me put it another way that is easy for everyone to understand... Driving your car with a DIRTY FILTER is like driving your car in DENVER instead driving it in SAN DIEGO -- or some place at sea level. Your car will be less powerful and you'll need more throttle to accelerate or maintain any given speed. But, at any given rate of acceleration or cruising speed your fuel consumption is exactly the same. The air filter causes a drop in pressure after the air passes through it. The throttle causes a further drop in pressure. The sum of the two drops is what the engine ingests. Whether this is from a small throttle opening and no air filter, or a restrictive air filter and a big throttle opening makes no difference. Fuel is metered based on mass of air molecues the engine ingests per unit time, not what causes the restriction in airflow. If this isn't the case, then your engine will be running too rich or too lean. It'll fail SMOG, stumble or stall.

Well, if you don't have a mass airflow meter, you have one of two things... (1) A Manifold Absolute Pressure (MAP) sensor. Restrictions create vacuum. The combined effects of the throttle and filter will collectively result in the pressure in the manifold being whatever it is (that's lower than atmospheric pressure). The engine meters fuel by knowing the engine rpm, the pressure & temperature (hence density) of the air in the manifold. And, it injects fuel based on what the programmed fuel map says. The effect is theoretically no different (if practically less accurate) than with a MAF meter. The filter has no effect on fuel economy only in the throttle position need to create the particular manifold pressure needed to achieve the same acceleration or maintain the same cruising speed. (2) A Carburettor. Here the air flows past a venturi sucking fuel in for it to mix with. The amount of fuel sucked in will depend on the pressure of the air flowing past it vs the atmospheric pressure. Again, the filter restriction reducing the pressure of the air going through the cabs will result in less fuel being metered by the carb(s). It'll be like driving the car at a higher altitude. Again, no difference.

Direct Injection resulted in the GREATEST LOSS OF ENGINE REFINEMENT in the last 50 years. A 1980s VW SOHC 8 valve engine is more refined at idle thann a direct injected BMW V12 of today. There is no getting around the fact that opening and shutting off a pintle with 1000+ psi of fluid pressure makes your engine clatter like a diesel. Manufacturers put acoustic insulation on their DI heads and use fuel rail accumulators to dampen the sound, but it'll never be quiet like port injectors working with tens of psi not thousands. The ONLY SOLUTION is what Toyota does on the Lexus engines. Use port injection at idle and low engine speeds. Switch on the direct injectors at higher RPMs and throttle openings. This also has the side effect of having fuel spray on the intake valves and keeping them clean of carbon deposits from the valve overlap and the PCV system. Only Lexus spends the money on having two fuel systems and two injectors per cylinder. That is why they are the king of refinement.

No. The point isn't that the effects of a clogged filter is too small to measure. The effects can be very significant. The point is that it DOES NOT reduce fuel economy because there is ZERO DIFFERENCE between restricting flow with the throttle body or restricting flow with a clogged filter! Restricting flow is how you throttle a gaosline engine. If you need 12 CFM of airflow to maintain 65 mph, it doesn't matter if that is coming from a big throttle opening and a clogged filter or a small throttle opening an a clogged filter. 12 CFM is 12 CFM. And, 12 CFM will be burned with the same amount of fuel. A clogged filter simply means that you cannot reach the engine's designed airflow with the throttle wide open. Imagine that your throttle cannot open past 80% or 90%. Does that affect your fuel economy? No. Not at all!

If you define "problem" as "indicative of mechanical failure or impending failure" it is not a problem. If you define "problem" as "lack of refinement or not confidence inspiring" it is a huge problem that damages the value of your brand! The LF3 (3.6TT) engine makes a rattling noise that sounds like a lose exhaust heat shield for about 5 secs when you start it. That's from the vacuum actuated turbo waste gates rattling before the engine build up enough vacuum to pull them open. The engine also makes a buzzing sound from the electric circulation pump after you shut it off for about 10 seconds. These are both normal and noted characteristics of the engine. But in a CTS VSport Premium that sells for $73K new, that is decidedly unrefined and I would have fired the engineer who allowed this kind of nonsense on the engine (were I in charge at the General).

A DIRTY AIR FILTER WILL NOT REDUCE FUEL ECONOMY! Sounds counter intuitive, but it's true! Here's why... In a gasoline engine, the engine's output is controlled by choking it with the throttle body. It restricts the airflow to the engine at all times except when you put the gas pedal to the floor. Whatever the airflow happens to be, it is measured by the Air Flow Meter which then tells the engine how much fuel to inject. A dirty filter reduces airflow to the engine just like the throttle! The filter and the throttle restrictions combined results in the net airflow to the engine. If you have a clean filter, you'll end up using a slightly smaller throttle opening (gas pedal position) to accelerate at the same rate or maintain the same speed. If you have a dirty filter, you use a deeper throttle opening (gas pedal position). But in both cases, it is the net airflow that determines the amount of fuel you burn! The engine doesn't care what is restricting its breathing be it the throttle or the filter or both! Now, a dirty filter will limit the maximum airflow you can get to your engine. It will reduce maximum horsepower and torque. So, it will make your car slower when you are really trying to go fast. With a really dirty filter, wide open throttle may be like 70% throttle. However, that WOT application will have exactly the same power and fuel burn as 70% throttle with a clean filter. It may take you 40% throttle to maintain 70mph in top gear instead of 25% throttle.But, again, that 40% throttle will have exactly the same output and fuel use as 25% with a clean filter. To get this bad you need to not change your air filter for 300,000 miles or something.ridiculous. Even then -- when driving "normally" around town or cruising down the freeway -- it'll have NO EFFECT on your fuel economy at all! A dirty filter is like putting a limit on how far you can depress your gas pedal! A slightly dirty filter may allow you 99% of your throttle. An unchanged filter with 100,000 miles on it may limit you to 90% throttle or something. But, it'll be no different from putting a brick under your gas pedal such that you cannot depress it fully. ZERO EFFECT on your fuel economy! Don't believe me? Do a little experiment. Next time you do an oil change, don;t change the air filter (yet). Drive 10 miles down your favorite stretch of not so busy freeway at a fixed speed and measure your fuel economy with your trip computer. Now change the filter and drive down the same exact stretch at the same exact speed. You will notice ZERO difference in your mileage before and after.

Having said the above... the claim by the illustrator that this has a similar effect to a twin scroll turbo is RUBBISH. A twin scroll turbo has nothing to do with accelerating exhaust flow or turbo spool up. It has everything to do with not contaminating the intake with exhaust back flow during the exhaust and intake valves' overlap period. At bottom dead center of the power stroke, the exhaust valves open sending high pressure exhaust pulse into the exhaust. At this same moment, the exhaust valves of the cylinder at top dead center of the exhaust stroke is still open while the intake valves are opening. This allows the exhaust gases to enter both the turbo and the cylinder at the beginning of the intake stroke. This is an INTAKE BREATHING problem. By keeping the exhaust paths of cylinders 1-4 separate from that of 2-3 the exhaust pulses cannot contaminate and interfere with the intake aspiration. That's the purpose of a twin-scroll turbo. Having two scrolls in parallel actually reduces the turbo's flow capacity and increases wall drag. The GM Double Volute design solves that and allow for exhaust segregation without flow restriction. The reward is 348 lb-ft from 2.7L at 1,500 rpms.

The 2.5T makes 310 lb-ft @ 2,000 rpm. Not exactly GM's 348 lb-ft @ 1,500 rpm from the double volute L3B (2.7T) but not bad. Also, the fact is that a 2.5L mill making 100hp/L (or less with 87 Octane) and 124 lb-ft/L is not exactly highly stressed. And, I am surprised that anyone thinks the lag is excessive when it is one of the least laggy turbocharged engines in production. The SkyActiv's 10.5:1 compression is about as high as you are going to get with a turbocharged engine. The turbo is technically very interesting although the results are somewhat inferior to GM's simper approach... Mazda has a flap in the manifold between the turbine and the exhaust ports. At below 1600 rpm, the flap close and forces the exhaust through a narrower passage. This increases exhaust velocity and helps spool the turbo quicker off idle. At higher engine speeds, the flap opens and allows the normal flow to the turbo. 310lb-ft @ 2,000 rpm, with possibly the best 800~1600 rpm spool characteristics, is more than you can expect from a 3.0~3.8L V6 and no slouch. High compression and excellent low speed spooling is great for cruise economy. I think the problem comes down to simple physics. 227~250 hp is not much to move around 4,300 lbs of stuff. The not too quick Acura MDX for example is "only" lugging 4,050 lbs with a 290 hp V6 engine. In the end, horsepower matters. Horsepower allows you to gear the transmission to solve a lot of problems. I don't see the CX-9 has "laggy". It is not. It is simply underpowered. It's power to weight ratio is similar to that of a 2.5L 4-cylinder, NA, Camry. And, hence, it performs like one.

It's not bad really. Not stellar, but not bad. And, you don't have to put Premium Gas in it -- as long as you don't mind losing 23 hp (227 vs 250).

It sounds labored because it is 237 bhp trying to lug 4,000 lbs around. It short shifts because it is smart! The new 2.0T (LSY) engine hits its torque peak of 258 lb-ft at 1,500 rpm. It hits its 237 hp power peak at 5,000 rpm and spend every bit of the last 2000 rpm running out of breathe. By 6000 rpm it is making less than 200 lb-ft. By 7000 rpm it is making closer to 150 lb-ft. You really don't want to rev that thing. The LSY is very quiet, refined and responsive from 1000 rpm through about 5000 rpm where it does its best work. In many ways it feels like the old Supercharged 3800 which -- despite popular slander -- is actually a very refined engine when not hustled. Most of the fuel economy gains come from shutting off the two middle cylinders in cruise and from the low lift economy cams also having a long intake duration which can then be phased to eat into the compression stroke and reduce the effective displacement as well has create an asymmetrically long power stroke. It's a part time "mild Atkinson" cam if you will.

Not exactly... Unlike the difference between transverse and longitudinal transmissions -- which are totally different animals -- there is no substantial difference between a lengthwise or sideways engine installation. We are talking about a different exhaust pipe, new air box and new dress cover. The last being largely cosmetic (so the lettering don't don't face the wrong way). 99% of the engine is identical. The differences are minute enough that GM doesn't even have separate RPO codes for transverse and longitudinal versions of the same engine. The FWD and RWD 3.6TT are both the LF3. The FWD and RWD 3.6 NA are both the LGX or LFX. The FWD and RWD "old" 2.0Ts are both LTG.

If it's the 9A it's probably the 9T65. It can work if they limit boost in 1st gear to moderate the input torque when the greatest amplification happens. 280 is not that far from 295. The Focus ST did that in 1st (back then) too. You can't responsibly drop in the 348 lb-ft 2.7T or th 368 lb-ft 3.6TT engines on the 9T65 like you could the 6T80 though. GM doesn't have a longitudinal 9A. They have the 8L45, 8L90, 10L80 and 10L90 with 8 or 10 speeds.

Anyway... I suspect that GM will have a high output Tripower Four at some point, just not for the Transverse FWD cars. I'll like to see a 2.7T High Output 4-cylinder probably around 450 bhp @ 5,700 rpm, 420 lb-ft @ 2,600~5,600 rpm, rev limited to 6,200 rpm. This will pair quite well with the 10L80 10-speed automatic transmission and it will be a true V8 replacement 4-potter. It'll be more than good enough for a CT4-V. Maybe even an XT4-V if GM will buy Ford's 8-speed Auto.