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What is Turbo Lag?
A true understanding of torque and horsepower and where turbo lag comes into play
Contributed by: Enginebasics.com
Let’s start this article out with a definition of turbo lag:
Turbo lag is the time it takes for a turbocharger to “light up” or produce positive manifold pressure drastically changing the power output of a motor.
Let’s assume you would like even more of an explanation. Remember that turbochargers are driven off of exhaust gasses. The gasses spin a turbine wheel that is connected to a compressor wheel that shoves compressed air into the engine providing it more air, and therefor the ability to make more power. It takes time for these turbine and compressor wheels to build up the speed required to push positive pressure air into the motor. This “dead time” between you putting your foot down on the gas peddle and the turbo providing full torque are what we call “lag”.
So why is everyone so upset with turbo lag?
An article was just published in Road & Track where the author went off for two pages about how the trend towards turbo cars is terrible and messing up the sound and balance, and turning great drivers cars into a mess of differing torque curves. He writes this as Ferrari is announcing the change of going twin turbo on the 488 GTB. Ferrari says this is to “meet emission standards” for government regulations. In the end he states that he is waiting for the day when he will cheer that a company says they will “end turbocharged motor production and go back to natural aspiration.”
Oh man. You would think the advertising/marketing guy for Ferrari wouldn’t so easily deceive a Road & Track top journalist, who one could argue has worked his way up to the top of the automotive journalistic pyramid because of his automobile insight and knowledge. The deception we are referring to is that Ferrari is going turbo because of emissions.
Now why should we not be buying into what Ferrari is trying to “pitch” to us? Well let’s look at the facts:
- Ferrari’s main competitors to the current 458 are the McLaren 650S, Porsche 911 Turbo S, and the Lamborghini Huracan. Two of these cars are turbocharged and one is not. The one that is not is a 5.2L V10 (Lamborgini), while the others are a v8 (McLaren) and a flat 6 (Porsche), both displacing 3.8L of displacement. There are two ways to make torque, which as we know translates into horsepower. You either add displacement or add forced induction. The choice then that Ferrari had to make is do we go forced induction or do we go displacement. I believe they chose forced induction because in the end it can make more power with less strain on the motor and on the budget.
- Forced induction can do exactly what displacement does, and that is adding torque. It should be noted though that as you add displacement the engines components like rods, crankshaft, and pistons increase in size which usually makes the manufacturer have to decrease the redline of what the motor can safety be revved to. What makes forced induction better then is that it can provide the torque of a large displacement motor, but do it on a small motor. This leaves the motor with the ability to have a high redline and do it reliably. So essentially it is the best of both worlds, high torque and high revs. Ferrari is known for high revving race motors, so were they really willing to up the displacement at the cost of lowering the redline to stay competitive with the turbocharged cars?
- Emissions have already been cut with the introduction of direct fuel injection and the increase in the volumetric efficiency of the combustion motor. Just look at the Lamborghini V10. It has no problem meeting the emissions standards with is larger displacement motor.
So what is the reality? The reality is Ferrari has said for years that it would never go forced induction and yet here they are doing it. Instead of looking like fools they have decided to play the blame game and blame it on emissions standards. The reality is their competition was leaving them in the dust and they had a choice. Either jump to a larger displacement V8 or V10 or go forced induction. The V8 was basically as big as it was going to get, so they would have to go to a larger V10. That would have required a WHOLE new motor, block, and major changes to the engine compartment, as the motors dimensions got bigger. They naturally took the smarter route, and kept their V8 with its low displacement and high redline, and just added some turbos.
Lets get back to the main discussion of turbo lag. Why was Ferrari so against turbochagers? Why was the Road & Track author so upset that the Ferrari was “selling out” and going to turbochargers? Why is Ferrari saying its emissions when the reality is it has nothing to do with it?
Answer: A terrible understanding of what turbo lag really is and the negative connotation the public has about turbocharger lag, so let’s talk about it.
On a racetrack while flogging a car to the very edge of its performance ability, having a car with two torque curves is going to be difficult to manage. One torque curve is when the turbo is spooling up and you’re just relying on the motors natural torque, and the other is when the turbo is building boost and forcing air into the motor. To have a vehicle in a corner and trying to balance throttle inputs this could be a nightmare, but hold on. How many of us will be flogging our cars on the track? Lets say 20% (Even that is high, the number is more like 10% of owners ever drive their car on a track but just go with it), and lets say of those 20%, 3% will have the track time and driving skill required to drive a car to the edge of its limits. Ok, so AT BEST we are talking about turbo lag seriously affecting 3% of the owners of turbocharged cars. Well what about the other 97% of owners. The other 97% of the owners really shouldn’t care that the car has two torque curves since it is doubtful that they have the skill to modulate the chassis balance of the car mid corner with throttle inputs anyway. Another argument might be that the second torque curve’s unpredictability would make any novice driver crash if they went full throttle in a corner and the turbo went full boost. Have you looked at the horsepower of sports cars today? If you go flat-footed in any of them, turbocharged or not, that rear end is probably going to come around on them if the traction control is turned off. So should 97% of the owners of turbocharged cars REALLY be complaining that the car has two different torque curves?
Next let’s talk about who should be complaining about turbo lag.
Small displacement motors. So that we can have a number to work from let’s just say 2.6L and smaller. Why should we only be including these smaller displacement engines in the discussion of lag complainers? Remember that a turbo charger doesn’t take away from the torque a motor naturally makes, but instead adds to it. A guy in a 1.8L Audi A4 will only be working with around 100 ft/lbs of torque before the turbo comes in to help. A guy in a 2.0L Mitsubishi Evolution will again only be working with around 100 ft/lbs of torque before positive pressure in the manifold from the turbo stats to bring that torque up. These small displacement cars with just 100 ft/lbs or torque to play with wouldn’t be considered peppy and would drive around at the same speed as a Honda Civic or Toyota Corolla. There really is no “get up and go” to them.
Now let’s go to the other end of the spectrum and talk about big displacement motors that are bigger than 2.6 liters. Take the popular 3.0L inline six Toyota Supra motor (2Jz) or the 3.0L or 3.2L inline six BMW motor. These motors with their larger displacement are making TWICE the torque at the same engine RPM when under no boost from the turbo. One would describe these motors as well powered, with plenty of torque to get them moving and be exciting. Think back to when you drove that old 1.6L Nissan 4 banger in high school and how gutless it was, but then you bought your first sports car later, and maybe you stayed in the Nissan family and bought at 3.7L 370Z. You touched that throttle and wow were you excited from the big displacement V6. Or maybe you jumped to your first muscle car and picked up a Mustang GT with its lovely V8 motor. Talk about power on demand.
I think we are all on the same page now, so say you choose to turbocharge that Mustang GT with its big V8 motor. Well now it has what we talk about as turbo lag. You get into the gas and while there is still the same power you had before you turbocharged the big V8, its not the power that you have once that turbocharger comes in and feeds your motor with gobs and gobs or air. So we complain and tell all our friends how we should have gone with a supercharger, or we bash everyone on the Internet who doesn’t choose a really small quick spooling turbo and that they are stupid for driving such a car on the street with lots of turbo lag. We argue with them that their car is no longer “streetable” and must be a drag car.
This is the biggest optical elusion to ever hit the automotive hobbyist and here is why. Ask yourself was the car quick before? Did it have good low-end torque and power before? Then why all the complaining of lag now and how it is no longer a street car? Well……..it’s because we as car enthusiasts have a short term memory. In 1999 when corvette came out with a 350 hp engine we thought the car was SO FAST, yet now go ride in one. You will be asking yourself why the car is so slow, and how you could have ever thought this was fast. Same thing happens when people turbocharge a car or drive a turbocharged car. They define the cars torque and horsepower as what they feel when the turbocharger is all in, so anything less than that sort of power we then describe as lag……but is it really lag as we think? Is the motor completely gutless till the turbo comes in? Should it really come with such a negative connotation that enthusiasts complain about it and companies make false marketing statements about it? Now to be fair, small displacement people complaining about lag and the lack of performance before the turbo lights up fine, but should we be complaining about the power of the car on a large displacement motor before the turbo kicks in?
Here is a gross example (this is a true story). A viper owner looking for more power started looking into forced induction. After getting on the viper forums and reading about the “lag” of turbochargers he went with a positive displacement blower for: “instant power and no annoying turbo lag.” Wow….what an interesting idea. The owner has now fallen into the turbocharger lag trap and now believe his viper will be gutless and have no power till the turbo comes in. The 8.2L v10 viper makes over 450 ft/lbs of torque at something like 2200 rpm and this owner doesn’t want to “wait for the power” so he avoided turbocharging? What is the world coming to? To conclude the story the owner did end up getting a supercharger, but sold the car shortly after as it would spin its wheels everywhere and became hard to drive. Later he told another Viper owner to “turbo their car so that the boost pressure could be variable and controlled. That with options like boost by gear, turbo was the way to go.”
Hopefully you think a little differently about turbo lag. It doesn’t have to have a negative connotation. Instead enthusiasts should invite the excitement of having a duel nature personality motor. One could argue it’s like having two motors all in one that can match the mood your in. Can be gentle and soft with decent gas mileage when you want, and an absolute animal when the time is right.
To sum it all up, don’t be like the Road & Track author. Ask yourself where your vehicle will be used the most and be honest with yourself if lag is really the big deal the internet wants you to think it is. And to conclude, look up any automotive writter on Ferriari's what the most iconic/best Ferrari of all time is? Nine times out of ten they will tell you the Ferrari F40. Why is that ironic……it’s one of the few turbo charged cars Ferrari has ever made. KABOOM, can't argue with that.
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How to Turbocharge and Tune your Engine
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