Does boost lag add character?

Lag is giving your opponent a gentlemanly head start.

My modded cars run properly sized ball bearing turbos, I don't get lag.

In reply to Honsch :

It's wonderful if you can afford the good stuff. Choosing to build for the challenge means the budget for turbo's has to be tiny. 
 But with knowledge much can be done on a tiny budget look at the Nelsons. They are impressive. 

Ball bearing turbos have been on production cars for more than two decades. They're not necessarily the big money choice :) Properly sized doesn't cost extra. 

With 70s turbo tech in the garage i definitely enjoy some lag and the following rush to the red line. It makes the car feel 50% faster than it really is. It feels much faster than a modern car with the same kind of performance, for me feeling faster is much more important than what the stop watch says, since im in it for the fun. But of course if it's way to much lag it starts getting annoying instead. 

I always thaught it would be fun to built a compressed air assist in to a turbo system. Adding it to the hot side would cool the exhaust gasses effectively removing energy so this got me thinking could you add it to the cold side?  A servo controlled air jet of compressed air on the cold side controlled by software the senses throttle change over a given period of time with a time delay to control its cut off as well as monitor monafold pressure to limit over boost?  

dean1484 said:

I always thaught it would be fun to built a compressed air assist in to a turbo system. Adding it to the hot side would cool the exhaust gasses effectively removing energy so this got me thinking could you add it to the cold side?  A servo controlled air jet of compressed air on the cold side controlled by software the senses throttle change over a given period of time with a time delay to control its cut off as well as monitor monafold pressure to limit over boost?  

I'd need to dig, but I could have sworn I read in a magazine AGES ago about some drag racing import (I can't remember what it was supra, s14, civic possibly) had an obnoxiously large turbo on it and they ran nitrous on the intake side to help spool when staging. No idea if it worked as intended or how successful it was. I want to say it was a blurb in super street? Like 15+ years ago now. 

So compressed air should function, would be less 'possibly explode things' as well.

Excessive turbo lag is not endearing it is annoying. The choice of the BMW pictured is an apt one. A friend used to race a 2002 turbo and he had to floor the gas pedal at the apex of a turn in order to get boost by the time he was exiting that turn. He said a miscalculation could be ...exciting (or boring, depending on whether he miscalculated for early or late).

One thing I do not understand is why people used to NA engines complain about lag with a turbo car.  What do they think the slow acceleration low down in the rpm band on an NA engine is? Cam lag?

Closest thing you get to an immediate boot in the back comes with supercharged cars, but then they run out of whoof earlier than the turbo does.

You want instant good acceleration?  Pony up the big bucks for a twin charged system using a supercharger down low and a turbo higher up.  The best is probably the Volvo T6 and T8 installations.

Another problem is that while manufacturers tend to opt for reasonably small turbos for fast action, people that want more power often go to a too large turbo and end up with excessive lag and then bitch about it even though they caused it.

I run a 2.0 in my daily driver that came with 260 bhp stock. I had the sense when modding it to stop with a larger impeller that gave very good performance lower down, and have 375 bhp/375 Tq. Others, hungry for power, use a much larger turbo that results in 450+ higher up but has significant lag down low. Of course then they complain about the lag, having caused it themselves.

wspohn said:

One thing I do not understand is why people used to NA engines complain about lag with a turbo car.  What do they think the slow acceleration low down in the rpm band on an NA engine is? Cam lag?

Shape of the power curve and turbo lag aren't the same.  Any engine needs to be in its powerband (however wide or narrow that may be) to make good power.  But with a laggy turbo, just getting the revs up isn't the whole picture.  You still get a delay in power production as you come back into the throttle from closed throttle even though you've downshifted to get into a good part of the power curve.  An NA engine doesn't have that problem. 

Pete. (l33t FS) said:

I would not want to confuse powerband with lag.  A turbo that hits late and hard is just sized that way.  Laggy turbos accelerate slower than the engine does - they lag behind the engine.

Ever drive a car that built no boost in 1st gear because the engine accelerated too quickly?

That's a big point. A turbo that only makes boost over a particular RPM, but does so as soon as you reach that point is something I'd call character, while one that takes a notable lag to start delivering boost when it hits that point is more of an undesirable flaw.

MadScientistMatt said:

That's a big point. A turbo that only makes boost over a particular RPM, but does so as soon as you reach that point is something I'd call character, while one that takes a notable lag to start delivering boost when it hits that point is more of an undesirable flaw.

The current prices for 930 turbos would seem to argue against the undesirability. :)

And yes, boost threshold (minimum RPM for boost) and lag are different things, but they are correlated.  All else being equal, a larger turbo means a higher boost threshold, a higher power potential, and yes, more lag.  Improved tech like ball bearings, fancy lightweight exotic material wheels, twin-spool inlets -- they all improve things, but that tradeoff between size and response is still present, just shifted a bit.

I stand by my assertion that most modern turbo cars are undersized and that the engine package would be better if they accepted a minor amount more lag in order to allow it to make full boost all the way to redline.  To be clear I'm not saying I want a car with a response like a 930, but the minor amount more lag that's present it the relatively few modern performance-oriented turbo cars is completely acceptable to me.  

 This is also why I'm disappointed that F1 is abandoning the MGU-H part of their hybrid system.  Using an electric motor to spin up the turbo has the potential to really change that inherent tradeoff.  I suspect it doesn't really matter in the end though, EVs will probably get rid of turbocharged ICEs before we'd get an MGU-H in a street car anyway.

dean1484 said:

I always thaught it would be fun to built a compressed air assist in to a turbo system. Adding it to the hot side would cool the exhaust gasses effectively removing energy so this got me thinking could you add it to the cold side?  A servo controlled air jet of compressed air on the cold side controlled by software the senses throttle change over a given period of time with a time delay to control its cut off as well as monitor monafold pressure to limit over boost?  

Ford did it in a WRC Focus a couple decades ago.

Titanium pressure tank in the rear bumper, stored pressurized air from the turbo and released it to the intake as desired.

I forget if it was banned or Ford agreed to stop using it or if it simply was not worth the complication, but technically all air entering the engine did come through the restrictor, just not all at the same time.

DjGreggieP said:

dean1484 said:

I always thaught it would be fun to built a compressed air assist in to a turbo system. Adding it to the hot side would cool the exhaust gasses effectively removing energy so this got me thinking could you add it to the cold side?  A servo controlled air jet of compressed air on the cold side controlled by software the senses throttle change over a given period of time with a time delay to control its cut off as well as monitor monafold pressure to limit over boost?  

I'd need to dig, but I could have sworn I read in a magazine AGES ago about some drag racing import (I can't remember what it was supra, s14, civic possibly) had an obnoxiously large turbo on it and they ran nitrous on the intake side to help spool when staging. No idea if it worked as intended or how successful it was. I want to say it was a blurb in super street? Like 15+ years ago now. 

So compressed air should function, would be less 'possibly explode things' as well.

Nitrous to get the turbo party started is fairly old, I remember reading about it in the 80s.  A lot of standalone engine controllers that can do nitrous control have an option for it, too.

Exhaust energy spins the turbo, making the engine make more power gives the exhaust more energy.

In reply to codrus (Forum Supporter) :

I agree about modern turbos being undersized. Most modern turbo cars Ive driven, have a tiny turbo that run out of steam too early, but are also hampered by horrible boost control components or tune. I get production costs and a tune that has a wide margin for safety, but still. A tune on a 1.4T ecotec or a diverter valve on a fiat 124 feels like a completely different car.

In reply to codrus (Forum Supporter) :

It's considerably more efficient to use the electrical power to directly drive the wheels vs engine boost. The end goal is the same- wheel torque. 

In reply to alfadriver :

Is it? I would think 30-40hp of turbo energy could create hundreds more horsepower.

What interests me is the history of turbocompound engines, and the idea that one could generate a sizeable amount of power that way.

Pete. (l33t FS) said:

In reply to alfadriver :

Is it? I would think 30-40hp of turbo energy could create hundreds more horsepower.

What interests me is the history of turbocompound engines, and the idea that one could generate a sizeable amount of power that way.

But making that additional horsepower means more fuel used.  From a pure mechanical efficiency standpoint, it's better to put 20hp directly to the wheels vs into the turbo.  That doesn't necessarily work out the same from a "produce maximum power and do it as quickly as possible" perspective. 

In reply to rslifkin :

I see what you mean there.  I suppose it ends up being what the end goal is: power production or minimal fuel used for a given maintenance power level.

rslifkin said:

Pete. (l33t FS) said:

In reply to alfadriver :

Is it? I would think 30-40hp of turbo energy could create hundreds more horsepower.

What interests me is the history of turbocompound engines, and the idea that one could generate a sizeable amount of power that way.

But making that additional horsepower means more fuel used.  From a pure mechanical efficiency standpoint, it's better to put 20hp directly to the wheels vs into the turbo.  That doesn't necessarily work out the same from a "produce maximum power and do it as quickly as possible" perspective. 

The comparison is kind of nonsensical.  Yes, making less power and going slower is usually more efficient than making more power and going faster, but that doesn't really seem relevant to the thread.  If you're looking for pure efficiency, you probably want to dump the ICE entirely and go with a straight EV.

The reasons F1 dropped the MGU-H have to do with inter-team politics and R&D costs, nobody there really cares about efficiency.

I've had three different setups on my 87 Supra with a 1jz swap. Stock twins with a downpipe upgrade had fantastic response, but was limited to about 350whp before compressor wheels are at "might shatter" levels of boost.

Went with a mid sized Comp 6265 DBB 0.70 housing. Out on the open road, it was phenomenal. Response was acceptable, lag was minimal if you had the rpm's above 4k. Good turbo if you remain engaged and drive spirited. Pulled hard through 8k ish. However... at lower speeds, like autocross, below 4k happens a lot, especially if you're on a course large enough to need 2nd gear, which is a lot of them. It had to go. Max potential of this turbo was somewhere in the 650-ish hp range.

Put a Garrett G25-660 0.92 on it, and the response is more like the stock twins, but it can be pushed a LOT harder. On paper, it's down about 120whp versus the Comp, but you wouldn't know it from driving the thing. Transient response is amazing, at pretty much any engine speed, and it no longer has that dead spot that the larger turbo had when autocrossing. No regrets here, apart from misunderstanding fitment potential for the reverse rotation version, combined with my manifold. Oops. Test fit before coating parts, folks!

Point I'm trying to make, is it all depends on your desired use.

alfadriver said:

In reply to codrus (Forum Supporter) :

It's considerably more efficient to use the electrical power to directly drive the wheels vs engine boost. The end goal is the same- wheel torque. 

Plus you can get at least some of that electrical power from deceleration, which is energy that's normally thrown away. 

In reply to te72 :

That is exactly the path I don't want to follow.  Replacing turbo's to achieve my goal. 
 I've gone conservative trying to avoid that process.  I don't need power down below about 3500 rpm I don't want to go over 7000 rpm. I'd like to. Stay around 9-10 Psi would be comfortable. But 14 is still in my comfort zone 

codrus (Forum Supporter) said:

 

The comparison is kind of nonsensical.  Yes, making less power and going slower is usually more efficient than making more power and going faster, but that doesn't really seem relevant to the thread.  If you're looking for pure efficiency, you probably want to dump the ICE entirely and go with a straight EV.

The reasons F1 dropped the MGU-H have to do with inter-team politics and R&D costs, nobody there really cares about efficiency.

 

It does matter.  The MGU-H costs a TON of money and adds very little.  Nowhere close to it's cost and complexity.  The goal is to put torque to the wheels, and using the less efficient path does not shorten lap times.  It's faster and more efficient to just drive the wheels.  Remember, there's a time delay from when you compress the intake air until you see it at the wheels, whereas putting that energy to the wheels does not have a delay.

If it were as useful as the basic hybrid system- which costs more- it would stay.

Pete. (l33t FS) said:

In reply to alfadriver :

Is it? I would think 30-40hp of turbo energy could create hundreds more horsepower.

What interests me is the history of turbocompound engines, and the idea that one could generate a sizeable amount of power that way.

So we don't need to start the discussion that using exhaust waste energy to turn the turbo is more efficient than electrical energy, do we?  It it were, everyone would be using belt driven superchargers instead of exhaust driven.  And remember, this is a boost limited system- so just adding more boost via electrical energy isn't an option.

The whole point of the e-boost systems is to reduce the boost lag, which is another way of saying a faster delivery to the wheels based on the driver input.  Given the delay of the spin turbine-increase intake pressure-combust more energy vs. just putting that same energy directly to the wheels- e-boost vs. more hybrid drive does not make sense- especially when one factors in cost and complexity.

alfadriver said:

So we don't need to start the discussion that using exhaust waste energy to turn the turbo is more efficient than electrical energy, do we?  It it were, everyone would be using belt driven superchargers instead of exhaust driven.

In a street car context you would only need to spin the turbo up when there isn't enough exhaust energy to spin it otherwise.  Once the exhaust gas is flowing and the turbo is spooled you shut the electric motor back off -- this is not an electric supercharger.

Also unlike the classic "electric supercharger", you don't need to power it with the alternator because this presupposes a hybrid car with a lithium/etc battery.  You charge that battery using an MGU-H in generator mode instead of a wastegate, recovering more of that wasted exhaust energy than you could get otherwise.

Incidentally, I suspect that if any OEMs were actually trying to build them these days, pure electric superchargers probably would be more efficient than belt-driven ones.  We're seeing an ongoing trend away from belt-driven accessories (electric power steering, electric water pumps, electric AC compressor) because the efficiency losses of turning that pulley when you don't need the accessory are higher than the efficiency losses of making and storing electricity.  You don't see it though because basically everyone has given up on superchargers (other than turbos) at this point.

The whole point of the e-boost systems is to reduce the boost lag, which is another way of saying a faster delivery to the wheels based on the driver input.  Given the delay of the spin turbine-increase intake pressure-combust more energy vs. just putting that same energy directly to the wheels- e-boost vs. more hybrid drive does not make sense- especially when one factors in cost and complexity.

Putting electric power to the wheels is not going to deliver the same degree lag mitigation as spinning up the turbo.  A turbo can easily double the power output of the motor, so we're talking about a need for over 100 hp to deliver the same kind of response. 

In reply to codrus (Forum Supporter) :

The problem with direct driven supercharging is that you use the mechanical power to make boost- which takes off some of the energy that can go down the driveshaft.  Whereas the whole point of exhaust energy is that you try to use as much as the waste heat going down the exhaust to recover some of it.  That's why exhaust supercharging is more popular than direct drive.

Still- this is a boost limited system- so the entire point of the e-boost system is to get to that limit faster.  And the whole point of that issue is to make wheel torque faster.  And direct drive of the wheels is the fastest path of using your electrical energy.

E-boost does not make more power in a boost limited system, it just makes it quicker.