RE: Let turbos be turbos: Tell Me I'm Wrong
Discussion
SuperchargedVR6 said:
themanwithnoname said:
SuperchargedVR6 said:
Same. Last time I dumped, it was via a big old 50mm TIAL blow off valve, which to be fair sounded far chunkier than those silly little Forge things.
Excellent! You're giving me bad thoughts - I'm about to embark on a Subaru adventure. I can see Tial assisting in making both some whooshy and some screamy noises in my near future - I do like an external wastegate as well. 
On the subject of turbos, I often hear reference to "wastegate chatter". I'm no expert, but the only noises I can hear from a turbo is the whoosh of air and surge when excess boost isn't dumped quickly enough i.e. the famous "cha cha cha cha". What the heck is 'wastegate chatter'?
s m said:
SuperchargedVR6 said:
themanwithnoname said:
SuperchargedVR6 said:
Same. Last time I dumped, it was via a big old 50mm TIAL blow off valve, which to be fair sounded far chunkier than those silly little Forge things.
Excellent! You're giving me bad thoughts - I'm about to embark on a Subaru adventure. I can see Tial assisting in making both some whooshy and some screamy noises in my near future - I do like an external wastegate as well. On the subject of turbos, I often hear reference to "wastegate chatter". I'm no expert, but the only noises I can hear from a turbo is the whoosh of air and surge when excess boost isn't dumped quickly enough i.e. the famous "cha cha cha cha". What the heck is 'wastegate chatter'?
About 30s in is real wastegate 'chatter' which is the wastegate managing peak boost https://www.youtube.com/watch?v=_K0LFadOKBc
About 35s in is a bit of surge https://www.youtube.com/watch?v=JCG9iWbYJoc
Of course its mostly knowing the difference between a ftftftftft sound and a tsutututututu sound. ft is good tu sounds good but is actually not great for your turbo - especially journal bearing ones.
..car makers cant win really...produce an old fashioned turbo engine and people moan about lag, produce one without lag and people moan about lack of a "kick". I loved the punch of my old 1.9 PD TDI but it certainly was scary when it ran out of boost mid overtake!! On the other hand I love the fact that my Mazda 6 2L petrol is sleepy most of the time, but seems very strong at the top end when I really go for it. On the Shaftesbury to Warminster road past East Knoyle there is a short piece of 3 lane dual carriageway up a pretty steep hill. I vividly remember my A3 TDI running out of gas in 4th gear mid-overtake having been piling on the speed a few seconds earlier and struggling past a slower car. This year on the same bit of road, My Mazda was charging towards the limiter in 3rd gear and despite the lack of torque made a similar overtaking move much more comfortable....
So personally I want a turbo with good grunt AND a strong top end....
So personally I want a turbo with good grunt AND a strong top end....
beenandgone said:
Interesting article. Perhaps I'm biased having not driven many modern turbos, but my skyline gtst is always a blast; a near 20 year old car with absolutely no driver aids. Not doing bad for an unopened engine...revs out to 7200rpm and a great sense of occasion. If you choose to let the boost wind on she gets lively, otherwise when you're on it she's always on boost between gears. Great fun.
Some friends of mine have had tuned skylines and they were great fun.
The picture, you show appears to be a Garrett (Honeywell engine boosting systems ltd) Variable nozzle turbo, which for a short time at the end of the last century, I was involved in the new product introduction of, as an Advanced manufacturing Engineer.
At the time the Vanes, could not cope with the temperatures in petrol exhausts, so the variable geometry was limited to deisels.
It also seems to have some sort of inlet pressure valve ? Dump valve perhaps.
Not sure that 15 years later they have managed to find a material to survive, but it would be great if they could because look at what the VNT does !
So when the Escort Cosworth was introduced it had a big turbo, but lots of lag, allowing tuning within the motorsport regulations, but later models had a smaller turbo for drivability when standard.
the GREAT thing about the way the vanes work on a VNT is that at low engine speeds a big turbine wheel would take a lot to get up to speed, and generate any boost at the other end, so the nozzles (vanes) close meaning the exhaust has to squeeze through a smaller gap, which means more velocity, which means the wheel spins faster, which means more boost at the other end . Obviously as you get to higher revs, the vanes open, and now you have a big turbine wheel which does not limit the exhaust back pressure so much as a smaller wheel.
Throw in Variable valve timing and sophisticated engine management and you get something which is all things to all men.
So when the Escort Cosworth was introduced it had a big turbo, but lots of lag, allowing tuning within the motorsport regulations, but later models had a smaller turbo for drivability when standard.
What does the customer want. No lag, high mpg and lots of torque and power.
At the time the Vanes, could not cope with the temperatures in petrol exhausts, so the variable geometry was limited to deisels.
It also seems to have some sort of inlet pressure valve ? Dump valve perhaps.
Not sure that 15 years later they have managed to find a material to survive, but it would be great if they could because look at what the VNT does !
So when the Escort Cosworth was introduced it had a big turbo, but lots of lag, allowing tuning within the motorsport regulations, but later models had a smaller turbo for drivability when standard.
the GREAT thing about the way the vanes work on a VNT is that at low engine speeds a big turbine wheel would take a lot to get up to speed, and generate any boost at the other end, so the nozzles (vanes) close meaning the exhaust has to squeeze through a smaller gap, which means more velocity, which means the wheel spins faster, which means more boost at the other end . Obviously as you get to higher revs, the vanes open, and now you have a big turbine wheel which does not limit the exhaust back pressure so much as a smaller wheel.
Throw in Variable valve timing and sophisticated engine management and you get something which is all things to all men.
So when the Escort Cosworth was introduced it had a big turbo, but lots of lag, allowing tuning within the motorsport regulations, but later models had a smaller turbo for drivability when standard.
What does the customer want. No lag, high mpg and lots of torque and power.
The turbo design is going to become less important for matching all engine situations (mainly transients) since we're seeing more hybrid power trains that can simply have torque-fill via electric motors while coming onto boost etc.
Eventually we'll probably see compressor and turbine decoupled so the turbine just scavenges exhaust gasses at opportune times (steady state) and generates electricity that is then used for in-fill when the compressor isn't spinning optimally, which itself can be spun up when required.
This will improve packaging and efficiency further I think. OK outright efficiency at certain points will be worse, but trying to make a turbo with a fixed shaft and a turbine and compressor to cover wide ranges is just bonkers vs decoupling and in-filling approaches.
Dave
Eventually we'll probably see compressor and turbine decoupled so the turbine just scavenges exhaust gasses at opportune times (steady state) and generates electricity that is then used for in-fill when the compressor isn't spinning optimally, which itself can be spun up when required.
This will improve packaging and efficiency further I think. OK outright efficiency at certain points will be worse, but trying to make a turbo with a fixed shaft and a turbine and compressor to cover wide ranges is just bonkers vs decoupling and in-filling approaches.
Dave
s m said:
Often it is turbo stall - the sound of the compressor blades trying to "chop" through a wodge of compressed air as the throttle is closed
No, that's not it.The sound is because of the surge.
When a turbo is operating inside the surge line for a given speed, a reduction in flow (ie reducing throttle opening) will result in an increase in pressure rise across the turbo and the system stabilises at the new flow.
Outside the surge line, as flow reduces, the pressure rise across the unit actually reduces as the turbo begins to stall, this leads to a reduction in flow which leads to a reduction in pressure rise with the result flow collapses. The compressor then re-establishes flow, pressure rise & flow increase but if the conditions remain the same, the compressor will stall again and flow will collapse again.
This cycle will repeat until the conditions that caused the stall are removed (ie turbo slows or flow can be established inside the surge line). This causes the sound.
A recirc/dump valve allows flow to be maintained to prevent surge.
The spinning assembly looses speed due to friction and work done. Work done is proportional to the mass of air moved by the compressor, and if the unit is not moving air, then it will slow less, however a dump valve maintains flow (to prevent surge) and actually contributes to reducing compressor speed.
Mr Whippy said:
The turbo design is going to become less important for matching all engine situations (mainly transients) since we're seeing more hybrid power trains that can simply have torque-fill via electric motors while coming onto boost etc.
Eventually we'll probably see compressor and turbine decoupled so the turbine just scavenges exhaust gasses at opportune times (steady state) and generates electricity that is then used for in-fill when the compressor isn't spinning optimally, which itself can be spun up when required.
This will improve packaging and efficiency further I think. OK outright efficiency at certain points will be worse, but trying to make a turbo with a fixed shaft and a turbine and compressor to cover wide ranges is just bonkers vs decoupling and in-filling approaches.
Dave
If you pick an RPM point, say 3500 to 4000 RPM, it's much easier to design the whole engine, including turbo to run efficiently under load at one point, rather than worry about the whole 700 to 10000 rpm, so if you only use the engine to generate electrical power for the battery, you can make it VERY efficient. That it won't actually be able to run at 3499 or 4001 rpm won't matter. Eventually we'll probably see compressor and turbine decoupled so the turbine just scavenges exhaust gasses at opportune times (steady state) and generates electricity that is then used for in-fill when the compressor isn't spinning optimally, which itself can be spun up when required.
This will improve packaging and efficiency further I think. OK outright efficiency at certain points will be worse, but trying to make a turbo with a fixed shaft and a turbine and compressor to cover wide ranges is just bonkers vs decoupling and in-filling approaches.
Dave
Having worked with application engineers at Garrett, I'd say the complication of designing the turbo to work at all load and rev ranges is the bit that did their mental health most harm.
SuperchargedVR6 said:
Tial is serious stuff! I had a Tial 44mm MVR external gate (water cooled) and what a thing of beauty it was. The project was a Garrett GT35R on a VR6 engine. That made some old school noises for sure
Love this onehttps://www.youtube.com/watch?v=CnRxJclk9UQ
Pit Pony said:
Having worked with application engineers at Garrett, I'd say the complication of designing the turbo to work at all load and rev ranges is the bit that did their mental health most harm.
Yes it's amazing how much current turbos work across such wide rev ranges and do so well generally at all points along it... given what things used to be like in the 80s and 90s.It obviously takes a lot of development work, since most of these things are feedback loop in nature too, going around in circles chasing efficiencies, which then move a bit when you move to find efficiency somewhere else
I can see how mental health gets a battering.
But I do kinda see the whole logic today becoming quite archaic given the increasing presence of regen/hybrid systems. Having a turbo running all the time is just like having an alternator running all the time, or cooling fans, or whatever else that we've seen slowly decoupled from engines and replaced with electric drive or clutched variants over the years!
Dave
Dan Trent said:
If we're stuck with turbocharged cars why not make them feel turbocharged?
Has that Chris Harris bloke been copying your homework for his latest column on that American website?http://jalopnik.com/dear-automakers-please-stop-ma...
The F10 M5 feels turbocharged, the power delivery builds and you get a real kick at 4K through to 7K it goes ballistic over that rev range, it has plenty low down as well makes 500ft/lb from 1500-6000rpm, it never feels laggy but it's underpinned with a 4.4V8 but you always feel you get rewarded for going through the rev range, if the tyres have the grip!
Mr Whippy said:
Too many arbitrary words there that are meaningless to use in absolute terms.
What is turbocharged meant to 'feel' like?
And torque low down, at 1500rpm, but not lag?
So at 1500rpm there is no lag between full throttle and receiving full torque? Not even 100ms?
I call b
ks 
Dave
I'd suggest you improve your reading comprehension. What is turbocharged meant to 'feel' like?
And torque low down, at 1500rpm, but not lag?
So at 1500rpm there is no lag between full throttle and receiving full torque? Not even 100ms?
I call b
ks Dave
Having the "feeling" that something isn't there is just that, it's the experience of the user, not a absolute statement of absence.
But I guess if you haven't experienced differing ends of the spectrum you might not understand.
otolith said:
Depends why lag bothers you I guess - if the engine is large enough displacement you aren't going to have to wait until something happens, but if it's the rubber band feeling that annoys you that will still be an issue on a big turbocharged engine.
Do you mean lag, or the lack of boost at lower revs ?otolith said:
I mean lag, though the same argument would apply to boost threshold. Personally, it isn't any lack of performance during lag that bothers me about it, so a bigger engine wouldn't improve matters.
I see what you mean. I nice powerful Turbo engine does have character but when you get back in a large revvy instantly responding n/a engine it's a breath of fresh airEach are fun I in there way.
Wills2 said:
I'd suggest you improve your reading comprehension.
Having the "feeling" that something isn't there is just that, it's the experience of the user, not a absolute statement of absence.
But I guess if you haven't experienced differing ends of the spectrum you might not understand.
But it is there, and it is still laggy.Having the "feeling" that something isn't there is just that, it's the experience of the user, not a absolute statement of absence.
But I guess if you haven't experienced differing ends of the spectrum you might not understand.
People used to say the 1.8T VAG unit when it arrived was amazing, lag-free, turbo that didn't feel like it was turbo... but it still was.
997T and it's VNT turbo, still laggy, just less so.
M5 V8 turbo, still laggy, just less so.
By definition a turbo will always be noticeably laggy.
If you feel it's not there then that is just your feeling. Feelings are hugely fallible. Bottom dyno is the most misleading dyno of them all. It makes a Renault 5 Turbo feel like 300bhp
Dave
Gassing Station | General Gassing | Top of Page | What's New | My Stuff