In engines with more than one turbocharger, how is the lag lessened?
Posted by HP_594@reddit | cars | View on Reddit | 15 comments
I was watching Initial D Fourth Stage, specifically the race between Keisuke Takahashi and Kyoko Iwase.
Keisuke is driving his FD3S RX7, which comes with the factory fitted twin turbo 13B, while Kyoko’s car, albeit the same model, has a single turbo 13B, chosen specifically for the hill climb course.
Kyoko’s car is easy to drive in the touge roads due to less power, but also suffers from turbo lag. However, Keisuke’s car has more power and less turbo lag, but it makes the car harder to navigate the touge.
So it begs the question, how does a twin turbo setup lessen lag in general? And how is it done in the case of triple turbo and quad turbo engines? Is it any different from that of a twin turbo?
ShesATragicHero@reddit
Honest answer?
Cubic inches.
hi_im_bored13@reddit
Since the other user answered your question, do also keep in mind there are different ways to set up turbos.
parallel turbos, where one half of the headers goes into one turbo, the other half into the other, they both run at the same time and just push a lot of air
sequential turbos, where there is one smaller turbo feeding from all the exhaust and likewise one larger turbo, the logic here is that the smaller turbo spools up quicker and gives some low end kick, then the larger turbo kicks in and gives you top end
Lots of early tt setups were to avoid lag, like in the rx-7, and were sequential. As turbo technology has evolved, lag is far less of an issue and we can deliver turbos that work well across the whole range, most tt setups you see now are parallel
ShesATragicHero@reddit
But BMW is peak German engineering and so reliable!
HP_594@reddit (OP)
What about triple turbo setups?
AFAIK, BMW diesels (some of them) had three turbochargers.
hi_im_bored13@reddit
just read that part of ops comment and edited my post just as you commented this lol.
I don’t know much about them. from the little i recall it’s one large turbo feeding into a parallel pair but i’d love to be corrected here if necessary
Przedrzag@reddit
This video seems to imply a triple sequential setup
Crazy95jack@reddit
This is the best answer. But now we can have (big) turbos with electric motors attached to reduce lag even further.
colin_staples@reddit
And in turbocharged performance cars that also have a hybrid system (McLaren P1, as one example) the hybrid system fills in the lower part of the torque curve to mask any turbo lag.
inter_fectum@reddit
Another interesting factor in lag is the cooling system. Maybe someone with more knowledge then myself will chime in and explain, but my understanding is air to liquid intercooling produces less turbo lag because water can transfer more heat so the volume of the intercooler is smaller.
Also, the platform I have the most daily experience with the single turbo B58 & two parallel turbo S58 the single turbo has much more torque down low, while the S58 only really hits at ~3500. That may just be tuning though.
DoctorBorks@reddit
Single turbo is deemed more reliable in the case of the fd rx7 as well. Variable geometry turbos like Porsche use today are used to make big turbos impeller physically smaller thus reducing the amount of exhaust pressure required to spool the turbo.
RamenNoodles3351@reddit
If you want more detail on this topic and turbocharging systems in general I would highly recommend Maximum Boost by Corky Bell. You can get a used copy on eBay for like $15 or find the pdf for free online. It’s a great read and extremely informative on how it all works and how you can do it yourself.
QLDZDR@reddit
Nitrous shot at the right moment
Nyarka@reddit
I think it has been answered -- in twin turbo setup, if you aren't doing any ECU stuff / anti-lag, you want a hybrid setup where are smaller turbo kicks in sooner/ lower RPM and give you some boost until higher rpm where the larger turbo kicks in.
Just for general driving, old school driver typically try to keep their rpm high around corners so that the turbo is always on. It may also just be their driving habit (in addition to controlling car traction) but watching videos from early 90s or so where you can see drivers maintain their rpm around most corners may give you some idea also (yes, that includes Senna and Keiichi Tsuchiya/Options/Video Option/Best Motoring) in youtube.
bandito-yeet-dorito@reddit
In many cases, each turbo manages one bank of cylinders, or 3 cylinders of an inline 6, or in the RX7s case, likely one for each rotor. This allows for smaller turbos, as each is only dealing with a few cylinders each. Small turbos means less lag(usually).
lsbich@reddit
They’re smaller and easier to spin basically