Sequential, compound or twin Turbo's

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
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Bandit1216
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Joined: Fri Oct 05, 2018 3:55 pm
Location: Netherlands

Sequential, compound or twin Turbo's

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Hi Guys

I hope this is allowed since there's not much F1 relevance:

For yours I'm walking around with the idea's what to do, should I ever win the lottery. I guess I'll never win it.

I would like to bring an idea past you and see what you think. I've been thinking why one almost never see's very small turbo's next to very big ones sequential or compounded. Like this one:

Image

I've seen small/big combo's, but almost never a big difference and mostly parallels. Probably because my idea is hard to get right and expensive, but even in racing it's rare (I think)

I would think this would be an excellent idea. Sticking to a 2 liter inline 4 as a reference, a very small one could spin as early as 1 bar @1500 rpm and perhaps 1.5 at @1750, turning the engine into a 4 to 5 liter from than point on. The very big one would then react on this volume and start at say 3000 (up to 8000), whereas it would have only started spinning at 5000 without the small one. (Just some figures out of my head.)

With this in mind, a 2 liter with 600 bhp's that doesn't have a turbo lag of 2 months, would not be very hard. A check to sadev for a 4 x 4, 1000 Nm gearbox would be advisable though. It will probably break more than temptation island. Not cheap, but possible.

As with the nizpro in the picture, I would think the small one would need to be exhausted though the big one. I would think it should at least start to be waste gated at 0,5 bar lower than the big one. If the small one would be at 1.5 and the big one at 2 bar for example, otherwise the small one would surely reach breaking point rpm at 4000 engine rpm orso. A very big waste gate would be needed closed at 1.5, yet fully open at 2, and in turn also be fed into the big ones exhaust inlet. It would be hard to select a pair that's are a perfect match for sure.

The inlet air would also need to be diverted in a way the big turbo will not surge the small one somehow. What do you think?

Parallel to this I would like to ask what you think about twin turbo's fed from 1 valve each cylinder. Hard to do, but Lancia did it ones.

Image

Since I'm a Peugeot man (sorry) underneath PSA UX and EW engine heads will also have that option, albeit the plumbing would be hard.

Image

This twin turbo fed from 1 valve each cylinder will work fine with 2 equally big turbo's, but what about 2 different sized ones? Would the path of least resistance be taken dominantly, even when the paths split so early in the head, being so close to the actual explosions? It would think the first pulse in the exhaust, the actual leftover from the explosion, would not take the path of least resistance very much, yet the actual outlet stoke will by some extend.

I hope my English is good enough so you understand my twisted mind.
But just suppose it weren't hypothetical.

mrluke
mrluke
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Joined: Fri Nov 22, 2013 7:31 pm

Re: Sequential, compound or twin Turbo's

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Assuming this is relating to racing engines rather than commuters, boost threshold doesn't tend to be that big an issue. The engine isnt going to spend much of its life at 1,500 rpm. Yes, you want a nice wide powerband, but it doesnt need to start that low. Therefore your turbo selection will be to maximise the rpm range that you will spend the most time in.

What we do see a lot of is development of anti lag strategies and by that I mean how quickly boost is available under transient throttle conditions above your boost threshold. e.g. if you are at 6000rpm and you go from 5% throttle to 100%. These technologies have varied from pre turbo throttles, throttle jackers, fresh air systems, subaru's rocket system etc right up to modern day MGU-H which effectively makes the turbo into an electronic supercharger decoupling spool from rpm/mass flow.

Jolle
Jolle
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Joined: Wed Jan 29, 2014 9:58 pm
Location: Dordrecht

Re: Sequential, compound or twin Turbo's

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mrluke wrote:
Tue Feb 08, 2022 1:29 pm
Assuming this is relating to racing engines rather than commuters, boost threshold doesn't tend to be that big an issue. The engine isnt going to spend much of its life at 1,500 rpm. Yes, you want a nice wide powerband, but it doesnt need to start that low. Therefore your turbo selection will be to maximise the rpm range that you will spend the most time in.

What we do see a lot of is development of anti lag strategies and by that I mean how quickly boost is available under transient throttle conditions above your boost threshold. e.g. if you are at 6000rpm and you go from 5% throttle to 100%. These technologies have varied from pre turbo throttles, throttle jackers, fresh air systems, subaru's rocket system etc right up to modern day MGU-H which effectively makes the turbo into an electronic supercharger decoupling spool from rpm/mass flow.
Indeed, racing engines have to be efficient at a very narrow power band, anything else is a waste.

The fun thing about that, is that the use and development of turbo racing engines look more like small underpowered cars then hypercars, who have to go around roundabouts and do trackdays. A Peugeot 207 with a small engine is driven within it's small power band all the time and doesn't really care about a bit of lag.

So, for those hyper sports cars, a multi turbo setup would be fun, but at the same time a pit pointless, because electrification of some parts in the drivetrain just does the same job but then better. Think P1 or the SF90 Stradale.

another fun concept to look at is the early versions of the VW TSI, with the compressor in parallel of the turbo. In theory a brilliant concept, no lag and plenty of torque at low rpm (the compressor was clutched and had a valve system to switch itself out of the air intake) but at the same time, when you drove around town, it as almost all of the time with the compressor engaged, guzzling gasoline (but so much fun to ride together with that first DSG!)

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Bandit1216
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Joined: Fri Oct 05, 2018 3:55 pm
Location: Netherlands

Re: Sequential, compound or twin Turbo's

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Yeah

Well my goal would be to build a rallycross-ish street car with stupid power that is still fun when driven in normal traffic. That is indeed a demand not seen very often and thus not seen often.

Wonder why the nizpro seems to have this setup. Perhaps the propeller curve is steeper than the turbo curve so they need the torque at low rpm to get going. A planing boat also has an strange torque demand. Very different reason, yet the same outcome.
But just suppose it weren't hypothetical.

Jolle
Jolle
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Joined: Wed Jan 29, 2014 9:58 pm
Location: Dordrecht

Re: Sequential, compound or twin Turbo's

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Bandit1216 wrote:
Tue Feb 08, 2022 2:32 pm
Yeah

Well my goal would be to build a rallycross-ish street car with stupid power that is still fun when driven in normal traffic. That is indeed a demand not seen very often and thus not seen often.

Wonder why the nizpro seems to have this setup. Perhaps the propeller curve is steeper than the turbo curve so they need the torque at low rpm to get going. A planing boat also has an strange torque demand. Very different reason, yet the same outcome.
Big turbo on a TSI engine, with the compressor still in use? a Polo would be a fun base...

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pgfpro
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Joined: Mon Dec 26, 2011 10:11 pm
Location: Coeur d' Alene ID

Re: Sequential, compound or twin Turbo's

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I personally would do a compound setup. I built three compound setups so far. A compound setup will give you the low-end torque of the small turbo and the high-end HP of the larger turbo. Drivability will be great. My first one was a 62mm turbo feeding a 40mm compressor turbo. Engine is a 4G63 2.0L. The large turbo was a mid-mount. It worked extremely well, full boost 42psig at 3800rpm. My new set up is going into my 71 Camaro it is an 88mm compressor feeding a 59mm compressor. Advantages are low end torque, low back pressure, both turbos' can be in their high efficiency area of their compressor maps. Disadvantages packaging and complex charge pipe lay out and hot side piping layout. I was going to post pics, but I don't have an image account right now.
building the perfect beast

sosic2121
sosic2121
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Joined: Wed Jun 08, 2016 11:14 am

Re: Sequential, compound or twin Turbo's

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Bandit1216 wrote:
Tue Feb 08, 2022 1:07 pm
Since I'm a Peugeot man (sorry) underneath PSA UX and EW engine heads will also have that option, albeit the plumbing would be hard.

https://scontent-ams4-1.xx.fbcdn.net/v/ ... e=62083622
I think only xu9j4 and xu10j4 (Mi16) have 8 exhaust ports.
This is xu10j4 head :D

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Bandit1216
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Joined: Fri Oct 05, 2018 3:55 pm
Location: Netherlands

Re: Sequential, compound or twin Turbo's

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sosic2121 wrote:
Tue Feb 08, 2022 9:23 pm
Bandit1216 wrote:
Tue Feb 08, 2022 1:07 pm
Since I'm a Peugeot man (sorry) underneath PSA UX and EW engine heads will also have that option, albeit the plumbing would be hard.

https://scontent-ams4-1.xx.fbcdn.net/v/ ... e=62083622
I think only xu9j4 and xu10j4 (Mi16) have 8 exhaust ports.
This is xu10j4 head :D
Ahhh. I stand corrected. They changed that with the EW.
But just suppose it weren't hypothetical.