Twin turbo a 4cylinder engine (1big and 1 small turbine)

mag9556

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mag9556

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Hi all,

Nothing to do try to do some research online but seem a bit blur here.
Let say if we have K3VETT with 1 ori IHI RHF4 turbine for pickup and another with bigger size for end power, what will be the advantage and disadvantages ya..
or we change to one IHI RHF3 and another one bigger..

Thinking of this since if small turbine no end power and big turbine will lag..

Any know please share ya:rock:
 

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vr2turbo

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How will you install so that small will feed low and big will feed high? I know the SC and TC combi system does the same thing. SC boost low and TC boost high but many say difficult to do....
 

ixeo

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ixeo

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No such thing as a K3VETT...

You answered yourself... big turbo will lag, small turbo run out of breath. What’s your objective anyway?
 

mag9556

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mag9556

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Wah.. so fast found the answer d... lol:adore:
Where got finish.. what is the advantage and disadvantage d...:hello:

No such thing as a K3VETT...

You answered yourself... big turbo will lag, small turbo run out of breath. What’s your objective anyway?
K3VETT... planing to do R&D more to come out with one d..:laugh:
finding something different to discuss d...
trying to pull the engine juicy higher without lag

:marchmellow:
 

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Izso

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nice wira .. but i wonder how he runs it? Daily driven or race only spec? Cuz this K3VETT fella sounds like a daily
 

Nightstalker1993

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Well, for one, it's called compound charging, not twin turbo and the plumbing is really complicated. I highly doubt you would want to go down that route as I don't think you have the engine bay space to accommodate it.

Advantages is that you get the power low down from the small turbo and also power up top from the large turbo, but the power up top in theory would be slightly lesser than if you were running a single large turbo only as the air has to pass through the small turbo which causes a slight restriction, but basically you get best of both worlds. Disadvantages is plumbing nightmare, need to buy 2 wastegates and possibly tuning nightmare as well.

Here's an image I borrowed off Google



So basically plumbing wise, exhaust manifold goes to small turbo, the output of that goes to the large turbo, the wastegate of the small turbo also goes to the large turbo, then the large turbo exhaust goes out as normal. For the cold side, the air goes through the large turbo first, then into the small turbo, then to the intercooler then engine.

At lower RPM, the exhaust gas is enough to spool the smaller turbo to reasonable speed, the compressor will then draw air THROUGH the large turbo and compress it, then once the exhaust gas is enough to spool the large turbo, the large turbo will push more air than the small turbo, and is basically forcing air into and through the small turbo. Basically you should be able to hear your turbo spool up twice, once at low rpm and another time at a higher RPM.

I also considered of doing this, but limited engine bay space and high cost and effort prevents me from doing so. Now I just run a single TD05 twin scroll turbo on my 1.8L engine and it gives me full boost from around 3.5-4k rpm all the way to my 8400rpm redline.
 

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Isn't the current twin scroll or VGT does the same thing? Technically I am old school only...lol
 

Nightstalker1993

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Isn't the current twin scroll or VGT does the same thing? Technically I am old school only...lol
No, it is far from the same thing. Twin scroll and VGT tries to expand the efficiency range of an existing turbo, but it won't be anywhere near the powerband of a properly setup compound charge system. Imagine 2000rpm-5000rpm full boost handled by the smaller turbo and 4500-8000rpm full boost by the larger turbocharger, in all you get a fat 2000-8000rpm powerband!

Also, VGT is only recently getting into petrol turbocharged cars in the Porsche if not mistaken, before this only Diesels use VGTs as it cannot sustain the high temperatures of a petrol engine. Twin scroll works by dividing the cylinder pulses entering the turbo, improving the spool up time and boost threshold slightly.
 
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Twin scroll for daily will be nice, flat torque range. Compound will be good for track full power all the way.....:driver:
 

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Twin scroll for daily will be nice, flat torque range. Compound will be good for track full power all the way.....:driver:
Actually it's the other way round. Compound charge will be damn nice for daily and a twin scroll would be good for racing. Imagine daily driving your car you can floor it at 2000rpm and get full boost going up that flyover and you're lazy to change gear, yet also able to pull all the way to 8000rpm when that idiot high beam you on the road not knowing what's under the hood.

You really only need a single large turbo for racing as your engine rpm will be operating at a very narrow range which would be the effective operating range of your turbo and a twin scroll turbo can expand that powerband slightly to make it even more useful.
 

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Here's an image I borrowed off Google

Wow, gotta to say although I understand how compound charging works, still that picture took me a while to process.

But great explanation on compound charging and the the above vgt and twin scroll, much more easier to digest that way
 

Tom

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Actually it's the other way round. Compound charge will be damn nice for daily and a twin scroll would be good for racing. Imagine daily driving your car you can floor it at 2000rpm and get full boost going up that flyover and you're lazy to change gear, yet also able to pull all the way to 8000rpm when that idiot high beam you on the road not knowing what's under the hood.

You really only need a single large turbo for racing as your engine rpm will be operating at a very narrow range which would be the effective operating range of your turbo and a twin scroll turbo can expand that powerband slightly to make it even more useful.
Would you say it's like twin charging but simpler?
 

ixeo

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Disadvantages is plumbing nightmare, need to buy 2 wastegates and possibly tuning nightmare as well.
Tuning a small responsive turbo, on a car from the 90s is a nightmare. Especially when you want a linear throttle response. I can only imagine the headache of this compound charging, especially in the transition stage between the small and the big turbo based on throttle input.

Because if its not tuned correctly, you will get a sudden boost while your throttle is applied in a linear fashion.

30% throttle input, 30% power,
50% throttle input, suddenly 90% power (because the boost control strategy isn't comprehensive enough)

K3VET, for daily use, seriously, it's enough. Stick it in a Kelisa and you have power to weight ratio of the original Lotus Elise mk.1. What more could you possibly want.
 

Nightstalker1993

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Wow, gotta to say although I understand how compound charging works, still that picture took me a while to process.

But great explanation on compound charging and the the above vgt and twin scroll, much more easier to digest that way
Thanks, I try my best to keep it simple, and that image really does help understanding the system greatly.

Also can watch this video, the explanation on the video is superb.


VGT and Twin scroll is nothing new, both pretty much have the same goal which is to expand the turbo's efficiency range. But still out of reach of the mainstream production cars yet due to most probably the high cost for a VGT turbo designed to withstand the heat of a petrol engine, and also the complicated control strategies required to operate the VGT mechanism. If you can't wait, you can get a Porsche :laugh: Also, the more moving part, the more chance of problems. I've seen the VGT vanes of a VGT turbo get stuck before so that's another thing to ponder as well.

Twin scroll turbos works by dividing the exhaust pulses, introducing the scavenging effect in a way and reduces interference between the pulses thus improving the engine as well as the turbocharger's efficiency. Since twin scroll turbos work by dividing exhaust pulses, the manifold design is of utmost importance and for a common 4 cyl, cyl 1 and 4 will be paired to 1 scroll while cyl 2 and 3 will be paired to the other scroll. If you install a single external wastegate on the system by combining both scrolls, you pretty much negate the benefits of a twin scroll as mixing between the cylinder pulses can then occur since you had basically combined the scrolls. A proper wastegate system on a twin scroll setup would require two wastegates. On a stock Evo 4+ turbo for example, there is actually 2 wastegate flappers operated by a common actuator so the gas really does stay divided all the way until after the turbo.

For more reading material on twin scroll turbos, can read a few links here

http://www.bmwblog.com/2010/01/02/twin-scroll-turbo-system-design-explained/
http://dsportmag.com/the-tech/twin-scroll-vs-single-scroll-turbo-test-the-great-divide/
https://www.rx7club.com/single-turb...s-single-scroll-vs-twin-scroll-turbos-903210/

so really, if possible, get a twin scroll turbo :laugh:

Would you say it's like twin charging but simpler?
No it is really completely different. Twin charging as in 2 identical sized turbos, main purpose is to reduce turbo lag by reducing inertial mass, but still suffers from choking up top. but even that seems to be phasing out now with more efficient turbochargers being introduced. Those people with RB and JZ engines which came with twin turbos are converting to single turbos and getting very good gains.

Compound charge on the other hand, as the video I attached describe, is really like running 2 seperate turbos, one for the low end and one for up top, vastly increasing your powerband. It's slightly different than staged turbo on certain production car where there are actually flaps or valves blocking/rerouting the gas flow while compound charge really is just suck air through this turbo and push air through the other turbo :laugh:
 

Nightstalker1993

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Tuning a small responsive turbo, on a car from the 90s is a nightmare. Especially when you want a linear throttle response. I can only imagine the headache of this compound charging, especially in the transition stage between the small and the big turbo based on throttle input.

Because if its not tuned correctly, you will get a sudden boost while your throttle is applied in a linear fashion.

30% throttle input, 30% power,
50% throttle input, suddenly 90% power (because the boost control strategy isn't comprehensive enough)

K3VET, for daily use, seriously, it's enough. Stick it in a Kelisa and you have power to weight ratio of the original Lotus Elise mk.1. What more could you possibly want.
nehh, tuning small turbo cars are really pretty easy. And the tuning headache I imagine would be tuning the boost control strategy and such, fuel and ignition should be as per standard tuning strategy. But yeah, K3VET, with a TD04 upgrade should be pretty nice to drive already though of course your boost threshold will be at a higher RPM now meaning your boost will come in later