Sequential turbos
Discussion
You have a few problems with your diagrams.
For example, when you big turbo is producing more pressure than the small one, the intake air will leak backwards out the small compressor!
There are a few "tricks" used to minimise the valves required, such as blowing the small compressor through the big one, which then only needs a simple one way flapper valve to help bypass the smaller compressor at high speed.
Also, you can use the std wastegates as part of the exhaust routing etc
However, these days, sequential turbo's are an un-necessary complication really!
For example, when you big turbo is producing more pressure than the small one, the intake air will leak backwards out the small compressor!
There are a few "tricks" used to minimise the valves required, such as blowing the small compressor through the big one, which then only needs a simple one way flapper valve to help bypass the smaller compressor at high speed.
Also, you can use the std wastegates as part of the exhaust routing etc
However, these days, sequential turbo's are an un-necessary complication really!
Max, in the above picture dose the mall turbo not over spin? Once the cold side valve is open there is equal pressure on both sides of the small turbo do little resistance. Also with not waste gate what stop the turbo just spinning faster and faster and blowing up?
There are also a few home grown examples that only require a waste gate on the hot side. have a look on Google to see some examples.
There are also a few home grown examples that only require a waste gate on the hot side. have a look on Google to see some examples.
PugLee said:
I was just wondering if ive got the basic idea here right?
Theyre simple drawings but hey i done them on paint!
Obviously I havent included everything just trying to get the basic understanding right first
Any constructive critisism welcome
PugLee
At stage 3, would you not bypass the small turbo altogether? If it's pitched for quick spool up at low revs, at high revs will it not just be heating the air up?Theyre simple drawings but hey i done them on paint!
Obviously I havent included everything just trying to get the basic understanding right first
Any constructive critisism welcome
PugLee
Ian
chuntington101 said:
Max, in the above picture dose the mall turbo not over spin?
Think about how a wastegate limits turbine speed? Now tell me the difference between opening a wastegate to the post turbine exhaust and to opening one into the pre-turbine exhaust of a much bigger turbine......Max_Torque said:
Think about how a wastegate limits turbine speed? Now tell me the difference between opening a wastegate to the post turbine exhaust and to opening one into the pre-turbine exhaust of a much bigger turbine......
This is how my head sees it....With a single turbo, the wastegate opens and the power is limited as less boosot is created. This means th amount of exhaust created is also limited.
With a sequential setup, when the bigger turbine gets going much more exhaust is created, would this not then overspin the smaller turbine if it's not taken out of the equation with a valve of some sort?
Help my poor head out here!
Luther Blisset said:
Not really, what matters is keeping exhaust manifold pressure at a reasonable level.
Having an additional big turbine there will do that,
if it's making 500hp there will be "500hp worth of exhaust gases" but you'll now have two routes out.
But if you don't cut the smaller turbine out of the loop, wont it spin way out its efficiency zone and heat up the intake air unnecessarily?Having an additional big turbine there will do that,
if it's making 500hp there will be "500hp worth of exhaust gases" but you'll now have two routes out.
Richyvrlimited said:
But if you don't cut the smaller turbine out of the loop, wont it spin way out its efficiency zone and heat up the intake air unnecessarily?
I suppose it all depends on spec, but the overall flow capabilities of two turbines should normally be sufficient. Bearing in mind the exhaust manifold pressure will be more or less equal at both turbine inlets.
BTW most set these up with a wastegate for each turbo, but the larger turbo will take the exhaust flow from the small turbine outlet and its wastegate. So, compounded.
Rigged up like that, and using internally wastegated turbos the hot side plumbing is relatively simple.
On the cold side as you say the compressed air being fed through the smaller compressor would heat up the air too much I would think (two 75% efficient compression stages = 56% total efficiency)
But as Max Torque mentioned this is deverted past a certain point.
Richyvrlimited said:
But if you don't cut the smaller turbine out of the loop, wont it spin way out its efficiency zone and heat up the intake air unnecessarily?
Why would it? You aren't asking it to produce 500bhp worth of air, since you now have a much larger turbo that the exhaust gasses can pass through.PugLee said:
Would anyone be able to point me in the right direction to get a check valve? I want to run 3" pipe work to the intercooler, so something of that size. A variable one would be the mutts nuts!
Cheers
Alternatively, use a normal electronic throttle unit to blend the two together
Max_Torque said:
Blow the small compressor THROUGH the large compressor, and use a simple flapper type passive bypass valve that opens to bypass the small compressor at high engine rpm
Alternatively, use a normal electronic throttle unit to blend the two together
Wouldnt the large compressor be limited by the flow capabilities of the small compressor? unless they each have their own seperate intakes?Alternatively, use a normal electronic throttle unit to blend the two together
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