I found this;

http://i68.photobucket.com/albums/i17/paulvolk/twinturbo_large.jpg

Anyone got any opinions? Mine is that by closing the exhaust loop from the manifold mounted turbo, it prevents the wastegate from operating effectively, thus preventing the system from depressurising correctly???
Not planning anything, just curious to hear opinions.

if i'm understanding that right, i bet the turbo lag would be terrible!

This is a serial setup and would be a killer.

I love it.


Turbo lag should be minimal

I think the objective was to reduce lag, by installing different size turbos, with the larger one producing more boost than the smaller one. Not sure how effective it would be mind...

I cant see how the pressure is releived though once the throttle is closed? The wastegate will operate, but it doesnt go anywhere other than into the circuit again.

i'd have thought you'd end up waiting for one turbo to spin up before the other one starts to spin up? i'd have thought 2 different size turbos in 'parallel' would have been better, because as you wait for the big one, the small ones already picked up some of the work

i cant get my head round that!might be the beer!is the wastegate exhausting into a screamer pipe?and just using one turb to try and keep the other one constantly spinning for no lag?must of cost a fair bit whatever it achieves!

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Originally posted by blakep82
i'd have thought you'd end up waiting for one turbo to spin up before the other one starts to spin up? i'd have thought 2 different size turbos in 'parallel' would have been better, because as you wait for the big one, the small ones already picked up some of the work

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as above , its in serial for lots of boost ie 60-100 psi .

a method employed in tractor pulling so can achieve the high boost and make the power band wider , compared to one single turbo making the boost .

the wastegate would work as normal - that is just a bypass of the turbine wheel to slow it down .

Older diesels ran without a wastegate since the turbos werent small enough to spool early to create overboosting problems , and diesels are tolerant of varying AFR .

More fuel makes more power , so as long as you dont force so much compressed air that effectively overcomes the mechanical strength of the engine your good to go .

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Originally posted by blakep82
i'd have thought you'd end up waiting for one turbo to spin up before the other one starts to spin up? i'd have thought 2 different size turbos in 'parallel' would have been better, because as you wait for the big one, the small ones already picked up some of the work

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and if its not enough boost there'll be enough derv cooling the pistons the smoke screen will hide you loosing! Carefully aimed exhaust is the key!

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Originally posted by Volvorsport


More fuel makes more power , so as long as you dont force so much compressed air that effectively overcomes the mechanical strength of the engine your good to go .

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Originally posted by MakeEverything
I cant see how the pressure is releived though once the throttle is closed? The wastegate will operate, but it doesnt go anywhere other than into the circuit again.

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Ha!.. Diesels do not have a throttle butterfly.
They are just an open tube.
The throttle pedal is connected to the Injector pump and just pumps in more fuel.
Hence the overpressurisation on no throttle is not a problem on a diesel.

Well thats how my land rover worked. These new fangled common rail diesels may be different.
Its the same reason why they have a belt driven vacuum pump for the servo brakes. as there was no throttle butterfly to close to create the vacuum needed by the brakes..

You lot are just Petrolheads
Us Diseasel Heads are a separate breed alltogether

i cant see tha picture as blocked at work but is the system set up simular to the new Saab twin turbo principal??
Saab TTid engine

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Originally posted by wilkingj
Ha!.. Diesels do not have a throttle butterfly.
They are just an open tube.
The throttle pedal is connected to the Injector pump and just pumps in more fuel.
Hence the overpressurisation on no throttle is not a problem on a diesel.

Well thats how my land rover worked. These new fangled common rail diesels may be different.
Its the same reason why they have a belt driven vacuum pump for the servo brakes. as there was no throttle butterfly to close to create the vacuum needed by the brakes..

You lot are just Petrolheads
Us Diseasel Heads are a separate breed alltogether

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Originally posted by Liam

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Originally posted by MakeEverything
I cant see how the pressure is releived though once the throttle is closed? The wastegate will operate, but it doesnt go anywhere other than into the circuit again.

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Think you may be getting your wastegates and dump valves mixed up. It's a dump valve, in the inlet air plumbing, which opens when the throttle is closed to relieve inlet pressure. This being a diesel, which doesn't have a throttle to close, probably doesn't need one.

The wastegates in this system will do what wastegates always do - regulate boost by bypassing exhaust flow away from the turbines according to their setting. These turbos look to have internal wastegates as is most common.

Liam

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Fit a Variable geometry turbocharger ,and forget about lag

completely pointless imho.....

mazda have a nice twin turbo setup on there rx7, but with the posted picture your smaller turbo has a smaller a/r on the inlet so will start to restrict the bigger turbo....would have been better running parralell than in series with a nice anti lag system....

just my opinion thou.....

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Originally posted by MakeEverything

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Originally posted by Liam

quote:

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Originally posted by MakeEverything
I cant see how the pressure is releived though once the throttle is closed? The wastegate will operate, but it doesnt go anywhere other than into the circuit again.

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Think you may be getting your wastegates and dump valves mixed up. It's a dump valve, in the inlet air plumbing, which opens when the throttle is closed to relieve inlet pressure. This being a diesel, which doesn't have a throttle to close, probably doesn't need one.

The wastegates in this system will do what wastegates always do - regulate boost by bypassing exhaust flow away from the turbines according to their setting. These turbos look to have internal wastegates as is most common.

Liam

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But when the throttle closes, the pressure increases until the turbo slows down and stops producing boost. In this instance, the actuator is operated by the inlet pressure, which opens the wastegate, so no im not getting them mixed up, just probably not explaining myself properly.

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The new (not even sure if its launched yet) BMW diesel V8 has sequential turbocharging, but knowing BMW, there's going to be a bypass valve in there somewhere to let more air into the bigger one when the smaller one has run out of puff..