Thread: compound turbo set up

Originally Posted by DRanged

Just spoke with our local diesel guy.
He was saying the hesitation at high speed open throttle is more than likely the lift pump not keeping up. Now there is a bigger lift pump available but he suggested fitting an electric pump after my swirl tank and see how it goes. Will give it a go I think.

J

I have fitted two elec lift pumps to my mates trucks which where having similar problems.

They where 1 hz and td42t how ever, but I imagine it being similar.

It solved the problem.

We used 5-7psi facet pumps.

Ok
Update time. Replaced the blown alternator oil line. Facet 4-8 psi fuel pump on the way. This weekend will see if I can get the waste gate to run at 20psi. My adjustable panhard rod bushes have collapsed so back to a standard for testing. Also will wrap both turbos and dump pipe. I think a 3" exhaust may help but it's not high up on the list. New flywheel and inertia ring will be first.

Justin

Originally Posted by DRanged

Ok
Update time. Replaced the blown alternator oil line. Facet 4-8 psi fuel pump on the way. This weekend will see if I can get the waste gate to run at 20psi. My adjustable panhard rod bushes have collapsed so back to a standard for testing. Also will wrap both turbos and dump pipe. I think a 3" exhaust may help but it's not high up on the list. New flywheel and inertia ring will be first.

Justin

Watching intently

ok
Played with the waste gate,but with its current pressure pick up (end of HP turbo housing) Max boost is 15psi. So i will move the pick up point to get 20psi. So basically now the engine runs quite good albiet a little lean in the upper range. I am hoping the facet fuel pump will help the lift pump.

So the IP will need modifying at some stage to get more fuel.
The flywheel will need an inertia ring at some stage.

With our future business plans the RRC will sit in the shed for a while.
I might get the chance to muck around with an inertia ring set up, but its not on the "to do list" so to speak.

Justin

Originally Posted by DRanged

ok
Played with the waste gate,but with its current pressure pick up (end of HP turbo housing) Max boost is 15psi. So i will move the pick up point to get 20psi. So basically now the engine runs quite good albiet a little lean in the upper range. I am hoping the facet fuel pump will help the lift pump.

So the IP will need modifying at some stage to get more fuel.
The flywheel will need an inertia ring at some stage.

With our future business plans the RRC will sit in the shed for a while.
I might get the chance to muck around with an inertia ring set up, but its not on the "to do list" so to speak.

Justin

What some find with waste gates on the HP turbo, is that using boost pressure doesn't work anywhere near as well as using drive pressure.

Nor does taking the boost from the LP turbo to the HP waste gate actuator work very well - has to be set too light and boost pressure causes the gate to creep open when you don't want it.

To use boost pressure, they replace the boost actuator with a spring and adjust the spring tension to control when the gate is opened by drive pressure.

Given that a weak wastegate actuator can be opened by drive pressure. It must be possible to do both.

A wastegate on the HP turbo which is opened by high drive pressure and opened by boost on the LP turbo. Hmmmm.
It would likely take a lot of monkeying with the size of the canister and the stiffness of the springs to get it right.

Originally Posted by Dougal

Given that a weak wastegate actuator can be opened by drive pressure. It must be possible to do both.

A wastegate on the HP turbo which is opened by high drive pressure and opened by boost on the LP turbo. Hmmmm.
It would likely take a lot of monkeying with the size of the canister and the stiffness of the springs to get it right.

Compounds bring a lot more variables and control issues compared to a single.

Just the various combinations of HP and LP turbos could see some work ok that way, but other combinations behave differently.

Based upon the experience of those on the competitiondiesel forum who have tried connecting the wastegate of the HP turbo to the interstage boost pressure (from the LP turbo) have mostly experienced problems.

The initial stage when you start to accelerate hard is the HP turbo starts to spool as though it is a single (but with more back-pressure at the turbine outlet). The LP turbo produces no boost.

The next stage is when the boost from the HP turbo and heat from the extra fuel create exhaust gas heat and flow that starts to spool the LP turbo.

Then the HP wastegate opens giving the LP turbine exhaust gas with more energy. Now as the HP turbo starts to fall away the LP turbo takes over.

When the LP boost is used to open the HP waste gate actuator the spring preload has to be lower and the drive pressure causes the gate to creep open. This adversely affects the initial spooling of the HP turbo and the pair become very laggy, EGT and smoke go up.

The concensus is that using drive pressure to control the waste gate of the HP turbo gives best results.

My compound set has a pneumatic actuator for the HP wastegate (no waste gate on the LP turbo), but on the engine it came off the management computer controlled the pressure signal. That solution could surpass results of the simple spring/drive pressure control, but it is more difficult to execute.

Originally Posted by Bush65

When the LP boost is used to open the HP waste gate actuator the spring preload has to be lower and the drive pressure causes the gate to creep open. This adversely affects the initial spooling of the HP turbo and the pair become very laggy, EGT and smoke go up.

Yes and I think that problem is solvable. In part by using a very large actuator, this means you get more spring pressure (to resist blowopen from drive pressure) while still being able to open it with the relatively low boost pressure you get in the LP compressor.
It may even be possible to run a pair of actuators to double the preload while keeping actuator pressures the same.

It's not an easy thing to try, but maybe one day when I get my own compound set installed.