Which turbo can I get away with

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Originally Posted by lambrover

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The pressure in the line between the injection pump and the injector will rise

yes the pressure will rise, but the pressure is predetermend by the injector crack pressure. Pump pressure or injection pressure will not change it self just because you have more pressure in the cylinder.


BTW, nozzles convert pressure in the fluid to velocity, and the energy is converted to kinetic energy. So the pressure drops across the nozzle from high pressure to the pressure inside the combustion chamber while the fuel is injected.

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I think this statement is not quite correct, as the fuel is pressurized from the plunger in the fuel pump it lifts the delivery valve of it's seat and fuel is passed through the injector line, when the pressurized fuel lifts the injector needle of it's seat the fuel passes through the holes in the nozzel its converted to a mist, there is no drop in pressure until the helix on the plunger passes the spill port, this causes a rapid drop in pressure and the delivery valve in the pump closes this stops the flow to the injector and the needle closes ceasing injection, once injection finishes you would have the nozzle under the same pressures as the combustion chamber but only when injection has finished.

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When I said that pressure drops across the nozzle I meant nozzle in the true engineering sense of the term. The 4BD1 has hole type, not pintle type nozzles. It is the actual holes that are the nozzles.

Perhaps it would have been clearer (less confusing) if I had said nozzle holes.

As I had said previously, nozzles convert pressure to velocity - the pressure drops so the velocity can increase (a basic law of physics for conservation of energy). Nozzles are used in many applications, and one of the important ones where the principles are well documented is nozzles for steam/gas turbines, where it is important to design them properly and make them as efficient as possible. The science concerning nozzles is well know and we mortals can't change it.

The same physics apply in the nozzle at the end of a garden hose and in the injector for a diesel engine.

When the needle cracks open from it's seat, at the 'pop' pressure, the pressure has to increase further because it has to compress the spring further to increase the flow area. This is a function of the spring rate.

There will be pressure drop across the needle seat, and further pressure drop across the nozzle holes.

It is the nozzle/hole geometry and the pressure drop (difference between nozzle inlet and outlet pressure) that is important for the spray pattern.

The needle (and pop pressure) is also important but it has other functions (think about ensuring pressure is adequate at the nozzle/hole inlet at the critical period between injection start and finish, think about leakage).

with the last couple of posts, good explination. I am happy with the outcome of this discusion it still surprises me though that this engine can handle that much boost.

I keep finding things like this

07-09 DODGE RAM 6.7L CUMMINS HOLSET VGT TURBO CHARGER:eBay Motors (item 370242557461 end time Aug-15-09 18:43:49 PDT)


Get movement due to the excitement, then discover they won't ship to Aus.

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Originally Posted by dobbo

I keep finding things like this

07-09 DODGE RAM 6.7L CUMMINS HOLSET VGT TURBO CHARGER:eBay Motors (item 370242557461 end time Aug-15-09 18:43:49 PDT)


Get movement due to the excitement, then discover they won't ship to Aus.

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People have started using these on the 3.9L Cummins 4BT (which is very much like the Isuzu 4BD1-T).

Most are being removed from the Dodge under warranty because the EGT system creates soot that cause the variable nozzle mechanism to stick. They could clean the soot away so they then function normally, but because it is under warranty that is not an option so they fit another new turbo.

So these that are removed are available $cheap$. They are low mileage and simple to restore.

The variable nozzle closes down to 4 cm^2, which is used as an exhaust brake on the dodge's. The latest ones have a new design billet compressor wheel that is more efficient provides much improved performance builds pressure sooner and moves more air at top end.

That particular turbo is a H351VE (H (Holset), 351 (size), V (variable nozzle), E (electronic).

IMHO the H351VE is too large for a 4BD1. The H341VE that be better.

The H351VE has been used with good results on the Cummins 4BT, but IIRC it was with the P7100 injection pump, which can deliver much more fuel than the A size pump on an Isuzu. IMHO without the appropriate fuel delivery it will not perform very well.

The biggest issue is how to control the variable nozzle on these Holset turbos. They have an electric motor (a stepper motor from memory) that is controlled by the ecu using CAN bus signals. There are reasonable stand alone CAN controllers that could be used, but AFAIK people who have tried, could not determine what signals the turbo provides/requires (this is not my field, so I am not terribly clear what is involved).

Some have made mechanical set-ups in place of the electric motor.

If it turns out that my Borg Warner turbo does not perform as expected. I would one with a mechanical linkage from a boost actuator.

My only problem with the Holset is the sheer size of the bloody thing, it is massive

The other day I found the whereabouts of a used and abused Disco Potato. I am not sure if it is for sale I do know it needs a rebuild. Being a T28 it's around the right size but is a duel bearing turbo overkill for my rev range?

It could make a good turbo swap for the TD5.

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Originally Posted by dobbo

My only problem with the Holset is the sheer size of the bloody thing, it is massive

The other day I found the whereabouts of a used and abused Disco Potato. I am not sure if it is for sale I do know it needs a rebuild. Being a T28 it's around the right size but is a duel bearing turbo overkill for my rev range?

It could make a good turbo swap for the TD5.

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T28 is a family of turbos and the disco potato (GT2860RS) is the biggest of the ones with 60mm compressors.
IMO it's bordering on too big for a single turbo and it isn't suited to the high boost pressures you need to deliver lots of grunt. It's on the edge of it's map at 20psi boost.
The turbine maps show you won't start to build boost until you're close to 2000rpm (half the rev range gone).
TurboByGarrett.com - Catalog

Where this GT2560R (this is actually the old T28) has a smaller trim turbine and should spool up around 25% sooner, but can still deliver the same boost as the disco-potato.
TurboByGarrett.com - Catalog

Just another case of the best ricer turbos not being the best diesel turbos.

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Originally Posted by dobbo

I keep finding things like this

07-09 DODGE RAM 6.7L CUMMINS HOLSET VGT TURBO CHARGER:eBay Motors (item 370242557461 end time Aug-15-09 18:43:49 PDT)


Get movement due to the excitement, then discover they won't ship to Aus.

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You could always us a US freight forwarding service - ebay us address shipping - Google Search

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Originally Posted by dobbo

... it's around the right size but is a duel bearing turbo overkill for my rev range?

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A ball bearing turbo should spool up quicker than a bushed turbo. So I would not say it was overkill for your rev range.

What is your max rpm?

It seems max rpm for stock engines can vary between 2500 and 3600.

You may find with a turbo, that the extra air will easily allow the rev range to expand.

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Originally Posted by Bush65

It seems max rpm for stock engines can vary between 2500 and 3600.

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AFAIK all factory (LR) 4BD1s have a max rpm of 3400 (or thereabouts).

Have you balanced your engine to get it to rev to 4400 smoothly???

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Originally Posted by isuzurover

AFAIK all factory (LR) 4BD1s have a max rpm of 3400 (or thereabouts).

Have you balanced your engine to get it to rev to 4400 smoothly???

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Mine appears to be 3600rpm. Confirmed through checking gearing and road speeds.
Mine was fully balanced, but it's still fairly noisey and grumbly above 3000rpm. Spends most of it's time between 1500 and 2000rpm.