Which turbo can I get away with

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Originally Posted by lambrover

I am in a bit of disbelief about the quotes off boost pressures from 30 to 60 psi, that seems abit far fetched to me. Can anyone explain how this is possable

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30 psi is practical with a single turbo, but you need to select one that has a compressor which is reasonably efficient at that boost pressure (many will just be heating the air - see compressor maps that Ben posted above).

60 psi is the domain of compound turbos.

Intercoolers are also required (IMHO above about 10 psi).

The fuel injection pump will have to be adjusted to obtain high boost, and significant mods are required to deliver enough fuel to make 60 psi boost.

When dobbo started this thread he only asked:

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How much boost can a 4BD1 safely handle and how big can you go with a turbo?
I can't think of any reason why it could not handle a large LP turbine but is 10 - 30psi to much for a n/a engine?

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And the facts given were:
40 psi with standard head gasket and bolts - although 50 psi has been achieved reliably.
60 psi is ok with stock head gasket and studs.

Much above 60 psi will require o-rings, but MLS gaskets (which the Isuzu uses) are not suited for use with o-rings (so you would need to get a gasket custom made).

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Originally Posted by lambrover

a ZD30 is a moden engine compared to a 4bd1 and was designed around those parameters thus the compression, head design, head bolt position tension, injection timing, bearings the block was all designed to be turboed at higher boost pressure.

I have been reading the info from this site about turboing a 4bd1 as I have one in the shed to fit to my county. I was speaking to a landrover mechanic the other week and mentioned the boost pressures claimed on this site and he said no way could the engine handle those pressures.

So is it the general concensis that on standard internals rods pistons that with a fuel tweak and an exhaust upgrade you can run 0 to 60 psi boost through this motor. I know these motors are strong but to me it seems to far fetched.

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How much does that Land Rover mechanic know about the 4BD1 engines? How much does he know about turbocharging?
How much does he know about the mechanical engineering and what contributes to engine component loads (e.g. inertia) and how these are influenced by turbocharging?
Where is his evidence?

The 4BD1 is a very strong engine (in some ways more so than the 4BT Cummins), will reliably rev to 4500 rpm and with the boost pressures stated above.

I haven't seen the internals of the ZD30, so can't comment on them.

The main area that modern diesels have advanced, when compared to the 4BD1-T, is in emissions, high pressure fuel injection and 4 valve cylinder heads (to allow the injector to be located in the centre of the head for better combustion). Generally their performance is moved higher up the rev range.

when you increase boost pressure to those extreme points you have mentioned a fuel increase, ie fuel metering is adjusted. but no one has mentioned injection pressure, when you ram these huge boost pressures into a engine the injection spray pattern is interupted as the pressure is a force acting against the ijection pressure, so to maintain a good spray pattern you must increase injection pressure to overcome the boost pressure.

I don't have the pump spec's with me but would be surprised if it was possable to increase it enough then you would have to re shim the injectors as well and with all that will the injectors handle that much heat going through them with out melting the tips

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Originally Posted by lambrover

when you increase boost pressure to those extreme points you have mentioned a fuel increase, ie fuel metering is adjusted. but no one has mentioned injection pressure, when you ram these huge boost pressures into a engine the injection spray pattern is interupted as the pressure is a force acting against the ijection pressure, so to maintain a good spray pattern you must increase injection pressure to overcome the boost pressure.

I don't have the pump spec's with me but would be surprised if it was possable to increase it enough then you would have to re shim the injectors as well and with all that will the injectors handle that much heat going through them with out melting the tips

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To squirt more fuel through the same injectors requires more pressure. So it's already happening and seems to balance itself out quite well.
AFAIK no-one has tried different injectors in a 4BD1(T) yet, but some have plans to do so.

Pistons will melt long before injectors will. The extra flow through injectors won't cause them to overheat.

[QUOTE=Dougal;1040698]To squirt more fuel through the same injectors requires more pressure. this is not the point I am trying to make, the pressure needed to inject into a naturaly aspirated engine is lower than injection pressure needed for a turbo charged engine, with low boost you can get away with the stock pressures but with high boost pressures I would think you would need to change afew things.

If you had a hose plumbed into a air tight bucket turned it on water would easily come out but now you plumb a air fitting into the air tight bucket to symulate boost the water flow would be hindered as it would be being opposed by the air pressure.

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Originally Posted by lambrover

[this is not the point I am trying to make, the pressure needed to inject into a naturaly aspirated engine is lower than injection pressure needed for a turbo charged engine, with low boost you can get away with the stock pressures but with high boost pressures I would think you would need to change afew things.

If you had a hose plumbed into a air tight bucket turned it on water would easily come out but now you plumb a air fitting into the air tight bucket to symulate boost the water flow would be hindered as it would be being opposed by the air pressure.

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Injection pressures are already far in excess of compression and combustion pressures.
Injector crack pressure is 2630psi according the 4BD1T FSM. That's not peak injection pressure, that's the opening and closing pressure.
30psi boost is not going to blow air back through your injectors.

The injection pump while being variable displacement is positive pressure. It just keeps upping the pressure until it can pump the volume it has to pump. It will only stop when something breaks or the engine driving it can't push hard enough.

As has been mentioned already, 4BD1T's have already been subjected to these boost pressures. Injection pressure didn't appear to be a problem.

The injection pump while being variable displacement is positive pressure. It just keeps upping the pressure until it can pump the volume it has to pump. It will only stop when something breaks or the engine driving it can't push hard enough.

An inline fuel pump is variable displacement (this is the metering) yes, but not variable pressure, to my knowledge. can you explain how a mechanical fuel pump automaticaly adjusts fuel pressure.

The displacement is variable, but for a particular operating position (controlled by the governor) the plunger displaces a particular volume of fluid.

The pressure in the line between the injection pump and the injector will rise to whatever is necessary to discharge the fluid. If it cannot discharge through the nozzle (as it does), then something else would fail because diesel fuel is practically incompressible.

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.

Edit: Because the nozzle geometry (size of holes etc) is fixed the pressure drop across the nozzle must change as the flow rate varies. The flow rate is a function of the plunger speed and varies as engine speed changes.

So if the flow rate increases, for a particular pressure at the outlet of the nozzle, the pressure inside the nozzle must increase.

If pressure increases at the outlet of the nozzle, then for a particular flow rate, the pressure inside the nozzle must increase.

It should be obvious then that the pressure changes often.

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Originally Posted by lambrover

An inline fuel pump is variable displacement (this is the metering) yes, but not variable pressure, to my knowledge. can you explain how a mechanical fuel pump automaticaly adjusts fuel pressure.

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John explained it pretty well. Let us know if you need more.

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.[/QUOTE]

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.

So if the flow rate increases, for a particular pressure at the outlet of the nozzle, the pressure inside the nozzle must increase.

If pressure increases at the outlet of the nozzle, then for a particular flow rate, the pressure inside the nozzle must increase.

It should be obvious then that the pressure changes often.[/QUOTE]

Ok yes that sounds good, I give it some more thought time for bed, big day tommorrow. good chat though