Thread: Turbo Lag?

What I am saying is that high boost at low rpm with mechanical injection is not the best solution to the problem. It is to do with the pressure inside the cylinder and the back pressure that this would create on the fuel pump. You have a mechanical pump that is driven off engine speed. Therefor, you will not get maximum pressure out of said pump until you up the revs a bit. It is not as simple as having 18psi from idle (although I have no doubt this would be awesome). You need rpm to overcome the back pressure and the only way to do that on a mechanically driven pump is with engine speed. Now, you over come these problems with a common rail because you have 30,000psi at you disposal from idle, more then enough to overcome the high boost pressure and low engine rpm. That is my point. This is the reason why I would not put a VNT on a mechanical injection motor.

Originally Posted by klappers

What I am saying is that high boost at low rpm with mechanical injection is not the best solution to the problem. It is to do with the pressure inside the cylinder and the back pressure that this would create on the fuel pump. You have a mechanical pump that is driven off engine speed. Therefor, you will not get maximum pressure out of said pump until you up the revs a bit. It is not as simple as having 18psi from idle (although I have no doubt this would be awesome). You need rpm to overcome the back pressure and the only way to do that on a mechanically driven pump is with engine speed. Now, you over come these problems with a common rail because you have 30,000psi at you disposal from idle, more then enough to overcome the high boost pressure and low engine rpm. That is my point. This is the reason why I would not put a VNT on a mechanical injection motor.

I know what you have written seems all logical but its not.
fuel pressure from a mechanical pump is constant though the rev range, as its a positive displacement pump with a fixed number of revolutions per crank shaft revolutions.
Secondly your comments on back pressure. I assume that you are talking about the difference between cylinder head pressure / combustion pressure and fuel pressure, and you have a point but this is not a mechanical verses electronic control issue. For example the TD5 is still a mechanical fuel pressure system as is the new v6 diesels.

every thing an electronic control system can do a mechanical system can do, the only reason that electronic systems are prevalent today is that they are cheep, cheep to manufacture, cheep to replace, and very cheep to change the state of tune. because electronic systems are now the mainstay development of mechanical systems have fallen by the way side. This is control systems, fuel pressure is and will be still mechanical.

The Isuzu still produces more motive energy for a given amount of fuel than any of the LR motors including the electronically controlled ones and there is next to no wires in site apart from oil pressure and water temp. so that blows that argument.

Meh,

I can assure you that there will be an increase in pressure from idle to 3000rpm (ie nominal pressure in a 300tdi fuel system is 200bar at idle upto a max of 300bar, this pressure increase is due to the increase in plunger velocity). It is not tuneable to the amount of fuel (to a point) that you will need for that amount of boost and that amount of rpm. Most fuel pumps on diesel motors are mechanical. They have to be. I would love to see an electronic fuel pump deliver 30,000psi, cant see it happening. This is the point that I am trying to make. You may need more fuel then it is possible to deliver at a certain rpm with mechanical injection because you cannot adjust the "phase" of the injectors. Pre-ignition could also raise its ugly head.

As for the 4BD1, this is 3.9L compared to 2.5. A much larger volulme to deal with, and so, should naturally have better torque.

So can someone please tell me if a VNC Turbo will work better than the original turbo???
Will it give me much more power??

Thanks

Yes, it will give you more power

Originally Posted by Peppercorn

So can someone please tell me if a VNC Turbo will work better than the original turbo???
Will it give me much more power??

Thanks

Yes, it will give a more usable spread of power and torque. The stock turbo isn't the worlds most efficient setup.

And FWIW here's the power/torque curves for the DTS Mitsubishi TD04 setup vs stock.

Goodonya Rick thanks!