RD28 Turbo options
Posted: 25 Jan 2020 09:41
So as we might all know, Reenen has dropped one of these RD28s into a Safari.
I can't recall the turbo he used, but if my grey matter hasn't gone too vrot, it was a standard factory turbo?
So for those that don't know the engine, it is a 2800cc straight 6 OHC engine that replaced the LD28, and was a factory option in the Y60 and Y61 (GQ and GU) or otherwise what was known as the Super Safari in some export markets.
The GQ had a standard mechanical pump (Bosch Zexel VE) and mechanical wastegate, the GU had a semi-electronic pump (Bosch VP?) and a mechanical wastegate as far as I know.
The problem was the operational spec of that engine:
91.9 kW at 4400 rpm 255 Nm at 2000 rpm
So as you can see, not a crapload of torque and only available around 2000rpm.
This was a function of the high revving engine : naturally aspirated, this engine produces max power at 4,800rpm and max torques at 2,400rpm, so it was built to rev.
The problem is that this is sub-optimal off road: high rev torque peaks often equate and translate to wheel spin.
So naturally, the Ozzies have already sorted out the problem: a Garrett GT2052 variable vane turbo off of the ZD30. The problem is the vane control and also the boost control and lastly, pump optimisation.
So as a total ignoramus when it comes to diesel turbo charging, here is the issue as I see it:
- more boost without more fuel = very little benefit, but less risk as long as cylinder head pressures are not outside of design specs
- more fuel without more boost = very little benefit, but with the risk of high EGTs and subsequent engine damage
- more fuel with more boost = the Holy Grail within design limits
Now the function of a variable vane turbo (also called a VNT: variable nozzle turbo) is to adapt the compression or aspect ratio to the engine demands using a set of rotating vanes or blades that can rotate their pitch like a variable pitch aircraft propeller. This implies that instead of having either low boost at low revs and high boost at high revs, or high boost at low revs and a wastegated limit at high revs like standard turbos, the VNT can provide decent boost at all revs.
https://en.wikipedia.org/wiki/Variable- ... rbocharger
This means a VNT will give optimum boost at low revs, and suddenly the RD28 can push decent numbers straight off idle. No more lag, torque at low revs, it's a win-win.
But to make use of this broad spread of boost, you need a pump that can provide the correct AFR (air fuel ratio) and never over fuel.
And that's where I'm stuck: vane control, boost control and pump tuning.
I can't recall the turbo he used, but if my grey matter hasn't gone too vrot, it was a standard factory turbo?
So for those that don't know the engine, it is a 2800cc straight 6 OHC engine that replaced the LD28, and was a factory option in the Y60 and Y61 (GQ and GU) or otherwise what was known as the Super Safari in some export markets.
The GQ had a standard mechanical pump (Bosch Zexel VE) and mechanical wastegate, the GU had a semi-electronic pump (Bosch VP?) and a mechanical wastegate as far as I know.
The problem was the operational spec of that engine:
91.9 kW at 4400 rpm 255 Nm at 2000 rpm
So as you can see, not a crapload of torque and only available around 2000rpm.
This was a function of the high revving engine : naturally aspirated, this engine produces max power at 4,800rpm and max torques at 2,400rpm, so it was built to rev.
The problem is that this is sub-optimal off road: high rev torque peaks often equate and translate to wheel spin.
So naturally, the Ozzies have already sorted out the problem: a Garrett GT2052 variable vane turbo off of the ZD30. The problem is the vane control and also the boost control and lastly, pump optimisation.
So as a total ignoramus when it comes to diesel turbo charging, here is the issue as I see it:
- more boost without more fuel = very little benefit, but less risk as long as cylinder head pressures are not outside of design specs
- more fuel without more boost = very little benefit, but with the risk of high EGTs and subsequent engine damage
- more fuel with more boost = the Holy Grail within design limits
Now the function of a variable vane turbo (also called a VNT: variable nozzle turbo) is to adapt the compression or aspect ratio to the engine demands using a set of rotating vanes or blades that can rotate their pitch like a variable pitch aircraft propeller. This implies that instead of having either low boost at low revs and high boost at high revs, or high boost at low revs and a wastegated limit at high revs like standard turbos, the VNT can provide decent boost at all revs.
https://en.wikipedia.org/wiki/Variable- ... rbocharger
This means a VNT will give optimum boost at low revs, and suddenly the RD28 can push decent numbers straight off idle. No more lag, torque at low revs, it's a win-win.
But to make use of this broad spread of boost, you need a pump that can provide the correct AFR (air fuel ratio) and never over fuel.
And that's where I'm stuck: vane control, boost control and pump tuning.
