Electric supercharger project for 2.2L turbo-diesel – P2 vs GTD2060VZK direct drive
Hi everyone,I've been reading several of the electric supercharger projects on this forum, particularly the Speedmaster P2 builds, and I'm currently designing an electric compressor system for my 2.2L turbo-diesel.
The engine already uses a relatively large upgraded turbocharger, and the purpose of the electric compressor would primarily be to improve low-RPM transient response and help the main turbo spool.
The electric compressor would mainly operate around 1,800–3,000 rpm rather than provide boost throughout the entire engine speed range.
The intended layout is:
Air filter → electric compressor → main turbo → intercooler → engine
with a large bypass around the electric compressor when it isn't required.
My initial target is approximately 0.3–0.5 bar of pre-compression, with short periods of high-power operation.
At the moment I'm considering two very different compressor options.
Option 1 – Speedmaster P2
This was my original plan.The major advantage of the P2 is mechanical simplicity. The compressor and bearing assembly are already complete and the unit is designed without an internal gearbox.
I would only need to design the electric drive, pulley ratio, mounting system and bypass, which there are some mode to make it and tested one.
From the information and testing I've found here, operating somewhere around 25–35k compressor rpm appears to be a reasonable starting region.
My concern is compressor matching.
The P2 is a relatively large compressor (~1,150 CFM maximum rating), while my engine is only 2.2 litres and I primarily need boost at low engine speed.
I'm therefore concerned about operating too close to the surge region at low airflow.
On the other hand, several people here have already experimented with the P2 electrically, so there is considerably more practical information available.
Option 2 – GTD2060VZK compressor
I already own a GTD2060VZK from an Audi 3.0 TDI.Its compressor wheel is approximately 43 mm inducer / 60 mm exducer, which appears much more appropriately sized for the airflow range I'm interested in.
However, mechanically this option is considerably more complicated.
I would probably not use the original turbo CHRA as-is.
The current idea would be to retain the compressor housing and compressor wheel and manufacture a dedicated electric compressor cartridge:
GTD2060 compressor wheel
→ custom short shaft
→ high-speed bearing assembly
→ high-speed coupling
→ brushless motor
I'm considering a pair of 10 mm ID hybrid ceramic angular-contact bearings and a dynamically balanced rotating assembly.
Direct drive is strongly preferred.
A belt step-up transmission is possible, but I would rather avoid the additional radial bearing load, belt tension, losses and complexity at these speeds.
The initial compressor speed target would be around 80,000 rpm, with the mechanical assembly ideally designed with enough margin to eventually test approximately 90–100k rpm if required.
The big disadvantage is obvious: compared with the P2, I would essentially have to engineer my own high-speed compressor cartridge.
Electric motor
For the GTD2060 direct-drive concept I'm currently looking at Lehner high-speed inrunners.One candidate is the Lehner 1540.
At around 60 V, the Lehner calculator gives approximately:
20 A → 79,256 rpm / 1.085 kW mechanical
40 A → 78,141 rpm / 2.236 kW mechanical
60 A → 77,027 rpm / 3.355 kW mechanical
with approximately 93% efficiency at the higher load points.
I've contacted Lehner directly and asked which motor/winding they would recommend for approximately:
- 80,000 rpm
- 4–6 kW mechanical power
- 5–10 second high-power bursts
- repeated intermittent operation
- air cooling only
- approximately 60–67 V supply
For the P2, the motor requirements would obviously be different(and some tested) because the compressor only needs roughly 25–35k rpm and could use a conventional high-power RC motor with a belt drive.
The main decision
This is really the part where I would appreciate opinions from people who have already built these systems.P2
Advantages:- complete compressor/bearing assembly
- much easier mechanically
- proven in several electric supercharger projects
- only ~25–35k rpm required for the boost level I'm initially interested in
- easy to change compressor speed with pulley ratios
- physically large compressor for a 2.2L engine
- possible surge/matching problems at low engine airflow
- belt drive and associated radial loads/losses
- possibly more electrical power than necessary
GTD2060VZK
Advantages:- I already own the turbo
- ~43/60 mm compressor seems better matched to a 2.2L engine
- potentially lower airflow requirement and electrical power
- very compact
- direct drive could eliminate the belt completely
- requires a custom shaft and bearing cartridge
- ~80–100k rpm operation
- much more demanding balancing and machining
- bearing selection and lubrication become critical
- little practical information available about electrically driving this particular compressor
Questions
I'd particularly appreciate input on:- For a 2.2L engine primarily needing electric assistance at 1,800–3,000 rpm, would you choose the P2 or a smaller ~43/60 mm turbo compressor?
- Based on experience with similar ~60 mm compressor wheels, what pressure ratio would you expect around 80k / 90k / 100k rpm?
- For those who have tested the P2, how far left on the map can it realistically operate before surge becomes a problem?
- Has anyone built a custom ball-bearing cartridge for an electrically driven turbo compressor?
- Has anyone successfully used a direct-drive motor/compressor arrangement around 80–100k rpm?
- Considering the additional fabrication required, do you think the smaller GTD2060 compressor offers enough advantage over the P2 to justify it?
Any test data or experience would be very useful.
Thanks!