- Oct 21, 2018
Spool Helix HPFP overdrive system
Spool Performance is really excited to introduce our latest product offering to the N54/early N55 community, the Helix overdrive unit. We have been testing this for almost a year now and here it is finally in a release post. We’ll try to structure this post in a way that we explain some of the details on the product, how it works, what the benefits really is etc. with some results we’ve gathered over the course of last several months.
What is the Helix?
The Helix is simply put, a planetary gearbox for your High-pressure fuel pump. It is very similar to what you would find in your automatic transmission. A planetary gearbox allows you to change gear ratios in an axial configuration. It consists of three types of gears- ring gear, planet gears, and a sun gear. In our configuration, the planet gears and the sun gear are on different rotating axles and the ring gear is stationary. The particular configuration of the gears and their spatial fixturing allows an axial increase in shaft speed from the input to the output of the unit.
The graphics above is a simple representation of the principle. The Helix unit uses helical cut gears for better load carrying capability, precision meshing, and longevity.
Why do you need it
The N54/early N55 high-pressure pump is a very capable and over-engineered piece of hardware. They do a good job supplying fuel at high pressures at stock power levels. As we start tuning and pushing more power, we start seeing drops in the high pressure. What is happening here is that the high-pressure pump is not able to pump as much fuel as the injectors are injecting into the cylinders hence causing the rail pressures to drop. The pump at this point is running out of displacement volume. With a rotary pump like the continental HPFP, an easier way to increase displacement is to spin the pump faster which results in an increased number of delivery strokes per cycle. The Helix helps you do exactly this and thus helps overcome a big limitation in N54/early N55 fuel systems without the complexity of a secondary port injection system.
Concerns on HPFP Longevity
It is no secret that the continental Hpfps have been subject to failures and recalls in the past. So we made it a high priority during testing to study the modes on failure and the effects of overdriving the pump on the failure modes. From investigating a number of failed units, two modes of failure were established as the most common. The first mode is inlet metering valve actuation failure due to failures in actuation solenoid coil and second is the limp home mode bypass valve leaking. The limp home mode valve connects the low-pressure inlet to the high-pressure outlet of the pump and remains closed as long as there is a higher pressure on the high-pressure side. It is designed to flow in the case of an hpfp failure. On older units, this valve starts leaking from high pressure to the low-pressure side preventing the hpfp from being able to build full pressure in the rails. The valve relies on rubber elements to seal under normal operation and we infer that prolonged use of E85 affecting the rubber is the main culprit behind this mode of failure. We did find cracked bellows as well but we estimate it to be very rare since only one out of more than 20 failed pumps were affected by this. We also analyzed the oil out of high mileage units and they showed very little metal content and physical examination of the swash plate, the springs and pistons proved that these elements are designed to last and had very little wear. In short, most failure modes on the hpfp unit are modes that are not affected by over spinning the pump in any way.
Fueling limits with the Helix
We have differentiated our current overdrives into two for different end-user scenarios. The Helix will support up to 600whp worth of flow on full e85 and 750+ on e60 mixes. The Helix Xtreme will support 750whp worth of flow on full e85 and 850+ on an e60 mix or other gasoline blends. Helix is currently ready for launch and the Helix Xtreme is still in longevity testing.
The horsepower numbers quoted were made possible only with changes to the stock DME inlet metering valve control tables. During our initial phases, we weren't achieving expected pressures in the rail at over 550 whp levels. Through bench testing the valve under flow conditions we quickly established that the limiting factor was the flow through the metering valve. Steven Brachulis and Ken Atkinson from @WedgePerformance were instrumental in helping figure out the calibration changes needed to flow more fuel through the inlet valve and we would like to take this opportunity to thank them for all the help on the tune development. Also want to thank Jake Yamona who was instrumental in helping set up RAM variable logging to monitor the parameters needed to understand and modify the calibration parameters and defining the needed tables for all the different ROMs. The xdf’s with the new tables will be released shortly and will be available to all major tuners.
Results and Flow Limits
In this section, we will include data logs from our beta and pre-release units along with details on the car from which the log is presented for Helix that is scheduled for release. Helix Extreme is still in beta phase and undergoing longevity testing. Logs and details for the Helix Extreme version will be released closer to its launch.
- N54 VTT stage 2+ 601whp 643wtq E60
- N55 335i 22psi big boost 3.4 full E85
- N54 6466 20psi 93 Octane
- N55 PS2 21psi full E85
- N54 FrankenTurbos full E85
- N54 6466 ST 26psi full e60
If you have any questions or would like to see more details/logs please send an email to [email protected]
Spool Helix Overdrive units are available for pre-order on our website http://spoolperformance.us/index.php?route=product/product&product_id=71
Pre order units are scheduled to ship first week of September 2019.