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Ditching belt-driven power steering for an electric pump

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Ditching belt-driven power steering for an electric pump

 
Old 10-09-2018, 02:45 AM
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TastyBacon
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Default Ditching belt-driven power steering for an electric pump

Warning, this is a novel, but if you're a technical type, you'll appreciate it. There are pictures too.

For the second time, I've had my power steering overheat during a HPDE event on a road course, and I've decided to go full overkill to solve it. Here's how I got to this point:
  • Did my first track day in the C5 last fall (not my first, but first in this car). It was only 50F outside, but I would start losing steering assist about 5 laps into each session. During lunch break and the following session, I ran to NAPA, bought a 12,000# GVW transmission cooler, spliced it in the return line from the rack to the reservoir, and zip-tied it in front of the radiator. Ugly hack job, but no more power steering problems the rest of the day!
  • Over the winter, I decided to clean up my oversized/hack job cooler install, so I got a smaller cooler that's actually sized for power steering and mounted it on the rack crossmember near the factory location. I wanted to just use the Z06 cooler but it wouldn't fit around my turbo intercooler pipe, so I got an aftermarket cooler about the same size (half as wide, twice as tall) and made a custom bracket and lines for it:


I figured this would be a nice clean solution to PS fluid overheating...nope! Just a couple weeks ago, I did another HPDE, and my problems were back. After several laps, I was losing assist again. After I got home, I started reading all about power steering, and that's how I came to the conclusion that the belt-driven pump has to go. Here's why:
  • A belt-driven power steering pump has a fixed displacement. It moves the same volume of power steering fluid every revolution.
  • Once the engine is turning around 2k RPM, the pump is moving enough fluid to give you all the assist you'll ever need. The excess volume of fluid that isn't required to maintain system pressure is just bypassed through the pump's internal pressure regulator right back to the inlet side of the pump.
  • At high RPM, the belt-driven pump is moving a ton of volume, and if you're hammering down a straightaway, you're using almost none of it! All that fluid is just being pumped in a tiny circle, wasting horsepower and adding heat. Makes sense that the places on the track I would most often lose assist were the first turns after a long straight.
  • Turn One, who make smaller-displacement pumps for track use, state that a factory Saginaw Type II pump like the one on the C5 consumes 8HP at 5,000RPM pump shaft speed. The pump is turning much faster than that at redline though; since its pulley is smaller than the crank pulley, the pump is overdriven. So it's safe to say I'm losing at least 10HP dumping heat into my power steering fluid until it foams and cavitates in the pump! F that!
There are several common solutions, but each of them come with their own problems:
  • Improve airflow to my cooler, switch back to a bigger cooler, or both. Still wasting 10HP heating the fluid.
  • Get a bigger PS pulley, underdriven crank pulley, or smaller displacement pump like Turn One. Still wasting some HP heating the fluid (Turn One says their pump consumes 5 when an OEM pump consumes 8, so save 3HP). Also get less assist at low RPM, which is annoying while parking, etc.
All of those solutions are just band-aids for a fundamental problem: belt-driven pumps work the opposite way you would want them to. At low RPM, they don't move enough volume to provide full assist, and at high RPM, they move WAY TOO MUCH volume and just waste power heating the fluid. So, F belt driven pumps. I'm removing mine and switching to this:



That's a TRW electric power steering pump from an '08-'09 Saturn Astra. It was under $100 from a junkyard including the mounting bracket and wiring harness. These Astra pumps are a lot more popular for retrofits in Europe and Australia (they got Astras as Holdens, Opels, and Vauxhalls for a lot longer than the 2 years we got them as Saturns in the USA). As you might expect, they seem especially popular with the drift guys who spend all day banging off the rev limiter. The instructions I've found say it has an internal pump controller and pressure regulator that will automatically increase and decrease the pump speed to maintain a fixed pressure. That means full assist at low RPMs; you can even wire the pump to a switch and still have power steering with the engine off. It doesn't require any sensor or data inputs (SWPS, VSS, CAN) to work, although there's a wire that all the instructions tell you not to hook up, and I'm guessing that's a data line of some sort. Best of all, it won't rob HP heating the fluid at high RPM.

I haven't done the retrofit yet but will post more pictures and info in this thread as I do. Thanks for reading.

Last edited by TastyBacon; 10-09-2018 at 02:49 AM. Reason: fixed typo
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Old 10-09-2018, 05:52 AM
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frodo84
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Interesting!
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Old 10-09-2018, 10:21 AM
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Originally Posted by frodo84 View Post
Interesting!
pretty cool though... where to you plan to mount it and what are you going to do about the old pump and pulley?... maybe you could just use the pulley as an idler so you don't have to make any belt modifications?
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Old 10-09-2018, 02:34 PM
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MAN,,,,,,,,,,,,,,,, I'm glad I read your post... THANK YOU for all that fantastic info.

We should ALL be doing this UP-GRADE!

Keep us updated on the install and outcome of the mod.

Bill
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Old 10-09-2018, 04:24 PM
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Thanks guys, glad you enjoyed my rant! Power steering is kind of a boring system--it just works, right? Considering the lengths people go and the money they spend to make 10 more HP, maybe it would be less boring if they knew what it was costing them at high RPM. The electric setup is not without its own potential issues, but when I learned that with the belt-driven pump, I was essentially paying (in HP) to shoot myself in the foot (with high fluid temps) I decided it has to go.

I'm thinking of mounting the pump in this area, behind the driver's front wheel (gallon jug used as a stand-in for the pump to approximate size):


I might be able to find room for it in front of the engine too, but I like the idea of getting some clutter out of the engine bay. The downside is that I would have to jack up the car, remove the left front wheel, and remove that access panel to check power steering fluid. But how often do you really need to do that, anyway? There are some pumps on Mazdas and Volvos that use remote reservoirs; that would've been a nice feature, but the Astra pump is well-documented to be easy to install, and I found a good deal on one, so I just went with it.

As for belt routing, it turns out that GM already sells a version of the Corvette accessory drive without power steering: https://paceperformance.com/i-197250...ve-system.html


Looks like all I need to do is unbolt my pump and get the same 1888mm 6-rib belt, and I'll be in business.

Last edited by TastyBacon; 10-09-2018 at 04:25 PM. Reason: added image
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Old 10-09-2018, 06:16 PM
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How much current does the electric pump need at maximum load?
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Old 10-09-2018, 06:31 PM
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A lot. I've read that maximum load is around 60A, and no load is around 6A.
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Old 10-09-2018, 07:31 PM
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I took a quick look at some comments on the Saturnfans website, and they reference it being hooked to the CAN bus - I guess that's the wire you don't hook up. Someone was retrofitting one to an older Saturn, and was using a 100 amp fuse - apparently it draws a bit more than 60 amps at full load. Also, they seemed to think it provides the same amount of assist as the engine driven Saturn pump, using the original engine driven pump rack, so that's a good sign - whether it delivers the same pressure and volume as the C5 pump, I guess you will find out! Some comments on the web in general about taking time to build pressure when you first turn it on. Again, you will have to decide whether that's a problem.

I really like the idea, and definitely will be interested to see how you get on.
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Old 10-09-2018, 08:04 PM
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Originally Posted by TastyBacon View Post
Thanks guys, glad you enjoyed my rant! Power steering is kind of a boring system--it just works, right? Considering the lengths people go and the money they spend to make 10 more HP, maybe it would be less boring if they knew what it was costing them at high RPM.
I'm all for making things better or stronger... it may seem boring but the same could be said about upgrading the driveline and stuff like that, you end up spending lots of money and don't notice much difference if any at all but things don't break haha... another good spot might be on the side of the radiator cradle under the driver side headlight, that would also make quick work of the lines since you have a pretty straight shot from there to the rack and won't have to maneuver anything around the engine... I'm not sure if having it mounted that low would cause any flow issues though
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Old 10-10-2018, 12:34 AM
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Thanks guys. I found this on the CRX community, good summary of the wiring and how to properly sequence power to get around the slow startup issues:
Electrical:
Pump has 2 big wires and 3 signal wires. Thick brown is ground, thick red is power. It doesn't need any relays, when pump is not signaled to operate it does not drain power. I've connected brown directly to battery terminal and shortened red one, finished with eyelet and fitted into fuse box, using 50A box fuse taken from some Civic fuse box. Opel uses 80A fuse there, but it would be bigger than EE8 battery fuse (70A) Also I've measured currents not exceeding 40A in normal operation and those fuses will easily survive short periods of overcurrent.

Now the signal part.
Long story short to have it factory-like:
-Brown - omit
-Black Ignition Connect to black with yellow stripe
-Blue with yellow Charging connect to white with blue stripe

Brown wire is some OBD signalling or some other useless data stuff. Pump will run when you supply +12V to two remaining wires, but there are still some options there:
-When you supply +12V at same time to both wires it will start like 9 out of 10 times winding up slowly up to speed. From time to time it will start instantly. This may be enough for you if you want to have it on a switch,
-When you supply power first to black and then to Blue/yellow it will instantly "jump start" to idle speed. When you remove blue/yellow (eg. engine stalled, no charging, but ignition on) it will slowly decrease speed keeping fading power steering for like 10 seconds. It will not "jump start" again until you disconnect black from +12V.
-When you keep blue/yellow at +12V and switch just black wire it will always slowly wind up and turn off instantly after you switch black off.
https://www.crxcommunity.com/viewtopic.php?f=4&t=214001
The stock C5 pump is 2.4-2.8 GPM and 1250-1350 psi. I haven't found pressure or volume specs for the TRW pump. It's been retrofitted successfully to such a wide variety of cars, and most modern cars are in a similar pressure range, so I'm not too worried about it, but it's possible I could end up with a little more or a little less assist than stock across the board.

I agree that under the headlight bucket would be a good place too, but my turbo plumbing is in the way

I will also be able to keep the C5's magnasteer variable assist system unmodified, since it uses a control valve mounted on the rack.
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Old 10-10-2018, 09:33 AM
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Don't forget, the C5 has a lot more tire on the road than a CRX, so the amount of "assist" needed is greater and that means more amps drawn. Since the Astra community has measured over 60amps, that 80 amp fuse sounds about right as a starting point. Fuses should always be rated well in excess of expected normal loads, otherwise they perpetually run hot. Plus, you would not want it to blow and leave you with no PS when you need it.
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Old 10-10-2018, 04:19 PM
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Yes, good point. I'll be using an 80A maxi fuse just like the Astra did.
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Old 10-10-2018, 07:50 PM
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Originally Posted by TastyBacon View Post
Yes, good point. I'll be using an 80A maxi fuse just like the Astra did.
What size is the wire? You might want to check that and size the fuse to protect the wire, just a suggestion.
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Old 10-10-2018, 10:15 PM
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I would suggest a minimum of 6 gauge cable, maybe 4 gauge if you can swing it. I'd highly recommend you come off the battery via a manually resettable circuit breaker (80 amp, maybe 100 amp depending on ambient under hood temps) and I also suggest you run the negative cable back to the negative terminal of the battery. The ground is just as important as the 12 volt positive to create a good circuit and keep the motor cool. 60 amps is no joke and as the unit gets used more intensely (like on a road course with big tires) the motor will heat up. This will cause it to be less efficient and try to consume even more amps as things heat up. I'd recommend using a duct of air pointed at the motor to keep the electric motor cool under race conditions. You can use something as simple and cheap as an inline bilge pump fan to accomplish this.

I'd also look at a new battery if yours has time on it, been discharged below 10.5 volts, etc. The better the battery condition the faster it can put out amps and the faster it can take a recharge to replenish its capacity which helps keep the electric motor cool.

You'll notice that on this companies 60 amp and 80 amp motors, they have fans installed to try to control the heat.
https://epasperformance.com/collecti...universal-race

I'm not a hydraulic power steering pump expert, but I doubt that it is consuming 10 hp at high rpms. I'm not sure why you're overheating so much in cool temps....I've tracked my car with R compound tires (315 square) in Calif heat with no boil over.

There is no free ride when it comes to energy....60 amps is near 1 hp but the alternator will have to consume more than that to make 60 amps due to losses as energy is produced.

I look forward to seeing what you come up with when it is all said and done.
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Old 10-11-2018, 02:41 PM
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Pretty fascinating stuff, subscribed to see how it turns out for you.
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Old 10-13-2018, 12:45 AM
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Old 10-14-2018, 02:23 AM
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The wire appears to be 8ga. Thanks for the suggestions, looks like Bussman makes a circuit breaker that doesn't cost much more than a quality fuse holder and fuses. Interesting option.

I'd like to keep the install fairly simple, so I'm not going to add any sort of cooling until it proves it needs it. I have heard of the column-mounted electric motors needing active cooling, but have not heard of the electric hydraulic pumps overheating.

Here's where I got my power steering pump horsepower number:
https://www.hotrod.com/articles/ccrp...ering-secrets/
From the article: "...8 hp is required to drive a typical Type II pump at 5,000-rpm shaft speed loaded at 700 psi."

The harmonic balancer OD is 7.5", and the crank pulley is 6.625", so when the engine is turning 6,200RPM, the power steering pump is turning about 7,000RPM. I'm not sure the power consumption scales linearly, but if it does, and the pump requires 8HP to drive at 5,000RPM shaft speed, it would take 11.2HP to drive at 7,000RPM shaft speed.
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Old 10-15-2018, 09:33 AM
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Super cool. Interested to follow along with this.
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Old 10-15-2018, 11:29 AM
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Give us some pics when you install it..

BC
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