rorik

I've been trying to figure out how to calculate this, but I'm coming up with nothing. I know that the pump is a positive displacement pump, so as rpm increases, the volume of fluid increases. Since the pump moves enough fluid to provide steering assist at idle, the vast majority of the volume it pumps at 8000rpm is a waste of energy. Same thing for the a/c compressor at high cruise speeds. So, has anyone actually dynoed their setup with and without the power steering belt on? I did a search, but like usual, it was totally pointless. And I was going to post this in the tech/misc section, but that too would have been pointless..

HiProfile

Key word is assist. Its just flowing fluid when not actively turning, which doesn't take all that much - it bypasses the rack's valves when not moving the steering.

Its been proven it takes ~5-7whp between stock NA to 200whp NA motors, but it also depends. The only reason I remove it is because its easier to fit a topmount in there w/AC than to create an AC and PS compatable ramhorn/log. I also need all the exercise I can get, I'm a fairly skinny guy.

For the AC, unless you have it engauged, the pulley free-wheels due to the magnetic clutch not being locked.

nfn15037

There really isn't much load on the pump unless you are turning the wheel. Expect less than 5 wheel HP (I've seen less gains on cars that I have dynoed with/without). Also, your thoughts on how to calculate parasitic losses are flawed. You need to add pressure into the mix, which is very low in a straight line and over 1200 PSI at full lock.

ATYPR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiProfile &raquo;</TD></TR><TR><TD CLASS="quote">Its been proven it takes ~5-7whp between stock NA to 200whp NA motors, but it also depends. </TD></TR></TABLE>

true, I've try this on a dyno

rorik

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nfn15037 &raquo;</TD></TR><TR><TD CLASS="quote"> your thoughts on how to calculate parasitic losses are flawed. You need to add pressure into the mix, which is very low in a straight line and over 1200 PSI at full lock.</TD></TR></TABLE>

I said I hadn't figured out how to calculate it! I don't know how to calculate hp from the pressure and volume of flow, (when driving in a straight line, ie dyno) neither of which I even know. However, what I wrote previously is still true, that an excess of flow is a waste of energy. That is why many new cars are coming out with electric systems, or electric/hydraulic hybrid systems. The manufacturers claim it saves a couple miles/gallon. I know some people use the mr2 electric pump, but it is designed to be used with a control circuit that drops the voltage when the pressure is low, which I don't know how to implement. I've also heard that several new gm cars, like the cobalt, use electric power steering pumps with that load sensing circuit built in, but I haven't researched that enough either.

Specifically, I just want to know how much hp the pump costs at 8000rpm on a gsr.. 5-7whp sounds about right. Now I wonder how much you could underdrive the pump and still get assist when parallel parking...and how much could be saved by underdriving it.

And another thing, I wouldn't really mind eliminating the p/s, but I don't think my rack would last long if I did. I've never driven a car with a tight manual steering rack, and it makes sense why. In a power rack, the hydraulic pressure on the rack's internal piston takes the stress off the pinion and rack gears, allowing them to last a hell of a lot longer.

mgro

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rorik &raquo;</TD></TR><TR><TD CLASS="quote">

Now I wonder how much you could underdrive the pump and still get assist when parallel parking...and how much could be saved by underdriving it.

</TD></TR></TABLE>
I use an AEM underdrive pulley on my 1994 EG hatch. The pulley is about 30% bigger than stock. Steering at idle works perfectly, just like stock. I assume losses will be lower inn proportion to the increase in pulley size, but I'm not sure as the pump has a rather complicated flow control system (see Helms manual).

rorik

That pulley sounds like a good idea to me..