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Discussion Starter #1 (Edited)
Hi everyone,

I am looking to modify my power steering pump to provide MORE assist to reduce steering effort. My new suspension setup has an aggressive caster value, and I am looking to slightly mitigate the increased steering effort by increasing the flow volume to the rack. I have a spare pump taken apart and I'm wondering if anyone here knows anything about modifying the pump.

From what I have gathered, enlarging a orifice will provide more volume. The flow control valve, bypasses excess pressure inside the pump, back into the inlet once it reaches a certain pressure built up in the pump from increased engine speed.
Will a slight enlargement in the dual orifice inside the pressure port union alone, be enough to increase a little bit of volume? I am aware that increasing volume will also place additional load on the seals inside the rack, so I'm looking to step it up at the smallest increments as possible.

Any ideas or advice?






**Edit**

I've found a link to a aftermarket power steering pump for another application. It looks like the assist, can be modifed by changing the blue fitting with different sized orifice. I wonder if this idea could be applied to the factory oil pressure union port?

Does anyone know if Factory flow control valve are made in different sizing orifices? According to the TSRM, they are lettered from "A" to "E" IIRC, and they are supposed to match the letter stamps on the case. However, idk if this is simply due to the case being machined to accept different sized control valves, or if there is actually a difference in the orifice.


https://www.onedirt.com/tech/steering-upgrade/improve-steering-feel-with-a-tuneable-power-steering-pump/
 

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Discussion Starter #2 (Edited)
Here's some more findings from last night. The brass fitting on the pressure port union, is a press fit. Meaning that it can be removed via a slide hammer. When you remove this plug, it'll reveal the dual orifice. The orifices, are also a sleeve, that is pressed fit into the union.



The pump also uses different unserviceable flow control valves, that are marked from letter "A" to "F", that are matched to different stamped Cases. I've measured the OD of these 2 valves, and they are the same, at 14mm top to bottom, so they are interchangable between different case housings. Hard to see, but the difference can be seen up close.



Control valve on the left, is from a pump "D". The one on the right, is a pump "E"
I wonder if different flow valves were used for different applications with the 2jz motor?
 

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I wonder if you can drill one more hole the same size without taking it apart. Are they easy to find another one?

Side note, sort of related. I was wondering the same thing and curious how hard it would be to retrofit a quick ratio electric steering rack into a Supra/SC. The faster electric rack should be a revelation in handling with the older chassis.

https://www.jegs.com/p/EPAS-Performance/EPAS-Performance-Universal-Electric-Power-Steering-Rack-and-Pinion/3571098/10002/-1

A little expensive but with a high amp alternator and high cca battery maybe it will reduce the load on the accessory belt as well and make the car handle better.
 

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Discussion Starter #4
I think it would be cutting it too close to the other two, by drilling one in the center. I enlarged one of them the next size up on the drill bit, which was something still really small, like a 3/32 of an inch iirc. I'm slowly stepping up to observe the differences it would make, and keeping in mind of the fact that increasing the flow to the rack would also place more load on the seals.

Toyota wants a minimum pressure of about 1050 psi or something like that, but since online PDFs are down, I'll have to check my own TSRM to be 100% sure. It would be nice to know what would their maximum intended pressure would be, so I can try to stay within Toyota's happy medium of pressure. It seems like the pro-touring guys like to send their steering stuff out to be modified over at Turn-one, so I just sent them an e-mail to see what do they think, or if they feel comfortable working with a 2jz power steering pump.

I know the flow control valves uses the same part # between GE and GTE pumps, but they are discontinued from Toyota. I'll have to dig a little deeper to see if the Port unions are the same as well. I've busted the orifice from the port union of my spare PS pump trying to tap it out with an extension and a mallet, so I'll have to find another port union for that pump eventually.

As far as the electric steering rack, it looks a little tricky with the Mkiv's crossmember, but I'm sure some mounts can be done by someone who has the imagination. Granna's has a faster ratio rack that is 100% bolt-on. It is a manual rack however, and I've driven my car on the factory rack without PS, and it was work out in dead stops for my scrawny ass lol. I'm going to guess the faster rack would work great with lower speed stuff once it's going, but what do I know?

On the contrary, the Mkiv has a fairly short wheel base, and the factory ratio probably contributes to a good deal of the car's high speed stability and precision. I remember the first time I've gone 150+ in the car, and I was surprised at how stable the car was to manuever at those speeds. If that were to be traded off with a faster rack, that could be a deal breaker for me.

I wonder if you can drill one more hole the same size without taking it apart. Are they easy to find another one?

Side note, sort of related. I was wondering the same thing and curious how hard it would be to retrofit a quick ratio electric steering rack into a Supra/SC. The faster electric rack should be a revelation in handling with the older chassis.

https://www.jegs.com/p/EPAS-Performance/EPAS-Performance-Universal-Electric-Power-Steering-Rack-and-Pinion/3571098/10002/-1

A little expensive but with a high amp alternator and high cca battery maybe it will reduce the load on the accessory belt as well and make the car handle better.
 

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I was thinking a hole at the top or bottom, not necessarily in the center. But enlarging the holes are easier to not mess it up. Let us know how it feels.

My Jaguar XFR has a faster hydraulic rack, maybe 1.5x and it is definetly requires more attention when you are going 150mph or more than a singled supra. But it is very stable. It doesnt float or move around. The on center dead spot is almost zero compared to the supra. But the feel and low to mid speed handling is amazing and fingertip effort, versus the Herculean upper body workout the supra is. In a autox, the supra is a handful to change direction fast not because its heavy or doesn't handle, just because the ratio is so slow and the dead spot in the center is too wide imo. Could we find or have a different gear made for the rack? Could you pull out the old gear and have it scanned in 3D? Have that turn company sell us a quicker gear for the factory rack.

Im not for making it a Ferrari F12 ratio, but maybe something in between. Maybe make two options. Jaguar has beautiful steering and their electric units are praised for feel and handling lately maybe i could swap a Jaguar electric unit in there.

Either way maybe the solution is both? More assist\flow with a little faster gear and some poly bushings? I would like to shrink the dead spot in the center as well. Makes the car feel low resolution when I know it isnt compared to modern performance machines.
 

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Discussion Starter #6
Will do. If they respond, I will ask them what would be a run down of having a faster gear set made. I would expect something low volume production or one off, would be very expensive unless there was a group demand for it, but it wouldn't hurt to know.


I was thinking a hole at the top or bottom, not necessarily in the center. But enlarging the holes are easier to not mess it up. Let us know how it feels.

My Jaguar XFR has a faster hydraulic rack, maybe 1.5x and it is definetly requires more attention when you are going 150mph or more than a singled supra. But it is very stable. It doesnt float or move around. The on center dead spot is almost zero compared to the supra. But the feel and low to mid speed handling is amazing and fingertip effort, versus the Herculean upper body workout the supra is. In a autox, the supra is a handful to change direction fast not because its heavy or doesn't handle, just because the ratio is so slow and the dead spot in the center is too wide imo. Could we find or have a different gear made for the rack? Could you pull out the old gear and have it scanned in 3D? Have that turn company sell us a quicker gear for the factory rack.

Im not for making it a Ferrari F12 ratio, but maybe something in between. Maybe make two options. Jaguar has beautiful steering and their electric units are praised for feel and handling lately maybe i could swap a Jaguar electric unit in there.

Either way maybe the solution is both? More assist\flow with a little faster gear and some poly bushings? I would like to shrink the dead spot in the center as well. Makes the car feel low resolution when I know it isnt compared to modern performance machines.
 

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Discussion Starter #8
Can you just modify the sensor or switch that adjusts PS feel from low to high speed to not switch from low speed mode?
Normally, yes. The Supra also has a low SAI, and caster values, so it's steering's holding force is typically pretty light for most. My setup has high caster, so it's steering is on the heavier side.
 
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