atb

Starting to mount up the accessories on the S4 engine in my OB track car. I'm curious if I need to transfer over the trombone cooler for the power steering system. Not really sure how necessary it would be on the track car.Easy enough to do.Even though the '79 didn't come with one the mounting holes are all there.
Appreciate any input.

GlenL

I wonder about its real need. Leaving belly pan off? '79 pump and rack or S4? If ya got it and it goes on easily then I'd go ahead and do it.

On a related and hijacking thought, what are you doing for transmission cooler?

atb

No belly pan on this one.
I was mounting the S4 pump, as it didn't look like the mounting holes for the top bracket on the earlier style pump are in the 32v block.
That does raise the interesting question of running an '88 PS pump on an early rack. Maybe not compatible pressure wise?
I'd need to make an adapter to bypass the cooler and connect the feed line directly to the pump, but looks like that would be pretty easy.
On the other hand, if I can't mix and match pumps/racks, I'll need to take a closer look at mounting the old style mounting bracket.

No trans cooler yet. That will go in on the second tear down of the car, and I plan on building my own.

Right now, I'm just trying to assemble the car so I can get it running and make sure everything works. The car's been totally re-wired, MS3.57 installed, later model tranny and engine, after market suspension, later model brake master cylinder with hand made brake lines, custom fuel lines.... so much to go wrong on initial start up . I'm convinced when I go to connect the battery for the first time I'm going to have a smoke show of biblical proportions. Lol.

dr bob

Adam --

I'd go with the PS cooler, maybe with something a little more than just the trombone loop.


Related sort of:

My Honda Pilot DD comes with a PS cooler of sorts, a finned trombone tube that sits in front of the radiator. Honda specs a bigger cooler for towing more than 3500 lbs with the car. I'm not sure why they would think a heavier towing load would cause need for more PS cooling, unless they figure that a heavier trailer is longer, and would therefore need more turning and backing when there isn't much airflow through the radiator/cooler area.

Back to the Porsche -- The cooler loop is there to protect the plastic reservoir from extremely hot fluid I'll guess. The ATF likes to stay below 175ºF just like motor oil. The PS pump is not a high-shear pump, so it doesn't add a huge amount of heat on its own, but there is some. Porsche figured that a loop of plain steel tubing sitting barely off the bottom of the floor in front of the radiator would be enough in all the conditions they tested the car in, including slow traffic in the Middle East summers and high-speed autobahn cruising. IMO, there's no reason to doubt that it would be enough for track duty. Even with the extra steering load of race tires, there's usually good airflow through that front box except when you are turning and backing. Getting in and out of the trailer might be the toughest duty that cooler will see.

Speedtoys

Definitely use one.

Cratering PS systems with fluid all over engine bays is a suck way to end a track day.

Id agree with Kibort that...its not LIKELY in the 928 design, but it will absolutely help the system, itself, if even a simple radiating loop with fins was added.

atb

Okay, so the cooler gets pirated from the S4 and put in the track car (if I use the later P/S pump).

So next question:
Anyone have any input on whether or not there's an issue running the 1988 P/S pump with a '79 rack? The rack updates don't line up with the pump updates. Racks changed in '82, and then again in '90. The pumps changed in '85 (maybe to accommodate the 5L block mounting?) and in '91. So I'm running a first generation rack with a second generation pump.

Rob Edwards

1985 service info tech, page 32: smaller pump due to larger alternator, but the flow rate and the operating pressure is the same as earlier pumps (75 +/- 5 bar). The '91 pump was the change to 100 bar.

No mention of the rack change in the '82 service info tech, but I'd bet that the '88 pump would be fine with a '79 rack.

FWIW, the Zombie doesn't have a PS cooler, but it's using an electric pump that sits on the floor of the passenger compartment- not sure how much being out of the engine compartment helps with heat load. Having burped PS fluid in my GT on an Autocross day, though, I'd definitely keep the cooler.

mark kibort

I dont use one and have no problems what so ever with over temp or spillage.
I dont know why you think its essential, but over 20 years of racing the 928 and no power sterring failures , is proof that the rack is up to the task

john gill

After my last rack overhaul in the GT , the ps guy suggested slowing down the pump speed as the track car doesnt need the manueverability in traffic , also decreased the load on the engine .
Not so easy to do in the track road car with all the working accessories , but a dedicated race car with other than stock components not so hard , will be in my development phase of the race car once it hits the track.

Speedtoys

You're asking to argue over a statement I never made.


Simply not going to play along Mark.

FBIII

So you use the term cratering of the power steering system and significant fluid loss. We are discussing the removal of a cooler loop that would lower fluid temperatures. I think Mark drew a pretty logical conclusion to your post unless you were implying something else.

mark kibort

this is the problem here... no one seems to understand english.
Jeff..... "definitely use one" means to me, that it is essential that you have one. i disagree... nothing to play around with here. just quoting you and your advice. you dont want PS fluid over your engine... put a sock over the PS container. if it blows, it blows, not because of temp, but because of pressure. hard fast movements make the pressure rise more than normal and at the track, you can blow a line or a seal, but thats not "cooler" related.

thank you!

this is a bad idea as well. its not running that fast and is very effective in giving control during high and medium speed turns. the PS pump is marginal at track speeds and moderate turns at 3500rpm, so slowing it down, after a downshift, and turn in to a 60mph turn, can be marginal for control. the pump can handle the RPM and is not at risk to wear out prematurely. and , contrary to the "ps" guys advice, in traffic is when you need the most amout of control and assist for quick reactions and steering actuation.
I notice PS steering effect reductions between turn 3-4 at sears and its only because the pump is not spinning hard enough to give the steering powered needed for that particular turn at that particular RPM

AO

I just blew apart my high pressure line from the pump to the rack. But you should have seen the condition of the hose. I went to a stainless braided line with AN fittings. Shouldn't blow apart for a long time. Temp on the other hand... not so sure if that is truly an issue. The car ran for many many years as is.

mark kibort

thats the real problem, not pressure, or temp, its age!! you got the right idea, but the stock replacement lines are more than adequate.

AO

Cost me $40... hard to beat that.