Slow power steering

[mustard-z]

My dad and I co-drive an XP autocross 78 280z at local events and run wide hoosier slicks which are pretty soft, 22.5x9.5x15 R35 compound on the front of our car. The car has a SBC with iron heads/waterpump, etc but aluminum air gap intake and the engine is mounted on JTR mounts and is attached to a T56 tranny connected to 84 corvette rear suspension. We have standard steering knuckles on the front with GC coilovers and 325lb springs. We've got home built tubular front swing arms using heim joints to relieve suspension stiction.

 

The car drives well and is very fast, the suspension transitions quickly but the steering lags behind leaving it tough to navigate full offset gates or "esses" at speeds of about 35-45mph and with the offsets distanced about 30-40 feet apart. Larger sweeping turns are OK and even tight turns seem OK provided there aren't large steering movements just prior to the turn.

 

We used info from this post to help us in our endeavor: LT1 w/ Subi rack

 

Our installation generally follows that link but uses an 87 Subaru Legacy rack AND pump, as we figured a matched set would be better than mix and match. We modified our crossmember to lower it to reduce bump steer. We made our own mounts to hold the pump appropriately and hydraulic flex lines to connect the two. We are using the proper fluid at the proper levels and don't notice any odd noises coming from the system.

 

The feeling of the steering on these quick transition turns feels like it "lags". Another way to state it is that the steering wheel force is quite variable, all the way from what it felt like with 225 DOT slicks on with manual steering to a fully power steered car with no problems using these wider soft slicks. Driving it in the pits is no problem and you can maneuver the car with ease. We're at a loss for what causes this problem other that some parts may be worn out with the pump/rack. It seems to us something like a pressure relief valve isn't opening soon enough causing the steering force to get real hard in the direction you are trying to reverse your steering input! Is this possible? Any info would be helpful, hoping that we could change a spring in the rack or change the pump and maybe that fixes it.

 

Thanks for any help,

Aren