Power Steering

[Prowordsmith]

I own a Mk.I Roadster that was assembled by someone else. It has a power steering unit. The problem is that the steering is so quick and responsive that I don't feel comfortable doing corners at even 7/10ths. It's not like any racer I've ever driven. I've learned there are different ratios that are available and perhaps my (from an '89 Mustang) might be a 15:1. How can I tell? How does one change the ratio?
When I come close to flogging the car, it feels like I am on the boundary of flipping the car at worst, spinning out at best.

[mcwho]

I have power steering also, not compete as yet. I have read in some of the blog posts that there is a spring in the ps pump that can be modified to change the rate of assist, not the ratio tho. My rack is about 3 turns lock to lock. That is a good starting point to see what your ratio is.

[pcww]

You can also adjust the flow of the fluid with this: http://www.summitracing.com/parts/hdt-ps-101/overview/
On the forum it is know as the Heidt's valve. You can search and there is a lot of info on the install. I have it but have not mounted yet.
Henry

[Bob Cowan]

The rack ratio is built in to the rack. The only way to change it is to change the rack as a complete unit.

[skullandbones]

I have a quick ratio rack and the modulating valve mentioned above. When you adjust the valve to "deaden" the steering about a turn and a half, the characteristics of the steering change dramatically. Also as mentioned, you can't actually change the ratio. It just allows you from getting into trouble by over reacting to the sensitive PS at full power. I have gotten used to the quick ratio with the damped feel but will adjust the valve maybe even a little more (reduce PS fluid flow to the rack) for track days and adjust it for max sensitivity for AX which will come next (also smaller steering wheel). I'm doing my first track day 1/25 and AX in March. You will not be disappointed with the adjustability. I think I added about $150 to add the Heidt's valve to the existing PS. Good luck, WEK.

[Jeff Kleiner]

To determine which ratio rack the car is equipped with tell us how many turns it is lock to lock. It will be either 2.5 or 3.

Before we get into other areas let's start simple and check your tire pressures. For 15" I recommend 24 pounds and a couple less for 17"s. Much more than that and it will begin to feel like the car lacks grip (which it will!).

I run the fast ratio steering rack with a Heidt's valve on the street and and track and it is rock steady whether the boost is all the way up or backed down. The car behaves the same either way, just the amount of effort required to turn the wheel changes. The big player in all of this is alignment; with power steering you can, and want to, run more positive caster to help the car track straight and return to center. Unfortunately the Mk1's fixed upper control arms do not allow for as much adjustablility as the later versions. Ideally we'd like to see 8 degrees or more but I don't think you'll get there with the limited amount of travel allowed by the Mk1 frame slots. Even at that though it should be able to be improved. Start by aligning it...if you can't attain 8 degrees go for as much positive caster as you can get along with .5 to .75 negative camber. You'll want toe in to be approximately 3/32" to 1/8". Note that I said TOE IN. This is very important; if it is toed out the car will get darty and twitchy lacking straight ahead stability.

Get this good baseline setup done and I bet you will see some improvement. Good luck!

Jeff

[CraigS]

Rather than spending the money on the Heidt's valve and the fittings needed (which will probably cost more than the valve) you can also reduce the pressure that the pump puts out. Depending what pump you have you can find a spring loaded relief valve under a plug that's about 7/8 inch diameter. Pull the spring out, cut off a coil or two, and reassemble. If you go too far, you can always shim it back w/ some small washers. If you have Mustang pump, do a search here and the other forum to find a spec for the length of the spring after trimming.