Super-fast ratio Corvette power steering rack in '88 Fiero

[Series8217]

I have a 1993-1995 Z51 power steering rack.. it has like 2 or 2.25 turns lock to lock and similar total stroke (sliiigghhttllyyy less) to the Fiero rack. It's narrower than the '88 Fiero rack, so it will fit in with some tie rod adapters a custom driver's side bracket. The 88 Fiero passenger side bracket looks like it will fit without mods.

Since it's such a fast rack I think it'll have similar steering effort to the stock manual rack, but it's going to make the car feel a lot more maneuverable, and probably kick ass in autocross (which I never do).

The only big issue I know I'll run into is not having enough caster or trail so that the steering returns to center quickly and doesn't float around on the freeway.

I have my front caster maxed out right now, but I think increasing the caster on the 88 front Suspension adds more trail than caster.. I get a lot of side-to-side oscillation on the freeway if I apply some steering angle and then let go abruptly. I have Konis set to the middle setting. Stock front swaybar and springs (cut a bit, so slightly higher than stock rate). I didn't notice the oscillation at all before I adjusted the alignment. I used to have stock shocks.. The oscillation didn't change much when I put the Konis on, so the oscillation must not involve much vertical wheel movement.

By the way, does anyone here have an '88 Fiero steering rack sitting out they can take some measurements of for me? I just have the rack shaft itself, otherwise the only rack I have is on my daily driver.

[fieroguru]

Have you seen this thread... Rickaddy88GT is running a ZR1 rack on his 88.
http://www.fiero.com/forum/Forum2/HTML/069722.html

My 86 Vette also had 2 turns lock to lock - I think it was swapped by the previous owner because the car was not a Z51 car and the turn signals didn't auto cancel unless you made a really sharp turn. So you might not need to find an actual ZR1 rack, but just a Z51 version.

[Series8217]

Have you seen this thread... Rickaddy88GT is running a ZR1 rack on his 88.
http://www.fiero.com/forum/Forum2/HTML/069722.html

Yeah I read through that thread.. people were having problems with the adapters Rick had made, so I think there are a lot of variations in the racks. I'm just going to do mine from scratch and make sure its right.

My 86 Vette also had 2 turns lock to lock - I think it was swapped by the previous owner because the car was not a Z51 car and the turn signals didn't auto cancel unless you made a really sharp turn. So you might not need to find an actual ZR1 rack, but just a Z51 version.

I think mine might be the Z51 rack too rather than a real ZR1.

[fieroguru]

What measurements are you looking for? I have a complete 88 front suspension including steering rack under a bench in the garage and could pull it out to do some measuring.

[Atilla the Fun]

The ZR1 of '90-'95 didn't get the 'vette's quickest rack. At 176 ('90) to 182 ('95) mph, you want slow steering.

[Series8217]

I split the Mustang steering rack discussion off into a separate thread since it's not part of this build: http://realfierotech.com/phpBB/viewtopi ... =3&t=17052

[Series8217]

The ZR1 of '90-'95 didn't get the 'vette's quickest rack.

Source? The ZR1 has the same rack as the Z51 option, which provided the quickest rack ratio available. However, my original post was incorrect about it being 2.0 turns lock to lock; it's actually 2.25 (fixed now).

http://www.zr1netregistry.com/firstking.htm

At 176 ('90) to 182 ('95) mph, you want slow steering.

No, you still want fast steering. You just don't want steering that's twitchy or light. Even with the fast ratio, the the 'vette has good steering feel thanks to a combination of the right caster, steering axis inclination, and near-zero scrub radius.

[fieroguru]

I think he is referring to the fact that there were 2.4, 2.25 and 2.0 lock to lock ratios available for the C4 vettes. The early Z51 cars had the 2.0, the base model was the 2.4 and the ZR1's (and probably some others) got the 2.25 (or atleast that is what the 1990 ZR1 specs show).

[The Dark Side of Will]

The Saleen S7 has insanely fast steering, and yet is stable enough at high speed.

As the steering gets quicker, you end up with more stringent requirements for on-center play (IE, less is permisible)

[cactus bastard]

By the way, does anyone here have an '88 Fiero steering rack sitting out they can take some measurements of for me?

I do too, I measured the width for you and got roughly 28 5/8" measuring to where the inner tie rods bottom out.

On the subject of stock 88 racks, what is this bolt for?

My first thought was that it was something left over from their power steering designs, but then shouldn't there be two of them?

[Series8217]

I think he is referring to the fact that there were 2.4, 2.25 and 2.0 lock to lock ratios available for the C4 vettes. The early Z51 cars had the 2.0, the base model was the 2.4 and the ZR1's (and probably some others) got the 2.25 (or atleast that is what the 1990 ZR1 specs show).

So there was a 2.0 eh? Hmm.. that may be what I have. I bought the rack awhile ago; I thought it was a 2.0 at the time. I guess I ought to do some inspectin'!

[Series8217]

A late thanks to cactus bastard for the measurements.

Power steering pump is mounted, and the engine-to-body high pressure PS line is done. I need to run the line to the front still, and also run a return line (I currently just have the return capped off at the pump).

I bought one of Rick's last sets of tie rod adapters. I might see about getting his bracket design laser cut and bent by a local metal shop I know.

[The Dark Side of Will]

Thought about running a hydroboost since you will have hydraulic power accessible at the front of the car?

[Nashco]

Thought about running a hydroboost since you will have hydraulic power accessible at the front of the car?

I fail to see the advantage in this application...why?

Bryce

[The Dark Side of Will]

hydroboosts tend to give better pedal feel than vacuum boosters. The American hydroboosts tend to be bulky and heavy, but BMW has some compact lightweight units, even with remote accumulators to make packagine easier.

[Series8217]

Thought about running a hydroboost since you will have hydraulic power accessible at the front of the car?

No, because I'm going to finish the steering and then sell the car...

[Series8217]

Got the adapters.

New tie rods are on the way. Once they arrive I'll put the adapters on the rack and see how well the bellows fit. The other thread on Old Europe indicates that one of the boots will be too short, so I will need to look around for an extension or a longer one.

[Series8217]

The 'vette steering rack is drilled all the way through the center, to allow air to flow from one side to the other as the bellows expand and contract. Cool stuff.

[Series8217]

I finished fabbing the bracket and prepping the crossmember (which is now out of the car). I just need to weld the mount on now.

[Series8217]

Got the subframe back in the car tonight, and the rack is in place. I still have to hook up the steering column (might need to clearance the firewall slightly). I haven't run the power steering lines all the way to the front yet, but the rack is very easy to turn without any fluid in it. To satisfy my curiousity, I'm going to try driving it without power while the power assist cylinder is still full of air. I suspect that much of the extra effort on a power rack with the engine off is due to the driver having to pump fluid through the rack. With just air in it, it might be tolerable.

If not, I can at least get a baseline for power steering feel at minimum assist. If it's too twitchy on the freeway when boosted, I may look into an electric pump which can reduce output at higher vehicle speeds.