Power rack and pinion conversion ?
- Thread starter Trbobuick
- Start date
POWERBRAKEBOB
Banned
- Joined
- Mar 28, 2005
12.7 quick steer boxes
It's only my opinion, but I have found that if the a-frames were not angled enough to put in huge amounts of caster, the rack conversions will not self center. The ZR-1 has 7 degrees, angled back a frames, AND, the spindle is located 1" behind the ball joint centerline. If you can't put that much caster in the rack align. then the car will handle like a unicycle. The reason they "chop" motorcycle frames is to add self-steering caster to the bike. These guys that put racks in their Mustangs and street rods, hate them. The steering is too twitchy at hwy speeds, They keep trying to cut the p/s pump pressure down to reduce the sensitivity. There is no way to put that much caster in non rack designed cars. We sell a 12.7 gear ratio new steering box, that makes the car handle incredible, and is a bolt-in. There is alos a 14-1 gear box, and a 16-1 box. The quick box, with a 1.250" sway bar,(oh, and a Hydroboost) will make the car an incredible performer and handler.
It's only my opinion, but I have found that if the a-frames were not angled enough to put in huge amounts of caster, the rack conversions will not self center. The ZR-1 has 7 degrees, angled back a frames, AND, the spindle is located 1" behind the ball joint centerline. If you can't put that much caster in the rack align. then the car will handle like a unicycle. The reason they "chop" motorcycle frames is to add self-steering caster to the bike. These guys that put racks in their Mustangs and street rods, hate them. The steering is too twitchy at hwy speeds, They keep trying to cut the p/s pump pressure down to reduce the sensitivity. There is no way to put that much caster in non rack designed cars. We sell a 12.7 gear ratio new steering box, that makes the car handle incredible, and is a bolt-in. There is alos a 14-1 gear box, and a 16-1 box. The quick box, with a 1.250" sway bar,(oh, and a Hydroboost) will make the car an incredible performer and handler.
Hi PBB,
I'm unclear as to why a rack conversion needs auxiliary help to self-center more than a recirculating ball box?
But back to the rack conversion, the most knowledgeable person about realistic options to make this happen that I'm aware of, is Mark Savitske at SC&C classics in Pennsylvania.
About removing 100lb weight from the front of the car: impossible. Even with an 800 Saginaw box, with PS pump, bracketry, and all steering components removed - that is - removing exactly 100% of what it takes to make the car steer in a stock configuration, you wouldn't remove that much weight. (I'd have to check the exact amount, but I think that figure is in the vicinity of 60-80lb.)
If you switch to a powered R&P with a light-weight pump, you might save about 30lb compared to stock.
But the real problem with a rack conversion is that to achieve reasonable bump steer, the rack would have to be extremely short, and to have a limited stroke. The reason is that the A/G body LCA's are long, and the separation between the two is short. To make matters even worse, their inner pivot axes converge toward the front.
But again, I'd recommend a talk with Mark Savitske. The last I heard, he was working on a special rack configuration to overcome this problem.
HTH,
MAP
I'm unclear as to why a rack conversion needs auxiliary help to self-center more than a recirculating ball box?
But back to the rack conversion, the most knowledgeable person about realistic options to make this happen that I'm aware of, is Mark Savitske at SC&C classics in Pennsylvania.
About removing 100lb weight from the front of the car: impossible. Even with an 800 Saginaw box, with PS pump, bracketry, and all steering components removed - that is - removing exactly 100% of what it takes to make the car steer in a stock configuration, you wouldn't remove that much weight. (I'd have to check the exact amount, but I think that figure is in the vicinity of 60-80lb.)
If you switch to a powered R&P with a light-weight pump, you might save about 30lb compared to stock.
But the real problem with a rack conversion is that to achieve reasonable bump steer, the rack would have to be extremely short, and to have a limited stroke. The reason is that the A/G body LCA's are long, and the separation between the two is short. To make matters even worse, their inner pivot axes converge toward the front.
But again, I'd recommend a talk with Mark Savitske. The last I heard, he was working on a special rack configuration to overcome this problem.
HTH,
MAP
POWERBRAKEBOB
Banned
- Joined
- Mar 28, 2005
12.7-1 quick steer box
I've Just Seen Too Many Conversions That Became Too "twitchy" With The Rack, And I Really Don't See Any Advantage In The Weight Savings, Compared To The Expense And The Alignment Grief. The 12.7 Box Bolts Right In, And Gives A Better, More Solid, And Reliable Feel. The Global West A Arms Should Give It Even Better Response.
I've Just Seen Too Many Conversions That Became Too "twitchy" With The Rack, And I Really Don't See Any Advantage In The Weight Savings, Compared To The Expense And The Alignment Grief. The 12.7 Box Bolts Right In, And Gives A Better, More Solid, And Reliable Feel. The Global West A Arms Should Give It Even Better Response.
POWERBRAKEBOB
Banned
- Joined
- Mar 28, 2005
12.7-1 quick steer box
I know what you mean about 100 lbs. on the front end. So, I weighed a stock steering box. It is exactly 26 lbs. A rack would be 15lbs. Is it worth $2000.00 and a miserable handling car? We don't have the new box on our website, but we are the distributor for those boxes. The site is "powerbrakesonline.com" P.M. me for prices.
I know what you mean about 100 lbs. on the front end. So, I weighed a stock steering box. It is exactly 26 lbs. A rack would be 15lbs. Is it worth $2000.00 and a miserable handling car? We don't have the new box on our website, but we are the distributor for those boxes. The site is "powerbrakesonline.com" P.M. me for prices.
Hi PBB,
I think you're closer to the truth about weight savings than others have posted here, although doing away with the centerlink and Pitman arm also help with the weight savings. But again - 80-100lb worth: impossible.
About twitchiness: after thinking about this a bit further, I believe there are two ways where I can see that an R&P setup might be twitchier than the equivalent recirculating ball steering arrangement:
1.) To achieve equivalent Ackerman correction requires that the R&P be mounted further back in the chassis than the centerlink is now. This means that as either wheel encounters a bump and is deflected slightly rearward because of the compliance of the LCA bushings, the bumped wheel will tend toward a transient toe-out condition.
2.) Since the R&P configuration is lighter, it also poses less inertia for a wheel to overcome when it encounters a bump, so the yaw acceleration in response to road irregularities will be higher. Remember that road irregularities create fore-aft forces on the wheel, and the centroid of these forces, if taken to be the geometric center of the contact patch, create a moment about the steering axis whose moment arm is roughly equal to the scrub radius. As we reduce the scrub radius, we reduce the upsetting moment created by road irregularities. But unfortunately, the scrub radius for the A/G body from the factory is ridiculously high (about +90mm,) so - no surprise - the stock design is twichy. (Nowadays, the design norm is not to exceed +25mm of scrub radius, but this also relates to the matter of torque-steer for FWD cars.)
There are two solutions here, I think:
1.) Reduce the scrub radius, or even make it slightly negative.
2.) Tweak the Ackerman and/or bushing compliance to create toe-in with a bump input (or under braking, equivalently.) But, this is somewhere between difficult and impossible to do without creating other problems, so really, we come back to scrub radius.
With these changes, you won't need to touch caster, but admittedly - the changes I'm talking about represent major surgery for the front of the car, which is why I've believed for years now, that the right way to an R&P conversion is to completely redesign the front-end of the car.
Best,
MAP
I think you're closer to the truth about weight savings than others have posted here, although doing away with the centerlink and Pitman arm also help with the weight savings. But again - 80-100lb worth: impossible.
About twitchiness: after thinking about this a bit further, I believe there are two ways where I can see that an R&P setup might be twitchier than the equivalent recirculating ball steering arrangement:
1.) To achieve equivalent Ackerman correction requires that the R&P be mounted further back in the chassis than the centerlink is now. This means that as either wheel encounters a bump and is deflected slightly rearward because of the compliance of the LCA bushings, the bumped wheel will tend toward a transient toe-out condition.
2.) Since the R&P configuration is lighter, it also poses less inertia for a wheel to overcome when it encounters a bump, so the yaw acceleration in response to road irregularities will be higher. Remember that road irregularities create fore-aft forces on the wheel, and the centroid of these forces, if taken to be the geometric center of the contact patch, create a moment about the steering axis whose moment arm is roughly equal to the scrub radius. As we reduce the scrub radius, we reduce the upsetting moment created by road irregularities. But unfortunately, the scrub radius for the A/G body from the factory is ridiculously high (about +90mm,) so - no surprise - the stock design is twichy. (Nowadays, the design norm is not to exceed +25mm of scrub radius, but this also relates to the matter of torque-steer for FWD cars.)
There are two solutions here, I think:
1.) Reduce the scrub radius, or even make it slightly negative.
2.) Tweak the Ackerman and/or bushing compliance to create toe-in with a bump input (or under braking, equivalently.) But, this is somewhere between difficult and impossible to do without creating other problems, so really, we come back to scrub radius.
With these changes, you won't need to touch caster, but admittedly - the changes I'm talking about represent major surgery for the front of the car, which is why I've believed for years now, that the right way to an R&P conversion is to completely redesign the front-end of the car.
Best,
MAP
Not trying to bash, but i have some questions...
Only 26 lbs ? Did you measure the complete steering system ? centerlink, inner tie rod ends, outer tie rod ends , power steering lines, pump, and reservoir ?
2000 bucks ?
From TRZ Motorsports - Performance Parts Manufacturing
Gbody Rack and Pinion Conversion Kit $650.00 319-3
All of the converted g bodys i have ridden in or driven seem to turn fine, im not sure what you mean by twitchy ?
Only 26 lbs ? Did you measure the complete steering system ? centerlink, inner tie rod ends, outer tie rod ends , power steering lines, pump, and reservoir ?
2000 bucks ?
From TRZ Motorsports - Performance Parts Manufacturing
Gbody Rack and Pinion Conversion Kit $650.00 319-3
All of the converted g bodys i have ridden in or driven seem to turn fine, im not sure what you mean by twitchy ?
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