C4 front conversion without taking body off

[Rick_L]

Some suspensions actually have the upper a-arm higher at the balljoint than at the frame pivot to increase this effect. The late C4 suspension does that.

That's what I was referring to with the control arm length statement. When you increase the height of the upper ball joint, that's what's important, not the actual length of the control arm.

As for my statement about the control arm length shortening - if you increase the SIA, that moves the upper ball joint inboard. If you raise the upper ball joint, that also moves the ball joint inboard since it must lie on the SIA line. I am assuming in this description that the inner pivot for the upper control arm does not move. Obviously you could move it too - and that's what the Gulstrand/Shelby mod does. All this is in the context of starting with a given setup and making changes, not starting over.

I agree with you that autocross results are not everything because it's a tight low speed course. On the other hand, that's one thing you can do to put numbers to mods on a street driven car. May not be perfect or ideal, but at least it gives you numbers which you don't get with a "butt dyno".

[rockytopper R.I.P 5-13-2017]

From the other site from the link I posted above about results of installing the taller ball joints and what they accomplish.

Quote "Stock tri-5 lower ball joints are positioned stud down. Installing a lower BJ with a longer stud will raise the vehicle ride height & create another issue due to the tri-5 short spindle height. The upper A arm will probably be pinned to the frame bumper. No need to figure the roll center with this configuration it is in the outfield.

When extrapolating suspension pivot points to determine roll center height a stock height 57 has an instantaneous center that does not cross the vehicle center line it intersects at the outside of the vehicle. This suspension design adds positive camber during bump, to the outside wheel during a turn & both wheels during braking.

A vehicle handles better when a loaded wheel changes to negative camber.

Using a stock height 57 with a 28" diameter radial tire which has a squat radius of 13" as an example: Installing a 1" taller ball joint in the upper control arm moves the instantaneous center across the vehicle vertical center line to the correct side of the vehicle. With this modification your front roll center is now 2.75" above ground, the suspension now changes to negative camber during bump, braking etc = a good handling vehicle that will roll a corner rather than plow through it..

Adding taller ball joints will effect camber setting with no effect on caster.

BTW: Upper ball joints experience more load force during hard braking than they get from suspension loading. The spindle acts as a lever through the ball joint trying to twist the upper control arm mount off of the frame.

[Maddog]

Rocky my car has essentially a stock front suspension except for C3 Corvette spindles. These spindles are 1" taller than stock 55-57 spindles and they also have a 7º steering axis inclination compared to the stock 3.5º. To install them, you have to use a bushing in the tapered hole for the lower ball joint, as the Corvette has a big ball joint pin. The other thing you have to do is shorten the upper control arm about 3/4". This is due to the change in steering axis inclination angle and also to the extra height. The stock steering arms bolt up but you have to enlarge the bolt holes from 7/16" to 1/2". You use a C3 front brake or any aftermarket setup that can be put on a C3. Stock C3 rotor diameter is 12" as opposed to 11" on the Chevelle brakes many use. I have some aftermarket aluminum calipers for a C3.

For the upper control arms, I had a set of Concept 1 tubular arms for a 55-57. These use a stock ball joint. Turns out that it was a relatively easy fabrication job to move the ball joint mount inboard 3/4". I doubt many other tubular arms would be this easy to mod. It is one place where the SC&C arms should work nicely, providing you could shorten them enough (and you probably can).

The drawback to the Corvette spindles is they are not dropped, and I've never seen or heard of dropped spindles for a C3. I want my car low, so bottoming out potentially is a problem. One good thing about the C3 spindles is that they only move the wheel outboard from stock by the extra thickness of a rotor compared to a drum. This amount to 1/4" per side.

The car is still under construction, so I have no first hand knowledge of how it will handle.

C2 and C3 Vet spindles are Impala spindles (1959-64), the pre 69 have the same 7/16" steering arm size holes but drilling to 1/2" is no big deal. You can use 2" drop spindles if you want to go that route as the 58-64 Impala drop spindles will be the same as your Corvette spindles. CPP's latest version is probably the best but I'm not 100% on CPP quality.

[chevynut]

When extrapolating suspension pivot points to determine roll center height a stock height 57 has an instantaneous center that does not cross the vehicle center line it intersects at the outside of the vehicle. This suspension design adds positive camber during bump, to the outside wheel during a turn & both wheels during braking.

Yes, that's because the upper a-arm pivot point is higher than the upper balljoint, because the spindle is so short.

Using a stock height 57 with a 28" diameter radial tire which has a squat radius of 13" as an example: Installing a 1" taller ball joint in the upper control arm moves the instantaneous center across the vehicle vertical center line to the correct side of the vehicle. With this modification your front roll center is now 2.75" above ground, the suspension now changes to negative camber during bump, braking etc = a good handling vehicle that will roll a corner rather than plow through it..

Not sure how he came up with those dimensions. Is there a diagram of this somewhere? I really wonder if just a 1" longer balljoint can do that. In order to move the instant center to the opposite side of the car the balljoint centers have to be further apart vertically than the a-arm shaft centerlines. I've never measured a stock tri5 suspension to see what the dimensions are.