Steering quickener

After installing the new steering arms, the steering effort was lower but the wheels did not turn as much with each revolution of the steering wheel. I wasn't too concerned until I took the car for a drive and realized that some hard back and forth on the steering wheel didn't result in a lot of lateral movement of the car. I considered changing to a quicker ratio steering rack but the MGB-GT rack is already only 2 turns lock to lock and only dedicated racing (read-expensive) racks are quicker. My solution was to add an Afco 2:1 steering quickener. It is basically a gearbox that takes one turn of the input shaft and  changes it to two turns of the output shaft. Here is a picture of it installed between the steering wheel and rack and pinion with video link just below the pic:

Video of before and after

New Steering arms

I plugged all the numbers for my steering into my Speed-Wiz program and it told me that I was not getting any Ackerman. Basically, Ackerman is when the inside front tire turns sharper than the outside front tire when going around a sharp turn. It is not as important on a road course as it is in autocross where the turns are much sharper. Changing Ackerman is not easy and is usually done by repositioning the steering rack or changing the length of the steering arms. I needed to move my steering rack back to improve Ackerman but that was not possible without a redesign of the front suspension. I decided to lengthen the steering arms.

I removed the MGB arms and used them to build a template with an adjustable hole where the tire rod end goes.

I used tubing with a 1/2" thick wall

And 1/2" thick flat bar for the in between areas. Here it all is, trimmed and ready for welding and 1 inch longer than the old arm.

Once welded I used a tapered reaming tool to get the hole where the tie rod bolts just right.

Sorry about the sideways picture. Painted and installed on the car. Now I can turn the wheels all the way and still move the car by hand. I can't wait to drive it.

Wheel and Tire decisions

As most of you know, I put 15" wheels on the car because I needed to clear the brakes. Then I found out that the radial slicks I planned on running were actually no good for autocross because the radials don't like rapid turning (such as a slalom) like the bias ply slicks. The only tire company which has 15" bias ply slicks in the right widths is Avon, and they are more expensive than Hoosiers or Goodyears and have no contingency.

   The price difference between 13's and 15's will pay for a set of new rims so, I broke down and ordered a set of 13" rims from Diamond Racing wheels. I took a chance that I would be able to modify the brakes to fit. The wheels arrived and with some minor tweeking, I got them to fit over the brakes. Then it came time to order tires, and problems arose. The Goodyear or Hoosier tires that are supposed to be the hot ticket in D/EMod are actually designed for Formula Atlantic cars. This means the front tires are 9.5 inches wide and the rear are 13 inches wide. This is not a problem for cars like a certain green Bugeye which has only 41% of it's 1850 lbs on the front tires, but I have 49% of 2250 lbs on my front tires.

   Now, I can make the car work on these skinny front tires, provided that I don't overload tires designed for a car 650 lbs lighter than my own, but they would be a compromise. I started to look again at the Avons, which to be fair to Avon, cost about the same as Goodyears or Hoosiers as long as you stick to 13 inch wheels. However, the Avon rep advised me that the 13 inch tires are designed for cars up to 1600 lbs and the 15 inch tires would work better for me. So, I decided to go with the Avon 10.7/21.5-15 in front and 11/23.5-15 in back. At some point I may want some rain tires and I can put those on the 13 inch wheels.

Measuring Center of Gravity (CG)

To properly calculate suspension set up, I needed to get an accurate measurement for the center of gravity. This proved both easier and more difficult than planned to figure out, here's how I did it:

I put the car on the scales and  inflated all four tires to the maximum recommended safe pressure of 40 psi. My total front weight was 1115 lbs with me in the car.

I had built some heavy duty steel stands that are exactly 12 inches high and put them under the rear of the car, with the scales on top of them. I got back in the car and noted the total front weight again-it was now 1135 lbs.

Longacre has a neat calculator on their website and all I had to do was punch in the numbers and it told me what my CG is. It calculated that my CG is 17.35" from the ground. Here is the link: Longacre racing website

Special tools

I had no place to get a jack under the back of the car so I built this folding piece that slides into the tow hook holes and has a platform on the bottom that fits perfectly on the jack.

I can adjust motion ratio of the shocks but it has been difficult getting an accurate measurement of how much X wheel movement equals Y shock movement. I built this telescoping tool that bolts in place of the shock and it has what's left of a Vernier caliper welded on one side. I simply take a measurement then raise the wheel up a known amount then check the measurement again. Voila', I know my exact motion ratio for that setting.

More improvements to rear suspension

After everything was bolted in, I discovered that I couldn't quite use all the range in my roll center adjustment and moving it up and down was cumbersome with the diffuser bolted on. I decided to change all that at once.

I began by fabricating a new crossmember out of 1/8" steel, here it is all tacked together ready for welding. I made the curves using a 5 gallon bucket.

Here it is welded in. I used some square tube that tightly slid inside the old and new crossmembers to tie them together better. I also added a screw jack (visible in the center of the pic) that runs down to a bracket attached to the pivot of the Woblink, allowing a roll center change with the turn of a screw.

I had to put a bracket from where the rod attaches to the axle to eliminate some unwanted flex. Since I weighed the car last I have added a heavier battery, eliminated both sway bars, added a tachometer and changed the whole rear suspension and the result is a 108 lb increase in weight. This is not a welcome change but I think the benefits of those changes will overcome the extra pork.