Daily Archives: July 25, 2019

Can’t stop thinking about the Mini and Sprint-T

First thing I was thinking about was making an oil pan for both that clears the bottom part of the front hoop, as that has to go right where the rear sump for the oil pan goes on both the SBC in the Mini Sprint-T and the LS engine in the Sprint-T. That’s not so hard for the SBC model in the model version of the Sprint-T, just cut the bottom off the oil pan and stick another one on that clears the frame parts. But for the LS engine in the real thing it’s a little more difficult. A completely new pan would need to be fabricated from scratch which is pushing my skills to the limit. I can do some stuff, I know how to do more stuff than I have the eye-hand skills to do.

In other news on the Sprint-T and its smaller cousin, major changes to the forward part of the frame for increased crash resistance and torsional rigidity. The crash resistance would come from bending the bottom frame rail to make it a single piece from the rear hoop to the front suspension mounts and making the full size version from 0.120″ wall instead of the previous version 0.060″ wall. Since the diagonal leading from the top of the front hoop to the front suspension crossmember would still be 0.060″ wall it would buckle first causing the engine to go under the passenger compartment in a frontal collision, with the lower rail failing at the bend to allow this. The other thing was a bolt-in set of diagonals that would triangulate the upper part of the front frame in race mode but be left off in street mode for better forward vision and to allow the upper diagonal from the front hoop to fail in a known way and direct the engine under the car in a frontal collision. The small amount of additional flex in street mode would be offset by the greater safety in frontal collisions, because while the bottom part is completely braced by the welded-on belly pan (with an access hatch for changing the oil) and the sides are triangulated by the upper and lower diagonal braces from the front hoop to the front suspension crossmember the top part is completely unbraced and would allow some deflection in torsion without the bolt-in brace. What I’m envisioning is a double triangle brace that would bolt in at both ends of the top member coming off the front hoop at both the front hoop and the front suspension crossmember and also the center of both the hoop and the front suspension crossmember. It would form overlapping triangles that run from the top of the front hoop to the center of the suspension crossmember, and a second triangle from the ends of the suspension crossmember to the center of the front hoop, and a piece that runs from one side of where the two triangles intersect to the other, making even the braces triangulated. I’m thinking this set of braces would be made from lighter wall tubing and also in a smaller diameter since it wouldn’t be highly stressed and also is mounted fairly high in the frame so someplace added weight is bad for center of gravity issues.

Also on the triangulation issues are the engine and steering box mounts. The steering box mounts need to be braced side-to-side so it doesn’t deflect under cornering loads and cause inconsistent steering reaction depending on speed (faster causes greater side loads on the steering requiring more input as speeds increase not related to slip angles from the tires, which reduces the feedback to the driver as to how much traction remains at the front tires), and the engine mounts need to be braced so they don’t become a point load on the lower rail of the frame and introduce a new buckle point in a frontal collision while at the same time it needs to provide a consistent buckle point for the upper diagonal to direct the engine under the car in that frontal collision. There are a lot of things to think about when you build a car from scratch, like where I brace the engine mounts.

Another thing I have been thinking about was the pushrod and rocker arm linkages for the front suspension. I have been thinking about this because it 1) allows for easy wheel rate and ride height adjustments going from street to race mode, and b) makes changing corner weights super easy. When changing the wheel rate the effective rate changes as the square of the ratio between the leg of the rocker arm attached to the axle and the arm attached to the spring and shock absorber so making the arm attached to the axle longer makes the rate go down while making the arm attached to the spring longer makes the rate go up, and adjusting both can give me the perfect rate for street and race without having to buy two (or more) sets of springs and shock absorbers, meaning I just need to carry extra pushrods that cost roughly $20 each instead of multiple sets of springs and shocks at anywhere from $100 to >$500 each. The ones I’m looking at now are $250 the pair or roughly $125 each. The other thing I have been looking at is how the rocker connects to the moving bits in the suspension, because the pushrod has to be over the axle, while the coilover has to be to one side or the other of the axle so it has room to travel. I guess this implies I need some method to make sure the rocker arm only rotates through the axis it is supposed to pivot on as a lever system and not on the axis between the pushrod and spring attachments because there is a moment arm between the two created by the need to have one on one side of the rocker arm and the other on the other side of the arm and not just on opposite ends of the rocker arm. Hypothetically with the rocker arm suspension one could adjust corner weights without needing to roll the car off the scales and drive around to get the shocks to settle because you never move the shock when adjusting the weight, only the pushrod.

And this is the wordiest I have been in quite a while, which just goes to show what my true passion is these days.