Making progress on the Mini Sprint-T on a Wreck-Free Sunday

I’m dashing this off between classes and services and meetings at church today because this is “do everything at once” day for me. I have been doing some mock-up work on the Mini Sprint-T while I was doing some thinking about posts during the week and managed to get the engine assembled to block, heads and intake manifold stage with the oil pan attached, then mocked that up to the mocked-up body and seats.

That thing sticking up out of the engine is a Vertex magneto, a kind of self-powered ignition system that used to be popular for race engines because the spark would get stronger at high RPMs. It had an output curve exactly the opposite of distributor ignition systems of the day, weak at low speed but very strong at high. The other reason why they were popular is you could leave the battery and starter off the car and just push start. When the engine spun over fast enough it would start and run until you switched it off. This saved weight because you could leave battery, made from lead, and the charging system off the car. For classes without a minimum weight, or with ridiculously low minimum weights, this was an important consideration.

Moving away from ’60s racing engines and back to the ’10s, notice the backs of the bucket seats peeking above the back of the body. This is because when I was sitting in the real body I noticed my forward view was pretty much non-existent when I sat on the bottom of the car, and that I needed to be between 9 and 12″ higher to see where the front of the car was so that I could avoid running into things. This has good and bad implications for this car. Let’s get the bad out of the way first, this is going to raise the CG a bit and also increase the frontal area. Moving to the good this raises the seat high enough to make fitting wide butts into the car not a problem. Broad shoulders are still a problem. Anyway this is high enough that the driveshaft tunnel will not intrude on the seat area, meaning one less packaging problem to worry about on the 1:1 car. It also means I will have room under the passenger seat to mount the battery without worrying about how to get to it for service. Mount the seat on a forward-pivoting platform with locking pins on the back and access to the battery will only take seconds assuming there is nobody passed out in the passenger seat. This will keep the weight to the rear of the car while reducing the polar moment of inertia, a measure of the car’s resistance to a change in direction. I will be able to mount a small battery upright, or a very large battery on its side.

I have also been thinking about the rear axle. Specifically, the torque arm forward mount and the panhard rod mount on the axle. What I came up with was utter simplicity for the forward mount to the arm and frame, two rod ends of opposite thread, one bolted to the torque arm and the other mounted to the frame at the transmission crossmember and the two connected by a threaded sleeve. Infinite adjustability of pinion angle, and fore and aft play to keep the actual fore and aft controls from binding. On the axle end it can bolt to the pinion support so that the torque arm mount to the axle also serves as a panhard rod mount, and a third job it can also function as the driveshaft hoop as it will be bolted solidly to the front of the rear axle and run alongside the drive shaft. I would just have to actually weld the hoop to the torque arm and the plate that bolts to the pinion support on the rear axle. The panhard rod would bolt to the rear of the mount to the pinion support below the lateral center of the rear axle.

Going back to that picture for a moment, you might have noticed the back of the body was propped up a bit, and the front was supported by the engine oil pan. This is because the body will be mounted on top of the 1.5″ square frame rails and the engine between those rails, so the bottom of the engine will be 1.5″ lower than the bottom of the body. That still doesn’t keep the distributor and the fuel injector throttle body from sticking up in front of the driver’s view but it does help a little. You can see the pad that a carb/fuel injector throttle body would mount to on the top center of the engine, just in front of the magneto.

Now I need to get some raw stock and build the frame for the Mini Sprint-T, make the mold for the vacuformed body and run off a few bodies to use, then buy or make wheels that fit the tires and wallah (voila), Mini Sprint-T that I can use as a planner for making the 1:1 scale version.

My co-installer for the stair rails was completely under the weather this morning so I’ll have another trip to the church to make to complete the installation. Yay /s

It’s getting late and I was up late last night and early this morning, so I’m a little yawn-y, and I’m having trouble composing sentences that make sense when I re-read them after typing. a LOT OF THAT IS i’M HITing a lot of typos tonight for some reason. So, bedtime.

PSA, Opus

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