Vacuum Forming Splitter

[Greg Amy]

Understand, your vertical idea might work...but I think you're overstating just how much "downforce" these things provide, versus just reducing underbody lift. I'd be shocked if there's more than 50-75 pounds vertical force total on that plane...time for a fish scale, string, and GoPro camera?

[Chip42]

might be. the good news is that the exposed area in the front builds a lot of positive pressure on top, which could be creating moment about the forward pin, and actually negating a lot of the loading to the rear pin from whatever low pressure there is.

I think an average pressure drop underneath + front end high pressure area is producing ~150-200# on the front wheels of our little MR2s, just based on the bowing of the 3/4" hardwood plywood planks we use. we don't have good ride height change data. But there's a LOT of exposure under the beak of an MR2, so it might be a more extreme example (though most of you all are seeing 50% higher top speeds and should expect a LOT higher loading for a given shape).
EDIT:
throwing some math at it, and rough numbers for all variables, making assumptions etc... the splitter on our MR2, which has ~6in of distance from the tip to the first support bolt would take ~20psi of pressure differential to deflect the tip 0.1in.
Damn I wish I had me some CFD...

[Z3_GoCar]

Standard 1/8" aluminum pop rivits sheer way less than even machne screw limit (memory says 250 - 400 lbs) But they'd also be subject to fatigue too. I'm thinking nylon bolts, but didn't see any at Home Depot to try. When I was a tween we used a single grade 8 1/4-20 as a sheer for our New Holland hay bailer. Once my dad tried a grade 5 (all he could find) but it was too ductile and sheered on start up. Lesson learned, strong but brittle failure was needed.

[lateapex911]

I used to vacuum form parts for a design studio I worked in. A splitter is going to be tough in that you'lll need to heat a large sheet, which means a large oven or other heat source, and secondly, you'll need a pretty good vacuum and a nice big and flat frame to house the material. It's all probably cake with the right tools, but for us homebuilders, it's a tricky operation.

[Z3_GoCar]

Chip, I've decided to take your advice and mount brackets from the aluminum bumper bar to the splitter. The front is a slotted pin and the rear is a nylon bolt for a sheer element. The final peice will be slotting/clearancing my new finder liners where they normally mount to the bumper cover and under tray.



The pin is formed from a 1/4 bolt and a 3/8" pin with 1/4 washer on the outside, the rear hole is for a 1/4" nylon bolt while the wood block is to prevent the angle from stabbing a tire (I'm going to trim the excess bolt off.



The bracket from the bumper bar to engauge with the pin in the rear facing slot and the nylon bolt with the rear hole. I made these out of steel angle because it's easier for me to weld angle than to machine aluminum.



My splitter, ready to be sealed and painted. I decided to eliminate the center cut back and go with a straight planform as the car's not likely to get sucked down to bad with 8oolb front springs and just over 3" of ground clearance.

[Z3_GoCar]

So, I used my new splitter at Thuderhill, worked well on Friday, Saturday, and half of the race on Sunday. Then in the middle of the race on Sunday, I went off at the back side of the hill at turn 5. The right side sheared the 1/4"x20 bolt but the left side held and bent the angle bracket, but tore the plywood off the carrage head bolts, but there's no damage to the nose of the car. So I guess it worked as planned.

[Matt93SE]

:thumbsup: I think?