How to make a solid first gen?
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Joined: Jul 2001
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From: Edmonton, Canada
Thanks guys, my fiance and I are heading off to get married this summer and then hopefully(trip is bankrupting me) we are going to purchase a home. I will be looking for a nice size garage to build up a car the way I have always wanted. I keep saying it's time for a second gen. but keep coming back to the FB so I think I'll start with the FB and buy a turbo 2 later. After the frame and suspension next will have to be an engine choice?
Airflow is my life
Joined: Aug 2002
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From: Orlando, Fl
Originally posted by elwood
As far as where to put the stuff -- here are my guesses, based on FEA motion models from other cars (I've never seen one for an RX-7 FB). Starting from the front of the car and moving rearward:
Upper Load Path Beam Roots -- where they come into the cowl sides (up at the dash board) usually sees a lot of vertical and lateral bending.
Front rail roots -- where the rails meet the dash panel and kick downward. This area where the rail section gets smaller usually sees a lot of vertical bending.
Cowl side to sill joint -- where the lower door hinge bolts, down through the front portion of the sill or "rocker" usually sees a lot of bending in the 'Y' plane.
Torque box -- that hat section that runs underneath the car, beneath where you normally put your feet, from the rails out to the sills. As the name implies, this part usually sees a lot of rotational force, like a driveshaft would.
The sills -- to save weight, I wouldn't fill the whole thing, but use enough of the stuff to close off the section every 1 1/2 feet or so. They see both Y-plane bending and torsional forces.
The 'yoke' that runs cross-car above the floorpan, just behind the front seats. Fill the outboard areas near the sill and the zone above the rear rails. This thing ties the sills to the rear rails and will see similar forces to the Torque boxes. (These really are the rear torque boxes on an FB)
Rear Rails -- where they transition from underneath the front floorpan to up the "waterfall". These will see 'Y'-plane bending.
The concept is simple -- you want to stiffen up the skeleton. The most important parts of the skeleton are the underbody points between the suspension force input points. For example -- the car's stiffness out at the front bumper beam isn't as important as the stiffness where the rails meet the dash panel.
Car underbodies (sedans, wagons, convertibles, and coupes) are basically three chunks joined together:
1. The engine box, which includes the dash panel and everything in front of it (front rails, upper load path beams, radiator surround, cowl/plenum).
2. The front floor, which includes the front floorpan, sills, etc.
3. The rear floor, which includes the rear floorpan, rear rails, etc.
Where these three main chunks join is where the car is normally the weakest. These are therefore, the points that need the most attention.
As far as where to put the stuff -- here are my guesses, based on FEA motion models from other cars (I've never seen one for an RX-7 FB). Starting from the front of the car and moving rearward:
Upper Load Path Beam Roots -- where they come into the cowl sides (up at the dash board) usually sees a lot of vertical and lateral bending.
Front rail roots -- where the rails meet the dash panel and kick downward. This area where the rail section gets smaller usually sees a lot of vertical bending.
Cowl side to sill joint -- where the lower door hinge bolts, down through the front portion of the sill or "rocker" usually sees a lot of bending in the 'Y' plane.
Torque box -- that hat section that runs underneath the car, beneath where you normally put your feet, from the rails out to the sills. As the name implies, this part usually sees a lot of rotational force, like a driveshaft would.
The sills -- to save weight, I wouldn't fill the whole thing, but use enough of the stuff to close off the section every 1 1/2 feet or so. They see both Y-plane bending and torsional forces.
The 'yoke' that runs cross-car above the floorpan, just behind the front seats. Fill the outboard areas near the sill and the zone above the rear rails. This thing ties the sills to the rear rails and will see similar forces to the Torque boxes. (These really are the rear torque boxes on an FB)
Rear Rails -- where they transition from underneath the front floorpan to up the "waterfall". These will see 'Y'-plane bending.
The concept is simple -- you want to stiffen up the skeleton. The most important parts of the skeleton are the underbody points between the suspension force input points. For example -- the car's stiffness out at the front bumper beam isn't as important as the stiffness where the rails meet the dash panel.
Car underbodies (sedans, wagons, convertibles, and coupes) are basically three chunks joined together:
1. The engine box, which includes the dash panel and everything in front of it (front rails, upper load path beams, radiator surround, cowl/plenum).
2. The front floor, which includes the front floorpan, sills, etc.
3. The rear floor, which includes the rear floorpan, rear rails, etc.
Where these three main chunks join is where the car is normally the weakest. These are therefore, the points that need the most attention.
Thanks -- well here's my last thought on the subject: Don't fill up the front rails forward of the shock towers or the rear rails aft of the rear axle. These zones are supposed to crush during impact events, and if you fill them up they won't be able to.
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