Leggman wrote:
My donor car is 52 inches inside
The body of the Focus goes past the outside of the tires. You lose some due to door thickness, and get 52 inches. But the "body" of a Sevenesque is the frame, which has to fit *between* the tires, with room for any forward links and tire movement. In practice, you're looking at 40 to 46 inches, outside-to-outside of the chassis. Minus the thickness of the side tubes and the center spine, which doesn't necessarily have to be on center. With a mid engined car you can narrow the spine to just wide enough to run the shift linkage through and get more hip room, not to mention the foot room from not having to accomodate a transmission and bellhousing.
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I will have the donor car delivered the first part of the week so More measurements can be taken.
I worked back-to-front. I didn't want to have custom axles made, so the inside-to-inside width between the tires, minus linkage, side rails, etc. set my chassis width. It all worked out fine for me, but I was prepared to pull the axles out a bit in the tripod joints to get another inch or two, and maybe use wheel spacers if I had to.
Since I was using aftermarket wheels, I backfigured from those, not the stock wheels.
The distance from the center of the tire to the front of the exhaust manifold (or intake, if you have one of those bassackwards engines) determines where the firewall goes. You can angle the axles forward a bit if you want; not all cars have the axles going straight out.
With the firewall, you then figure the angle of the back of the cockpit, which would ordinarily be close to the seat back angle. That gives you a triangular space across the middle of the car. KB58 welded up a custom fuel tank and put it there. I'm using it for storage.
With the back of the cockpit set, you can find out how long the cockpit needs to be. Sit on the floor with your back against the wall and measure to the soles of your shoes. Then add room for pedal travel; four to six inches, perhaps. That establishes the front of the cockpit.
While you're against the wall, put your hands out at a comfortable "holding the steering wheel" position and measure that. Note that you'll be leaned back a bit in the car. Add four to eight inches and that's the distance to the dashboard.
The base of the windshield can be anywhere from the back edge of the dash, forward.
The front wheel centerline can be anywhere ahead of the front bulkhead. If you use the Focus rack and pinion you can ignore the "front steer" vs. "rear steer" question and just go with what you have. Unless the Focus rack is pathologically wide or narrow you can lay out the front suspension geometry to accomodate it.
Doing the front end geometry isn't as intimidating as it looks. You'll also probably wind up designing your own independent rear end; I don't know if the Focus uses McPherson struts, but if it doesn't, they're usually too tall to use without sticking out the top or making a really high rear deck. If they're not you'd have a big win as far as saving time and effort, though.
(note: there are now short struts and strut inserts to accomodate the "slammed" custom car market)
You'll have to do the front (and probably rear) suspension no matter which end the engine is in...