Thread: How to build an early hotrod frame

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This is a subject that has a large number of variables, that I will try and deal with. These variables, in an overview, are the width from outside to outside of the framerails, the overall length front to rear, and the most difficult to establish, vertical height, between main frame rails and the kicked up area over the rear axle and possibly over the front axle.
In terms of length, (wheelbase) a general rule of thunb is as follows---Most older car bodies will have a clearly defined position (designated by the wheelwell indentation where the rear wheels normally go) which gives the center of the rear axle. The minimum distance from the firewall of an old car to the drivers side of the radiator, when using a small block chev engine is 31 ½”, using a short waterpump and an electric fan. (this makes the assumption that you are not running an indented firewall, although most model A fords can take up to a 4” indentation without losing so much legroom that they become uncomfortable to drive.)
If you are using a “spring over axle” front-end, as per model A or 32 Fords, then the centerline of the front axle sets directly underneath the front spring, which sets directly below the front crossmember, which in turn sets directly below the center of the radiator thickness----thus, for frame design purposes, we will assume a 2” thick radiator, which puts the centerline of the front wheels, axle, spring, and front crossmember 1” out beyond the drivers side face of the radiator.
So---- To establish overall wheelbase, measure from the center of the rear wheelwell on the car body, out to the firewall, then add 31 ½”, then add 1”, and that total figure will give you the required wheelbase front to rear, with no firewall indent at all. If you think that you can live with a firewall indent, then subtract the amount of firewall indentation that you can live with from the total figure, and that will be your total front to rear wheelbase.
This is not the total length of the frame. If you are using the spring above axle front end mentioned above, then the tapered “frame horn” portion of the frame will generally extend approximately 10 to 11” beyond the center of the front crossmember, and then end---Note that if you are not running front fenders, then this bit of frame running foreward beyond the front crossmember is more of a cosmetic feature than anything else, although it makes a good place to run a front spreader bar/license plate holder, or a place to bolt front bumper brackets to.---Or it can be dispensed with completely, and have the frame end at the front crossmember.
I will add more to this post when I have time---its going to be a long one.---Brian