There are often some adjustments needed when cramming modern power plants into early cars. In this article we will follow Jason Scudellari at the In The Garage Media Tech Center as he modifies the firewall, toeboard, and floor of his Brookville 1929 Ford roadster body (sitting atop a Speedway Motors chassis) to accommodate a small block Chevy engine and a TREMEC TKX5 speed manual transmission.
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In this case, the upper mounting tab was cut off the bell housing to minimize the size of the cutout needed on the firewall.
The back of most V8 engines is knobby and convoluted, so it often makes sense to take an incremental approach, nibbling away at the firewall, toeboard, and floor until sufficient clearance is created. It’s usually a good idea to position the engine as far back as practical. This gets more of the weight transferred to the rear and on early cars, often, extra room is needed between the engine and the radiator so a proper fan can be fitted.
The bell housing is placed over the firewall and the upper edge is marked for trimming.
It’s worth mentioning that if you mount the engine back a lot, it does put more weight on the rear wheels, but it will reduce the foot room for the driver and passenger and make underhood engine access more challenging. Usually, finding a reasonable compromise is the best approach.
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An abrasive cut-off wheel is used to slice through the firewall.
Scudellari had to haul the engine in and out of the chassis several times to get a good fit, and at one stage he removed the bellhousing and cut down the top mounting tab. That allowed the front edge of the bellhousing to be traced against the firewall for one of the first trimming operations. The best results come from going slowly and surely at this stage. You can always fill in any areas that were inadvertently cut oversize, but it’s best if you can get it right the first time.
With the engine positioned close to its final location, the firewall is marked for trimming on the passenger side where clearance is needed for the valve cover.
After cutting away enough of the firewall and toeboard the engine could be brought back to its final position and the task of filling the open areas could begin. Most of this is done by making a pattern from chipboard, transferring it to sheet metal, cutting and shaping the metal, and welding the pieces into place. Scudellari found a steel sphere at Industrial Metal Supply, and he was able to cut a section from it to make a beautifully contoured recess for the distributor.
A step drill is used to make holes in the corners of the cutouts. This is a great way to get nicely radiused corners.
Every project will have its own unique elements, but the general procedure shown here should work for many cars. MR
The cut-off wheel is used to make straight cuts between the corners.With the engine back in place, a view from the rear of the firewall shows that a little more trimming is needed.With the passenger side of the firewall trimmed, the engine can be slid a little more and the driver side can be marked for trimming.A piece of chipboard is trimmed to make a pattern for the recess needed on the passenger side.A strip of 16-gauge steel is cut for the recess, and the bends needed in the corners are formed by hammering over the frame rails, a convenient surface with a nice radius.With the perimeter of the recess welded into place, a chipboard pattern is made for the rear surface.Here’s a view of the finished recess for the passenger side cylinder head.The firewall is trimmed away to make clearance for the distributor and the center portion of the engine.With the distributor and spark plug wires installed, it is apparent that a little more room is needed for adequate clearance.A clever way to make a nicely curved recess for the distributor is to start with a pre-formed steel sphere. This was cut down to get the needed portion.The firewall is marked from the inside for trimming to meet the hemispherical indentation.The piece of metal that will fit against the dished recess is rough-cut and curved by bending over a compressed gas cylinder.A panel clamp is used to align the dished recess with the lower metal piece, and they are tack-welded together.After the two parts of the recess are welded together, the front edges are trimmed to fit and the recess is tack-welded into place.Chipboard is used to make patterns for the remaining filler pieces needed on both sides of the recess.With all the filler pieces welded into place and the welds ground smooth, you can see just how well the rear of the engine nestles into the firewall.Chipboard is used to make a pattern for the bell housing cover.This plastic bucket turned out to have just the right curvature for bending the bell housing cover.A mounting flange was attached to the cover, allowing it to be screwed snugly to the firewall.The transmission cover was shaped and fitted into place.A recess is needed for the shifter. A large hole saw is used to make a perfectly round hole in the transmission cover.With a coat of textured black paint, the modifications to the firewall, toeboard, and floor are finished in a very professional manner.
