Switching side pipes to under car exhaust?

[Three Peaks]

If you're buying a completed/used car, look for a street car with the undercar exhaust already installed. There are a few of them available for sale if you look.

However, if you are interested in building a car with undercar exhaust you'll need to look for a kit or manufacturer with a chassis that allows for a little "customization". The FFR and several other manufacturers offer the option of cutting the holes for the sidepipes, so you can start out with a body without the cut outs.
Several manufacturers have out riggers that can easily be modified as the car above to accomodate pipes/mufflers in the space under the seats. Ovalized pipe can help in this area to minimize clearance issues.
The cars with floor mount pedal box will be most difficult to deal with but not impossible. Trying to get around the pedal box, master cylinders, clutch slave cylinder and all of the other pieces under the car can be difficult but not impossible. It seems a car with the hanging type pedal box would be best suited to fitting the undercar exhaust on the driver's side.
Going over the rear axles is problematic in these cars. There is barely enough room for the axles and suspension to work properly, much less add exhaust pipe to the equation. This is obviously why most guys exit the pipes just in front of the tires. I've wondered if it would be worthwhile to build a "false trunk frame" inside the existing frame of cars with a trunk frame and aluminum trunk sides/bottom. You would lose a bit of trunk space, but you could gain a channel on both sides of the trunk to install the exhaust pipe to avoid the axle and still have it open to air on the outside for cooling purposes. This would also give you a channel to go over the gas tank and exit behind the gas tank without interfering with the suspension and/or roll bar mounts.

Of course, this option may not work well with cars with a fiberglass tub for the driver compartment or trunk.

Bob