In the previous months, we've begun to show you the finer points to swapping a Three-Valve 4.6L Mustang powerplant into the Fox-body chassis. Luckily, the Mustang aftermarket is onto the trend, and many of the needed parts for the conversion are readily available. One of the hardest parts we ran into (so far) is the exhaust-namely the headers. Being that the 4.6L is significantly wider than the old 5.0L, real estate for headers is at a minimum.
American Racing Headers (ARH)...
American Racing Headers (ARH) of Amityville, New York, sent us a set of custom 13/4-inch headers. The primary tubes are bent for a Two-Valve, SN-95 application but have the correct flanges for our Three-Valve Hot Rod crate engine.
When we began to plan this phase of the project, we did a lot of research and looked into both long- and short-tube headers-we even tried the factory cast manifolds. In the end, we went with a hybrid header of sorts. American Racing Headers (ARH) of Amityville, New York, fabricated a set of Two-Valve mod motor headers with Three-Valve flanges so it would bolt up to our FRPP Hot Rod crate engine. The guys at ARH only tack-welded the primary tubes to the flanges and collectors so modifications could be made to ensure correct fitment.
For our installation, we headed back to Coastal Chassis Dyno in Tampa, Florida. With loads of experience in fabricating custom turbo kits, Sam Lippencott and Horacio Ramos are veterans when it comes to customized exhaust systems.
We knew that going into this part of the project could require a significant amount of time and fabrication to get it right, but we also knew it was something we only wanted to do once. With our ARH headers in hand, we began test-fitting the tubes, as well as making the necessary modifications for a perfect fit. After a few hours in the shop, we had pipes on the engine and were ready to take on the next step in this build.
When our exhaust plans began...
When our exhaust plans began to take shape, we weren't sure if the headers would fit in our Fox without being modified. ARH tack-welded our headers together so we could modify the primaries easily if needed. It also included a few extra pieces of 13/4-inch tubing with various bends in the event we needed to reroute the tubes.
Sam Lippencott started by...
Sam Lippencott started by supporting the engine from the top so we could remove the Maximum Motorsports K-member.
This gave us plenty of room...
This gave us plenty of room to measure and test-fit both headers.
Lippencott started by sliding...
Lippencott started by sliding the passenger-side header into place. This side was fairly close to fitting with no modifications.
The only needed modification...
The only needed modification was to the floorpan. After a little massaging, the header slid right in and bolted up.
Although it is an extremely...
Although it is an extremely tight fit, the header does not hit anything on the passenger side.
The only needed change to...
The only needed change to the header itself is shortening of the collector. Given the location of the transmission crossmember, the collector needs to be moved as far forward as possible to allow for the midpipe to clear the crossmember mount.
Even though we had much more...
Even though we had much more room on the driver side, the steering shaft and K-member were fairly sizeable obstacles.
Lippencott and Horacio Ramos...
Lippencott and Horacio Ramos planned out how to route the primary tubes before breaking the welds on the headers.
Lippencott started by removing...
Lippencott started by removing the front primary tube.
This tube was initially routed...
This tube was initially routed over the rest of the tubes and intersected the steering shaft on its way to the collector.
With the first tube removed,...
With the first tube removed, the header was reinstalled, followed by the K-member. It was instantly apparent the rear primary was also obstructing the steering shaft and needed to be modified.
Lippencott then removed the...
Lippencott then removed the back tube and began to lay out the new primaries.
The first bend of the rear...
The first bend of the rear primary was reused. Lippencott simply cut the tube shorter on the flange side, making the initial bend tighter. The tube was slid into place, checked for clearance, and marked, before being tack-welded into place.
After bolting the header to...
After bolting the header to the engine, Lippencott and Ramos hoisted the K-member back into position and measured for the front primary.
After cutting the extra tubing...
After cutting the extra tubing to acquire the needed bend and length, Lippencott began assembling the new primary.
Flattening the edges on a...
Flattening the edges on a belt sander ensure all of the cuts are flat for the correct fit.
Lippencott and Ramos then...
Lippencott and Ramos then fabricated the rest of the new primaries. This is a lengthy process due to the necessary test fitting.
Once the primary tubes were...
Once the primary tubes were fabricated to the correct shape, Lippencott shortened the collector side of the primaries as much as possible before tack-welding the collector into place. This will give us plenty of room to route the midpipe around the transmission crossmember.
After spot-welding the headers...
After spot-welding the headers together, they were sent back to ARH. The ARH crew will handle all of the finish-welding, as well as making provisions for the O2 sensors.
A side-by-side comparison...
A side-by-side comparison of both headers shows how much we were able to shorten the primaries.
The driver-side header now...
The driver-side header now has ample room for the steering shaft to run between the primaries with no interference. Once our headers come back from ARH, we can button up the rest of the exhaust with an X-style midpipe kit and mufflers we have left over from another project.
Check back next month as we...
Check back next month as we upgrade the rear suspension in our Three-Valve Fox with a torque arm from Maximum Motorsport.