1979 F100 Exhaust System
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Exhaust System

As part of the EFI conversion, I was originally going to try and use a Mustang exhaust system as my starting point, but it turned out that the Mustang exhaust (specifically, the "shorty" style factory headers) try to use the same physical space as the original mechanical clutch linkage on the truck, so a different solution needed to be found. I could try to switch to a hydraulic clutch or go with a custom exhaust system will full length headers designed for this truck. I did some research, and found out that I could use the hydraulic clutch setup from an 84-90 F series with a 5.0L or 4.9L and an external clutch slave cylinder. That was good news - it was possible and folks had done it before, so I knew it would work. If I went that route, I would have needed the proper bellhousing, slave cylinder, hydraulic line, master cylinder, and some or all of the pedal bits to make it all work. And the bellhousing, hydraulic line, and clutch pedal bits are all "used items" that I would have needed to hunt down and get decent ones. The price was also prohibitive - at least $400 by the time I was done, and I would have to pull the trans to replace the bellhousing, plus take out the pedal assembly to do that work. Yuck. I researched the exhaust system, and found out that I could piece together a basic exhaust system that exits in front of the rear axle using Summit brand headers, mufflers, and X-pipe plus some header reducers with O2 sensors built into them for a bit over $300. Since I knew that the Mustang exhaust was going to have to be modified anyway to fit this truck, ~$300 to get legal from a noise perspective was a good place to start, so I ordered the pieces.

Getting the headers installed was an unbelievable chore. The driver's side went in mostly OK from underneath with the front of the truck up on ramps, but one tube hit a small metal heat shield on the engine mount I was using. To remove the shield and allow the header to fit, I had to unbolt the motor mounts from the frame, jack up the motor, unbolt the mount from the engine, remove the shield, and then put it all back together again. I also had to remove the oil dipstick tube from the engine, and even then it was a really tight fit to get the header into place - but I got it in. The passenger's side header was Just Plain Evil, and it eventually went in from the top. I tried doing it from underneath at various stages, but it just wouldn't go in. First, I had to remove the starter. Then the engine had to be unbolted from the frame and jacked up as far as it would go to make clearance between the starter bulge on the bellhousing and the frame for the header collector to move into place. Finally, I ended up having to remove the motor mount from the engine to get clearance for one of the header tubes to slide down and have the header sitting roughly in place but not bolted to anything. After all that, I was able to re-install the engine mount to the block and lower the engine back into place, then reinstall the starter, and finally bolt the header to the engine. I also had to remove and re-route the fuel vapor line that goes to the charcoal canister. The original routing came up over the frame and then dove down under the raised pad that the engine mounts to - and it was hitting one the header tubes. I pulled the fuel vapor hard line towards the back of the truck, removing it from a series of mounting clips along the entire frame (and yes, it was as fun as it sounds) and re-routed it to stay on top of the frame all the way up to the charcoal canister area and thus avoid the headers entirely. Then I put it back into the original clips all the way down the frame to secure it in place. I also had to reroute the starter cable - the original routing followed the frame and then jumped over to the starter - with the headers this would have had the cable passing right between two tubes in a very small space - a bad idea. The new routing will go to the front corner of the engine and then follow the oil pan rail to get back to the starter. Later model F-series trucks used this same routing, so I know it works just fine.

Even after attempting to "adjust the engine" on it's mounts, the header collectors are still uncomfortably close to one of the crossmembers. This truck has three crossmembers around the engine and transmission - the usual front one under the engine and the usual rear one at/for the trans mount - plus a middle one that goes under the front of the transmission. The middle one isn't connected to the transmission, but it is connected to the suspension pieces on each side of the frame and I think it helps prevent the frame from moving around under load. The headers exit just above and behind that crossmember, but there is less that 1/2" of clearance in a couple of places - it looks like about 1/4" on the passenger's side. Not good. I may end up removing and notching that area of the middle crossmember on each side, and I'll get to practice my welding skills if I do that. I I do decide to do this, I would probably just get some 5" diameter steel pipe sections of proper thickness, cut some depressions in the existing crossmember right under the collectors, and then just weld in pieces of the 5" pipe as stiffeners to the original crossmember. Subtle, and helps preserve the stiffness of the original crossmember.

The X-pipe will sit just under the tail of the transmission, behind the transmission mount. The driver's side pipe from the header to the X-pipe will run fairly close to the speedo cable and to the shift linkage - there isn't much room in that area because there was no factory exhaust in that area. Even with factory dual exhaust, both sides of the exhaust ran down the passenger's side of the truck to avoid the second/"forward" fuel tank on the driver's side if the truck was so equipped. This truck is not so equipped, so I'm just running a traditional/basic dual exhaust setup to keep it simple - K.I.S.S. :-) The transmission crossmember will also likely need some form of adjusting/re-working to make it work around the X-pipe. The header collectors appear to exit with the exhaust pipes aimed squarely at the transmission crossmember. If I do this modification, I would probably get/create a U-shaped piece of steel in a thickness roughly matching the original crossmember, then basically cut out the crossmember sections where the exhaust would go through, and then weld in the U-shaped pieces in place of what was cut out to allow the exhaust to go through. As for how to position the U-shaped pieces (ala, is the "open section" on top or on the bottom), it would be based on what fit best with the exhaust mounted in the truck.



I found a set of older BBK 1 5/8 unequal length headers for a 5.0L Mustang really cheap - another Craigslist deal. I was going to use them here, but they didn't fit, so maybe they'll fit on my 1964 Ranchero 5.0L EFI swap project.

1979FordF100-034.jpg (2227742 bytes) 1979FordF100-035.jpg (2215389 bytes)

Here's the first set of Ford 302/5.0L exhaust headers I had laying around that I tried to use. They are supposedly for an early Mustang, but I tried them here to see if I got lucky and they worked. I wasn't lucky and I'll have to buy new headers for this truck. You can clearly see how the driver's side header has the tubes spread to allow the clutch linkage to go between them. This part actually seemed to fit OK - which is not too surprising since that part of the header would be the same on any 302 Ford engine. Unfortunately, the collector ended up hitting the crossmember that goes under the front of the transmission. Oh well - it was worth a try.

1979FordF100-044.jpg (2523302 bytes)

Here are two reasonably good pictures of the trans crossmember with the header collector outlets in front of it. I'm going to have to modify the crossmember to allow the exhaust to fit through this area when it comes time to do the exhaust system, so I wanted to get some pics of it.

1979FordF100-112.jpg (2534928 bytes) 1979FordF100-113.jpg (1968054 bytes)



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Page last updated 06/28/2009 10:50:40 AM