Under Car Exhaust - Part 1

[SCFFR]

Before I even ordered my MkIV base kit last November, my plans were to build a street version roadster with smooth hood, full bumpers, glove box and street-style gauge layout, no roll bar and under car exhaust. So far, the biggest challenge has been the exhaust system since it has to be fabricated from scratch. Wanted to post some pics on the progress I have made so far.

What I thought would be the easiest part of the build, the headers, turned out to be the most frustrating. The FFR manual references two shorty headers (Ford Racing and MAC) that will fit my 351W-base engine and clear the oil filter and mechanical fuel pump. I ordered a set of the MAC 351W swap headers from CJ Pony Parts and was immediately told there would be a 6 week wait while MAC manufactured the headers. When I followed up on week 6, I was told that MAC hadn’t started on them yet so I canceled the order and with the refund ordered a set of BBK 351W swap headers from Summit Racing. They arrived in three days but unfortunately the rear tube on the drivers side hit the inner footwell panel. Thought about making a recess in the panel but the tube looked like it would also hit one of the 1" square tubes. I considered having the header tube cut but since the headers were ceramic coated, really didn’t want to do that. After posting my situation, got a response that the Ford Racing swap headers would fit but they had been out of production for a few years. I was extremely lucky that I found a NOS set on eBay for $200. I was very relieved when they fit perfectly with absolutely no interference.

Now that I had the starting point for the system, I concentrated on the pipes and mufflers. I purchased some straight oval pipes, low profile mufflers (2.25" tall) with oval inlets and some oval connectors from Spin Tech. The oval pipes are 1.75" tall which will provide the greatest amount of ground clearance. I also bought a selection of tight turn 2.5" u and j bends from Summit Racing along with a pair of header connectors. Started by cutting the slip-on ends of the header connectors off so I would have a short piece of 2.5" pipe to weld onto one of the 90 degree j-bends (all joints are welded - no slip joints except into mufflers). I then fitted the muffler under the seat pan and held it into place with some wire while I fitted the oval pipes. Although Spin Tech makes a straight oval to 2.5" round pipe connector, I made my own. I cut a 5" piece of 2.5" round pipe, inserted a plug in one end to keep it from collapsing while I squeezed the other end in a vise to get the oval shape. With a little work with a body hammer, it was easy to get the oval shape to match up exactly with the oval pipe. To maximize the ground clearance, I used a 90 degree vertical connector to get the pipe turned up before I added the straight connector. Although not absolutely necessary, if you change from oval to round pipe under the car, you defeat the purpose of using the oval pipe.

Once I had the oval pipe in place and exiting in front of the footwells, it was a matter of figuring out the correct angles and lengths and cutting the pieces out of the u and j-bends. I spot welded all of the joints until the section was completed and yes, I did have to take it apart several times and refit. I bought a handful of stock exhaust pipe hangers from the local auto parts store and used the pieces and some flat bar stock to make hangers to hold the mufflers. I made a double hanger for the pipe in front of the muffler and a single one at the very rear of the muffler. The bottom of the mufflers is the lowest part of the system and sticks ½" below the bottom of the 4" main chassis rails.

I plan to use black exhaust wrap around the pipe under the car to help control heat into the floorpans. Still deciding on whether to get the entire system ceramic coated or paint with a hi-tem exhaust coating since most of the pipe will be wrapped (will definitely have the headers ceramic coated).

Still have plenty of work to do but I think all of the difficult work is done. For the pipe over the rear end, I think I will take the flexible metal radiator hose/pipe that came with the kit and bend it into the shape I will need and take it to a muffler shop and have it bent. There are just too many bends for me to cut and weld together for that section. I will have to wait until the body is fitted before I add the tail pipes but that should be relatively easy.

In terms of cost, I estimate that I will have close to $1,000 in the complete system including the headers but not counting the cost of ceramic coating. Definitely more work that installing a set of side pipes but I didn’t have to deal with some of the issues with the body cutout and header alignment. It was a fun and challenging part of the project.
Will post Part 2 when I get the rest of the system completed.

Thanks,

Ron

Exhaust1.JPGExhaust2.JPGExhaust3.JPGExhaust4.JPGExhaust5.JPG

[SCFFR]

More pics. In the last one, you can see how little the mufflers extend below the bottom of the main chassis rails.

Exhaust6.JPGExhaust7.JPGExhaust8.JPGExhaust9.JPGExhaust10.JPG

[GWL]

Excellent work.

George

[skullandbones]

I've been waiting to see how you have progressed. Are you planning to adjust the ride height a little to compensate for the 1/2 in hang down of the muffler? I have a couple of O2 sensors that are right at the same height as the 4 inch tubes. Also, I would guess you are going with 15 inch wheels for that kind of look but is that your plan? Those pipes and other components look very well fabricated. You shouldn't have to replace it for a long time. Nice work! WEK.

[CraigS]

You are doing really excellent work.I've built some regular round exhaust systems over the years and know how difficult it is, and I've never needed to work w/ the tight spaces you are. Are you going to use locknuts on the hangers so you can leave the bolts/nuts loose and allow them to move? One other thing to consider is that the system will grow in length as it warms up so allow some room for that.

[riptide motorsport]

Fantastic work !!

[Jim1855]

Great looking construction, your time, efforts and design show in the details.

I had a chance to drive a roadster (not FFR), it did have undercar exhaust, w/o hood scoop or roll bar. Nicely civilized, well as much as a Cobra can be. The rear exhaust allowed almost normal conversations and with the Roush 427 stacked EFI it drove like a "normal" car.

Good luck on your build I hope it fulfills your dreams.

Jim

[emac]

Very nice work. Your car is going to be amazing! I can't wait to see it finished. I would consider ceramic coating the exhaust. My headers are coated and my j pipes aren't. According to one of those thermo guns they are at least a couple of hundred degrees different.

I used some self adhesive heat barrier from Summit on my foot boxes. The driver header is very close to the aluminum and I couldn't feel heat on the inside. I don't know how that stuff would hold up under the bottom, but it gives you something to think about. Keep us posted!

Edit: I would also add that according to my thermo gun the temps drop quite a lot as you go away from the engine, as you would expect. So, you may only need to ceramic coat the just under the interior. Just a thought.

Ernest

[SCFFR]

Thanks to everyone for their feedback. In answer to your questions, yes I used locknuts and left things a little loose to allow for movement. I also used a self-adhesive heat barrier from Cool It between the muffler and bottom of seat pan however there is a significant air space there so shouldn't be a problem. I will also use a strip of the same heat barrier between to footwell bottoms and the exhaust pipes. With the combination of heat barrier and exhaust wrap, I should be okay on heat.
Yes, I will adjust the ride height to compensate for the amount of muffler that sticks below the main chassis rail. I have a 1967 MGB/GT with a 3.4L V5 and T5 that has 4" of clearance between the bottom of the exhaust and ground that I have driven for years with no issues. Also I am using the 15" wheels for that original look.
I used 16 gauge exhaust pipe where possible which should be more durable and is easier for me to weld. Working with the oval pipe was easier than I had anticipated. I realize that the difference in diameters between the oval and 2.5" round pipe was only 0.75", but it was enough of a difference to impact ground clearance.
When I take the headers to get ceramic coated, I will take the pipe/mufflers and get an estimate on getting them coated. The one and only local place (75 miles) charges about $20 a foot for pipes so maybe it won’t be too expensive. Plan B will be to paint with VHT flat black and clear for that satin look. Not quite as durable but easy to repair.

Next step if to get the body on and getting it fitted to the chassis. I'll be able to get the rear sections of exhaust pipe fitted them.

Thanks again to everyone!!

Ron

[Gumball]

Simply outstanding. Very elegant solution to the challenge!!!

[emac]

I used a place in Nashville called Nitroplate. Recommended to me by several forum members. They coated my heat shields. Prices were reasonable, very good quality/customer service, and fast turn around.

[SCFFR]

Thanks for the tip Ernest. Have decided to get the under chassis section with mufflers ceramic coated but will paint the over axle section and tail pipes with VHT black and clear paint.

[LesMurray]

I have a quick question about your build, specifically around the wheels and tires. I understand you are using 15" wheels - what size wheels and tires are you going with? Will you use the same size on all four corners or go oversized on the rears?

Thanks.

[skullandbones]

x2 on the ceramic coating of the mufflers. It seems like magic the way my pipes cool down after stopping the car. You can easily tell the difference between the headers and side pipes (not ceramic coated but BBQ paint). At some point, I can touch the headers and not burn my finger and then touch the pipe right next to it and it would burn like hell if you don't take it off. I read that it is easy to attain a 75 to 100 degree difference in the engine bay temp which can add up to extra hp, too. Of course, if you still have a problem with the heat on the floor you can paint that as well. Hope you finish soon so we can see some more pics. Thanks, WEK.

[SCFFR]

Les,

I'm using 15" FFR wheels and Cooper Cobra tires................245's on the front and 295's on the rear. It doesn't appear that getting the rear section to go over the axle will be a problem. Will make up a template out of some flexible exhaust tubing and tape it into place and will take it to the muffler shop and have them bend up a piece.

Ron

[Bill_VA]

x2 on Nitroplate. They did an awesome job on my sidepipes. I also sent them my oil pan, intake, and timing chain cover.

[David Hodgkins]

Outstanding work Ron! Any plans to use your exhaust as a template for others?

[SCFFR]

David,

I would be more than happy to share part numbers, suppliers, dimension, pics and any other information I have to anyone interested.

Thanks,

Ron

[David]

Ron, just wanted to mention in this thread as well... dude, you're a craftsman! Really really nice work man.

David