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74_5.0L_Z

My custom made headers and exhaust system

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One of the few things that I ever paid someone else to do on my car was the exhaust system. Eleven years ago, I bolted on my Dynomax block huggers and drove to the local muffler shop to have an exhaust system built. It was made of crush bent 14 gage aluminized steel and had a pair of Flowmaster mufflers at the back. I was never happy with it. It sounded alright, but the poorly made headers and even more poorly made exhaust were not something I was proud of. So last year I decided to do something about it: I removed the old exhaust and cut it into pieces so that I could not possibly reinstall it, then I built myself a set of custom long tube, stainless steel headers. The process was a serious pain in the rear, but it is now finished.

 

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To start the process, I carefully measured the front of my chassis and the engine to determine where all of the important features are in relation to the engine. I established a coordinate system with 0,0,0 at the back of the block, the x axis aligned with the centerline of the crank, the y axis to the driver side, and z up. In the process of taking measurements, I determined the critical dimensions necessary to route the primary tubes from the exhaust ports to the collectors without contacting the steering shaft, block, frame, driveshaft tunnel, and other things that get in the way. The critical dimensions include the position and orientation of each of the exhaust ports relative to the crank centerline. The dimensions were used to generate a SolidWorks model of the headers. Here are some images of the SolidWorks models of the chassis and headers.

 

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The routing of the tubes was calculated using a computer program that I wrote which takes the following parameters as input and gives the following values as output:

 

Input:

 

L1 Length of first straight section of tube exiting port

S Desired length of Header tube

Xp X Position of port relative to centerline of crank

Yp Y Position of port relative to centerline of crank

Zp Z Position of port relative to centerline of crank

 

Orientation of port

 

Xc X Position of collector entry relative to centerline of crank

Yc Y Position of collector entry relative to centerline of crank

Zc Z Position of collector entry relative to centerline of crank

 

Orientation of collector entry

Bend radius of mandrel bends used to make header.

 

Output:

 

Lengths of straight sections and degree and orientation of bent section required to route the header.

 

The calculated header dimensions were put into the SolidWorks model. Many iterations were tried until I had models with which I was satisfied.

 

 

Once satisfied, I made a fixture to build the headers using a junk engine on an engine stand. The fixture allowed me to rigidly place the flanges and collectors into their prescribed positions and to assemble the pieces into position for welding. The images below show the passenger side header pieces assembled and ready to weld. The hose clamps were used to hold things together for tack welding.

 

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The headers are now complete and installed, but here are some more pictures of the assembly on the garage floor prior to installation.

 

 

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I now have an exhaust that is all mine and of which I am not ashamed.

Edited by 74_5.0L_Z

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My student license for SolidWorks expired, so I no longer have access at home. I do however use Creo Pro/Engineer at work.

 

I would need some very specific information to make a usable model for someone else. I might be persuaded.

 

The headers have 1.75 inch diameter primary tubes with an average length of 26 inches from flange to where they enter the slip-on merge collectors. The shortest tube is 23.75 inches and the longest is 27 inches. I was initially going to try for a longer primary tube length (29 - 32 inches), but packaging drove me to the shorter length.

 

I purchased the merge collectors on eBay about five years ago (I've been planning this project for a long time).

Edited by 74_5.0L_Z

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I got the exhaust installed and took the car to the TrickPro Motorsports for some tuning on their SuperFlow dyno.  I installed my Ford 327 (5.0L stroker) in 2009 and have been controlling it using a stock A9P EEC-IV computer for several years now.  It has run but until now it hasn't been running well.  The stock computer was programmed to control a 302 ci engine with 9.2:1  compression and 19 lb/hr injectors.  It's not unexpected that it was having trouble controlling a 327 with 10.3:1 compression and 30 lb/hr injectors.

 

Prior to tuning I was able to get some pictures of the installed exhaust while the car was on the lift.

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Before we started tuning, I wanted to get some baseline runs with the headers installed.  The only thing on this car that has changed since the engine was installed in 2009 are the headers and exhaust.  So I figured it would be nice to do a comparison.  In February 2009 when we broke this engine in on the same dyno, it made 348 rwhp and 365 rwtq.  Now in September 2013 after changing the headers and exhaust, the car made a maximum of 385 rwhp and 402 rwtq.  I'm really happy with the amount of power that I found with these headers and exhaust system.  I am making an additional 37 rwhp and 38 ft-lbs of torque.  What was really interesting is that with the old exhaust, the car ran really rich at WOT (~11.5:1 AFR).  After changing only the exhaust, the car was running really lean (~16.5:1 AFR at WOT).  I'll post videos and dyno charts later in the week.

 

Here are a couple of picture of the car on the dyno:

 

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The second picture shows Bryce at TrickPro monitoring O2s and figuring out how to tune the car.  When I took the car in it was idling like crap and had idle  air fuel mixture of 19.5:1 and  16.5:1 wide open throttle that wandered all over that map.  When we left the car was purring like a kitten with stable 15.7:1 idle O2 reading and a solid 12.7:1 wide open throttle air fuel mixture.  He programmed a Diablo Sport chip to control the fuel and timing of the computer.  While we were at it we also upped the rev limit to 7000 rpms.  The thing runs so much better.  I had been putting off tuning until I could make my headers and exhaust, but now I wish that I had tuned it long ago.

Edited by 74_5.0L_Z
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A friend who went with me to do the dyno tuning took some cool pictures of the car and the exhaust with his Go Pro.

 

The first two are good views of the underside of the car and show the layout of the mufflers and fuel cell.

 

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The other two are just cool shots of the car and the shop.

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Edited by 74_5.0L_Z

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I have way too much time in the headers.  There are a few reason that it took so long.  First, this was the first time I have made a set of headers.

Second, stainless steel is expensive, and I wanted to get every cut perfect the first time.  Lastly and most importantly, I was trying to finish my Masters Degree in Mechanical Engineering.  So, time to work on the car was in short supply.

 

The program that I wrote to calculate the bends actually began as a project for my Robotics class.  I convinced the professor that the procedure to calculate the bends for a header was the same as that required to solve the kinematics of a robot arm with seven degrees of freedom (which it is).  So, I spent a semester doing the math and writing the code to figure the header tube paths.

 

I finished that class in 2011,  but had several classes to finish for my degree so the headers went on hold while I collected parts and finished school.  I finished my degree in April 2013 and finished the headers in August.

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The program that I wrote to calculate the bends actually began as a project for my Robotics class.  I convinced the professor that the procedure to calculate the bends for a header was the same as that required to solve the kinematics of a robot arm with seven degrees of freedom (which it is).  So, I spent a semester doing the math and writing the code to figure the header tube paths.

 

Hrm, I did a split grad/undergrad intro to robotics class for my CS bachelors... I distinctly remember the math for more than 3 degrees of freedom getting an order of magnitude more difficult with each additional degree of freedom added.

 

It was a fun class, but I'll stick to CS for a masters.

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