Frequently Asked Questions

This Custom Header FAQ; Frequently Asked Questions section is the most commonly asked questions regarding our header mockup kit. GP Headers Inc. Will help you get your project on the road with our unique and easy to use custom exhaust manifold / header mockup kit. Please have a look at the questions below if you are questioning if this kit is for you or are having trouble figuring out the system for your application. Of course feel free to call us anytime you need help before ordering if you have a question that is not covered here.


Why use PVC?
Simple. It’s because PVC is economical and easy to work with. The use of PVC pipe and fittings really allows us to get the true form of each bend and proper positioning of each component within the exhaust manifold system. While other header mockup kits look really good and look simple to use they are a bit deceiving. You must understand that they do not come with flanges for your actual engine along with collectors to allow for fabricating exact tolerances. PVC when fabricated and fastened is really rigid and allows for the system to be shipped to us without much fear of losing the close tolerances that your application demands.
What is included in the mockup system?
We include flanges for your engine cylinder head, Aluminum fixtures for odd angle bends the appropriately sized collectors, and secondary flanges if necessary along with 90, 45 and 22 degree PVC pipe fittings. We also include a bag of self-tapping screws for securing everything once you’ve made your design.
What in addition do I need to get started?
You will need to get 1.5” Schedule 40 PVC straight tube. The length is determined by your application and is entirely up to you generally these are sold in 10’ lengths. This is not economical for us to ship to you and should be only a few dollars at your local home center. It is recommended that you pick up some more 1.5” PVC connections from the home center only in case you are working with multiple design ideas. A worthwhile tool is a miter saw to make quick cuts of the PVC pipe. If you do not have a miter, a hacksaw or sawzall should do the trick.
How many Connections are in the kit?
A typical 8 Cylinder mockup kit will include 8 aluminum elbows to thread into the flanges, 6 aluminum bends, 6 – 90Degree fittings, 6 – 45Degree Fittings and 4 – 22.5 Degree Fittings.
I’m not sure what kind of design I want, or have a complicated primary pipe route what do I do?
If you are planning on playing with a few design ideas or dealing with really complicated routes it can really pay off to buy more 1.5” pvc fittings at your home center to have on hand. Generally speaking you are then allowed to have a design of a primary tube mocked up while you make another design for that same primary. If one design didn’t work out, you will have the old design readily available without having to re-construct it. This is not needed, only a great way to save time or visualize things differently.
How difficult is the header mockup system?
If you have everything on hand, a collector secured and in location along with an idea of how to approach your design it is very easy to use this system, just like construction blocks. It’s best to have the collector in place first. It will make it more like connecting the dots and cut down on your time with designs that are just impractical from the beginning.
What is the best and easiest way to get started?
Make sure your engine and transmission is installed with proper mounts, steering shaft is connected as well as power steering / AC and any other accessories you plan to run. The best way to start is find a place for your header collector within the system and secure it in place. Make a jig out of wood or metal to prop it up, zip tie it or tape it, etc. Make sure you have enough clearance from shafts and frame rails. *Don’t forget to add an exhaust manifold gasket in-between the head and the flange as sometimes the smallest tolerances can make the difference in the final product.
I have a unique application or uncommon engine. How does this work?
We have or can get flanges for most applications but we don’t have them all. If you have a CAD file of your particular cylinder head exhaust side that would be best. If you do not we will require an exhaust manifold gasket for your cylinder head so we can measure it and draw it on the computer to have it made. That will need to be sent in before we get your mock up system ready.
How do I secure everything in place?
We send you a bag of self-tapping screws that can be used to secure everything once you get your design is completed. If there is any play in the aluminum joints that we provide you can drill deep enough and drive in a provided screw. If you do not predrill the hole large enough the self-tapping screws will break.
How do I determine the primary pipe size?
This is a difficult question to answer; it all depends on your application, modifications and goals. It is something that can be discussed at the time of ordering. Even then we are only going off of charts and experiences in the past.
How do I determine my collector size?
The collector size is determined both from the primary and secondary size in the manifold. We usually select this after discussing the application, modifications and goals of the engine.
What is clocking and do I need to clock the primary tubes to the collector?
Clocking of the primary to the collector is when the pipes are arranged on the collector in such a way that it works with the firing order of the ignition system. It is not necessary to clock the primary tubes to the collector, generally things are so tight and difficult to get to that we don’t have a choice but to arrange them on the collector as they are best fit.
How can I achieve equal length primary tubes?
If you are trying to achieve equal length we suggest using a cloth or flexible measuring tape and taking note of how many fittings and lengths of the PVC you are using for each cylinders primary pipe. Once we get the mock up back in house we can further tweak within reason the lengths to match closer. **This can be rather difficult to achieve and just may not be an option in certain applications.
My mockup is flexing too much because of weight on the secondary pipe. How do I fix this?
This is simply fixed by welding or securing a rod or square tubing from the header collector to the mockup flange. To do this you must have all the PVC in place and secure with the self-tapping screws. Reduce as much flex into the system as possible and only then tack weld a piece of metal or secure the metal with screws from the collector to the supplied flange.
The PVC is too bulky and I cannot make connections, how can I fix this?
There are times when the PVC fittings are too bulky and you cannot make connections because they are touching. Depending on your primary pipe location you might need to grind away some of the outer surfaces of the fitting – reducing the outside diameter of them. A belt sander usually makes quick work of these fittings. Please be sure to wear appropriate personal safety equipment.
Can you include a flex connection?
Yes we can include flex joints in our systems upon request. The two most common types are the mesh with corrugated metal inside or a bellows type flex joint.
Can I mark a location for a O2 bung? Wideband?
Yes we can accommodate the use of a wideband or screw in type of O2 sensor. Please indicate at the time of sending your mockup back where this is to be located and what connection you need.
What finishes are available?
All of our manifolds are made with USA 304 Stainless Steel. Our standard finish is brushed stainless. We offer polished stainless as well as ceramic coated options. Prices will vary depending on what you are wanting.
I’m done but really worried about clearances what do I do?
Simple! Make some small spacers out of your straight PVC pipe that will take up the gap. Tape or secure them in place and take pictures of the mock up install so we know what we are looking at. We will then accommodate these when making the final product.
I’m done with my mockup what do I do now?
Make sure everything is tight and secure on the Mock up. We don’t want it moving in shipping. Find a box big enough and over use packaging material to get it to us safely. Send back any remaining unused pvc joints, aluminum joints and flanges that were supplied with the mock up. Please send it back via UPS to GP Headers Inc, 19767 Highway 34 , Barnesville MN 56514.
What is the turnaround time?
We tend to run about a 4-5 week lead time once we receive your completed header mock up. Of course that can be swayed either way depending on workload and especially if we have your head flange in stock or gasket available to at least make a CAD drawing of it. We complete and handle orders in the order they were received. We can be more accurate about lead time if you contact us.
I have an application that is unique and want to have you make these so I can market these on my own. What do I do?
Great news, we love to hear about unique applications and multiple piece orders. We will be happy to work with you on getting your first mock-up system correctly finished. From there we will send you the final product so it meets your expectations. If all is well we will need the header back so we can make the appropriate jig for replicating it based upon your order quantity. Private labeling and branding is possible when teaming up with us.

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