Headers 101
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Headers 101
I am reletively new to the import scene, having spent mytime around american muscle and the strip as soon as my dad could no longer keep me out of his tool box. Even though I am new to this arena some things carry over and one of those things is header technology.
I have seen many threads discussing headers and there lack of bang for the buck, various other notions. With all that I figured I would jot down some knowledge gained over the years and passed on by those smarter than me. I hope this thread helps anyone looking into headers for any auto and helps explain why not all headers are created equal.
When asked what a header does, everyone automaticly replies; "it reduces backpressure, and helps the engine breath." The part they don't know is that while thats good, another important part is it creates a vacuum. This vacuum occurs as one tube emits exhaust gasesit also draws out the gas from the next cylinder as the exhaust valves open. This is commonly refered to as scavanging, and its good thing! This can not happen though if your headers are not designed properly. There are basicly 4 areas where a header design can go sour:
1) Primary Tubes
2) Collector
3) Area beyond Collector
4) The Outlet
Primary Tubes
Primary Tubes should basicly be the diam. of the exhaust ports, using bigger tubing simply distracts from the scavenging effect. You want to use the smallest diam. that can handle the air flow at your desired redline rpm. Smaller tubes pull the power band to the low/mid redline range, and larger tubes push the power band to the upper redline range.
The tube length follows the opposite rules. The shorter the pipe the higher the power band is pushed, and the longer the pipe the power band is pulled back down to the low/mid power band.
So if your looking for power gains in the low/mid rpm range, you would go with smaller diam tubing and run the tubing longer. Those wishing to see the power gains up in the redline area would go with large diam tubing and keep them short.
example: a N/A 4cyl engine with demands for power gains on the low/mid range would not want these fat tubed shortie headers floating around. The optimum header would be one that has primaries roughly 1 3/4" diam and over 34" long before the collector.
If you wanted the power up top then you would go with a 2" diam tubing and run shorter tubing around 26".
Following the above theory you just learned about tuned length headers. These headers are tuned to aide the engine operate optimally at certian rpm ranges.
Collector
While primary diam/length is very important, the collector is area where it all comes together and is the make or break of optimal performance!
Since this topic is geared toward a 4cyl engine, thats all I will cover, and thats good because the v-8 header has issues that we luckily do not face. It is said the 4cyl engine has the optimim firing cycle because every 180 degree of engine rotation there is at 1 exhaust pulse in the collector. As 1 enters the collector the next exhaust valve is opening and helps create a vacuum to pull the exhaust out of the engine.
The key is aligning the tubes to the rotational firing pattern of the engine. This aligning helps with the scavenging effect, gas exiting a tube and passing over the tube beside it creates more suction on the tube than it would a tube on the opposite end of the collector.
Now that you know how the tubes should be aligned in the collector, we need to look at the collecter itself. How large should it be? How long of a taper do we need before we hit the outlet? Both are very important in ensuring the air flow is not disrupted/disturbed.
The rule of thumb is that a collector should roughly be 20% larger than the size of your primary tubing. So if if your tubing is say 1 3/4" then you want a collector roughly 2" diam. Now I could go on about how the tubing is merged inside the collector, etc.. but I am gonna pass on that because this is a help thread and not how to build a header thread.
Area beyond the Collector
This area should be where the collector diam. resizes to the size of the outlet. Short tapers/expansions are bad! No expansions are just evil! A 1" expansion is to little, a 2" expasion is better, but a 3-4" is considered optimum. This gives the air flow a gentler adjustment to the upcoming exhaust pipe size, and is a pretty busy and turbulant area. Due to all the turbulant air flow we really want to help smooth it out before it gets into the exhaust pipe.
Outlet
Not much to say except this sets you up for your exhaust pipe size. you can go bigger here, but you never want to go smaller than the size of your collector. Going bigger than the collector size is really not needed if you ensured the header met the checkpoints outlined above.
Phew! That was alot more thant I thought it would be, but if it helps then it's all good!
Now on to the reason I made this post, threads stating headers did nothing, etc...
IMO most the headers I seen that are available for the d17a series look like a joke. True there are some that follow the info I covered, but for the most part I have seen alot that simply look like they copied the oem header and used bigger tubing to impress the public.
Speaking of the oem a2 header, I think if you extended the section after the collector and before the outlet out by 2" it would perform better than these shortie fat tube headers. With that said, the shorty would be better at giving you power up in the redline rpms, but that extended oem header would show you the power along the low/mid end and thats where this lil engine needs it most.
These ebay headers are a joke imo, some are basicly the oem header with larger diam. and then there are the versions that really amuse me... the ones where the collector meet right at the outlet and do not really have a after collector extention at all.
It's really a shame that the good header designs are in the unrealstic price range, but so are these cat back exhaust kits /shrug.
If your searching for a header for a d17a, pick up a oem 01+ EX header and either modify it yourself or take it to a muffler shop and have them modify it is your best/cheapest route. Have the tube lengths adjusted and have the collector extension adjusted. Remember tubing under 26" give power up top and any length over 34" gives you the power down low/mid range. And the reason we extend the area after the collector out 2-3" is to reduce turblulance and facilitate a better air flow transition to the exhaust pipe.
I have seen many threads discussing headers and there lack of bang for the buck, various other notions. With all that I figured I would jot down some knowledge gained over the years and passed on by those smarter than me. I hope this thread helps anyone looking into headers for any auto and helps explain why not all headers are created equal.
When asked what a header does, everyone automaticly replies; "it reduces backpressure, and helps the engine breath." The part they don't know is that while thats good, another important part is it creates a vacuum. This vacuum occurs as one tube emits exhaust gasesit also draws out the gas from the next cylinder as the exhaust valves open. This is commonly refered to as scavanging, and its good thing! This can not happen though if your headers are not designed properly. There are basicly 4 areas where a header design can go sour:
1) Primary Tubes
2) Collector
3) Area beyond Collector
4) The Outlet
Primary Tubes
Primary Tubes should basicly be the diam. of the exhaust ports, using bigger tubing simply distracts from the scavenging effect. You want to use the smallest diam. that can handle the air flow at your desired redline rpm. Smaller tubes pull the power band to the low/mid redline range, and larger tubes push the power band to the upper redline range.
The tube length follows the opposite rules. The shorter the pipe the higher the power band is pushed, and the longer the pipe the power band is pulled back down to the low/mid power band.
So if your looking for power gains in the low/mid rpm range, you would go with smaller diam tubing and run the tubing longer. Those wishing to see the power gains up in the redline area would go with large diam tubing and keep them short.
example: a N/A 4cyl engine with demands for power gains on the low/mid range would not want these fat tubed shortie headers floating around. The optimum header would be one that has primaries roughly 1 3/4" diam and over 34" long before the collector.
If you wanted the power up top then you would go with a 2" diam tubing and run shorter tubing around 26".
Following the above theory you just learned about tuned length headers. These headers are tuned to aide the engine operate optimally at certian rpm ranges.
Collector
While primary diam/length is very important, the collector is area where it all comes together and is the make or break of optimal performance!
Since this topic is geared toward a 4cyl engine, thats all I will cover, and thats good because the v-8 header has issues that we luckily do not face. It is said the 4cyl engine has the optimim firing cycle because every 180 degree of engine rotation there is at 1 exhaust pulse in the collector. As 1 enters the collector the next exhaust valve is opening and helps create a vacuum to pull the exhaust out of the engine.
The key is aligning the tubes to the rotational firing pattern of the engine. This aligning helps with the scavenging effect, gas exiting a tube and passing over the tube beside it creates more suction on the tube than it would a tube on the opposite end of the collector.
Now that you know how the tubes should be aligned in the collector, we need to look at the collecter itself. How large should it be? How long of a taper do we need before we hit the outlet? Both are very important in ensuring the air flow is not disrupted/disturbed.
The rule of thumb is that a collector should roughly be 20% larger than the size of your primary tubing. So if if your tubing is say 1 3/4" then you want a collector roughly 2" diam. Now I could go on about how the tubing is merged inside the collector, etc.. but I am gonna pass on that because this is a help thread and not how to build a header thread.
Area beyond the Collector
This area should be where the collector diam. resizes to the size of the outlet. Short tapers/expansions are bad! No expansions are just evil! A 1" expansion is to little, a 2" expasion is better, but a 3-4" is considered optimum. This gives the air flow a gentler adjustment to the upcoming exhaust pipe size, and is a pretty busy and turbulant area. Due to all the turbulant air flow we really want to help smooth it out before it gets into the exhaust pipe.
Outlet
Not much to say except this sets you up for your exhaust pipe size. you can go bigger here, but you never want to go smaller than the size of your collector. Going bigger than the collector size is really not needed if you ensured the header met the checkpoints outlined above.
Phew! That was alot more thant I thought it would be, but if it helps then it's all good!
Now on to the reason I made this post, threads stating headers did nothing, etc...
IMO most the headers I seen that are available for the d17a series look like a joke. True there are some that follow the info I covered, but for the most part I have seen alot that simply look like they copied the oem header and used bigger tubing to impress the public.
Speaking of the oem a2 header, I think if you extended the section after the collector and before the outlet out by 2" it would perform better than these shortie fat tube headers. With that said, the shorty would be better at giving you power up in the redline rpms, but that extended oem header would show you the power along the low/mid end and thats where this lil engine needs it most.
These ebay headers are a joke imo, some are basicly the oem header with larger diam. and then there are the versions that really amuse me... the ones where the collector meet right at the outlet and do not really have a after collector extention at all.
It's really a shame that the good header designs are in the unrealstic price range, but so are these cat back exhaust kits /shrug.
If your searching for a header for a d17a, pick up a oem 01+ EX header and either modify it yourself or take it to a muffler shop and have them modify it is your best/cheapest route. Have the tube lengths adjusted and have the collector extension adjusted. Remember tubing under 26" give power up top and any length over 34" gives you the power down low/mid range. And the reason we extend the area after the collector out 2-3" is to reduce turblulance and facilitate a better air flow transition to the exhaust pipe.
Joined: Sep 2002
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From: NV
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ya im pretty happy with the oem header, altho i've noticed the tubes tend to build up carbon fast, which shrinks the diameter. i may just send it for jet coating one day.
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