Technical Question On Headers
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From: T.O./VA
Technical Question On Headers
I was reading on an article that Michael Delaney wrote up about how primary tube lengths affect the torque curve. Here's the excerpt...
Longer tubes will allow more torque at lower rpms.
Longer tubes will speed up air flow velocity. The flow velocity of 240 ft/sec and peak torque will occur at an earlier rpm compared to a shorter tube. Changing the length of the header primary tubes does not increase the value of peak torque like diameter does. Instead length changes the behaviour of the torque around peak torque along the rpm band.
If you imagine the torque vs rpm curve from a dyno to be like a see-saw: then, on a see-saw there is a point where the plank sits to allow it to rock up and down. This is usually in the middle of the see saw and is also called the fulcrum. On our torque vs rpm curve, imagine the peak torque to be the fulcrum, although this fulcrum doesn't necessarily have to be in the middle like the see-saw...it can be moved. Changing length "rocks" the torque curve about the peak torque.
If you have a longer primary header tube, the torque curve will "rock" in such a way that the left side is higher than the right side. There is higher torque at earlier rpms before peak torque. There is less torque at later rpms after peak torque.
If you shorten the length of the primary tube, the torque curve will will have the see-saw with the right side higher than the left. So there is more torque at later rpms after peak torque.
I thought that the traditional 4-1 header, such as the JDM ITR header, reaches peak power later than a tradional 4-2-1 header, at the expense of midrange power. Thus the old adage stating that the tradional 4-1 is for high-end power and the tradional 4-2-1 is for midrange. So why does it state in this article that longer tubes allow more torque at lower RPMs? Doesn't this go against tradition?
[Modified by CPR, 12:24 PM 4/8/2002]
Longer tubes will allow more torque at lower rpms.
Longer tubes will speed up air flow velocity. The flow velocity of 240 ft/sec and peak torque will occur at an earlier rpm compared to a shorter tube. Changing the length of the header primary tubes does not increase the value of peak torque like diameter does. Instead length changes the behaviour of the torque around peak torque along the rpm band.
If you imagine the torque vs rpm curve from a dyno to be like a see-saw: then, on a see-saw there is a point where the plank sits to allow it to rock up and down. This is usually in the middle of the see saw and is also called the fulcrum. On our torque vs rpm curve, imagine the peak torque to be the fulcrum, although this fulcrum doesn't necessarily have to be in the middle like the see-saw...it can be moved. Changing length "rocks" the torque curve about the peak torque.
If you have a longer primary header tube, the torque curve will "rock" in such a way that the left side is higher than the right side. There is higher torque at earlier rpms before peak torque. There is less torque at later rpms after peak torque.
If you shorten the length of the primary tube, the torque curve will will have the see-saw with the right side higher than the left. So there is more torque at later rpms after peak torque.
[Modified by CPR, 12:24 PM 4/8/2002]
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From: Weed Country, Holland, Netherlands
Re: Technical Question On Headers (CPR)
There is more than gas flow energy. There is also wave energy because the exhaust gasses are coming out in pulses.
About the JDM 4-1. It actually shifts the max torque peak from 7300rpm to 6200rpm!!! You can't compare two totally different headers with each other. The length of the primaries is NOT the only difference between the JDM and the USDM header......
About the JDM 4-1. It actually shifts the max torque peak from 7300rpm to 6200rpm!!! You can't compare two totally different headers with each other. The length of the primaries is NOT the only difference between the JDM and the USDM header......
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Re: Technical Question On Headers (EuroITR1689)
There is more than gas flow energy. There is also wave energy because the exhaust gasses are coming out in pulses.
About the JDM 4-1. It actually shifts the max torque peak from 7300rpm to 6200rpm!!! You can't compare two totally different headers with each other. The length of the primaries is NOT the only difference between the JDM and the USDM header......
About the JDM 4-1. It actually shifts the max torque peak from 7300rpm to 6200rpm!!! You can't compare two totally different headers with each other. The length of the primaries is NOT the only difference between the JDM and the USDM header......
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From: Weed Country, Holland, Netherlands
Re: Technical Question On Headers (CPR)
That is comparing 4-2-1 with 4-1. It's too different to see what the effect of the diameter of the primaries does to the torque curve....
The length of the secondaries in a 4-2-1 plays a role too....
Example:
[Modified by EuroITR1689, 6:45 PM 4/8/2002]
The length of the secondaries in a 4-2-1 plays a role too....
Example:
[Modified by EuroITR1689, 6:45 PM 4/8/2002]
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From: Toronto, On, Canada
Re: Technical Question On Headers (CPR)
you need 4 pics up to describe the whole picture: diameter, length, layout, and merge collector size and angle.
Originally posted by SMSP a loooonnnng time ago during more gentile times
...Why do we have all these aftermarket headers that only make small
increases in power? Because the consumer wants something that is "BOLT
ON" easy. So the commercial manufacturers have to end the header in the
same spot as the stock downpipe and therefore, design may be limited.
Once you are <U>willing</U> to make further mods to your system further
power can be <U>extracted.</U> Notice I didn't say produced. I believe
headers <U>release</U> the power a given engine is capable of and are
one of many things that help make an engine more efficient at making
power. Headers also help define the power curve of an engine.[/B]
The same goes for cams,pistons and cylinder head porting. Header
tube size effects gas velocity/energy. Controlling gas velocity will
effect where the meat of your torque curve is. If the primary is too big
and hence, the gases see a large immediate <U>area change</U> (port vs
tube) the engine will be flat in the low/mid range since the <U>gas
velocity will drop and lose energy</U>. So, single size large tube
headers will probably only work well in very high rpm ranges and since
most of us don?t have 6 speed sequential boxes they don?t do us much
good. Header tube <U>length</U> tends to <U>rock the torque curve about
its peak</U>, shorter tubes should net you more <U>area under the curve
after the torque peak</U>, in a given rpm range, where longer tubes will
do the opposite.
Merge collectors also effect the torque curve. By definition they merge
gases from 2 or more tubes into one. In general, <U>gentle merge angles
will broaden the curve </U> versus more radical angles. This brings
us back to the packaging problem: merge collectors with smaller
convergent angles take up more space. Go back and look at the Spoon
4-2-1 collector and its angles, I would call them very radical. It
almost looks like one secondary will force gas back up the other. I
would love to look at data from some pressure taps at the end of each
primary and secondary.
One other thing to remember is that above certain rpms and in a rpm
range that an engine will be operated, collectors may not be too
important. When was the last time you saw a 4-1 or a 4-2-1 collector
on a Top Fuel funny car?
The final thing with the exhaust side of an engine that is over looked
is the tailpipe size & length, and muffler location. All these will also
effect the torque curve and this also has to do with where the area
changes occur.
...Why do we have all these aftermarket headers that only make small
increases in power? Because the consumer wants something that is "BOLT
ON" easy. So the commercial manufacturers have to end the header in the
same spot as the stock downpipe and therefore, design may be limited.
Once you are <U>willing</U> to make further mods to your system further
power can be <U>extracted.</U> Notice I didn't say produced. I believe
headers <U>release</U> the power a given engine is capable of and are
one of many things that help make an engine more efficient at making
power. Headers also help define the power curve of an engine.[/B]
The same goes for cams,pistons and cylinder head porting. Header
tube size effects gas velocity/energy. Controlling gas velocity will
effect where the meat of your torque curve is. If the primary is too big
and hence, the gases see a large immediate <U>area change</U> (port vs
tube) the engine will be flat in the low/mid range since the <U>gas
velocity will drop and lose energy</U>. So, single size large tube
headers will probably only work well in very high rpm ranges and since
most of us don?t have 6 speed sequential boxes they don?t do us much
good. Header tube <U>length</U> tends to <U>rock the torque curve about
its peak</U>, shorter tubes should net you more <U>area under the curve
after the torque peak</U>, in a given rpm range, where longer tubes will
do the opposite.
Merge collectors also effect the torque curve. By definition they merge
gases from 2 or more tubes into one. In general, <U>gentle merge angles
will broaden the curve </U> versus more radical angles. This brings
us back to the packaging problem: merge collectors with smaller
convergent angles take up more space. Go back and look at the Spoon
4-2-1 collector and its angles, I would call them very radical. It
almost looks like one secondary will force gas back up the other. I
would love to look at data from some pressure taps at the end of each
primary and secondary.
One other thing to remember is that above certain rpms and in a rpm
range that an engine will be operated, collectors may not be too
important. When was the last time you saw a 4-1 or a 4-2-1 collector
on a Top Fuel funny car?
The final thing with the exhaust side of an engine that is over looked
is the tailpipe size & length, and muffler location. All these will also
effect the torque curve and this also has to do with where the area
changes occur.
Tuan
[Modified by Michael Delaney, 10:26 AM 4/8/2002]
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