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Old 12-06-2014, 01:21 AM   #106
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Originally Posted by Sakib View Post
Next thing I want to know is how I can evaluate, before purchasing, what "semi-tuned" headers are better than others, from a technical engineering standpoint.
Probably the most common example for 3.7L Mustangs are the BBK and Mac shorty headers. Each makes different compromises, and it's impossible to say for certain which set of compromises is "better" without doing a direct performance evaluation of each. However there are a few things that can be seen from the pics available online.

BBK:
-Obviously unequal length
-Consistent bend radii
-Medium length collector

Mac:
-Closer to equal length
-One pinched bend per side
-Short collector

While I don't proclaim to be an expert on tuning headers, I do have a few opinions on the physics behind them. First is that, especially on V6 and cross plane crank V8 engines, header tube length tuning does not work like most people think it does. As such, I'm not convinced that equal length is as critical as it is given credit for on a street car, but I would still give the nod to Mac on this item. Second is that smooth bends will out flow crimped bends, in which regard the BBK is definitely superior. Third is that a collector volume and geometry is important. Without having seen a well lit photo into the collector end of each, I don't know which is actually fabricated better, but BBK looks to have the likely advantage. Ultimately if it was my money on the line, I would make my gamble on the BBK over the Mac for shorty designs...But (not butt) dyno testing could just as easily prove me wrong too, as there is often more going on than meets the eye.
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Old 12-06-2014, 02:31 AM   #107
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Quote:
Originally Posted by Driven5 View Post
Each makes different compromises, and it's impossible to say for certain which set of compromises is "better" without doing a direct performance evaluation of each. However there are a few things that can be seen from the pics available online.

BBK:
-Obviously unequal length
-Consistent bend radii
-Medium length collector

Mac:
-Closer to equal length
-One pinched bend per side
-Short collector

While I don't proclaim to be an expert on tuning headers, I do have a few opinions on the physics behind them. First is that, especially on V6 and cross plane crank V8 engines, header tube length tuning does not work like most people think it does. As such, I'm not convinced that equal length is as critical as it is given credit for, but I would still give the nod to Mac on this item. Second is that smooth bends will out flow crimped bends, in which regard the BBK is definitely superior. Third is that a collector volume and geometry is important. Without having seen a well lit photo into the collector end of each, I don't know which is actually fabricated better, but BBK looks to have the likely advantage. Ultimately if it was my money on the line, I would make my gamble on the BBK over the Mac for shorty designs...But (not butt) dyno testing could just as easily prove me wrong too, as there is often more going on than meets the eye.
I looked at many many brands for my last build and for me it was definitely between Kooks and ARH.
Kooks are very good quality for sure and very popular but they are mid length headers and I needed a longer primary and a specific collector size and taper so I gave ARH my measurements and they made up a custom set for me. The results worked out quite well and I couldn't be happier. Car pulls like a freight train from just off Idle through 7400 RPM. Torque is way up there and super flat through the whole power band so I must have done something right somewhere....or maybe I just got lucky.
If I could give one word of advise it would be this:
You don't need nearly as big of a header as you might think you need or some folks will tell you. Bigger is not always better. Right size is always king.
And with that....I'll shut up.
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Old 12-06-2014, 03:10 AM   #108
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Bigger is not always better. Right size is always king.
Words to live by...And that's what I keep telling my wife.
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Old 12-06-2014, 03:31 AM   #109
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Words to live by...And that's what I keep telling my wife.
...and she buys it? LOL.

Good reply Driven5
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