shomethe$$$
SHO Member
Something not right there, I would respectfully have to disagree, I would never put BBB's on and then shorten the horn.
BBS and ported intake runners
- Thread starter shotime1994
- Start date
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jonheese
Used-To-Know-It-All
Why not?
That's in essence what (most) everyone does now when they remove the horns after a BBB install. (Of course, that's way too much shortening to compensate for the small diameter increase of the BBBs.)
Edit: I don't mind you disagreeing (I actually prefer it, since it keeps us looking for the truth), but it does no good to say that you disagree without a reason why. You know what I mean?
Edit 2: Never mind. I was wrong in my original post. Keep the length of the horns the same.
That's in essence what (most) everyone does now when they remove the horns after a BBB install. (Of course, that's way too much shortening to compensate for the small diameter increase of the BBBs.)
Edit: I don't mind you disagreeing (I actually prefer it, since it keeps us looking for the truth), but it does no good to say that you disagree without a reason why. You know what I mean?
Edit 2: Never mind. I was wrong in my original post. Keep the length of the horns the same.
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frosho
WOLFMAN
FWIW I agree with you Jon. I've been following this discussion and everything you've said sounds right. I think shomethe$$$ is confused.
shomethe$$$
SHO Member
You all are going to mislead people, look at the equation for resonance he posted, area is in the numerator and volume and length is in the denominator.
jonheese
Used-To-Know-It-All
Yup, you're absolutely right. As the cross-sectional area (S) goes up, the total volume (V) will also go up by the same amount, thus they will cancel each other out. So if you want the resonant frequency to remain the same, you don't want to change the overall length (L) of the resonating chamber.
This equation (which I misread in my first reading of that article, I thought the V was a lowercase gamma) actually shows us something important about the Helmholtz resonant frequency phenomenon:
If the cross-sectional area of a resonating tube is kept the same while its length is changed, its resonant frequency will be changed inversely by a sqrt(2) factor. Meaning, if you increase the length, you will decrease the resonant frequency by a factor of sqrt(2), and vice versa.
This effect is due to the fact that both L (length) and V (volume) are included in the denominator of the above equation, and they both change by the same amount as the length of the tube is changed.
My original contention above would have resulted in S growing (because of the larger average cross-sectional area), V remaining the same, and L shrinking. This would exaggerate the increase in resonant RPM, which is the opposite of what we actually wanted to do.
So, in other words: Never mind.
I'll go back and edit my previous posts to reflect my new-found knowledge. Thanks, shomethe$$$.
Edit: I kept asking you why you thought that, but you never gave a reason. All you had to do was say that!
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frosho
WOLFMAN
jonheese
Used-To-Know-It-All
If you want the resonant RPM to remain the same, keep the horns the same length. The increase in diameter and the corresponding increase in volume will cancel each other out in the equation for determining resonant frequency, so the resonant frequency will remain the same.
Expanded to the most general case, the length of the intake path determines the resonant frequency (aka "tuned" RPM) of the system, regardless of the cross-sectional area. In other words, no matter how fat the intake tube(s) are, their length is all that matters here.
jonheese
Used-To-Know-It-All
Yes, that's correct.
You have three choices when installing BBBs:
1. Leave the stock diameter horns in place. This will restrict air flow, reducing the effectiveness of the BBBs. Not so good.
2. Remove the horns entirely. This will shorten the intake path, thus increasing the resonant RPM of the system slightly, but still allowing better airflow than stock-diameter horns. You will probably have turbulent air at the mouth of the butterflies, and you're losing the velocity stack that the horns give you, so your velocity and flow won't be as good as it could be. Better.
3. Fabricate/purchase stock-length horns with the proper BBB diameter. This will keep the intake path the same length, so the resonant RPM will remain the same and will have better airflow than #1 and probably #2. Best.
You have three choices when installing BBBs:
1. Leave the stock diameter horns in place. This will restrict air flow, reducing the effectiveness of the BBBs. Not so good.
2. Remove the horns entirely. This will shorten the intake path, thus increasing the resonant RPM of the system slightly, but still allowing better airflow than stock-diameter horns. You will probably have turbulent air at the mouth of the butterflies, and you're losing the velocity stack that the horns give you, so your velocity and flow won't be as good as it could be. Better.
3. Fabricate/purchase stock-length horns with the proper BBB diameter. This will keep the intake path the same length, so the resonant RPM will remain the same and will have better airflow than #1 and probably #2. Best.
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jonheese
Used-To-Know-It-All
Aha, the $64,000 CDN question.
