BBS and ported intake runners

[Brook24v]

Very simple way to settle this, Dyno numbers with horns in/out. Then we can see where the loss/gain plays out in the graphs..

Dyno numbers can vary from run to run due to changing conditions. If the car saw a 3 hp gain, it would be hard to rule out where it actually came from. I've had cars that varied almost 10whp between each pull with no other changes.

Actual flow numbers would be the only way to prove anything. But since it is a fact that the horns restrict air flow with the use of BBBs, I'll always throw mine straight in the trash. There are bigger things to worry about on the SHO.

 

[turbo79]

Dyno numbers can vary from run to run due to changing conditions. If the car saw a 3 hp gain, it would be hard to rule out where it actually came from. I've had cars that varied almost 10whp between each pull with no other changes.

Actual flow numbers would be the only way to prove anything. But since it is a fact that the horns restrict air flow with the use of BBBs, I'll always throw mine straight in the trash. There are bigger things to worry about on the SHO.

The stock velocity stacks may restrict, but since I'm after driveability and not HP at the top of the rev curve I think I'll keep the stacks, even with BBBs. Most of the time I want secondary power between 4,500 and 6,000, pulling out of medium speed corners with few straightaways.

Maybe I'll contact Hilborn about a custom set, the same length but with a diameter to match the BBBs. They'll probably laugh, or want to charge $500.00, but it may be worth a try.

The stacks themselves seem to be mandrel bent steel tubing with flared ends, the base(s) where they attach to the butterflies may be the complicated part. I'm also going to contact my local automotive machinist, and see if he works with tubing.

I must seem obsessed or crazy, but then consider what kind of car I am tweaking... :sun:

 

[kconnor]

Back in the ‘60s and ‘70’s you could buy a velocity stack to fit the mouth of your Holley carburetor, just like the one you see in the above picture of Smokey and that Chevy motor. It was usually worth about 10 horsepower or so over just an open carb. B&M used to sell (probably still do) a kind of plastic insert you would install onto you carb that would smooth and contour the air going into it. It was worth a few horsepower. Both devices smoothed and contoured the air flowing into the carburetor reducing turbulence and therefore increasing airflow. Probably is what the SHO’s air horns are designed to do. I suspect that increase in sound people comment on when they remove the horns is caused by increased turbulence. Just saying.

 

[turbo79]

Back in the ‘60s and ‘70’s you could buy a velocity stack to fit the mouth of your Holley carburetor, just like the one you see in the above picture of Smokey and that Chevy motor. It was usually worth about 10 horsepower or so over just an open carb. B&M used to sell (probably still do) a kind of plastic insert you would install onto you carb that would smooth and contour the air going into it. It was worth a few horsepower. Both devices smoothed and contoured the air flowing into the carburetor reducing turbulence and therefore increasing airflow. Probably is what the SHO’s air horns are designed to do. I suspect that increase in sound people comment on when they remove the horns is caused by increased turbulence. Just saying.

I just spent some time at Hilborn Fuel Injection's web site, looking at the techie stuff, and velocity stacks definitely are worth a hp increase through increased velocity into the intake port. I'm not going to blow off their many years of more than just talk and speculation. Now I'm on a mission...

 

[95atxbuffalosho]

Do BBB's really make a big difference?

 

[LOUDSHO92]

Yes..

 

[95atxbuffalosho]

Do BBB's really make a big difference?

 

[jonheese]

Is there an echo in here?

Edit: I mean, ahem...

Yes..

 

[turbo79]

Do BBB's really make a big difference?

I've heard about 10 hp, and noticeable through the butt dyno. But, my goal is to bring that HP increase to near the rev range that the original velocity stacks are designed and tuned for. Unless you are talking about a casual track or racing car, who drives around WOT above 6,000 rpm all the time? Well, not me, anyway...

 

[jonheese]

I agree 100%. I'm very interested to hear what you find. If you can get someone to make reproduction horns upsized to fit the BBB inner diameter, for a reasonable (eye of the beholder) price, I'd definitely give them a shot.

 

[Toolman]

Bah, just turbo it! A turbocharged flute sounds amazing!!

 

[turbo79]

Bah, just turbo it! A turbocharged flute sounds amazing!!

Easy for you to say! If I had an unlimited budget, and could afford new trannys, axles, and/or a wave trac.

But I can't...

 

[turbo79]

I agree 100%. I'm very interested to hear what you find. If you can get someone to make reproduction horns upsized to fit the BBB inner diameter, for a reasonable (eye of the beholder) price, I'd definitely give them a shot.

Here's some food for thought: The length of the stock horns is "tuned", so to speak, to give optimal flow at a certain RPM, so removing the horns when installing BBBs will change (raise) that optimal RPM. However, if you're making bigger horns to get that optimal RPM down, remember that there's more to it than just length. It's actually the volume of the air in the entire pipe (from valve to horn) that is "tuned" to vibrate at that frequency, so since you're changing the diameter of the butterfly and the horn, you'll actually need to make the new horns a smidgen shorter than stock to keep the same optimal RPM.

I'm not sure if the volume change % between the stock butterflies/horns and the BBBs/bighorns is really significant; making the big ones the same length as stock may only change (lower) the optimal RPM by like 10 RPM or something...

But it is something to consider if you're having big ones fabbed up.

Example that illustrates this: If you have two musical flutes that are both 18" long, but one has a slightly larger inner diameter, the larger one will have a lower "tuned" frequency, even though they're both the same length.

That's good techie stuff, thanks! Maybe Hilborn will have some insights on the matter; they sure would have a lot of data and may have specific formulas for diameter / length / rpm that they would share.

 

[jonheese]

The idea is that you want the volume of the entire pipe (from the end of the horn to the end of the intake port in the head), to be the same (assuming that you don't want to change the stock resonant RPM). So if they're going to do volume comparisons, they would need, at a minimum, the horn, the butterfly assembly, the secondary tube, and the head. If you want to keep the "tuned" RPM the same as stock, you'll want the volume of that entire "pipe" to be the same. If you want to change that tuned RPM (or if you want to calculate the tuned RPM after-the-fact), it's a simple proportional change formula.

In other words, if you increase the volume of that pipe (that's the entire pipe, from horn to head, not just a portion of it) by 5% from stock, then the resonant RPM of the new system will be 5% lower than stock. Etc.

Edit: Never mind. I am wrong in these posts. Keep the length of the horns the same.

 

[shomethe$$$]

I agree 100%. I'm very interested to hear what you find. If you can get someone to make reproduction horns upsized to fit the BBB inner diameter, for a reasonable (eye of the beholder) price, I'd definitely give them a shot.

Here's some food for thought: The length of the stock horns is "tuned", so to speak, to give optimal flow at a certain RPM, so removing the horns when installing BBBs will change (raise) that optimal RPM. However, if you're making bigger horns to get that optimal RPM down, remember that there's more to it than just length. It's actually the volume of the air in the entire pipe (from valve to horn) that is "tuned" to vibrate at that frequency, so since you're changing the diameter of the butterfly and the horn, you'll actually need to make the new horns a smidgen shorter than stock to keep the same optimal RPM.

I'm not sure if the volume change % between the stock butterflies/horns and the BBBs/bighorns is really significant; making the big ones the same length as stock may only change (lower) the optimal RPM by like 10 RPM or something...

But it is something to consider if you're having big ones fabbed up.

Example that illustrates this: If you have two musical flutes that are both 18" long, but one has a slightly larger inner diameter, the larger one will have a lower "tuned" frequency, even though they're both the same length.

Your saying opposite things here, I think your going to mislead people, please edit.

 

[jonheese]

Your saying opposite things here, I think your going to mislead people, please edit.

I don't see where I said any contradictory things, but I edited it for more clarity and took out some wordiness where it wasn't really necessary.

Is that better?

Edit: Never mind. I was wrong in my original post. Keep the length of the horns the same.

 

[shomethe$$$]

Nope, the way I interpreted your post is a bigger diameter butterfly will require a shorter horn to keep the same resonance? because that goes against Helmholtz theory, you had it right initially in the post

 

[jonheese]

Well, maybe I just don't understand the concept right, because that is exactly what I'm saying.

Consider these two scenarios:

1) Stock intake, stock butterflies, stock horns

2) Stock intake, BBBs, custom horns made to the same length as the stock ones, but with a larger diameter to match the BBBs

The Helmholtz resonant frequency is determined by the volume of air in the system (or more accurately, the volume of the pipe that the air is flowing through). In scenario 2 above, the overall volume of the system is slightly larger than the overall volume of the system in scenario 1, because the two "pipes" are the same length, but portions of them have different diameters. Thus, their resonant frequencies will be different (more volume = lower resonant frequency).

Now, we consider a third scenario:

3) Stock intake, BBBs, custom horns with a larger diameter to match the BBBs, but slightly shorter than the stock ones, so that the volume of the butterfly/horn combined matches the stock butterfly/horn

In scenario 3, the resonant frequency (and thus the "tuned" RPM) will match the stock system in scenario 1, because the overall volume of the secondary pipe is the same.

Did I miss something here?

Edit: Never mind. I am wrong in these posts. Keep the length of the horns the same.

 

[shomethe$$$]

Yes, its not correct, your first statement was correct, look at the area not the volume.

 

[jonheese]

The area of what? What first statement?

Everything I've ever read about Helmholtz resonance has to do with volume, so looking only at (any) area figure is ignoring one dimension of space.

http://www.phys.unsw.edu.au/jw/Helmholtz.html
http://physics.kenyon.edu/EarlyAppa.../Helmholtz_Resonator/Helmholtz_Resonator.html

"The resonant frequency of a Helmholtz resonator depends on its volume, and a cylindrical resonator permits the volume of the resonator to be changed by sliding the tubes in and out."

"The purely Helmholtz resonance can be investigated by keeping the body volume constant."

Edit: Never mind. I was wrong in my original post. Keep the length of the horns the same.

It's all about volume, so if you increase the cross-sectional area of the tube, you must shorten it or else you'll lower the resonant frequency.

Can you please explain what I've said wrong here?