The Myth: Resonance Tuning vs. BackPressure
Thread Starter
Registered User
Joined: Sep 2002
Posts: 655
^ This thread hasn't even started 
My guess to your question is - no.
The wave tuning will occur within the intake plenum and runners
to help create a low pressure area at the throttle blade(s).
The supply of sufficient, cold, "unturbulent" air is the responsibility
of the air ducts.
The reason I believe this is because, once the wave 'sees' the
air filter, air cleaner housing, hood, etc...there isn't much to help
overcome the obstructions.
Mabye OldSS in onto something when he mentions the position
of the carbs and air intake? The higher up from the plenum, the
more increase in velocity due to pressure differential?
Is that why dyno tests are done using a large "velocity stack"?
To remove Eddy currents and increase incoming air speed?
My guess to your question is - no.
The wave tuning will occur within the intake plenum and runners
to help create a low pressure area at the throttle blade(s).
The supply of sufficient, cold, "unturbulent" air is the responsibility
of the air ducts.
The reason I believe this is because, once the wave 'sees' the
air filter, air cleaner housing, hood, etc...there isn't much to help
overcome the obstructions.
Mabye OldSS in onto something when he mentions the position
of the carbs and air intake? The higher up from the plenum, the
more increase in velocity due to pressure differential?
Is that why dyno tests are done using a large "velocity stack"?
To remove Eddy currents and increase incoming air speed?
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Zero_to_69
^ This thread hasn't even started
My guess to your question is - no.
The wave tuning will occur within the intake plenum and runners
to help create a low pressure area at the throttle blade(s).
The supply of sufficient, cold, "unturbulent" air is the responsibility
of the air ducts.
The reason I believe this is because, once the wave 'sees' the
air filter, air cleaner housing, hood, etc...there isn't much to help
overcome the obstructions.
Mabye OldSS in onto something when he mentions the position
of the carbs and air intake? The higher up from the plenum, the
more increase in velocity due to pressure differential?
Is that why dyno tests are done using a large "velocity stack"?
To remove Eddy currents and increase incoming air speed?
^ This thread hasn't even started
My guess to your question is - no.
The wave tuning will occur within the intake plenum and runners
to help create a low pressure area at the throttle blade(s).
The supply of sufficient, cold, "unturbulent" air is the responsibility
of the air ducts.
The reason I believe this is because, once the wave 'sees' the
air filter, air cleaner housing, hood, etc...there isn't much to help
overcome the obstructions.
Mabye OldSS in onto something when he mentions the position
of the carbs and air intake? The higher up from the plenum, the
more increase in velocity due to pressure differential?
Is that why dyno tests are done using a large "velocity stack"?
To remove Eddy currents and increase incoming air speed?
Height of carb above runners could be to control plenum size (tunnel ram) or that plus flow and mixture distribution.
Intake velocity in the manifold runners probably relates more to cross section area of runner and flow (CFM).
"Velocity"stack on carb is to smooth airflow (as you said) to get more air in, not tune or really increase velocity. Base plate of air cleaner does about the same thing.
Registered User
Joined: Feb 2004
Posts: 291
From: Abbeville , LA
MaxRace, have you ever played around with Terminator boxes?
-----------------------
No , ..what is Terminator Box ?? website ??
and "use" the Collector to fool engine into thinking Primaries are correct length..don't worry about your primaries
playing around with the Primary pipe lengths have a very much lesser effect than making same changes on Collector side
Tuning Collector lengths/diameters is worth more !!
on highly-scienced out SuperStock combos that have been on dyno many times, and have tried collector and primary pipes till we found best combo..when we did try Merge collectors there wasn't any deifferences or not much
when we tried Merge collectors on regular engines with normal headers, the Merge collectors have many times helped the bottom end of torque curve
mostly because a street or some brand headers have TOO SHORT of collector length to begin with
and using the "longer" merge collector usually results in better torque
-----------------------
No , ..what is Terminator Box ?? website ??
and "use" the Collector to fool engine into thinking Primaries are correct length..don't worry about your primaries
playing around with the Primary pipe lengths have a very much lesser effect than making same changes on Collector side
Tuning Collector lengths/diameters is worth more !!
on highly-scienced out SuperStock combos that have been on dyno many times, and have tried collector and primary pipes till we found best combo..when we did try Merge collectors there wasn't any deifferences or not much
when we tried Merge collectors on regular engines with normal headers, the Merge collectors have many times helped the bottom end of torque curve
mostly because a street or some brand headers have TOO SHORT of collector length to begin with
and using the "longer" merge collector usually results in better torque
Registered User
Joined: Feb 2004
Posts: 291
From: Abbeville , LA
on the Intake side =
the intake runner lengths/diameters influence HP/Torque more
than the Plenum
just the opposite with headers=>where collectors are more important
the intake plenum=similiar to Exhaust Collector effects
but less effective in tuning
the intake runners = similiar to header primaries effects
but more effective in tuning
the intake runner lengths/diameters influence HP/Torque more
than the Plenum
just the opposite with headers=>where collectors are more important
the intake plenum=similiar to Exhaust Collector effects
but less effective in tuning
the intake runners = similiar to header primaries effects
but more effective in tuning
Registered User
Joined: Feb 2004
Posts: 291
From: Abbeville , LA
"Velocity"stack on carb is to smooth airflow (as you said) to get more air in, not tune or really increase velocity. Base plate of air cleaner does about the same thing.
--------------------------------------------------------
a Velocity stack can hurt performance
a carb likes to breathe from sides as well as top
and a well-designed air cleaner base will make more HP/Torque
in many cases than a velocity stack
the velocity stack lost 2+mph on my old C/SM Camaro
--------------------------------------------------------
a Velocity stack can hurt performance
a carb likes to breathe from sides as well as top
and a well-designed air cleaner base will make more HP/Torque
in many cases than a velocity stack
the velocity stack lost 2+mph on my old C/SM Camaro
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
this is a link to a web site that has this terminator box, if you have time to read the hole article you should, i know you wont agree with all thats said, but this guy has tons of credability, he has a very impressive background and has his OWN dyno and machine shop for personal use. David Vizard is whom i'm talking about and he wrote the article. Let me know what you think.
This guy also wrote a Cam Dynamics program which as far as i know only Motor Machine & Supply has. It will pick out teh perfect cam timming events given your combo, then they will pick an off the shelf cam that comes closest or give you the exact specs to have it custom ground.
this is the exact page:
http://www.geocities.com/MotorCity/T...2/vizard10.jpg
this is the whole article:
http://www.geocities.com/MotorCity/T...92/vizard.html
I am partial to this guy; he can do wonderful things with stock parts that only we could do with bolt on parts.
This guy also wrote a Cam Dynamics program which as far as i know only Motor Machine & Supply has. It will pick out teh perfect cam timming events given your combo, then they will pick an off the shelf cam that comes closest or give you the exact specs to have it custom ground.
this is the exact page:
http://www.geocities.com/MotorCity/T...2/vizard10.jpg
this is the whole article:
http://www.geocities.com/MotorCity/T...92/vizard.html
I am partial to this guy; he can do wonderful things with stock parts that only we could do with bolt on parts.
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
does it sound like these people are blowing smoke?
http://www.xpipe.org/AUTO_Corvette.html
http://www.xpipe.org/AUTO_Corvette.html
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by 408TA
does it sound like these people are blowing smoke?
http://www.xpipe.org/AUTO_Corvette.html
does it sound like these people are blowing smoke?
http://www.xpipe.org/AUTO_Corvette.html
As far as the sound pressure or whatever causing the increase, "blowing smoke" might be apt. Of course, if you buy the hype you probably get the power increase. Assuming there are no objectionable resonances, and you like the look and sound, and the 18 hp is real, all that's left is fit and price.
$1295 seems a little steep for a 2-1/2 C4 catback, when a Corsa system is $1040 retail. That almost 25% more than Corsa.
You pays yer money and you takes yer choice....or is that chance?
Thread Starter
Registered User
Joined: Sep 2002
Posts: 655
Need some brain power please.
Clarify Absolute Pressure (for the book Scientific Design of Exhaust
and Intake Systems).
"The measurement of pressure relative to the pressure in a vacuum, equal to the sum of the pressure shown on a pressure gauge and atmospheric pressure. "
Atmospheric pressure at sea level is 14.7 lbs./in^2
So...when the book states a value of 14.0 lbs./in^2 (abs), he is
stating the atmospheric pressure at his current altitude ....in addition to the gauge reading produced by the function of the
engine (IE: Exhaust gas velocity).
(See page 20)
When he states a pressure without the "(abs)" suffix...this is the
pressure at rest (atmospheric at current elevation) ?
(See page 90)
Here's a good link for those that really want to feel stupid
:
http://scienceworld.wolfram.com/phys...mospheres.html
Clarify Absolute Pressure (for the book Scientific Design of Exhaust
and Intake Systems).
"The measurement of pressure relative to the pressure in a vacuum, equal to the sum of the pressure shown on a pressure gauge and atmospheric pressure. "
Atmospheric pressure at sea level is 14.7 lbs./in^2
So...when the book states a value of 14.0 lbs./in^2 (abs), he is
stating the atmospheric pressure at his current altitude ....in addition to the gauge reading produced by the function of the
engine (IE: Exhaust gas velocity).
(See page 20)
When he states a pressure without the "(abs)" suffix...this is the
pressure at rest (atmospheric at current elevation) ?
(See page 90)
Here's a good link for those that really want to feel stupid
:http://scienceworld.wolfram.com/phys...mospheres.html
Last edited by Zero_to_69; Mar 17, 2004 at 10:02 PM.
Registered User
Joined: Feb 2004
Posts: 291
From: Abbeville , LA
"The measurement of pressure relative to the pressure in a vacuum, equal to the sum of the pressure shown on a pressure gauge and atmospheric pressure. "
============================================
Absolute_Pressure = Atmospheric_Pressure + Gauge_Pressure
When he states a pressure without the "(abs)" suffix...this is the
pressure at rest (atmospheric at current elevation) ?
==================================
without (abs) should just mean only the reading on the Gauge
page 90 would also be just gauge pressure
not absolute pressure
but just pressure in psi above zero referrence point
the zero point is also just gauge pressure on page 90
and to confuse you more
the zero point is atmospheric pressure
it would make the Chart confusing if the zero point were atmospheric pressure value
the +6 would then be 14.696 + 6 = 20.696
the -6 would then be 14.696 - 6 = 8.696
the zero would be 14.696
the range = 12 units
============================================
Absolute_Pressure = Atmospheric_Pressure + Gauge_Pressure
When he states a pressure without the "(abs)" suffix...this is the
pressure at rest (atmospheric at current elevation) ?
==================================
without (abs) should just mean only the reading on the Gauge
page 90 would also be just gauge pressure
not absolute pressure
but just pressure in psi above zero referrence point
the zero point is also just gauge pressure on page 90
and to confuse you more
the zero point is atmospheric pressure
it would make the Chart confusing if the zero point were atmospheric pressure value
the +6 would then be 14.696 + 6 = 20.696
the -6 would then be 14.696 - 6 = 8.696
the zero would be 14.696
the range = 12 units
Registered User
Joined: Feb 2004
Posts: 291
From: Abbeville , LA
Zero_to_69
if you would also look on page 89 at chart 5:8
its a very good example of >= "double multiple" pipe length
i had posted in previous posts....i've found this same concept/theory of wave tuning to work in majority of my dyno tests with exhaust systems
pressure recordings are at 2000 rpms
notice 1st upper most wave .... pipe is 5 feet 2 inches
or 62 inches total length
a postive pressure wave forms at TDC
now notice 2 nd wave ...with pipe at 40 inches
a negative wave is centered during TDC overlap period
3rd wave with pipe at 19 inches
a negative wave is again centered on TDC overlap period
4th wave with pipe at 8.5 inches
a toss up , with very small amount of negative wave
whats the pattern ??
a double multiple in pipe length is pattern
40 inches is great
so half of 40 inches is 20 inches...and 19 inches in chart is close enough to double mutiple that it also works
and half of 20 is 10 inches ...but 8.5 inches is futher off percentage wise, and there is diminishing effect of how far you can take this theory to
also notice that the next double-multiple would be 80 inches for next negative wave to be centered on TDC overlap period
finally, notice whats happening at the length in between
80 inches to 40 inches ( 60 inches)
since 60 inches is not a double multiple of best length
and is in fact windsup to be in the worst length range
so at 62 inches (close to 60 inches) the chart shows a bad positive pressure wave centered at TDC overlap period
=======================================
my dyno is in country aways from city
allows me to dyno test without dyno mufflers or extra lengths
that can sometimes skew data
if find in overwhelming majority of tests , that when the collector's
internal length is found that makes the best average amount of Torque and HP ...then you "double" that collectors internal length
you can catch negative pressure wave at TDC overlap period
in majority of cases....however, there are also diminishing returns
if taken to extremes in either direction.
if you would also look on page 89 at chart 5:8
its a very good example of >= "double multiple" pipe length
i had posted in previous posts....i've found this same concept/theory of wave tuning to work in majority of my dyno tests with exhaust systems
pressure recordings are at 2000 rpms
notice 1st upper most wave .... pipe is 5 feet 2 inches
or 62 inches total length
a postive pressure wave forms at TDC
now notice 2 nd wave ...with pipe at 40 inches
a negative wave is centered during TDC overlap period
3rd wave with pipe at 19 inches
a negative wave is again centered on TDC overlap period
4th wave with pipe at 8.5 inches
a toss up , with very small amount of negative wave
whats the pattern ??
a double multiple in pipe length is pattern
40 inches is great
so half of 40 inches is 20 inches...and 19 inches in chart is close enough to double mutiple that it also works
and half of 20 is 10 inches ...but 8.5 inches is futher off percentage wise, and there is diminishing effect of how far you can take this theory to
also notice that the next double-multiple would be 80 inches for next negative wave to be centered on TDC overlap period
finally, notice whats happening at the length in between
80 inches to 40 inches ( 60 inches)
since 60 inches is not a double multiple of best length
and is in fact windsup to be in the worst length range
so at 62 inches (close to 60 inches) the chart shows a bad positive pressure wave centered at TDC overlap period
=======================================
my dyno is in country aways from city
allows me to dyno test without dyno mufflers or extra lengths
that can sometimes skew data
if find in overwhelming majority of tests , that when the collector's
internal length is found that makes the best average amount of Torque and HP ...then you "double" that collectors internal length
you can catch negative pressure wave at TDC overlap period
in majority of cases....however, there are also diminishing returns
if taken to extremes in either direction.