As I am disassembling my Q for the chain job I stopped to look at the inlet system. I know much discussion and experimentation has occurred on this subject. On the filter box are several empty reservoirs. Are these a harmonic damper or a pulsation damper? I found a lot of debris inside one on the side of the box next to the vapor canister. Some dirt and sand, and a McDonald's receipt from March of this year! Maybe instead of a damper, they serve as some sort of pre-cleaner area? Something like the radial fins on a Donaldson design air filter?
firedane
Tech question - curiosity
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Q45tech
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- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
If you think about it the air flow is not continuous but a series of Guassian shaped pulses each 248 degrees wide and overlapped every 90 degrees peak to peak.4 pulses per rpm, ---650 [x4] /60= 43.3 Hz, 2000 rpm= 133 Hz, 6900= 460 Hz.
http://hyperphysics.phy-astr.g....html
At 50 C [132F] the speed of sound is 362 M/sec0.226 Meters =8.9" is a 1/4 wave [closed end stub] at 6,000 rpm @50F, but it drops 5% [5700 rpm] at 0 C[32F]. The 18" [twice 8.9"] distance from the open mid point of the valve thru the runner to the plenum allows a 2nd reflected boosting wave to hit the valve when it is 2/3 closed adding 3-5% more final air into the cylinder depending on temperature at 6,000 rpm.
The 26" distance from the plenum neck thru the throttle body MAF and to the MAF cone inside the air box is roughly 275 Hz [1/2 wave open].....oh my goodness that comes to 3900-4000-4100 rpm, the publish torque peak adjusting for differences in air temperature.
The rest of the system out to the input funnel in front of the radiator is, tuned to 1750 and 2000-2100 rpm to enhance mpg at 55-60 mph.
There are 5 diffferent resonances in the plenum and runnners plus the 4 in the system from plenum on out. 9 in all.
No wonder changing to something like a K&N Cone causes such havoc.....especially below 4,000 rpm!
It amazes me that owners don't understand that every little hose, wire, clip, and bend has been engineered to do something positive. They spent years getting it as good as the 1988 knowledge base would allow!
http://hyperphysics.phy-astr.g....html
At 50 C [132F] the speed of sound is 362 M/sec0.226 Meters =8.9" is a 1/4 wave [closed end stub] at 6,000 rpm @50F, but it drops 5% [5700 rpm] at 0 C[32F]. The 18" [twice 8.9"] distance from the open mid point of the valve thru the runner to the plenum allows a 2nd reflected boosting wave to hit the valve when it is 2/3 closed adding 3-5% more final air into the cylinder depending on temperature at 6,000 rpm.
The 26" distance from the plenum neck thru the throttle body MAF and to the MAF cone inside the air box is roughly 275 Hz [1/2 wave open].....oh my goodness that comes to 3900-4000-4100 rpm, the publish torque peak adjusting for differences in air temperature.
The rest of the system out to the input funnel in front of the radiator is, tuned to 1750 and 2000-2100 rpm to enhance mpg at 55-60 mph.
There are 5 diffferent resonances in the plenum and runnners plus the 4 in the system from plenum on out. 9 in all.
No wonder changing to something like a K&N Cone causes such havoc.....especially below 4,000 rpm!
It amazes me that owners don't understand that every little hose, wire, clip, and bend has been engineered to do something positive. They spent years getting it as good as the 1988 knowledge base would allow!
Tuned intake system
So, if I am reading this right then the extra chambers do work with the pulse waves and help to tune the resonance. Yes I agree that some people think engineering on even an air hose is for convenience and fit. Look at the flipped over air lid on a piece of Detroit iron. I have a hard time explaining air pressure and temperature over the center of an engine vs. low pressure areas and cool air at the front. The intake sounds louder when you romp the throttle so it must be better. Hey - the Rijke tube resonator on the website is great. Great explanation of heat and air mass pulsation. I work with water flow a lot in my hydraulics classes for the fire department. We have to work with friction loss as a factor. How much does that come into play with air movement? We also calculate for bends in the tubing. Does the shape of the tube from the MAF to the throttle body come into play with such a short distance?
firedane
firedane
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Thats why I averaged the inside length vs the outside length and used 26" as the average and submitted a range 3800-4200 rpm for the tuning point.
Curves are a lot more important when fuel is suspended in air as the changes in velocity around the curve will cause fuel to puddle out.
The max velocity/mass is 230 grams per second in a 3 " diameter pipe [7 sq."].
They had to build a lot of models to get it just right so that when the sand particles hit the filter, then fall down and to the left into the trap when the velocity slows.
I have experimented with a 2 " hole in the lower right side section of air box fed by a 2 " pipe from the fender well. While it reduces the vacuum created above 4,000 rpm by 2"W.C. or [7.5">5.5" W.C. above the filter] it disrupts the action of the sand trap! And of course the resonances below 4,000 rpm.
Need a super computer to model the particle flow.But the improvement is so marginal [as we know a K&N cone only adds 4 HP with the hood open sucking in cool room air] so each 1.6-2" W.C. might be 1 HP......as 4HP is lost by the extra 6.5" W.C. restriction of the air box forward. What we don't know is how much better the more typical 750-4,000 rpm range behaves and how much fuel improvement they got on the highway.
If it doesn't improve things by 5 HP [1.5%] it isn't worth doing!
Curves are a lot more important when fuel is suspended in air as the changes in velocity around the curve will cause fuel to puddle out.
The max velocity/mass is 230 grams per second in a 3 " diameter pipe [7 sq."].
They had to build a lot of models to get it just right so that when the sand particles hit the filter, then fall down and to the left into the trap when the velocity slows.
I have experimented with a 2 " hole in the lower right side section of air box fed by a 2 " pipe from the fender well. While it reduces the vacuum created above 4,000 rpm by 2"W.C. or [7.5">5.5" W.C. above the filter] it disrupts the action of the sand trap! And of course the resonances below 4,000 rpm.
Need a super computer to model the particle flow.But the improvement is so marginal [as we know a K&N cone only adds 4 HP with the hood open sucking in cool room air] so each 1.6-2" W.C. might be 1 HP......as 4HP is lost by the extra 6.5" W.C. restriction of the air box forward. What we don't know is how much better the more typical 750-4,000 rpm range behaves and how much fuel improvement they got on the highway.
If it doesn't improve things by 5 HP [1.5%] it isn't worth doing!