Title: Air Intake Velocities
Description: & drag...
Description: & drag...
greeneyes - October 8, 2009 11:59 AM (GMT)
Any fluid engineers in the club??
I'm just planning the airbox for the twin SUs on the daughter's KE70.
Its 1300cc so in each 360deg stroke two cylinders fill, or about 650cc (2/3L).
At 6000rpm it will suck 4000L/min (2/3 of 6000)
or close to 70L/sec. So a 210L drum empties in 3seconds!
That needs to fit down an intake pipe of about 60mm diam, or say 20sq cm.
So my 70,000cc passes down a 20sqcm pipe at almost 25M/sec, say, the boundary of an inner-city section per sec.
Am I right?? There is sure to be a lot of drag in the intake pipe, making me wonder if an open air filter in the engine bay might be better. The filter is a RAV 4 one, 310x157 so an area of nearly 500sq cm. That's 25 times the size of the intake pipe, so the drag is nothing in comparison.
The carbs are 1inch & 1/4 so their combined area is also about 20sq cm, and the air must fly down the throats at 12M/sec each.
I'm just planning the airbox for the twin SUs on the daughter's KE70.
Its 1300cc so in each 360deg stroke two cylinders fill, or about 650cc (2/3L).
At 6000rpm it will suck 4000L/min (2/3 of 6000)
or close to 70L/sec. So a 210L drum empties in 3seconds!
That needs to fit down an intake pipe of about 60mm diam, or say 20sq cm.
So my 70,000cc passes down a 20sqcm pipe at almost 25M/sec, say, the boundary of an inner-city section per sec.
Am I right?? There is sure to be a lot of drag in the intake pipe, making me wonder if an open air filter in the engine bay might be better. The filter is a RAV 4 one, 310x157 so an area of nearly 500sq cm. That's 25 times the size of the intake pipe, so the drag is nothing in comparison.
The carbs are 1inch & 1/4 so their combined area is also about 20sq cm, and the air must fly down the throats at 12M/sec each.
roman - October 9, 2009 04:40 AM (GMT)
I remember reading somewhere.
Every 10 degrees temperature change in air temp, is worth 2% horsepower.
So question becomes, is the difference in air temperature enough to offset the pressure drop caused by the additional piping?
Given that every car I've ever seen opts to scoop air from in front of the radiator panel (added bonus of being high pressure area) I'd say yes.
As well as that many of the intake piping before the air filter box snakes and bends outside of the gaurds and back in to make them long enough to be a tuned length... I dont think the drag caused by sucking through a pipe is as great as people imagine, if it was a huge cause of drag, utilising harmonics with tuned length pipes wouldnt be applicable, and manufacturers wouldnt go to the trouble.
I'm running a quad throttle setup, and spent a lot of time looking into whether (from a performance point of view, not sound!) it would be better having them open, or in a box, with cold air feed.
One thing I did, was look at race cars with similar intake design and engine displacement... BTCC cars, all high strung 2 litre NA motors running individual throttles, and they ALL run inside an air box, with air feed coming from the front of the car.
The full benefits from doing so wont be apparent on a dyno where the car is stationary and engine lid open, but there are other ways to test whether or not there's a positive gain from doing so (manometer)
Julian Edgar and his cronies did some tests, and with a well set up cold air feed from a high pressure zone in the front of the car, the air was still *above* atmospheric pressure on the far side of the air filter, meaning it was less restrictive than having no filter, and a shorter pipe which stopped in the engine bay.
I think the best series of articles that I've ever read, to do with intakes, is from Julian Edgar on the Autospeed website:
http://autospeed.com/cms/A_1361/article.html
http://autospeed.com/cms/title_Eliminating...29/article.html
Doesnt cost anything to do a bit of homework before shelling out $$$ for some mods that might not work as well as you'd hope. :)
My airbox has the air inlet facing at the base of the trumpets, so that the air comes into the box and settles evenly around them, rather than biasing one runner or the other and causing it to lean out. Same way blacktop 4AGE airbox does it.
Every 10 degrees temperature change in air temp, is worth 2% horsepower.
So question becomes, is the difference in air temperature enough to offset the pressure drop caused by the additional piping?
Given that every car I've ever seen opts to scoop air from in front of the radiator panel (added bonus of being high pressure area) I'd say yes.
As well as that many of the intake piping before the air filter box snakes and bends outside of the gaurds and back in to make them long enough to be a tuned length... I dont think the drag caused by sucking through a pipe is as great as people imagine, if it was a huge cause of drag, utilising harmonics with tuned length pipes wouldnt be applicable, and manufacturers wouldnt go to the trouble.
I'm running a quad throttle setup, and spent a lot of time looking into whether (from a performance point of view, not sound!) it would be better having them open, or in a box, with cold air feed.
One thing I did, was look at race cars with similar intake design and engine displacement... BTCC cars, all high strung 2 litre NA motors running individual throttles, and they ALL run inside an air box, with air feed coming from the front of the car.
The full benefits from doing so wont be apparent on a dyno where the car is stationary and engine lid open, but there are other ways to test whether or not there's a positive gain from doing so (manometer)
Julian Edgar and his cronies did some tests, and with a well set up cold air feed from a high pressure zone in the front of the car, the air was still *above* atmospheric pressure on the far side of the air filter, meaning it was less restrictive than having no filter, and a shorter pipe which stopped in the engine bay.
I think the best series of articles that I've ever read, to do with intakes, is from Julian Edgar on the Autospeed website:
http://autospeed.com/cms/A_1361/article.html
http://autospeed.com/cms/title_Eliminating...29/article.html
Doesnt cost anything to do a bit of homework before shelling out $$$ for some mods that might not work as well as you'd hope. :)
My airbox has the air inlet facing at the base of the trumpets, so that the air comes into the box and settles evenly around them, rather than biasing one runner or the other and causing it to lean out. Same way blacktop 4AGE airbox does it.
roman - October 9, 2009 04:45 AM (GMT)
This quote is of particular relevance, considering the latest automotive trend 'fact' is that putting a drop in aftermarket air filter is the best way to set up your air intake:
| QUOTE |
| Oh, you might also be contemplating dropping an aftermarket filter insert into your airbox. Chances are you won't gain a thing; based on our previous intake testing, the standard filter element in an un-touched intake system is responsible for only around 3 percent of the total restriction. A drop-in replacement won't make any noticeable difference. Again, though, the 'advantage' of a washable aftermarket filter might be attractive to you - it depends on the cost of new OE filter replacements versus the initial cost of the aftermarket filter and any necessary washing chemicals. Keep in mind filtration performance as well. |
In other news:
Good god, I think I just peed my pants a little :vrrrm:
http://www.youtube.com/watch?v=PoLi8NZJYu0
greeneyes - October 9, 2009 06:44 AM (GMT)
Thankyou Roman- I also hauled a book out of the library called Applied Fluid Mechanics, but nearly died when I opened it up and the first thing I saw was Reynolds Number..
Bought back my Food Tech days at Uni when I hated engineering and physics! :D
It did have a graph showing that air looses 25% of its mass if you heat it from 40deg to 80deg.
So, plenty of reading in the next week, the Micheal Knowling articles look great.
Love that Starlet! :woot: 1970s and already twin cam 16valve, injected, slide throttle bodies & a 5 speed! Even a synthetic rear leaf with panhard and tramp arms.
Bought back my Food Tech days at Uni when I hated engineering and physics! :D
It did have a graph showing that air looses 25% of its mass if you heat it from 40deg to 80deg.
So, plenty of reading in the next week, the Micheal Knowling articles look great.
Love that Starlet! :woot: 1970s and already twin cam 16valve, injected, slide throttle bodies & a 5 speed! Even a synthetic rear leaf with panhard and tramp arms.
roman - October 10, 2009 05:44 AM (GMT)
Also, another thing to consider... (It's rainy today and I CBF working on the car, something I've been mulling over for a while, feel like a rant so bare with me haha)
Air isnt flowing constantly, it's a series of pulses.
Just like intake runner length, you can tune the length and size of the pipe leading to the airbox/plenum to suit a particular frequency/rpm.
If your 4 cyl engine is doing 6000rpm, then the frequency of the pulses of air being sucked into the airbox around the carbs is gonna be 6000rpm x 4 cylinders / 2 (because it's a 4 stroke)
So 12,000 induction events per minute, frequency of 200 hertz.
So, goal is to find area of airbox, and length of inlet pipe that will give a resonant frequency of 200 hertz. Doing so will give a mild supercharging effect, as a reflected pressure wave enters the airbox just as the next lot of air is coming in.
Thankfully when people make boxes for sub woofers and so forth they use the same principal, so there is a lot of info on tuned box sizes.
Plug some approx dimensions of a planned airbox size into here:
http://www.lautsprechershop.de/tools/index...elmholtz_en.htm
And see what rpm it's going to work at. Can adjust inlet length/diameter up and down until you find something with a resonance which works primarily in an rpm range which you're looking for.
Will put in my airbox setup as an example.
Intake pipe length is 480mm
Intake pipe inside diameter is 80mm.
Airbox L x W x H is approx 400 x 180 x 180mm.
This gives a resonant frequency of the airbox, of 43.5 hertz.
Which is 43.5 x 60 /4 x 2 = resonance occuring at 1305rpm... Bugger! Not quite what I was wanting to acheive, ahaha!
(Was hoping it was gonna end up being some sort of number that makes me sound like I knew what I was doing when I made it)
Aaahh well, maybe air filter box has a better intake resonance....
approx 150 x 300 x 250 airbox dimensions, 480 x 80mm outlet pipe.
Hmmm 49 hertz... 1470 rpm... D'oh!
To get a resonance working at 6000rpm, fiddling round with the calculator a bit, I'd need a resonator in the intake piping with dimensions of 150 x 150 x 150mm, 50mm long pipe 80mm wide.
To get any sort of resonant affect for an airbox around carbs, you'd need to make the volume of the box quite small!
So, in conclusion.
Maybe disregard everything I've said, cos it's not gonna help at all :D
Air isnt flowing constantly, it's a series of pulses.
Just like intake runner length, you can tune the length and size of the pipe leading to the airbox/plenum to suit a particular frequency/rpm.
If your 4 cyl engine is doing 6000rpm, then the frequency of the pulses of air being sucked into the airbox around the carbs is gonna be 6000rpm x 4 cylinders / 2 (because it's a 4 stroke)
So 12,000 induction events per minute, frequency of 200 hertz.
So, goal is to find area of airbox, and length of inlet pipe that will give a resonant frequency of 200 hertz. Doing so will give a mild supercharging effect, as a reflected pressure wave enters the airbox just as the next lot of air is coming in.
Thankfully when people make boxes for sub woofers and so forth they use the same principal, so there is a lot of info on tuned box sizes.
Plug some approx dimensions of a planned airbox size into here:
http://www.lautsprechershop.de/tools/index...elmholtz_en.htm
And see what rpm it's going to work at. Can adjust inlet length/diameter up and down until you find something with a resonance which works primarily in an rpm range which you're looking for.
Will put in my airbox setup as an example.
Intake pipe length is 480mm
Intake pipe inside diameter is 80mm.
Airbox L x W x H is approx 400 x 180 x 180mm.
This gives a resonant frequency of the airbox, of 43.5 hertz.
Which is 43.5 x 60 /4 x 2 = resonance occuring at 1305rpm... Bugger! Not quite what I was wanting to acheive, ahaha!
(Was hoping it was gonna end up being some sort of number that makes me sound like I knew what I was doing when I made it)
Aaahh well, maybe air filter box has a better intake resonance....
approx 150 x 300 x 250 airbox dimensions, 480 x 80mm outlet pipe.
Hmmm 49 hertz... 1470 rpm... D'oh!
To get a resonance working at 6000rpm, fiddling round with the calculator a bit, I'd need a resonator in the intake piping with dimensions of 150 x 150 x 150mm, 50mm long pipe 80mm wide.
To get any sort of resonant affect for an airbox around carbs, you'd need to make the volume of the box quite small!
So, in conclusion.
Maybe disregard everything I've said, cos it's not gonna help at all :D