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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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  #281  
Old 20th April 2014
greer greer is offline
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I am so very pleased with my 1200C spark plug boot breather mods. Thank you, 1200C!

Sarah
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  #282  
Old 4th June 2015
cheechust cheechust is offline
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I put on a k&n and now I need to remap it,started reving way to high if I put it back to stock will it fix the problem or do I got remap it now no matter what?
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  #283  
Old 26th February 2017
msandli msandli is offline
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Quote:
Originally Posted by whittlebeast View Post
Here is the math if anyone wants to know

from http://hondaswap.com/forced-inductio...ram-air-41316/

<<< snip >>>

RAM AIR

Operating Conditions
Temperature = Tair = 20C = 293K
Atm. pressure = Pair = 14.7PSIA
Cpair = 1005J/KgK
K = 1.4
The Cpair and K are constants for air.

Case 1 @ 100Kmh (62Mph) = 27.78m/s

Calculating temperature of the ram air

Tramair = ((Vcar^2/2gc)/cp) + Tair
Tramair = (((27.78m/s)^2/2(1kgm/Ns^2)/1005J/kg) + 293K
Tramair = 293.4K

The temperature increased by 0.4K or 0.4C.

Pram = Pair (Tram/Tair)^(k/(k-1))
Pram = 14.7PSIA (293.4K/293K)^(1.4/(1.4-1))
Pram = 14.75PSIA - 14.7PSIA
Pram = 0.05PSIG (gauge pressure)

So as you can see driving 100kmh will only have a gain of 0.05 psi! now lets try for 200kmh.

Case 2 @ 200Kmh (124Mph) = 55.5m/s

Calculating temperature of the ram air

Tramair = ((Vcar^2/2gc)/cp) + Tair
Tramair = (((55.5m/s)^2/2(1kgm/Ns^2)/1005J/kg) + 293K
Tramair = 294.5K

The temperature increased by 1.5K or 1.5C.

Pram = Pair (Tram/Tair)^(k/(k-1))
Pram = 14.7PSIA (294.5K/293K)^(1.4/(1.4-1))
Pram = 14.97PSIA - 14.7PSIA
Pram = 0.27PSIG (gauge pressure)


I know this is an old post, but this analysis is incorrect. His conclusion is basically right, but that's just luck.

In words, Bernoulli's equation is merely a form of conservation of energy:

Pressure + kinetic energy + potential energy = constant.

After making a few assumptions, we can calculate the pressure rise of the air in the air filter housing. Admittedly, some of these assumptions might be dubious, so this will be a "best case scenario." To make the math easy, we'll assume that the air entering the ham can is brought to rest. Therefore, the gauge pressure rise of the air will be:

P = 1/2 * density * velocity^2

Air density = 1.225 kg/m^3
velocity = 30 m/s (~67 mph)

Therefore, P ~ 550 Pa = .0798 psig pressure increase

Remember, this would be a best case scenario: the air flow into the snorkel is very turbulent, is partially blocked by the stock front header, and the air obviously doesn't come to a complete stop inside the ham can. Therefore, the pressure boost from this "ram air" effect is likely much less. Even it were enough to matter, the largest air restriction in most people's intake tract is - you guessed it! - the throttle valve. Any increase in pressure upstream of the valve would be accompanied by a decrease in throttle usage to maintain a certain speed, but the total amount of air going into the engine would basically be the same. However, it would be interesting if someone ever installed a pressure tap on a ham can and took some measurements.

Rant over. I'm months away from earning a Ph D in mechanical engineering, and the linked analysis really bugged me. Ask yourself: do you think the air entering your intake warms up by nearly half a degree centigrade (roughly a full degree Fahrenheit) just because you're driving through it (the author's first step)??? If this were true, it would mean a carb works by changing the temperature of the air flowing through the throat, rather than changing its velocity (and therefore, pressure).

Also, this is not a jab at whittlebeast. He didn't do the calculations, he just linked them. I very much enjoy (and learn a lot from) reading his posts on tuning.
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  #284  
Old 27th February 2017
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Quote:
Originally Posted by msandli View Post
I know this is an old post, but this analysis is incorrect. His conclusion is basically right, but that's just luck.

In words, Bernoulli's equation is merely a form of conservation of energy:

Pressure + kinetic energy + potential energy = constant.

After making a few assumptions, we can calculate the pressure rise of the air in the air filter housing. Admittedly, some of these assumptions might be dubious, so this will be a "best case scenario." To make the math easy, we'll assume that the air entering the ham can is brought to rest. Therefore, the gauge pressure rise of the air will be:

P = 1/2 * density * velocity^2

Air density = 1.225 kg/m^3
velocity = 30 m/s (~67 mph)

Therefore, P ~ 550 Pa = .0798 psig pressure increase

Remember, this would be a best case scenario: the air flow into the snorkel is very turbulent, is partially blocked by the stock front header, and the air obviously doesn't come to a complete stop inside the ham can. Therefore, the pressure boost from this "ram air" effect is likely much less. Even it were enough to matter, the largest air restriction in most people's intake tract is - you guessed it! - the throttle valve. Any increase in pressure upstream of the valve would be accompanied by a decrease in throttle usage to maintain a certain speed, but the total amount of air going into the engine would basically be the same. However, it would be interesting if someone ever installed a pressure tap on a ham can and took some measurements.

Rant over. I'm months away from earning a Ph D in mechanical engineering, and the linked analysis really bugged me. Ask yourself: do you think the air entering your intake warms up by nearly half a degree centigrade (roughly a full degree Fahrenheit) just because you're driving through it (the author's first step)??? If this were true, it would mean a carb works by changing the temperature of the air flowing through the throat, rather than changing its velocity (and therefore, pressure).

Also, this is not a jab at whittlebeast. He didn't do the calculations, he just linked them. I very much enjoy (and learn a lot from) reading his posts on tuning.
Connie Kalitta, top fuel dragsters...5/6 psi at topend. 300+mph
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  #285  
Old 27th February 2017
msandli msandli is offline
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Those intakes don't open into a relatively cavernous air filter housing either. I bet a lot of computer time has been spent on those intakes to maximize every single 0.001 extra psi gain possible, and they definitely are NOT at part throttle. When 0.001 seconds matter, it makes a difference.

Those top fuel dragsters are really impressive pieces of machinery. I know this is off topic, but here are some really impressive pics of a dragster motor:

http://www.motoiq.com/MagazineArticl...orsepower.aspx

Again, the important thing is that there is not enough of a "ram air" effect on a stock sportster air intake to even worry about, and it really doesn't have any effect unless you're at WOT. It's probably greater than zero, but you'd have to have a pretty expensive gauge to measure it. You may as well buy fancy spark plug wires for better performance.
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  #286  
Old 27th February 2017
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Folkie Folkie is offline
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Quote:
Originally Posted by msandli View Post
You may as well buy fancy spark plug wires for better performance.
True. Some people do actually do that though.
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  #287  
Old 27th February 2017
msandli msandli is offline
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At this point, I'm 99% convinced the best way to increase the performance of any bike is for the rider to buy some lessons at a track. I'm 0.9% convinced that it's to do some true wideband O2 dyno tuning. I'm 0.1% convinced that it's for the rider to lose some weight (just by observing who I generally see riding a Harley). On a mainly street driven vehicle of nearly any make, I'm convinced messing with the intake is the last thing someone should do. Again, the throttle blades are the biggest obstruction in a bike or car on the street (on the opposite end, the exhaust is always "wide open," hence why upgrading it first makes sense).

Anyways, enough off topic. I really like the look of ElectricCityIron's setup (post 193). It's very tempting to do that to mine, as it appears to create the most open stock filter housing possible, while still offering good protection from the rain (I ride as long as the roads aren't icy, a rare thing in Atlanta). I'm curious if this design increases inlet temps appreciably, as the stock intake at appears to deal with that fairly well.
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  #288  
Old 16th June 2019
jazzman jazzman is offline
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Hi folks,
I'm doing the breather mod 1200C posted on my 2005 883. a few questions;
1) what size long socket for the breather bolts? I put some callipers on it- seems 14mm is correct, but US bike should be 9/16 ? How big is the hole in the back of the bolt?
2) I've read most of this thread. I think I'll just buy a K&N filter with the stock airbox. It seems they flow better, not worried about filtration as l don't ride on dirt much.
My question is, has anyone actually tested the flow of the stock airbox? It has a hole twice the size of the carburettor and several holes in the bottom. Surely any restriction to airflow into the carb comes from the filter not the housing?
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  #289  
Old 16th June 2019
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Quote:
Originally Posted by jazzman View Post
1) what size long socket for the breather bolts? I put some callipers on it- seems 14mm is correct, but US bike should be 9/16 ? How big is the hole in the back of the bolt?
Yes: 9/16". I prefer a 6 point socket: the flats are so shallow it's easy to damage them with a 12 point.

Not sure exactly how big the hole in the back of the bolt is: 1.5mm? 1/16"? The hole in the front is 5/16".

Here's the stock breather bolt:











It's zinc passivated steel. Not sure what sort of steel. It may actually be zinc passivated cream cheese!
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  #290  
Old 16th June 2019
jazzman jazzman is offline
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Thanks for that Folkie!
I wanted to know the hole size as l was worried my new breather tubes may restrict air flow, but no worries there! I'm surprised it is so small.
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