Brain Teaser

[Barbarian]

Here is a little paradox that I found intriguing. The solution took me a little bit of thought. The question is this: We all know that engines in general require an approximately 15:1 ratio of air to fuel which is mixed by the carburator. This means 15 parts of air are burned up for every 1 part of gasoline. So if you burn 2 gallons of gas, you should only be sucking 30 gallons of air through your air-filter.
The question is, why do filters get dirty so fast when they are only passing a small amount of air through them?

 

[Rooster]

For me, the answer is simple. Given the fact that I am noticeably slower than most riders, i am seldom in the lead. this combined with the fact that I am riding in a dusty area, the air is far from pure, having losts of dirt particles suspended in it. With this information, I can easily say that I am sucking in quite a bit of dust with my air, resulting in a very dirty filter.

 

[Barbarian]

Nice try but that is not the answer.

 

[yzeater]

Because of the air's velocity

 

[Barbarian]

No.

 

[VintageDirt]

Because the 15:1 ratio is by weight, not volume?

 

[Rich Rohrich]

Wes is right.
Barbarian - You need to present your basic facts correctly before you attempt to be clever. It's not a brain teaser it's just a manipulation of the facts, and it just further confuses an important basic concept that lots of people already have a bit of trouble undserstanding.

Air/Fuel ratios are not based on VOLUME they are based on mass or the weight of the components. So for every 1 pound of fuel (approx 22 ounces of fuel by volume) you have to pass 15 POUNDS of air which is a whole lot more than 15 times the VOLUME of the 22 ounce volume of the fuel. I'm moving this thread to the BASIC forum where it belongs.

 

[VintageDirt]

Hah!

 

[Barbarian]

Correct VintageDirt! You win the 1st annual Barbarian engineering achievement award. You may copy this e-mail onto your resume.

 

[VintageDirt]

Thanks Barb. But I no longer require a resume since I will no doubt die at my current job.

 

[yzeater]

I think Rich knows what he's talking about. BTW, I just saw the pic in Gorr's book of you behind your YZF...it's nice to put a face with a name

 

[Barbarian]

Rich Rohrich, your response only shows your arrogance.

 

[Rich Rohrich]

OR YOUR IGNORANCE :)

 

[Barbarian]

No, only your arrogance.

 

[Rich Rohrich]

I can live with that ;)

 

[Studboy]

He he, Rich "Rip him Another One" Rohrich strikes again! BTW, I was wondering, is that really you behind your bike in Eric's book? Curious minds need to know!

 

[yzeater]

I think it is...the man is um not very tall, very bulky (not fat, just built like a brick), and the YZF is shortened

 

[WoodsRider]

So tell me the combustion air requirement (in CFM) for a 2-cycle 250 MX bike running at WFO?

 

[Rich Rohrich]

Originally posted by WoodsRider
So tell me the combustion air requirement (in CFM) for a 2-cycle 250 MX bike running at WFO?

Woods - You ALREADY know ;) that you can do a simple volumetric air flow estimation based on percentage of cylinder filling versus displacement. But you also know it's just a crude represenatation of what is actually happening in the cylinder :confused: and the volume of air is miniscule compared to the behemoths you work with everyday. :)

 

[WoodsRider]

Originally posted by Rich Rohrich
But you also know it's just a crude represenatation of what is actually happening in the cylinder...

Especially if I've been screwing around with the jetting again. :scream:

 

[Rcannon]

Since there is not a dumb forum, I will ask this here. How much volume would 15 lbs of air take up?? Would this be a 12 x12 room full?? More? less??

 

[jmics19067]

for a 250cc two stroke at 100% volumetric efficiency at 8 000 rpms I got 70.65cfm. Is my math correct? I am not quite certain of my metric to American conversion. is 2.54 cubed the relation ship between cc's and cubic inch?

 

[biglou]

RC-8400 cu.ft. is my guestimate based on jmics numbers above and burning one gallon per hour. *Shrug*

 

[Rich Rohrich]

Originally posted by WoodsRider

Especially if I've been screwing around with the jetting again. :scream:

..... gurgle, gurgle, GULP, gurgle gurgle DOOOOHHHH :eek:

 

[Rich Rohrich]

Originally posted by jmics19067
for a 250cc two stroke at 100% volumetric efficiency at 8 000 rpms I got 70.65cfm. Is my math correct?

jmics - are you sure you didn't double the air consumption ? :eek: