looking for the formula
TECH Fanatic
Joined: Sep 2004
Posts: 1,124
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From: Las Vegas
Velocity at the TB, velocity of the intake port, velocity at the valve, velocity of the exhaust port... exhaust.... ??
We will need a little more information. There is more than one equation envolved to solve this.
We will need a little more information. There is more than one equation envolved to solve this.
that's getting too specific. there's a generic formula to calculate this. i've seen it before and used it once in a post of mine to convey my meaning about airflow and the chance of fuel puddling at 2000 rpms when using a wet kit. and i've searched and haven't found my post.
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On The Tree
Joined: Jun 2006
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You have to know the cross sectional area at the place you want to figure the velocity. That's the only way it can be done.
You need the CFM and the cross sectional area to calculate velocity.
600CFM moves slower through a 3" hole then it does through a 2" hole.
You need the CFM and the cross sectional area to calculate velocity.
600CFM moves slower through a 3" hole then it does through a 2" hole.
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Originally Posted by mrr23
that's getting too specific. there's a generic formula to calculate this. i've seen it before and used it once in a post of mine to convey my meaning about airflow and the chance of fuel puddling at 2000 rpms when using a wet kit. and i've searched and haven't found my post.
Teching In
Joined: Mar 2006
Posts: 44
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To figure out approximate average velocity through a crossectional area, the area of the crosssection and divide it into one square foot, then multiply that value times the CFM flow rate.
Example a 8 inch diameter tube flowing 543cfm.
radius = 8/2 = 4 inches
crossection area of tube= 3.14159 * 4 * 4 = 50.26544 sq inches
1 square foot = 144 sq inches
vel = (144 / 50.26544) 543 = 1555.5817277238595742919986376325 feet per min.
Example a 8 inch diameter tube flowing 543cfm.
radius = 8/2 = 4 inches
crossection area of tube= 3.14159 * 4 * 4 = 50.26544 sq inches
1 square foot = 144 sq inches
vel = (144 / 50.26544) 543 = 1555.5817277238595742919986376325 feet per min.
Staging Lane
Joined: Jun 2006
Posts: 63
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From: Michigan
The generic formula is:
Volumetric Flow rate = Velocity * Area
Rearrange for velocity: Velocity = Flow/area
This is pretty much what Connclark is saying above but this is the formula it comes from. Make sure your units for flow and area are the same(ft, in, mm, etc.) and you'll get avg velocity.
Al
Volumetric Flow rate = Velocity * Area
Rearrange for velocity: Velocity = Flow/area
This is pretty much what Connclark is saying above but this is the formula it comes from. Make sure your units for flow and area are the same(ft, in, mm, etc.) and you'll get avg velocity.
Al
10 Second Club
Joined: Nov 2002
Posts: 1,471
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From: Berkeley, California
If you want to understand airflow in the induction path of internal combustion engines, Bernoulli’s law, which relates airflow pressure and velocity under specific conditions, can be helpful. But it can also be misleading if not applied correctly. The branch of physics involved, fluid dynamics, is notoriously complex so knowing when Bernoulli’s law does and does not apply is difficult. Science alone can not provide expertise in this area. You also need intuition and experience.
TECH Fanatic
Joined: Jun 2002
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From: Upstate NY
Originally Posted by mrr23
ok then, let's say i want to figure out the speed of the air going through an LS1 intake at 2000 rpms.
Max power @ 2000? or part-throttle cruise? Stock or modified engine? It's about 165 cfm @ 2000 with WOT (wide open throttle) producing max power thru headers and open exhaust. That's about 55 ft/sec (or 37.5 mph) at the intake opening for the WOT condition quoted above.
Why 2000? Just what is it you are really interested in?
Last edited by Old SStroker; Aug 14, 2006 at 09:25 PM.
this is getting too specific.
i'm interested in how fast the air is moving through one runner of an LS1 intake at 2000 rpms at WOT. stock motor.
it's another one of those how low of an rpm is it safe to activate nitrous.
there was a post some time ago where i used a simple basic formula to figure out how fast air was moving through a basic one cylinder motor. then you would multiple by 8 to get a more total volume of air for a v8 motor.
this reminds me of a test i took back for my first responder course. (pre-EMT class)
Q: person isn't breathing and unconsicous. what do you do?
A: CPR
unfortunately, doctors would fail this question more than an average person because they thought too deeply into it. they kept bringing variables into the equation. is the person bleeding? does the person have a fractured skull? neck injury? leg cut off?
i really appreciate and understand how thorough you guys are trying to be. but, i'm just looking for a basic formula. like the one ProdriveMS put up. hell that might be the one i'm looking for, but i think there was a couple more variables in the one i'm looking for and posted about here once a while ago. and yes, i've used the search function to try and find my old post. hell, it could've been on another site.
i'm interested in how fast the air is moving through one runner of an LS1 intake at 2000 rpms at WOT. stock motor.
it's another one of those how low of an rpm is it safe to activate nitrous.
there was a post some time ago where i used a simple basic formula to figure out how fast air was moving through a basic one cylinder motor. then you would multiple by 8 to get a more total volume of air for a v8 motor.
this reminds me of a test i took back for my first responder course. (pre-EMT class)
Q: person isn't breathing and unconsicous. what do you do?
A: CPR
unfortunately, doctors would fail this question more than an average person because they thought too deeply into it. they kept bringing variables into the equation. is the person bleeding? does the person have a fractured skull? neck injury? leg cut off?
i really appreciate and understand how thorough you guys are trying to be. but, i'm just looking for a basic formula. like the one ProdriveMS put up. hell that might be the one i'm looking for, but i think there was a couple more variables in the one i'm looking for and posted about here once a while ago. and yes, i've used the search function to try and find my old post. hell, it could've been on another site.
Originally Posted by Old SStroker
Max power @ 2000? or part-throttle cruise? Stock or modified engine? It's about 165 cfm @ 2000 with WOT (wide open throttle) producing max power thru headers and open exhaust. That's about 55 ft/sec (or 37.5 mph) at the intake opening for the WOT condition quoted above.
Why 2000? Just what is it you are really interested in?
Why 2000? Just what is it you are really interested in?
i guess when i said this, it wasn't a good reason?
a little more specific. have a tiny thread about activating nitrous below 3000 rpms. as usual, i'm the proponent of so long as the motor and drivetrain can handle it, then do it.
then, i get this:
and this:
come back with this right off NX site:
and this:
Originally Posted by mrr23
it's another one of those how low of an rpm is it safe to activate nitrous.
then, i get this:
That is not good info...not to fight about it, but NX told me directly not to run wet shot below 3,000 rpms in an LS1....if you are spraying at 2,000 you are pushing your luck according to NX. I would never tell a fellow LS1 member to spray at 2,000 rpm's....this is way to low.
I understand that once you nail it out of first, your car will never even drop to 2,000 rpm's under WOT ever again...my car is an M6 and after shifting out of first, my rpm's (even on bad shifts) do not drop below 4500 rpm's, so the window switch at this point is only protecting me from a missed shift after 6,000 rpm's, but first gear kicks on at 3,600 for me....safe, lets me have time to hook and as soon as the tires plant....my NX 150 wet turns on.
2000 is crazy....do a vote...I bet less than 5 people with a stock motor is spraying that early.
This is an NX opinion not mine!
I understand that once you nail it out of first, your car will never even drop to 2,000 rpm's under WOT ever again...my car is an M6 and after shifting out of first, my rpm's (even on bad shifts) do not drop below 4500 rpm's, so the window switch at this point is only protecting me from a missed shift after 6,000 rpm's, but first gear kicks on at 3,600 for me....safe, lets me have time to hook and as soon as the tires plant....my NX 150 wet turns on.
2000 is crazy....do a vote...I bet less than 5 people with a stock motor is spraying that early.
This is an NX opinion not mine!
My friend didn't have a window switch. Bogged off the line. Blew his intake. Car went up in flames. My suggestion is not spray below 3000k.
Originally Posted by NX
The RPM level is not as important as is the motors ability to rev freely when the nitrous is engaged, I.E. If the vehicle is in low gear, nitrous can be engaged at any time, but if the vehicle is in a higher gear moving at a slow speed when the nitrous is engaged the engine will detonate and damage will occur.
The RPM level is not as important as is the motors ability to rev freely when the nitrous is engaged, I.E. If the vehicle is in low gear, nitrous can be engaged at any time, but if the vehicle is in a higher gear moving at a slow speed when the nitrous is engaged the engine will detonate and damage will occur.
but, it wasn't because of the nitrous. it was because of the motor's inability to rpm upward. this is a debate that will go for sometime.
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
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From: Upstate NY
Originally Posted by mrr23
i guess when i said this, it wasn't a good reason?
In the stock LS1 I referenced, (from a good engine simulation program) average intake port velocity was about 80 feet per second (fps) @ 2000 and increased linearly with rpm. (160 fps @4000 and 240 fps @ 6000).
Intake flow (CFM) is not linear with rpm as you might expect, but it's fairly close. If a "150" shot injects the same amount of nitrous and fuel independent of rpm, it could easily be too much for a slow rev from 2000. In first gear engine speed is increasing over 1000 rpm/sec.
Originally Posted by CamKing
To Calculate CFM:
(Displacement in Cubic Inches)x(Engine RPM)/3456=CFM
(Displacement in Cubic Inches)x(Engine RPM)/3456=CFM
CFM = ((Displacement in Cubic Inches)x(Engine RPM)/3456)xVE