The Physics Involved with Intake Design
Thread Starter
Registered User
Joined: Jul 2002
Posts: 9,280
Likes: 1
From: knoxville, TN
Blitz- the short ram had some improved throttle response.. at first, but once the engine bay got hot i.e. traffic, had runs, then the heat bog was too much to bear.
Gearhead- I will search those sites and get back to you.
Gearhead- I will search those sites and get back to you.
Thread Starter
Registered User
Joined: Jul 2002
Posts: 9,280
Likes: 1
From: knoxville, TN
Originally posted by Eri_S2k
So you are Telling me That AEM CAI is Better That Comptech?
So you are Telling me That AEM CAI is Better That Comptech?
To convince me that there was a significant enough difference to even risk hydrolock, I'd have to have definitive proof of principle backed up by several reputable dynos....that's just me.
Registered User
Joined: Oct 2002
Posts: 1,871
Likes: 0
From: Scottsdale
OK - first off - I am a chemical engineer (Masters) working for one of the largest filter companies in the world. You use Darcy's law to describe the flow through the filter, or you can simply take it as a pressure drop that slowly varies over time at a given flowrate. In most cases, the dp through the filter is a linear function with velocity (if you don't take into account the increase in particle load onto the filter with increasing velocity).
After that, the dp loss through the intake tubing is a function of the velocity of the gas through the pipe (friction factor), the number of bends, radius of bends, etc. The throttle is basically what is called a butterfly valve in chemical engineering. It works by varying the pressure drop across the valve by position. In other words, a WOT has a lower pressure drop than a part open throttle.
Even though air is a compressible fluid, Cranes says that you can consider a compressible fluid a non-compressible fluid if the pressure drop is less than 10% of the total pressure. I don't believe that would be the case here though, because you don't have much pressure drop to work with (i.e., the difference between atmospheric pressure and suction pressure of the engine).
The total pressure drop through the intake runners is the sum total of the dp thru the filter, the turns that the runner makes, the throttle, and the turns into the individual runners. The traditional way of describing the dp across each individual piece is to sum the resistance values (K values) for each piece and add in a piping loss factor. The fun part is that with compressible fluids, the velocity increases as the pressure drops.
When one hones the intake, all one is doing is reducing the K factor for that individual pipe and restriction.
Now with that said, the really good ones factor in the runner length, velocity, cam timing, and valve opening (Helmholtz tuning (organ pipe effect)) to actually make the intake runner add to the power output of the engine. That is why some companies put in different runner lengths for different RPM's (like the Taurus SHO engine or (some) BMW engines.
Sorry people, I have been verbose, but this is the type of thing I do on every project I get in. Welcome to my world LOL
PS. as far as one intake being better than another - be careful, I would bet the dp across the filter is significant, especially since the aftermarket filters I have seen are significantly smaller than the OEM filter (i.e., less filter surface area). Unless the media they use is a great deal more permeable than OEM media, they would have greater pressure drop.
In addition, there is another factor which describes filter media capabilities, and it is called dirt holding capacity. We looked at one aftermarket filter, and it was greatly more permeable than an OEM filter, but lost permeability really fast because it had very little dirt holding capacity.
With that said, I just use an OEM filter, and change it fairly often.
BTW, the filter company I work for does not make any aftermarket performance filters - we mainly work with refineries, petrochemical plants, airlines, etc. so I have no axe to grind.
After that, the dp loss through the intake tubing is a function of the velocity of the gas through the pipe (friction factor), the number of bends, radius of bends, etc. The throttle is basically what is called a butterfly valve in chemical engineering. It works by varying the pressure drop across the valve by position. In other words, a WOT has a lower pressure drop than a part open throttle.
Even though air is a compressible fluid, Cranes says that you can consider a compressible fluid a non-compressible fluid if the pressure drop is less than 10% of the total pressure. I don't believe that would be the case here though, because you don't have much pressure drop to work with (i.e., the difference between atmospheric pressure and suction pressure of the engine).
The total pressure drop through the intake runners is the sum total of the dp thru the filter, the turns that the runner makes, the throttle, and the turns into the individual runners. The traditional way of describing the dp across each individual piece is to sum the resistance values (K values) for each piece and add in a piping loss factor. The fun part is that with compressible fluids, the velocity increases as the pressure drops.
When one hones the intake, all one is doing is reducing the K factor for that individual pipe and restriction.
Now with that said, the really good ones factor in the runner length, velocity, cam timing, and valve opening (Helmholtz tuning (organ pipe effect)) to actually make the intake runner add to the power output of the engine. That is why some companies put in different runner lengths for different RPM's (like the Taurus SHO engine or (some) BMW engines.
Sorry people, I have been verbose, but this is the type of thing I do on every project I get in. Welcome to my world LOL
PS. as far as one intake being better than another - be careful, I would bet the dp across the filter is significant, especially since the aftermarket filters I have seen are significantly smaller than the OEM filter (i.e., less filter surface area). Unless the media they use is a great deal more permeable than OEM media, they would have greater pressure drop.
In addition, there is another factor which describes filter media capabilities, and it is called dirt holding capacity. We looked at one aftermarket filter, and it was greatly more permeable than an OEM filter, but lost permeability really fast because it had very little dirt holding capacity.
With that said, I just use an OEM filter, and change it fairly often.
BTW, the filter company I work for does not make any aftermarket performance filters - we mainly work with refineries, petrochemical plants, airlines, etc. so I have no axe to grind.
Thread Starter
Registered User
Joined: Jul 2002
Posts: 9,280
Likes: 1
From: knoxville, TN
AWESOME!!! Thanks for posting!
I have two questions:
(1) Regarding in bay intake systems i.e. Comptech, PRM, and stock length would aversly effect airflow wouldn't it? Wouldn't increasing the legnth, while keeping the other factors constant increase both head loss and friction loss?
At the same time, how does ambient air temp effect the system.
I have two questions:
(1) Regarding in bay intake systems i.e. Comptech, PRM, and stock length would aversly effect airflow wouldn't it? Wouldn't increasing the legnth, while keeping the other factors constant increase both head loss and friction loss?
At the same time, how does ambient air temp effect the system.
Registered User
Joined: Oct 2002
Posts: 1,871
Likes: 0
From: Scottsdale
Ideal gases (like air at low temperature (atmospheric temperature)) expand when heated. So the reason people go to cold air intakes is that it gives a denser air charge to the engine. Higher density: more oxygen - more oxygen: more fuel - more fuel: more fun.
There is also a preignition concern as air intake temps rise. The temperature rise in the cylinder due to combustion is a function of the inlet temperature. And, if I remember correctly, the ignition temperature is pretty constant (not sure about this, perhaps someone like Road Rage would know) - so the higher the inlet air temperature, the closer you get to preignitiion.
Now then as far as runner length (i.e., intake length), dp is linear with length - in other words there is an increase in dp with length. However, don't get too excited about additional length, the dp associated with length is typically pretty small unless the velocities are way up there. The real culprit, from a head loss standpoint are bends, changes in diameter, the throttle itself, and other restrictions in the intake runner.
When I get to work, I can pretty quickly figure out the dp per ft of linear pipe, meaning no restrictions.
Again, the intake runner's function is to not only get clean (hopefully) cool air into the engine, but through the Helmholtz effect, it should also aid in producing more power at certain RPM ranges.
I know very little about the Helmholtz effect other than when applied in the right setting, it can produce some pretty awesome music (refer to Bach's Cantata and Fugue in D minor - pipe organ). Sorry got sidetracked, runner length (and other factors) are used to create a pressure wave at intake valve opening in certain RPM ranges.
If I were designing an engine, I would try and create this effect at dips in the torque curve, unless it hurt power output where you need it.
There is also a preignition concern as air intake temps rise. The temperature rise in the cylinder due to combustion is a function of the inlet temperature. And, if I remember correctly, the ignition temperature is pretty constant (not sure about this, perhaps someone like Road Rage would know) - so the higher the inlet air temperature, the closer you get to preignitiion.
Now then as far as runner length (i.e., intake length), dp is linear with length - in other words there is an increase in dp with length. However, don't get too excited about additional length, the dp associated with length is typically pretty small unless the velocities are way up there. The real culprit, from a head loss standpoint are bends, changes in diameter, the throttle itself, and other restrictions in the intake runner.
When I get to work, I can pretty quickly figure out the dp per ft of linear pipe, meaning no restrictions.
Again, the intake runner's function is to not only get clean (hopefully) cool air into the engine, but through the Helmholtz effect, it should also aid in producing more power at certain RPM ranges.
I know very little about the Helmholtz effect other than when applied in the right setting, it can produce some pretty awesome music (refer to Bach's Cantata and Fugue in D minor - pipe organ). Sorry got sidetracked, runner length (and other factors) are used to create a pressure wave at intake valve opening in certain RPM ranges.
If I were designing an engine, I would try and create this effect at dips in the torque curve, unless it hurt power output where you need it.