-
Welcome to The Truck Stop! We see you haven't REGISTERED yet.
Your truck knowledge is missing!
- Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
- We have tons of knowledge here for your diesel truck!
- Post your own topics and reply to existing threads to help others out!
- NO ADS! The site is fully functional and ad free!
Problems registering? Click here to contact us!
Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!
Fender fresh air vent
- Thread starter Burning oil
- Start date
buddy
Active Member
Sometimes you might like that
bison
Well-Known Member
I think i know in what direction :smile5:
NVW
Well-Known Member
I just noticed but I bet it went to your initials.):h
chickenhunterbob
New Member
- Messages
- 65
- Reaction score
- 0
Yo that Great White, some of the high pressure created by the ~18 sq ft front is routed through an enclosed path into the passenger side fender (about 95,000 cu ft per mile at 60), creating a slight pressure area there, introducing a vent on the outer fender (low pressure area) may negate that pressure, but probably not significant either way, just that yer intended pressure may be hobbled by your introduced vent in the low pressure area, eh?
buddy
Active Member
Considering that hardly any of that 18sq ft routes to the fender, we might assume all of the air that goes into one of the bumper holes actually goes into the fender, thats about 6"x4" and a mile is 5280ft. The area of that space in front of that hole is 0.5x0.33x5280= 880cu ft.
I doubt half that makes it into the fender because of all the holes and small ducting but fortunately, that air pump of an engine is only passing about 200cu ft in that mile at 1800rpm. That is unless you are boosting, then you are pulling more CFM, possibly twice as much.
I doubt half that makes it into the fender because of all the holes and small ducting but fortunately, that air pump of an engine is only passing about 200cu ft in that mile at 1800rpm. That is unless you are boosting, then you are pulling more CFM, possibly twice as much.
Matt Bachand
Depends on the 6.5
chickenhunterbob
New Member
- Messages
- 65
- Reaction score
- 0
haha, was just something I recalled from a few years back from a paper that gmctd wrote...now this doesn't make any mention or an air duct in the fender to be good or bad, but does explain the GM air intake system, and alludes that it may well be difficult to better...and lots of numbers for you to ponder Buddy...:smile5:
Let's talk air flow -
Air is a fluid.
Ok, I feel all those raised eyebrows, out there - but, no, I'm not any further around the bend than previously, so rest easy, folks.
Definition of fluid is ability of a substance to move thru, or fit into, a container without altering the shape of that container.
And, yes, I am familiar with the concept of a balloon, for all you hecklers.
Water, sand, flour, Diesel fuel, oil, air - all fluid substances.
Fortunately for us, air is right in there, as a fluid.
We can channel it, direct it, compress it, heat it, cool it, store it - most of us even breathe it, every chance we get.
As does this big stinky air pump we all are so addicted to.
Displacing 400 cubic inches every other 360deg crank rotation - it is an engine requiring 4 distinct cycles to do that deed, two per rotation -, it can pump ~400 cubic feet per minute at ~3000rpm.
Air flow is measured per unit volume, usually in cubic feet for automotive use - a dimensional area 12" by 12" by 12".
Flow rate is measurement of unit volume - cubic inches, cubic feet, cubic yard, etc - per unit of time - second, minute, hour, etc.
400cfm per 3000rpm indicates a minimum requirement for ducting and filtration which permits maximum attainable efficiency.
Simple math would indicate this pump cannot move 400cfm at idle, but we would not want to size an intake system based on the minimal flow.
Or, restrict it to only 400cfm - we have a turbine-driven compressor stuffing air into the intake at up to 2.5x pressure ratio, derived by (Boost + Baro) / Baro.
Which means, at maximum power and rpm, we require a system allowing ~1000cfm flow rate.
Would seem to require an enormous filter and ducting, right?
4", maybe even 6" diameter required here?
No girly-man 3"dia ducting gonna hold this big hoss back, that's fer sure!
Well - remove the rubber compressor inlet duct, and take a gander at the actual compressor intake diameter, where the blades are.
"Durn!! Whur's my tape maisure - thet cain't be right!!"
Remember - that's 1000 cubic feet flowing over a 60 second interval, about 17 cubic feet per second.
Now, think about this - if the flow rate of the supply air pump - the turbo compressor - is only equal to the demand air pump - the engine - no pressure will be developed in the system, and no advantage will be gained.
400cfm in, 400cfm out, 1:1 pressure ratio - may as well remove the compressor, as that's just Baro input, same as naturally aspirated.
However, if the flow rate of the supply pump exceeds the demand flow rate, excess flow will stack up in the intake as pressure - the greater the excess, the greater the pressure.
The GM-8, in recent tests, easily generated 20psi Boost on oem 63mm fuel rate, up to 2500rpm, where tests were limited to prevent DTC-78 and resultant power loss.
Factory '95 air box and curved intake duct, AC filter element - all stock.
So - 17cuft/sec - 1000cfm - doesn't seem to be limited much by that 2" compressor inlet diameter, so where's the need for 4" ducting? 6"???
The 3"dia where the inlet ducting is mounted\clamped should suffice for straight ducting, but a path requiring several sharp bends could benefit from the larger 4" diameter for less flow restriction.
Unless - the 3"ducting were plumbed up to the radiator bulkhead to take advantage of the cooler air available there, under high pressure.
Flow rate can be improved by increasing the diameter of the duct.
3"dia provides an area of 9.5sqin, and 4"dia provides 12.5sqin, where sufficient real estate is available for the increase. </
Flow rate can also be improved by increasing the flowing pressure.
These trucks have about an 18sqft frontal area, hood to bumper, headlite to headlite - that pushes quite a lot of air out of the way, at any speed.
Move the truck forward 1 foot - 12 inches - and it has displaced 18 cubic feet of air.
At 60mph - 1 mile (5280ft) per minute - it will displace 95,040cfm.
Now, comparing the truck's effective 'flow rate' of 95,040cfm to the 6.5L absolute maximum effective flow rate of 1000cfm, it can be seen that, again, where the supply is more than the demand, it will stack up as pressure.
Stick your hand out the window, palm forward, at 30 - 45 - 55 - 70mph, to get a sense of the available pressure.
We can use that pressure to increase the flow rate of the oem factory intake system, simply by providing a dedicated path from the hi pressure area at the bulkhead to the air filter box.
No worries about twists, turns, curves, bends - it will get there, at most any speed, with no loss of effectiveness.
I mean - come on, now! 95,040 cfm vs 1000cfm. A measurable loss of effectiveness?
I don't think so.
And, much cooler and denser than the flow thru the radiator.
(reader interpolation\extrapolation required for other speeds)
Let's talk air flow -
Air is a fluid.
Ok, I feel all those raised eyebrows, out there - but, no, I'm not any further around the bend than previously, so rest easy, folks.
Definition of fluid is ability of a substance to move thru, or fit into, a container without altering the shape of that container.
And, yes, I am familiar with the concept of a balloon, for all you hecklers.
Water, sand, flour, Diesel fuel, oil, air - all fluid substances.
Fortunately for us, air is right in there, as a fluid.
We can channel it, direct it, compress it, heat it, cool it, store it - most of us even breathe it, every chance we get.
As does this big stinky air pump we all are so addicted to.
Displacing 400 cubic inches every other 360deg crank rotation - it is an engine requiring 4 distinct cycles to do that deed, two per rotation -, it can pump ~400 cubic feet per minute at ~3000rpm.
Air flow is measured per unit volume, usually in cubic feet for automotive use - a dimensional area 12" by 12" by 12".
Flow rate is measurement of unit volume - cubic inches, cubic feet, cubic yard, etc - per unit of time - second, minute, hour, etc.
400cfm per 3000rpm indicates a minimum requirement for ducting and filtration which permits maximum attainable efficiency.
Simple math would indicate this pump cannot move 400cfm at idle, but we would not want to size an intake system based on the minimal flow.
Or, restrict it to only 400cfm - we have a turbine-driven compressor stuffing air into the intake at up to 2.5x pressure ratio, derived by (Boost + Baro) / Baro.
Which means, at maximum power and rpm, we require a system allowing ~1000cfm flow rate.
Would seem to require an enormous filter and ducting, right?
4", maybe even 6" diameter required here?
No girly-man 3"dia ducting gonna hold this big hoss back, that's fer sure!
Well - remove the rubber compressor inlet duct, and take a gander at the actual compressor intake diameter, where the blades are.
"Durn!! Whur's my tape maisure - thet cain't be right!!"
Remember - that's 1000 cubic feet flowing over a 60 second interval, about 17 cubic feet per second.
Now, think about this - if the flow rate of the supply air pump - the turbo compressor - is only equal to the demand air pump - the engine - no pressure will be developed in the system, and no advantage will be gained.
400cfm in, 400cfm out, 1:1 pressure ratio - may as well remove the compressor, as that's just Baro input, same as naturally aspirated.
However, if the flow rate of the supply pump exceeds the demand flow rate, excess flow will stack up in the intake as pressure - the greater the excess, the greater the pressure.
The GM-8, in recent tests, easily generated 20psi Boost on oem 63mm fuel rate, up to 2500rpm, where tests were limited to prevent DTC-78 and resultant power loss.
Factory '95 air box and curved intake duct, AC filter element - all stock.
So - 17cuft/sec - 1000cfm - doesn't seem to be limited much by that 2" compressor inlet diameter, so where's the need for 4" ducting? 6"???
The 3"dia where the inlet ducting is mounted\clamped should suffice for straight ducting, but a path requiring several sharp bends could benefit from the larger 4" diameter for less flow restriction.
Unless - the 3"ducting were plumbed up to the radiator bulkhead to take advantage of the cooler air available there, under high pressure.
Flow rate can be improved by increasing the diameter of the duct.
3"dia provides an area of 9.5sqin, and 4"dia provides 12.5sqin, where sufficient real estate is available for the increase. </
Flow rate can also be improved by increasing the flowing pressure.
These trucks have about an 18sqft frontal area, hood to bumper, headlite to headlite - that pushes quite a lot of air out of the way, at any speed.
Move the truck forward 1 foot - 12 inches - and it has displaced 18 cubic feet of air.
At 60mph - 1 mile (5280ft) per minute - it will displace 95,040cfm.
Now, comparing the truck's effective 'flow rate' of 95,040cfm to the 6.5L absolute maximum effective flow rate of 1000cfm, it can be seen that, again, where the supply is more than the demand, it will stack up as pressure.
Stick your hand out the window, palm forward, at 30 - 45 - 55 - 70mph, to get a sense of the available pressure.
We can use that pressure to increase the flow rate of the oem factory intake system, simply by providing a dedicated path from the hi pressure area at the bulkhead to the air filter box.
No worries about twists, turns, curves, bends - it will get there, at most any speed, with no loss of effectiveness.
I mean - come on, now! 95,040 cfm vs 1000cfm. A measurable loss of effectiveness?
I don't think so.
And, much cooler and denser than the flow thru the radiator.
(reader interpolation\extrapolation required for other speeds)
Paveltolz
Доверяй, но проверяй
Ok, it's official...my head hurts!
What's worse is I get it.
What's worse is I get it.
buddy
Active Member
The majority of that 95000cuft is getting diverted around the truck and through the radiator, which does not go to the air intake. So that doesnt mean the fender is pressurized that much.
Yep, not all of the displaced air is going to the air filter inlet. Its got to be a very small % of that.
The way I read the post was, in the very last sentence, its better to have a vent to the outside where cooler/denser air is.
"And, much cooler and denser than the flow thru the radiator."
I seem to remember a tape for messuring pressures. It would change colors with more PSI applied to it. Anyone know of that?
buddy
Active Member
Yeah, other than pulling air from the outside, I dont agree much with what that post was trying to say.
Do you think the people that pop those little vacuum testers on the air intake are doing it with their fresh filters because that huge filter is actually too restrictive, or is it because the turbo had to suck the air through the fender?
Do you think the people that pop those little vacuum testers on the air intake are doing it with their fresh filters because that huge filter is actually too restrictive, or is it because the turbo had to suck the air through the fender?
Matt Bachand
Depends on the 6.5
I really look forward to the testing with the fender vent. I have always thought that air pulled through fender vent hole with fender blocked will yield cooler IAT's. Regardless of any venturi effect or not.
I believe that the fender acts as a air pre-warmer, especially since its on the fanwash side, that fender gets HOT HOT HOT after a good pull, the less air that passes through that fender to reach the air cleaner the better IMO.
I believe that the fender acts as a air pre-warmer, especially since its on the fanwash side, that fender gets HOT HOT HOT after a good pull, the less air that passes through that fender to reach the air cleaner the better IMO.
Thats a good point Matt. My fender is black and you cant touch it in the summer months.
I think you meant to say, the MORE air that passes.......
I think you meant to say, the MORE air that passes.......
great white
Well-Known Member
Perhaps a better usage of a "fender vent" intake in the discussion of "cold air" would be to provide an escape path for the high pressure air created at the front of the truck to escape past the filter intake.
Let's see if I can describe this properly:
The fender (at least my 98 is and my 89 was) is essentially the "duct" which brings cold air from the high pressure area created in front of the truck to the air box. There's a "deflector" in the fender just after the filter opening for the filter box. This means the area "theoretically" should have higher pressure air (at highway speeds) to feed the box when the engine takes a gulp.
Now, if you wanted to ensure the "air charge" was cool, you'd need to ensure movement as air caught stagnant in the fender could be heated by the mechanisms already mentioned in previous posts.
Remember, the fender duct is subject to a LOW pressure area at highway speed due to the flow past it.
Starting to see a method in the madness?
You place a fender duct PAST the box intake and the high pressure in front of the truck will flow to the low pressure area at the fender vent. This ensures colder air than normal, and a more effective "ram air effect".
In order to take advantage of the air flow in the newly created high to ow pressure "duct", you simply place a "scoop" like construction in the airstream in the duct and direct the air into the filter box. Much like you would when you stick your hand out the window and scoop extra airflow into the cab on a hot day.
we use similar air management schemes to cool aircraft radiators and components effectively without creating excess drag. In fact, ducting high pressure air to low pressure zones (or wake if you will) reduces drag and makes the entire vehicle more effective. But that's another discussion....
I seem to recall the newer super duties use a similar construction in their fender vents, or it could have been an aftermarket kit. Dunno.
Edit: quick pick I just googled -
i recall seeing one somewhere where the SD fender tract had been cut open and you could see they also used a "scoop" like structure in the duct. Can't find it right now though...
Keep in mind this is all highway speeds, around town is a nil benefit....interesting to think about though...
Let's see if I can describe this properly:
The fender (at least my 98 is and my 89 was) is essentially the "duct" which brings cold air from the high pressure area created in front of the truck to the air box. There's a "deflector" in the fender just after the filter opening for the filter box. This means the area "theoretically" should have higher pressure air (at highway speeds) to feed the box when the engine takes a gulp.
Now, if you wanted to ensure the "air charge" was cool, you'd need to ensure movement as air caught stagnant in the fender could be heated by the mechanisms already mentioned in previous posts.
Remember, the fender duct is subject to a LOW pressure area at highway speed due to the flow past it.
Starting to see a method in the madness?
You place a fender duct PAST the box intake and the high pressure in front of the truck will flow to the low pressure area at the fender vent. This ensures colder air than normal, and a more effective "ram air effect".
In order to take advantage of the air flow in the newly created high to ow pressure "duct", you simply place a "scoop" like construction in the airstream in the duct and direct the air into the filter box. Much like you would when you stick your hand out the window and scoop extra airflow into the cab on a hot day.
we use similar air management schemes to cool aircraft radiators and components effectively without creating excess drag. In fact, ducting high pressure air to low pressure zones (or wake if you will) reduces drag and makes the entire vehicle more effective. But that's another discussion....
I seem to recall the newer super duties use a similar construction in their fender vents, or it could have been an aftermarket kit. Dunno.
Edit: quick pick I just googled -
i recall seeing one somewhere where the SD fender tract had been cut open and you could see they also used a "scoop" like structure in the duct. Can't find it right now though...
Keep in mind this is all highway speeds, around town is a nil benefit....interesting to think about though...
Last edited:
buddy
Active Member
That would essentially remove your high pressure, but may allow more air to circulate through the fender. But it is essentially the opposite of RAM air. RAM air is to pressurize the air intake to stuff more air in, and this would be lowering the pressure in the fender and the engine would have to suck harder 
Although it probably would be cooler from circulation, and not because it would draw the air from the vent. Just as GW said.
If you put a scoop on that could work to pull the air in, but then you would need to see how far the airstream gets divereted away from the fender at high speeds.
Although it probably would be cooler from circulation, and not because it would draw the air from the vent. Just as GW said.If you put a scoop on that could work to pull the air in, but then you would need to see how far the airstream gets divereted away from the fender at high speeds.
ak diesel driver
6.5 driver
I think the idea is to have a large intake opening and a small outlet so as to create more pressure than an enclosed system
davo727
Member
Id like to have some kind of ram air on my trucks but I think I would need some kind of cable operated diverter valve to switch the flow from a dry location under the hood for the times here when the sky opens - sometimes the rain here is like driving underwater.
great white
Well-Known Member
That would essentially remove your high pressure, but may allow more air to circulate through the fender. But it is essentially the opposite of RAM air. RAM air is to pressurize the air intake to stuff more air in, and this would be lowering the pressure in the fender and the engine would have to suck harder
If you put a scoop on that could work to pull the air in, but then you would need to see how far the airstream gets divereted away from the fender at high speeds.
Nope.
In the theoretical system I described, the "scoop" structure in the high speed airflow in the duct provides a positive pressure in the adjunct ducting to the filter.
The added benefit is the airstream is moving and, as such, cooler.
I'm familiar with ram air setups, I work on them all day. For both induction and cooling in aircraft.
Of course, this is all "moot" in around town driving. Vehicle at legal highway speeds only provide minimal pressurization at best. The best you can hope for is a cooler air charge. Or, a "duct" in a "sealed system" could have a scoop structure outside the fender to direct air in. This would be just as effective, but wouldn't look very good....
Now, if you're ripping around at 130 mph or so, things are a bit different with pressurization benefits...
buddy
Active Member
Ive never seen a ram air intake with a vent. Ram air goes straight into the intake. If air can flow out of a vent and into the intake, then the pressure is less. In ram air you are trying to slow air velocity in the ducting to keep it statically pressurized
some of us do rip around at 130mph
some of us do rip around at 130mph