Open element, or Cold air intake?

[blazerbones]

I've made tentative plans to change up my CAI approach... I run the stock setup now and have a spare that I was gonna mod in, for dual intake...

But recent decisions in build direction have me planning a whole different and hopefully innovative approach... It'll be a first for this forum as far as I know...

This sounds promising...

 

[ryoken]

Should be pretty trick... custom, functional cowl induction.... Decided I wanted to free up the space that dual tubes would take up front...

I've recently decided to go with the fiberglass fenders, inners and 3 1/2" cowl hood.... perfect time to mod the hood.. custom composite airbox, 6" x 14" filter, softseal, etc...

I actually have most of the parts in my attic for a factory Chevelle flapper door. but I'll see how, and if, that comes together once I get the hood over the summer and build the airbox and fit my gauges under the back lip...

 

[Hogback Fabrication]

I disagree with most of the posts so far in this thread, here's why:

Any restriction in the sytem is a loss of efficiency. Most of the efficiency is lost in the design of internal combustion engines but:

Any time you hear a carburetor or throttle body said to flow XXX CFM, that doesn't mean that is the maximum amount of air it can flow. That means that XXX CFM is the amount of air it can flow with a certain pressure drop:

i.e. a 4 barrel carb that flows "750 CFM" can flow 750 CFM of air air through it with a 1.5" Hg pressure differential (2 barrel carbs are generally rated for 3" Hg, which means they flow much less air than their CFM # might indicate compared to 4 barrel carbs).

For reference. atmospheric pressure is 29.92" of Hg.


So, since everything is based off of sea level:

A 750 CFM 4 barrel carb will have ~30" Hg pressure on the top side of it and ~28.5" Hg pressure on the bottom side while flowing 750 cubic feet per minute of air through it.

A 750 CFM 2 barrel carb would only flow ~27" Hg @ 750 CFM.

If your intake (stock, restrictive) takes away another 1" of Hg you are losing a few percent of power to the wheels.

I made up the 1" number but most aftermarket companies advertise significantly more than a 4% increase in airflow.


The deal is that everything (air filter, throttle body/carburetor, intake manifold, cylinder head, exhaust manifold/header, exhaust) has an effect on the efficiency of the motor. If the intake flows better, the motor has less vacuum to overcome and becomes more efficient.

Seriously, that's it.


There are plenty of arguments against aftermarket filters (oil messing with sensors, filtering ability, etc.) but most aftermarket filters are much less restrictive than the OEM stuff.

 

[dyeager535]

I'd like to see actual numbers if we are going to claim GM's intake is the restriction. I can't assume the air intake is restrictive based on claims of companies wanting your money. You seem to be assuming it's a restriction, no one so far has proven that, that I've seen.

Colder air is denser, something like every -10*=+1HP, that easily can undercut potential gains from better flow. Can't ignore that fact.

 

[Thunder]

Well you can talk CFMs and HGs all you want. I wont argue with your facts. But then real life comes along and makes numbers irrevelent.
Fact is. There is not much out there in the way of intake systems. For TBI trucks that have to meet Calif. emissions.
About all there is is a smooth tube that replaces the stock flex tube on the intake.
You cant change the stock air cleaner housing because of the heat riser which is a required emission part. Even putting on a open element is illeagal in Calif. Not that it does you any good any how.
I have proven to myself that the stock TBI CAI is better than open element filter.
I have a G-tech. It is a little thing about the size of a radar detector that mounts to the window or dash. It gives 0-60 times, 1/4 mile times, Hp and G force.
I set it up on my K5 on a hot summer day with the engine fully warmed up.
My 0-60 times were around 2 tenths faster with the stock CAI than with the open element. The hotter it got the slower my K5 got with the open element.
I could also notice a diference towing between the 2. My K5 has more power on hills with the stock system with K&N filter
I know a few people who tried open element on their TBI trucks. Worked good in the winter but when summer came They all switched back to stock. Because of noticible loss of power. Got to say "I told you so"
A stock CAI and K&N, will flow plenty for stock TBI.
The most restrictive part of the stock TBI system is the air filter housing riser/ spacer between the TB and aircleaner.. If you replace that with a velocity stack. Cfm-Tech call them power chargers. you have to cut a bigger hole in the bottom of the housing But You will gain considerable flow and also low end because velocity stacks speed up air flow at low RPM building torque faster. Will pass smog too.

 

[Chevy305]

I disagree with most of the posts so far in this thread, here's why:

Any restriction in the sytem is a loss of efficiency. Most of the efficiency is lost in the design of internal combustion engines but:

Any time you hear a carburetor or throttle body said to flow XXX CFM, that doesn't mean that is the maximum amount of air it can flow. That means that XXX CFM is the amount of air it can flow with a certain pressure drop:

i.e. a 4 barrel carb that flows "750 CFM" can flow 750 CFM of air air through it with a 1.5" Hg pressure differential (2 barrel carbs are generally rated for 3" Hg, which means they flow much less air than their CFM # might indicate compared to 4 barrel carbs).

For reference. atmospheric pressure is 29.92" of Hg.


So, since everything is based off of sea level:

A 750 CFM 4 barrel carb will have ~30" Hg pressure on the top side of it and ~28.5" Hg pressure on the bottom side while flowing 750 cubic feet per minute of air through it.

A 750 CFM 2 barrel carb would only flow ~27" Hg @ 750 CFM.

If your intake (stock, restrictive) takes away another 1" of Hg you are losing a few percent of power to the wheels.

I made up the 1" number but most aftermarket companies advertise significantly more than a 4% increase in airflow.


The deal is that everything (air filter, throttle body/carburetor, intake manifold, cylinder head, exhaust manifold/header, exhaust) has an effect on the efficiency of the motor. If the intake flows better, the motor has less vacuum to overcome and becomes more efficient.

Seriously, that's it.


There are plenty of arguments against aftermarket filters (oil messing with sensors, filtering ability, etc.) but most aftermarket filters are much less restrictive than the OEM stuff.

I think some of your numbers are off...

29.92" of HG is a perfect vacuum. 14.7 psi is atmospheric pressure at sea level, or 0" of hg.

 

[Blue85]

If your intake (stock, restrictive) takes away another 1" of Hg you are losing a few percent of power to the wheels.


Seriously, that's it.

I agree with you that everything in the system adds restriction to the whole and the CFM ratings of parts just tell you pressure drops, not "maximum possible flow".

However, if you only think in terms of restriction, you miss the point. The goal is to get as much air/fuel in the combustion chamber as possible. Hot air is less dense, so neither open element or CAI is "win-win". The question is which effect is dominant - the air density or the flow restriction. And we already know which one it is for these trucks.

 

[noJeepshere]

I know a few people who tried open element on their TBI trucks. Worked good in the winter but when summer came They all switched back to stock. Because of noticible loss of power. Got to say "I told you so"

got to agree to that. my carbed 350 is gutless on a hot summer day with the open element. only problem is, the engine didnt have the factory tubing when i pilfered it from my niehbors truck.

 

[Hogback Fabrication]

I think some of your numbers are off...

29.92" of HG is a perfect vacuum. 14.7 psi is atmospheric pressure at sea level, or 0" of hg.

I'm pretty sure 1 atm = 14.7 psi = 29.92" Hg

A little proof (Wikipedia )

 

[Hogback Fabrication]

Well you can talk CFMs and HGs all you want. I wont argue with your facts. But then real life comes along and makes numbers irrevelent.
Fact is. There is not much out there in the way of intake systems. For TBI trucks that have to meet Calif. emissions.
About all there is is a smooth tube that replaces the stock flex tube on the intake.
You cant change the stock air cleaner housing because of the heat riser which is a required emission part. Even putting on a open element is illeagal in Calif. Not that it does you any good any how.
I have proven to myself that the stock TBI CAI is better than open element filter.
I have a G-tech. It is a little thing about the size of a radar detector that mounts to the window or dash. It gives 0-60 times, 1/4 mile times, Hp and G force.
I set it up on my K5 on a hot summer day with the engine fully warmed up.
My 0-60 times were around 2 tenths faster with the stock CAI than with the open element. The hotter it got the slower my K5 got with the open element.
I could also notice a diference towing between the 2. My K5 has more power on hills with the stock system with K&N filter
I know a few people who tried open element on their TBI trucks. Worked good in the winter but when summer came They all switched back to stock. Because of noticible loss of power. Got to say "I told you so"
A stock CAI and K&N, will flow plenty for stock TBI.
The most restrictive part of the stock TBI system is the air filter housing riser/ spacer between the TB and aircleaner.. If you replace that with a velocity stack. Cfm-Tech call them power chargers. you have to cut a bigger hole in the bottom of the housing But You will gain considerable flow and also low end because velocity stacks speed up air flow at low RPM building torque faster. Will pass smog too.

Honestly, the post you're responding to was theory and not based on my experience with K5 TBI CAI's. The bottom line:



A less restrictive intake makes a motor more efficient.

Warmer air entering the motor probably makes the motor more efficient but lowers its power output



If the CAI's for K5's let warmer air enter the motor there probably isn't much advantage.

 

[Chevy305]

I'm pretty sure 1 atm = 14.7 psi = 29.92" Hg

A little proof (Wikipedia )

Actually, we're both right....

If you ever look at a vacuum/boost gauge, 0 is atmospheric pressure, then the needle will go to the left scaling up to the max perfect vac of 30inHG, and to the righ up to 30psi. However, this pressure reading all relative because it is gauge pressure, while you are talking about absolute pressure.

http://en.wikipedia.org/wiki/Vacuum
http://en.wikipedia.org/wiki/Pressure_gauge

Vacuum is often also measured using inches of mercury on the barometric scale or as a percentage of atmospheric pressure in bars or atmospheres. Low vacuum is often measured in inches of mercury (inHg), millimeters of mercury (mmHg) or kilopascals (kPa) below atmospheric pressure. "Below atmospheric" means that the absolute pressure is equal to the current atmospheric pressure (e.g. 29.92 inHg) minus the vacuum pressure in the same units. Thus a vacuum of 26 inHg is equivalent to an absolute pressure of 4 inHg (29.92 inHg - 26 inHg).

Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure.
Gauge pressure is zero referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted.

Here's a table that shows you how absolute pressure and gauge pressure work:

Put simply, vacuum is just negative gauge pressure, but it is not displayed as negative numbers.


Also this is a nice article that I found:
http://en.wikipedia.org/wiki/Manifold_vacuum

 

[RENO88]

So, translated in english your saying that its still benefitial to have an open element? Right?

 

[Chevy305]

So, translated in english your saying that its still benefitial to have an open element? Right?

oh um,i have no clue....

I run an open element and have been wanting to put in the K&N filter top thingy.

I think its all personal preference...

 

[RENO88]

It's staying on. Ill still get a bigger element to try just so I know, and I can tell if its worth doing.

 

[Thunder]

It's staying on. Ill still get a bigger element to try just so I know, and I can tell if its worth doing.

Total waste of money IMO.

 

[dyeager535]

I may draw the line at the smaller filters. GM decided in the early 80's that they'd go with the "tall" filter on some of the trucks, and many of those seemed to be 305's. (my '83 for instance)

The tall filters must have served some purpose. I wouldn't doubt it was an increase that it was in conjunction with the 800CFM carbs many (if not all) of the 305's in trucks got, serving probably to increase torque production, somewhat masking the lack of 45 cubic inches.

Either that or was used when the charcoal filter was used in the air cleaner, to make up for the decreased overall flow due to two filters. I don't believe I've seen a "tall" filter without the charcoal filter.

 

[ryoken]

a 6" tall, 14" air filter is certainly gonna flow more than a 3".... And only help the situation... Can't see it being a waste of money when the price difference is probably minimal.. This all depends on what the mill wants tho..... imo, the stock CAI flows plenty for a stock motor.. healthy 383? you can bet I'd be looking to free up some CFM's...

a cold air source is still far beneficial imo over any open element....

 

[blazerbones]

Actually, we're both right....

Bingo! Absolute pressure vs. gage pressure.

Best of both worlds... fully functional cowl induction... like Ryoken's planning. Colder air... less restriction... some forced air induction at speed. That's what I'm talkin' about!

Now if I can just spare the cash and accomplish the fabwork...

 

[70jimmy]

I have thought about something like the old (50's model?) pickups had the vent that would open up right in front of the windshield. It had a screen and hooking a hose from that straight into the top of the air cleaner housing.

Or a ram air type set up like the Trans am's had (think smokey and the bandit)

 

[sandawgk5]

It's staying on. Ill still get a bigger element to try just so I know, and I can tell if its worth doing.

Do not try to get it smogged with an open element as you will be failed on visual. Run it all you want but put your original back on to get the smog done and make sure the little stove pipe is on there from the exhaust up to the air cleaner housing.

If you have out of state plates disregard what I just said as you don't need to smog

Dik