modified intakes (Air Filters)

I don't care if the increase is one horsepower... i'd like to gather opinions and evidence as to the effects of a simple aftermarket air filter.

Our shop foreman is SO not in agreeance that a less restrictive air filter can increase performance.

What do I think? Well, if you have 200 hp, and divide it up among different functions of the engine, you must recover at least a fractional portion of that power and have it used for better things like accelerating, rather than induction...

Does this make sence to anyone? Is powerblock on Spike lying to the masses every week-end?

Remember, I'm not talking about a HP increase, but a transfer of expent energy...if that makes any fucking sence. Any links for good evidence is appreciated, I'm pretty much ready to strangle my foreman because he's got the younger guys looking at me like I know nothing at all.

The difference in pressure loss between a stock filter and a high flow filter such as K&N is usually very small, to small to result in any significant power gain. If the intake and filter is modified, a somewhat larger gain is however possible.

they're better for air-flow accross the filter. basically, they just let more air in. they'll often use a looser weave and better material, so they still filter out the bad crap in the air, but let more air in.

the power gain is very small, but it is there. although, this is not always the case and it has been known that replacing a standard filter element with a "performance" one can reduce power. this isn't always the case though.

This question is so heavily dependent on vehicle design you can not answer it generally for all applications.

I used to own an old Triumph that had such a restrictive stock intake design, that when I replaced it with something aftermarket it ran so lean I had to put the stock intake back on.
It was pretty clear that the original design with its paper filters crammed into a little box was not doing a good enough job. In order to replace it I would have needed to rejet the carbs, or replace them. (In the end I replaced them, along with a few other bits ;) )

But, this was a on a car designed in the mid 60s and car designers have learned an awful lot since then.
I used one of the filters I had tried on my Triumph in my old SiR Civic, and noticed no difference what so ever other than a slight change of tone in the intake sound. This was a change from a paper filter that was about 70% efficient to a foam filter that was over 97% efficient. If there was a restriction in the SiR's intake system, it wasn't from the filter.

ok...

when only changing the filter, IMO, most applications, there will be no visible improvement on a dyno.

Cold intakes, as mentioned, can have a noticable effect, depending on the vehicle (aka, how badly the stock intake was designed)

Reducing restriction isn't automatically an improvement. In bike land, many people will remove the entire intake system all together and put individual air filters on the carbs. The back pressure change is huge, and requires a lot of jetting changes to make it run right. But the power difference is usually minimal, if any, and then you have heat issues, hot air getting to the filters, sometimes unevenly across the cylinders.

But thats another subject.

interesting... I really thought that the ease at which the air could be pulled into the engine could result in better usage of the engines power. As I mentioned, I'm not talking about making more power, but using more power for acceleration.

If I can push one hundered pounds across a flat floor at one speed, surley pushing with one hundered pounds on the same object on a decline will produce a higher speed, since it is now easier. In either case I'm still pushing with the same force.

As for the filters, I see it as less restriction. Like when you do a compression test, as Max Wedge taught me... it's most accurate to do it without an air filter on, to ensure you get as much air into the cylinder as you can.

What I am really trying to do is fine tune my understanding. I'm not talking about intake plumbing, temps, or INCREASING horsepower. I guess I'm saying that it is safe to call it a fact that while high-flow filters don't increase hp, they do improve efficiency.

Having said that, I can't imagine quite yet why the results would not show on a dyno. If the engine gets slightly better VE, breathes quicker, you'd think it would achieve it's max torque earlier, however marginal.

I'm sorry to beat this to death, but understanding is paramount here... hopefully somebody can get real technical here

There is a lot more to it than just the level of restriction. Pulse tuning is a big factor.

There is also the reservoir-effect. If you have a large volume in the air box, the relative restriction of the system won't matter until very high flow rates.

as long as the minimum or nominal or whatever flow of the filter is above the max flow of the engine, then you are ok

It's quite simple really.

Measure the pressure drop at the throttle body with a standard filter.
Measure again with aftermarket filter.

I doubt you'll see any difference.

interesting... I really thought that the ease at which the air could be pulled into the engine could result in better usage of the engines power. As I mentioned, I'm not talking about making more power, but using more power for acceleration.

That's not really how it works. An engine makes its power, period. Its not that there is more of the power available with a free-flowing intake, its that a restrictive intake reduces power that the engine can make - which slows acceleration. For instance, if you have an air filter/intake that has zero restriction and the engine makes 200 hp you will accelerate at a certain rate. If you replace it with a restrictive intake, its not that you're wasting some of that 200 hp on sucking air and you're slower... its that the engine is only making 190 hp.

What I am really trying to do is fine tune my understanding. I'm not talking about intake plumbing, temps, or INCREASING horsepower. I guess I'm saying that it is safe to call it a fact that while high-flow filters don't increase hp, they do improve efficiency.

If they improved intake efficiency, they would increase power. That is to say, if they were a restriction before, increasing filter/intake flow would result in more power. They're all linked.

Having said that, I can't imagine quite yet why the results would not show on a dyno. If the engine gets slightly better VE, breathes quicker, you'd think it would achieve it's max torque earlier, however marginal.

Like I said above, if the air intake were a restriction, it would show up on a dyno when you increased intake flow. Your logic is spot-on. The air intake (that is to say all of the tubing from where its initially ingested to the throttle body) has almost nothing to do with the engine's tune. It will restrict peak HP in the higher RPM range if its a restriction, but as long as enough gets there, its fine. You kinda can't go too big. Many stock intakes are adequate and adding an aftermarket or improved air filtering/ducting won't increase power (or efficiency) any at all.

I'm sorry to beat this to death, but understanding is paramount here... hopefully somebody can get real technical here

As long as I'm around, I try to stay the king of beating things to death. I've been lacking the last few months :) Thanks for the opportunity!

Let's say you had an engine that made 200 hp with no intake/filter at all. You dynoed it and you saw the 200 hp. Now cover 1/8 of the TB with duct tape. You'd probably still see 200. Cover 1/4 of the TB and you might see 180. Cover 1/2 and you'll probably see 150. Its not that the engine is still making 200 but wasting some on intake restriction, its that the engine makes less power.

Think of it like your respiratory system. Its possible that your body is capable of a certain amount of work that is beyond your lung's capacity to supply oxygen. In that case, increasing your respiratory system's efficiency will let you do more work before tiring. Its also possible that your respiratory system is overkill but your muscles are weak. The first analogy is like a big V8 breathing through a little intake. The second is like a little 4-banger breathing through a 10" pipe.

A picture to further beat a dead horse :)

Here is the same engine in two different simulations on Desktop Dyno. The only difference is that I simulated a high RPM restriction on the one. Notice how they start out absolutely identical but the restricted one starts dropping power in the upper RPMs. That's what accounts for your efficiency loss and acceleration loss; an actual loss of power, not just that the power was wasted on intake restriction.

http://i162.photobucket.com/albums/t264/curtis73/3.jpg

Good explanations. Basically, IF the replacement filter is a less restricitive design, you should see a slight increase. Depends on the car, motor (turbo/na) etc.

Basically, IF the replacement filter is a less restricitive design, you should see a slight increase.

if its less restrictive AND the engine was being choked before. Going from a 10" dia. inlet pipe to a 12" inlet pipe won't do any good on a 100-hp 4-cylinder. Just supplying more air won't make more power. It will only make more power if it was restricting air before the change.

in other words.....

less restrictive filter would allow the engine to do what it can do more easily but it won't make it do more than it's capable of.

word. i put a k&n filter on my old camaro and learned this lesson the hard way. it doesn't increase power unless your engine was pulling air through a straw in the first place.

I like Curtis' analogy. the difference between a 10" and 12" intake pipe. Thats pretty accurate too, in reality. The air filter, by itself, most 4 cylinders are fairly good sized, compared to some others

If you want to make a real difference on your efficiency, bump your compression ratio up 2 points.