2004 to 2020 Mazda 3 Forum and Mazdaspeed 3 Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
422 Posts
Discussion Starter #1
I'm curious on the 2.5 if anyone knows what psi it runs at. Preferably I'd like to know under load at the higher rpm range.

For example, WOT @ 5k = psi?
 

·
Registered
Joined
·
14 Posts
Probably you mean vacumm under WOT, considering these are not turbo or supercharged engines, you won't see any signifcant "boost" or PSI on the intake by measuring it with a MAP sensor. If any, it would be on the tenths of 1 PSI and probably under intake resonance range or something, i might be wrong so don't take my word for it :p
 

·
Registered
Joined
·
367 Posts
Manifold pressure at WOT is generally zero unless you`re boosted by either a supercharger or turbocharger. Even a well designed ram air system won`t provide more than a couple of psi and you`ve got to be moving at 70+mph for it to be effective.
 

·
Registered
Joined
·
422 Posts
Discussion Starter #4
Copy...maybe I'm using the wrong wording. I'm just trying to get an idea of how strong the pull is inside our air boxes at the high rpm ranges. We've already established that the engine at max is a bit under 300 cfm (around 280-ish I think).

It just seems like when talking air (whether it is vacuum or pressure) things like to use ratings in PSI..or maybe they don't.

So for example, say I wanted something to kick in at only high RPM's based on suction. .. what would that magic number be :)
 

·
Registered
Joined
·
367 Posts
There may be a better way to go about whatever it is you want to do. The only things typically triggered by manifold pressure are boost related needs like methanol injection or electronic traction control.
 

·
Registered
Joined
·
422 Posts
Discussion Starter #6 (Edited)
Ok..well I'll spill the beans...it is a crazy idea I know but hey..ya never know.

So I've been reading alot about the stock air box vs. sri vs. losing low end torque vs. hot air temps....and so on.

There are several folks that have kept the stock air box and have noted that it can keep up with a Sri until the higher rpm ranges. Many feel like the stock air boxes are better engineered (tuned) otherwise.

So I thought to myself...why can't we have both? One user who was doing some testing showed that he eliminated the upper limitation by removing the snorkel. However it then sucked hot air and lost any gains via timing pull.

Now on the flip side, there are people that have cut holes in their air box and maybe even gone as far as to run a tube down to colder areas. However they have now just de-tuned the entire box for all ranges. For example there is a posting somewhere about the resinator and how it does more than just sound.

Anyway, so I got the idea that one could use a spring loaded air check valve. Installed via an extra 2" hole in the box, at lower loads/rpm it would stay shut as to not effect the oem engineering. However when on the throttle approaching those higher Rpms... it would open up and give it that little extra breathing.

The key of course would be to get one that stays shut until approaching that 5k + range.

Some concepts....

http://www.hottubworks.com/part-1-CV-AIR2S-item-hottub-check-valve.php

https://www.amazon.com/gp/aw/d/B00B95UUJQ/ref=pd_aw_sim_sbs_79_3?ie=UTF8&psc=1&refRID=7ZD2KJWT3GCV3K7CR9N6

This one is even adjustable...

https://www.dultmeier.com/products/0.689.1008.3567/5703

I don't even know if we'd have to worry about funneling cold air because at that point, you'd be booking down the road and have plenty of air flow into the engine bay.

And best of all...this would be inside the box so it would look stock for us CARB people. Just a small hole and the little bit sticking out could be painted black to blend in.
 

·
Super Moderator
Joined
·
5,578 Posts
Ok..well I'll spill the beans...it is a crazy idea I know but hey..ya never know.

So I've been reading alot about the stock air box vs. sri vs. losing low end torque vs. hot air temps....and so on.

There are several folks that have kept the stock air box and have noted that it can keep up with a Sri until the higher rpm ranges. Many feel like the stock air boxes are better engineered (tuned) otherwise.

So I thought to myself...why can't we have both? One user who was doing some testing showed that he eliminated the upper limitation by removing the snorkel. However it then sucked hot air and lost any gains via timing pull.

Now on the flip side, there are people that have cut holes in their air box and maybe even gone as far as to run a tube down to colder areas. However they have now just de-tuned the entire box for all ranges. For example there is a posting somewhere about the resinator and how it does more than just sound.

Anyway, so I got the idea that one could use a spring loaded air check valve. Installed via an extra 2" hole in the box, at lower loads/rpm it would stay shut as to not effect the oem engineering. However when on the throttle approaching those higher Rpms... it would open up and give it that little extra breathing.

The key of course would be to get one that stays shut until approaching that 5k + range.
What you are talking about is manifold absolute pressure. On a NA car, it pretty much tops out at whatever the current barometer pressure is, it can't be more. It can be lower depending on rpm and load. Vacuum is the difference between MAP and ambient. Don't confuse air flow with air pressure.
To activate a door as you describe, that would be vacuum actuated. However, you can never have too much air flowing into the box as the engine can only pull what it needs to run. It is after all just a big air pump. There would be little point to a door that opens to let in more air as long as the primary opening is sufficient.
Most SRI units don't have a box around them, airflow is unrestricted. However, this allows hot underhood air to be drawn in also. The engine sensors (MAP, MAF) read this as reduced air density, so fuel delivery is pulled to compensate, leading to less power. Stock air boxes seem to have sufficient flow for at least stock power, SRIs don't generally make enough difference to be noticeable, and any power gains are lost due to the hot air ingestion.
There are intakes out there that have long tubes to draw cold in from elsewhere, but the problem is usually those inlets are located in place where other stuff gets drawn in too. Many intakes are low in the grill or in the wheel well, prime spots for water ingestion.
The intake tube does have a resonator. Its called a Helmholz resonator chamber. What it does is prevent resonation waves from restricting airflow in the midrange. This is why so many who install open SRI intakes report a midrange power loss. Here is an explanation from a more technical source:

Pressure Wave Harmonics
Air flowing into your cylinder head's intake port doesn't move in a straight line while the valve is open, then politely stop in its tracks to await another valve opening. When the valve closes, the moving column of air slams into it, then compresses and bounces back like a spring. This pressure wave travels backward at the speed of sound until the intake runner opens up or it hits something, and then it bounces back toward the cylinder. This is the "first harmonic." The pressure wave actually bounces back and forth two or three more times before the intake valve opens again.

Intake Tube Pulses
The resonator in your intake is technically known as a Helmholz resonator, an acoustic device used to control pressure wave harmonics. Air bouncing back out of your engine and into the intake tube doesn't do it in a single pulse the way it would in a single intake runner; the multiple pistons put out pressure waves at their own intervals, and some of those are going to try to bounce back in while others are going out. The result is a "clog" or high pressure area in your intake tube that ultimately limits airflow through almost the entire rpm spectrum.

The Resonator
Adding an expansion chamber to the intake tube forces air coming back out of the engine to slow down to fill the cavity, thus expending a great deal of its energy and slowing the pressure wave reversion. This slowdown allows fresh air to flow toward the engine without fighting pressure reversion waves the entire way, thus aiding in cylinder filling. Since these pressure waves are essentially sound, giving them a place to expend their energy before exiting the air filter box ends up dampening the intake noise and quieting the engine. Thus, the resonator helps to make the engine paradoxically quieter and more powerful.


Now, I think what you are trying to do is increase flow into the motor by opening a door to let in more air. That is not going to make a difference. You just need a large enough intake opening to allow enough air in, nothing more.
The intake will flow at a certain rate at any given rpm (velocity, not pressure). For best power at any given rpm, the intake runner needs to be at the optimum length and diameter for the engines needs. Most cars use a compromise that works ok but is only really good at a certain rpm range, usually midrange as thats where most normal daily driving is done.
A couple high end cars, Porsche for one, have vacuum actuated intake runners that change according to rpm to maximize power across the full rpm range.
 

·
Registered
Joined
·
2,952 Posts
Ok..well I'll spill the beans...it is a crazy idea I know but hey..ya never know.

So I've been reading alot about the stock air box vs. sri vs. losing low end torque vs. hot air temps....and so on.

There are several folks that have kept the stock air box and have noted that it can keep up with a Sri until the higher rpm ranges. Many feel like the stock air boxes are better engineered (tuned) otherwise.

So I thought to myself...why can't we have both? One user who was doing some testing showed that he eliminated the upper limitation by removing the snorkel. However it then sucked hot air and lost any gains via timing pull.

Now on the flip side, there are people that have cut holes in their air box and maybe even gone as far as to run a tube down to colder areas. However they have now just de-tuned the entire box for all ranges. For example there is a posting somewhere about the resinator and how it does more than just sound.

Anyway, so I got the idea that one could use a spring loaded air check valve. Installed via an extra 2" hole in the box, at lower loads/rpm it would stay shut as to not effect the oem engineering. However when on the throttle approaching those higher Rpms... it would open up and give it that little extra breathing.

The key of course would be to get one that stays shut until approaching that 5k + range.

Some concepts....

1-CV-AIR2S Air Check Valve. 2 inch Socket. 1/4 pound spring - Spa Parts Shop

https://www.amazon.com/gp/aw/d/B00B95UUJQ/ref=pd_aw_sim_sbs_79_3?ie=UTF8&psc=1&refRID=7ZD2KJWT3GCV3K7CR9N6

This one is even adjustable...

https://www.dultmeier.com/products/0.689.1008.3567/5703

I don't even know if we'd have to worry about funneling cold air because at that point, you'd be booking down the road and have plenty of air flow into the engine bay.

And best of all...this would be inside the box so it would look stock for us CARB people. Just a small hole and the little bit sticking out could be painted black to blend in.
The JCW airbox of the R53MINI does just what you're thinking.


Euro noise regulations dictated MINI to do a JCW Box w/ two modes of operation. Below 4500 rpms the intake pulls in air like most intakes, through a larger cone air filter through the standard tubing. However above 4500 rpms a flap in the back of the intake opens and draws cold air from the left cowl (below the windshield) to increase air-flow.
A modified copy known as DaveF in the MINIworld just leaves the rear hole open w/o the flap. Again, MINI's intake location is so near the cowl where cooler air gets in.:)
Running a hose to the M3 cowl might help.
 

·
Super Moderator
Joined
·
5,578 Posts
The JCW airbox of the R53MINI does just what you're thinking.
Same idea, different application. That is done for sound suppression, not power. Obviously the box made too much noise for Euro regs, so intake volume at low rpm was reduced to make it legal. The other hole opens up at higher rpms to compensate.
If the intake was large enough to accommodate the motors mass airflow requirements to begin with, that second hole would not have been needed.
Noise compliance could have been achieved using a proper resonator in the intake.
Adding more holes to the intake box won't make more power unless the intake box is restricted to begin with. All you get is more noise. You can't increase air intake beyond ambient pressure without some sort of forced induction.
Running an intake back to the cowl will improve things. Cowl induction is a long proven method to get more power out of an engine. There is a high pressure zone at the base of the windshield. Running the intake from the cowl forces ambient air in instead of the hot underhood air sucked in by an SRI.
Here is such an intake on my MX5-
good for about 5 hp

 

·
Registered
'15 Mazda3
Joined
·
162 Posts
Wow, all this technical info, when a simple answer will suffice. On a normally aspirated engine (non-boosted) the throttle body allows a certain amount of intake air. If there is a restriction before the throttle body(too small of a hole or tube) in the inlet of the intake box, thereby reducing the amount of air reaching the throttle body, then adding bigger/more hole(s) will help increase the amount of air reaching the throttle body. That is why (many years ago) the first thing a street racer would do is remove the old style snorkel breather and use an open element breather.
 

·
Registered
Joined
·
422 Posts
Discussion Starter #11 (Edited)
Thanks all for the feedback.

All the facts that ^^^ said was a summary of all the stuff I've been reading (just didn't dive into it here because most of it is known).

I guess in its simplest form, the snorkle itself, appears to be the largest restriction point of our stock air boxes and is what causes the small shortcoming at the top end.

However removing the snorkle not only cuts off your path to cold air, but also takes the Helmholz resonator out of the equation as well, which messes with the underlying 'tune' of the box.

I would agree that the best fix would be redesigned snorkel assembly that was basically larger however, since that is not a possibility, I was thinking of a mod that would only kick in when needed, otherwise leaving everything matched as designed.

In the end, most sri are not feats of engineering but simply a tube with a filter to provide high end air flow with no consideration for low end trade offs.

What we need is a stock box low-mid that converts to an sri in the highs. I would think that is doable.
 

·
Registered
Joined
·
422 Posts
Discussion Starter #14
Yeah I've been thinking of some ideas.. wish I had a bit more play money to experiment with. I'd need to build a DYI flow machine and then pick up a used OEM air box to test. My plan would be to shoot for something at least 400 CFM (leaf blower maybe). Rig something up with my metering fan (like I did in the OEM Air Box flow test thread), and test each piece.

So in theory, my steps would be...

Test flow without Air box attached to DYI... to establish base voltage number.
Attach full air box (without Filter) .... must see a drop in flow number to be valid. If not, would need more CFM
Remove Snorkel (leaving Lid and Box)... note flow number..
Remove box (leaving just lid) ... note flow number.


My thinking is that this would allow me to determine what section of the box is causing the largest restriction in flow. Then I could focus on that section to come up with ideas on opening up a secondary air source, but only when needed.


Right now I'm kind of eyeballing that felt filter area in the back of the snorkel...but trying to figure out if that is there for In-flow, or out-flow. Simple fact is, anyone can cut a hole in an air box, but doing true R&D takes a lot of time and even more money... which unfortunately I don't have a lot of either :)
 

·
Registered
Joined
·
422 Posts
Discussion Starter #16
You are way overthinking this.....


Oh I don't know...do you think the folks that designed that cowl tube, or any SRI didn't do some contemplation first? I would hope so.

We all know that Mazda had to make compromises....how else can we find out what the compromises were on the air box? Unless you know a mazda engineer?
 

·
Super Moderator
Joined
·
5,578 Posts
Oh I don't know...do you think the folks that designed that cowl tube, or any SRI didn't do some contemplation first? I would hope so.

We all know that Mazda had to make compromises....how else can we find out what the compromises were on the air box? Unless you know a mazda engineer?
Actually, the engineers at Mazda did not leave a lot of room for improvement and did not need to compromise anything as far as the airbox goes. The airbox design on the 3 and other models is pretty close to optimal. There is not much in the way of restriction in the airbox as it comes from the factory, and not enough to cause a power loss. That is why there is not one single aftermarket intake for these cars that makes any sort of difference in the real world.

The non-FI engine will only suck in as much air as it needs, no more. As long as the total combined size of the intake openings in the box is no smaller than the size of the butterfly in the throttle, thats all you get. Bigger or more holes won't matter.
What you want for non-FI power gains is flow control, ie length and diameter of the intake runners in the manifold, and intake air temperature control. Mazda, and most any other maker, does compromise on many things. The design of the intake manifold is such a compromise. You can't have a fixed size runner that gives best low end power, best mid range power and best top end power. So, you design it to get a good mix across the power band. You can get a power increase in one part of the powerband by changing the intake manifold design but only at the expense of power everywhere else. This is not something you can do with the air box.
There is not a lot you can do to control intake air temperature without resorting to FI with intercoolers or ice boxes. What you can do is keep underhood air out and keep IATS down by insulating the air box as much as possible and channel in ambient air from outside. This is one reason why free flowing open SRIs don't work. They suck in underhood air that is well over 100°F. FWIW my IATs were ~53°F or 8° above ambient (45°) today as long as the car was moving, and went up another 10° when going through town and all the traffic lights, and back down once traffic freed up.
 
1 - 17 of 17 Posts
Top