Ft Liquordale

My mechanic and I noticed on the front of the intake box, the opening is partitioned. On the right, there is a flap that is regulated by a pressure hose. If the hose is disengaged, the flap is open at all times. This, obviously, will provide more air to the engine. What, if at all, are some possible positive and/or adverse results? I don't know if my but dyno is any good, but I think I feel more pep off the line. I can hear the Renesis a little more as well.

rotarygod

The "flap" stays closed below about 7250 rpm or so. This lets all the air flow through the longer section of intake pipe. This actually does serve a purpose as the filter box it tuned by using these pipes. At higher rpm's where there would be a benefit from retuning the intake system, the flap opens up and does just that. It again tunes the engine for good power above 7250 rpm. It does serve a purpose. If you left this open full time yes the engine could get more air but it wouldn't utilize it very well. The intake box is now tuned out of the rpm range and you'd probably lose power below it's opening point. Best to leave it alone unless you plan on entirely replacing the intake with a new one. The stock one is a tuned system. Aftermarket systems are not. They just rely on pure quantity of air.

Ft Liquordale

mucho gracias! I will plug that sucker up until my new intake is in or I can do a better analisys on it. So you don't think it's an emissions thing?

Doctorr

You just heard from the famous RotaryGod, that it's there to tune the intake for power, and your reply is "OK I'll just plug it up till i get my hot-air intake installed"......

a/ You will lose torque below 7250 rpm, not good.

b/ Your new intake will be sucking warm air right out of the back of the radiator, also not good.

c/ You still think it's "an emissions thing", OK, knock yourself out...

S

wakeech

two points:

liquordale, read what the man has to say, not every four or five words. read it, understand it.

ray, havin' a little identity crisis?? "s"

MazdaManiac

iTrader: (3)

A man comes across a Corky Bell in his shop -

man : "Whats this thing?"
CB : "Its a wastegate actuator."
man : "Whats it do?"
CB : "It opens the wastegate on the turbo to stop it from accelerating past its boost target."
man : "You mean it slows the turbo down?"
CB : "In a sense."
man : "Wouldn't the turbo spin faster without it?"
CB : "Well, yeah. But you don't always want the..."
man : "Won't spinning the turbo faster make more boost?"
CB : "Yes, to a point. But the system is tuned to make power within a range in which the turbo is most efficient. You need the wastegate."
man : "Oh, OK. I see. I'll just take mine out so the turbo spins faster."
CB : "But then you won't have any way of controlling the boost pressure!"
man : "You just said that the wastegate will slow the turbo down. I don't want to..."
CB : "But you need to have the wasega..."
man : "I want my car to be faster!"
CB : "But you need the wastegate, regardless of how fast..."
man : "But it will slow down my turbo! I don't wan't that!"
CB : "The wastegate won't make your car slower, just the turbocharger after a certain..."
man : "You sound mighty confused, old man."

wakeech

i believe an "lol" would be appropriate.

lol. :D

Ft Liquordale

A. Rotary God is not the voice of the manufacturer. He said it PROBABLY wouldn't utilize the extra air well. Meaning...He is not 100% sure.
B. I still respect his assumption, because it makes sense. I will make more heads or tails from it when I can.
C. The tuning is for the STOCK BOX
D. After market intakes utilize the bulk air instead of the tuning. Did you read his post?
E. Who said I was putting a HOT AIR intake on my car? That does not make sense. The only one like that is the K&N kit, in which I have paid enough attention to this board not to put one on my car.
F. From what I understand, the key in the past with rx7's has been finding bottlenecks the the manufacturer put in for strict Mazda emissions standards and tuning for lower HP levels. This will be researched, I assure you.
G. Thank you for your concern and quick responses!

rotarygod

Doctorr: You crack me up!

Ft Liquordale: I would just leave it alone and let it work as it was intended to. The primary length tube is tuned for a lower rpm. This is why the flap opens at 7250, to again tune the intake to a higher rpm. The automatic cars do not have this door. They also have redline at 7500 rpm so they don't need it. Their primary intake pipe is longer than the long one on the manual cars to tune for a lower average power. If you keep it open, you will lose power in spots below 7250 rpm since you have done away with the lower rpm tuning and gain absolutely nothing anywhere else. The total intake area to the factory airbox is actually smaller than that of the MAF or the throttlebody yet the system makes almost the same power as an unrestricted aftermarket intake. That is the benefit of tuning. There are many 2nd generation RX-7 people that think "wiring open" the auxillary ports will give them more power. All they did was to lose some usable power lower in the rpm range and gain nothing. Unless you are completely replacing the entire intake, leave it alone and let it function normally. If it worked better with it open all the time, Mazda would have designed it that way.

Ft Liquordale

Geeze! I put the tube back! It has been together sinse the first post from rotarygod. Doctorr, your comments were off base and Asinine. Thank you for your condescention.

Broke_Apex_Seal

maniac is funny...............

MazdaManiac

iTrader: (3)

I just call 'em like I see 'em!

You gonna be around at work on Thursday? I was thinking about swinging by.

Ft Liquordale

you need an eye doctor then

MazdaManiac

iTrader: (3)

What are you talking about?

thered1996

There's wisdom to the design -- sort of a less expensive answer to the variable length intake system on some engines. Long pipes improve the low end due to the inertia of the air column. Wide open is best for higher RPMs. This system adapts to both conditions, it seems.

Wonder what they'll put on the 2006 models?

Ft Liquordale

I believe the flap covers the long pipe (away from the intake) on lower RPMs. This system apperently breathes better with high frequency on the low RPMs and Low Frequency in high RPM's. I am still a neophyte and trying to understand the physics of this. But I am sure it will hit soon enough.

Anyhow, explain to me this adaption.

rotarygod

The long pipe is always open. The flap door merely opens the shorter pipe in addition to the longer one.

Ft Liquordale

Wow! you guys are quick! so lower freq at low RPM? Physics tells me the faster the air, the higher the freq, right? Does opening the extra pipe increase the resonate frequency? And does this, in a sense make it choke?

Also, what affect would widening the intake pipes have?

rotarygod

Lower the rpm the lower the frequency. Just listen to your car as you rev it up to verify this.

By opening the extra pipe up the resonant frequency is much higher. There is also a little added intake area.

By enlargening the intake pipes you do get more air into the engine. However with a tuned system, making the pipes larger also tunes them to a higher frequency. They would also have to be made longer. You need a technical understanding of acoustics to fully comprehend why this is so. Anything you do to the system has to be dealt with in at least 2 areas at the same time. Changing only one this won't help you and will probably hurt. In other words to maintain a tuning frequency when you make a pipe larger, you also need to make it longer. If you change the size of the airbox, you also need to change either the length or the width of the intake pipes. There are limitless combinations to think about.

When aftermarket companies remove this system and replace it with a cone, they are trading off resonant tuning for sheer airflow. So far only Greddy has actually realized that you can still tune an intake based in this intake pipe length and diameter. It is based in acoustic pipe tuning. They have a system that is larger is size than the throttlebody and very long, with the filter next to the passenger side wheel. This tunes the intake at a lower rpm and makes the gains very nice over an average usable powerband. Many people criticise it though due to fears of water getting in the pipe. Without getting technical I will say athat unless you consistently drive through lakes and flood waters, you wont have this issue with a low filter. The other companies just give you an adapter with a filter and let it tune it like it tunes it. I personally don't like this approach but there are some gains to be had from it in certain spots.

Ft Liquordale

why would making the tubes larger increase frequency? I am thinking like a tuba or a trumbone compared to a trumpet. The wide tube would make the tonal frequency lower. And you need a shorter pipe to raise the pitch.

I did a search for the greddy. Interesting illustration. I'd be scared to put that on my car unless it was my leisure car. Is that how long you are saying they had to make the pipe to preserve frequency? that is crazy.

rotarygod

Like I said you need a knowledge of acoustics to understand why tuning works that way but it does. Tuning has nothing to do with length or width of a pipe on their own. It is a relationship between the two but it is not based on total area. It is a volume/velocity relationship. If we have a pipe that is 2" diameter and another one that is 2.5" diameter, make them the same length, and attach them to a box individually, the smaller diameter pipe will tune to a lower frequency. The same holds true if we have 2 pipes of the same diameter but of differing lengths. The longer one tunes to a lower frequency. It gets confusing pretty quickly.

A Tuba, Trumpet, Trombone, etc. all use horn loaded acoustics. A certain length and width pipe will resonate at 1 frequency as well at the frequecies at octaves away from it although at lower intensities. We call these octaves, harmonics. A horn will resonate at the throat (the small side) at a high frequency, the mouth (the large side) will resonate at a low frequency, and the rest of the horn will resonate at every frequency in between the two as well as at all of the harmonics. Depending on if the horn curvature is hyperbolic, exponential, parabolic, conical, etc. will determine the efficiency within this range, the amount of distortion within this range, as well as also determining the total length necessary for the horn. Since this air slows down drastically as it passes through the horn, it gains pressure. We hear this gain in pressure as an increase in volume. The same holds true of the resonant frequency of the RX-8 intake. We want it to resonate at strategic spots to help pressurize the incoming air. Again, lots of technical stuff to understand.

A Trombone plays lower as you slide the slide out. This makes the Trombone's effective length longer and makes it play lower. Remember that I just said the expansion flare also determines the length. It also determines what frequencies will benefit most at this length. The mouth of a horn will not always be the same size to play the same frequency depending on how everything else is done. It is a ratio with the throat size, expansion rate, and length.

Lost you yet? The intake tuning of the RX-8 is actually a very complicated issue. There is more than one way to deal with it. The Greddy system tunes for lower in the powerband than the other systems. This gives it more usable power in the rpm range we drive in a majority of the time. As with anything I can get very technical and long winded as to why a low mounted filter isn't near as dangerous as everyone thinks it is but I'll just skip it for now.

wakeech

it's not the speed of the air that determines the frequency, it's the speed the motor is turning.

the pressure waves come from the opening and closing of the intake/exhaust ports (by way of valve, or in this case, rotor moving over them). the faster the engine is turning, the more air it's sucking in at a time, and the higher the frequency of these pulses.

the thing with the width of pipe is to try and get the air to an optimum velocity (high as possible without too much drag loss) to improve the volumetric efficiency (how well it fills the combustion chamber). when you're at a low rate of flow, an appropriately narrow tube is required, and diameter moves up with increasing rates of flow (to keep loss to an optimal low).

the length of the pipe has to do with tuning them to the "sound" of the engine at a certain speed, so when they resonate, the "valley" (lowest point of pressure, aka BDC) is at the open end of the intake tube, and the "peak" (highest point of pressure, from the force of the port closing) arrives back in the combustion chamber. this creates the highest net difference in pressure between the atmosphere outside the engine, and the combustion chamber to the point where you can get a greater than atmospheric difference (a "supercharging" effect) without a mechanism applying force to the air.

i just left my computer for a number of hours, and wouldn't be surprised if this was already explained

rotarygod

We posted at the same time. Yeah what he said. Wakeech has a much simpler way of saying things than I do!

Ft Liquordale

you two should write a book. I am glad the analogy worked.

A few more things, because I think this evolving to a very informative post like I hoped.

#1 how does the type of filter affect tuning with cone vs. flat and thinner materials.

#2 I am assuming exhausts work in a very simmilar fassion. What should a consumer look for when buying an exhaust.

#3 How do ECU modifications affect the tuning. What is adjusted when...if at all.

rotarygod

I personally like flat panel filters better. Cone filters have more filter area than the typical panel filter but internally they are much more turbulent. We have air coming in from every direction and then trying to combine together in a small space and steer its way into the opening. On a panel filter the air slowly (if the intake box is designed good) moves through the panel filter and then converges again in a much less turbulent manner. The air never really has to turn very sharp. It flows very easily into the inlet. This is probably why some people who have aftermarket intakes on their RX-8s have found stumbling in certain spots. Cone filter turbulence. I'd rather find a way to design the biggest airbox that I could so the biggest panel filter I could get would fit in it. Something like a filter from a big Dodge diesel truck.

As far as exhausts go I wrote a thread on that which should help you out.

https://www.rx8club.com/showthread.p...threadid=22500

ECU adjustments don't affect tuning. They are tuning! Having a poorly tuned ecu is like running a carb with the wrong jet sizes. It isn't the carbs fault. It is the tuners fault. In this case it's Mazda's fault that the factory ecu leaves much to be desired. Canzoomer has already shown 20+ rwhp gains just from retuning alone. Along with some exhaust work and more aggressive tuning he has found 40+ hp gains. Tuning is everything.