So i juss installed my agency power exhaust system. i gotta say that it sounds awesome!! haha i had the jic magic exhaust with the B&B test pipe but i wanted a bigger system because they were 2.5" exhaust. the agency is 3". So i drove with it for about 5 minutes or so but it seems as if i lost power. so my question here is if the 3" exhaust really better than the 2.5". btw, i have an aem cold air intake and a pulley.
one more question guys, since i couldn't find a 3" doughnut that connects the race pipe to the catback, i took my car to a muffler shop. they put a 2.5" doughnut and did some stuff to it and it finally fit. they told me to get a 3" doughnut at pepboys or autozone but none of them have it. so do i really need the 3" doughnut cuz it seems as if they closed the gap i had with the doughnut they put in. (do you guys think this is the reason i feel a loss of power?? maybe?? haha)
thanks guys

I think that 2.5" doughnut may act as a restrictor plate on your 3" exhaust.

well i saw the guy at the muffler shop shaving the doughnut so it fit the 3". damn... is it juss me thinking that i lost power??

if your car is NA, you may not have enough backpressure, crazy i know. there are some threads on it around here. im feeling to lazy to search.

if your car is NA, you may not have enough backpressure, crazy i know. there are some threads on it around here. im feeling to lazy to search.

That is BS. Back pressure is always bad. Back pressure never gives you more power.

What you feeling is probably lost of Torque but you might of gain on high.That why i tell everyone waste the extra 100.00 and get your car dynoed.

Ya so I have that AP exhaust... The sound is awesome, and even better with a HFC... But what I think you might be getting confused between is how loud your car sounds compared too how fast it actually goes... I feel like I'm goin slow all the time... My car is sooo much louder especially after I got my HFC installed (between that and stock cat I ran with a midpipe for some 5,000 miles)... But more importantly is when I had that midpipe on, I felt what you are describing, a complete loss of that torque feel and a slowing off my 8 (extremely especially compared to how loud my 8 was)...

this is the exhaust i have...but not yet installed ...did you guys get the test pipe? if so do you have it installed...ne flames?

well i am gonna go get my car dynoed on 3/31. hopefully its just me. but yea, my should should be shooting flames because of the catless race pipe.

btw, bryan, do you think it really is giving me a loss of power because of less back pressure? i've heard from a friend that a car needs back pressure to get hp. if not, like you said, it yields some hp. argh... would this be fixed once i get the wet nitrous kit?

did you reset the computer so it could learn new fuel trims quickly?

Does anyone have a dyno sheet of the AP exhaust (pre and post)? I am really interested in it but leaning to the JIC........

oh i should reset my pcm?? haha i shall do that today:). thanks teamrx8. hahah hopefully after that SOEMTHING will feel different.

chickenwafer, in my honest opinion, the jic magic FEELS better. haha it seemed as if i had power in the low rpms all the way to the top. but the agency feels like it juss frees up power at the top and it lacks power or torque at the bottom end. As for sound, the agency is wayyy louder and wayyy lower. so yea. if you have any questions juss pm me. i had the jic with b&b test pipe.

are you supposed to reset the pcm after and exhaust install. i havent. is that bad?

i dont THINK it is necessarily bad that you dont reset your pcm but it wont hurt if you do. plus i think if you reset it, then your pcm can learn your new exhaust system and make some arrangements. etc.

ill do that today. all i do is press the brake pedal 20 times with key in on, right?

back pressure allows a motor to have more torque... usually from my knowledge you use 3 inch or bigger for turbo applications... you are not so concerned with bp but with the additional amount of air you want to flow out of the system... why you ask... well the more air you can get out of the system the more air the turbo can push in the system... thus creating more power....

na apps should feel a loss of power due to the loss of bp... but as team said the resetting the fuel curves in the pcm should help a little

hahaha yea. i reset my pcm and went for a ride. now i am 100% sure that my car has lost power:(. it feels wayyy slower. hahah dang i should start saving up money for that wet nitrous kit. hahah
so to sum all this up, the 3" exhaust is only for FI setups right?? not n/a because there isn't enough air flowing out and therefore not creating enough backpressure.

i gotta say this guys... im sad!!!:( hahah

btw, thanks to whoneedspisotns and teamrx8:) haha

On the matter of the 2.5" "donut" being shaved to fit the 3" pipe; if they really spent the time and effort to cut it when they could have simply used a pipe stretcher like I did, that might be illustrative in this case.

Resetting the PCM; the Renesis has such low overlap between the intake and exhaust ports that getting a less restrictive exhaust is unlikely to effect the fuel trims but with a catless midpipe it wouldn't hurt to do it. Disconnect the battery for a few minutes.

Loss of power; probably a slight loss of off-idle throttle response that typically occurs with exhaust upgrades such as these. The gains on the top-end, like above 6,000 rpms, definitely offset any actual or perceived losses in response. However, my guess is that the loss of power issue would be psychosomatic. See item #2.

As regards backpressure; please do a search on the topic and look for a conversation that was led by Rotarygod. It was detailed and accurate and I am far too lazy to reproduce it or link it here. The short story is there are several factors that effect the relationship between backpressure and power production and to oversimplify the issue as whoneedspistons has done ignores all the important elements.

In summary, what I can say from my own experience is that when I simply replaced my factory cat-back with a Borla 3" system provided no perceived power gains but when I removed my catpipe and installed a Bonez 3" catless midpipe, the gains were easily noticed.

hahaha yea. i reset my pcm and went for a ride. now i am 100% sure that my car has lost power:(. it feels wayyy slower. hahah dang i should start saving up money for that wet nitrous kit. hahah
so to sum all this up, the 3" exhaust is only for FI setups right?? not n/a because there isn't enough air flowing out and therefore not creating enough backpressure.

i gotta say this guys... im sad!!!:( hahah

Maybe your 8 is slow? Other than that, your kinda being very presumptious. I felt a bigger difference with Racing Beat's ram air than I did this exhaust (until I ran with AP's midpipe). Until you run with a midpipe you shouldn't be taking this exhaust so harshly to heart so quickly... Trust me, I was addicted too setting I-45 on fire for months until I finally took that trifling midpipe off... I also learned how to create that popping sound rotaries are noted for... It takes particular timing concerned too throttle/shifting... But I would get either trouble or adoration when it comes to dual 4" tips spitting 5 foot flames...

i always had a catless midpipe. i had the b&B test pipe and jic exhaust. the reason i cahnged it is because i am going nitrous in the near future so i wanted a 3" full exhaust. so now i have the catless racepipe from ap and the exhaust. but iono why it feels to me as if i lost power. i juss wanted bigger pipping.

so i juss got off the freeway and i am quite upset. i really thought it was my mind telling me that my car is slower than it was before but i juss know for sure that it is. my car revs up sooooo slowly.. its not funny. argh... i really hope i can find the problem to this a plug it! haha
do you guys think a leak in the exhaust my cause a big loss of power??

charlse r... i have never seen that thread... and i was speaking with experience with other cars not this one.... a rule of thumb is that you need back pressure to help with torque at low rpms... it would be like changing to a plenum intake mani from the stock mani it will effect the cars performance differently in a na setup compared to a fi... that is why i specified with my experience

it wasnt an oversimplification just general knowledge of past experience without the detail... short and sweet... but i do appoligize if there was false info given

It's not false info that I was concerned with, it was that exhaust velocities are what determine the rpm range at which a given engine will develop its peak torque and the nature of that torque curve, as well. What I was trying to avoid was a detailed conversation on the matter when it has already been published on this forum. To me, a similar controversy is the one surrounding flywheel weights and the misunderstandings of how that effects driveability. We often ignore or forget the human subjective interpretation, i.e. "butt-dyno", element in these queries as to changes in real or perceived power output. Without getting into the detailed conversation on exhaust velocities and how they alter an engine's characteristics is to, by definition, oversimplify the discussion. That's not to say you're wrong, just that the details make all the difference to the reader who has yet to learn these things.

so i juss got off the freeway and i am quite upset. i really thought it was my mind telling me that my car is slower than it was before but i juss know for sure that it is. my car revs up sooooo slowly.. its not funny. argh... i really hope i can find the problem to this a plug it! haha
do you guys think a leak in the exhaust my cause a big loss of power??

Revs slow? You have something else wrong with your car.

Revs slow? You have something else wrong with your car.

i dont think it. it was okay before the installation. argh maybe its just me. im gonna go get that 3" doughnut and put it in. hopefully that will make the difference:). but yea... my car reved very slowly yesterday night. it was weird because it seemed like it was taking forever to hit 100. i usually hit it quickly.

btw, does anyone know where i can get a 3" doughnut. i can't seem to find ANYWHERE that they sell it. i've checked midas, autozone, pepboys. anyone know where i can purcahse it?

The funny thing about the concern over backpressure and torque is that the effect of backpressure is directly related to the amount of overlap between the intake and exhaust cycles and the Renesis is said to have no overlap. On the other hand, a 3" system from the manifold back will typically net 10-15 h.p. on the RX-8.

Another way to reset the ECU is to pull the room fuse in the driver's kick fuse panel (the 15 amp fuse that is on the bottom).

Leave it out for 30 seconds. Reinstall.

If after a hundred miles you don't notice an improvement then there could be another issue with the car.

From my experience the car doesn't seem to have as much torque in the lower RPMs as when there is a cat pipe. It is also a deceptive thing because of the noise it creates having a catless midpipe a person feels the car should be going faster for the amount of noise it is producing.

In the higher RPMs there is a definite improvement with a cat delete pipe.

I think the need for backpressure is misunderstood. Backpressure is bad. Your motor has to actually work pumping out the exhaust gases. How is that good?? Could you imagine if your motor could get away with that pumping penalty... well it sorta can.

What you have is a situation where you have bigger piping optimized for a higher rpm window. What's happening at the low end is the enlarged pipe diameter is actually causing slower exhaust velocities compared to say when you had the smaller diameter piping on (This is also why you can't go too large either on intake manifolds). The smaller the diameter, the higher the air velocity and momentum you will attain for a given CFM, but within limits. If you can sustain high enough air velocity, it'll be like leaving a vacuum to help assist the next exhaust cycle.

The trade off for bigger piping is helps free up restriction AT a certain operating range.

F22, what you point out is exactly why I said that the Renesis is peculiar in that, even with almost no overlap, a well designed 3" exhaust without a cat still gains 10-15 h.p.

haha yea i juss gave up this idea of losing power once charles talked about the gains in the upper rpm range. i guess it'll pay off later:). im not worrying about it anymore. hahah thanks guys

If you have a very noticeable loss of power you have lost lots of hp - maybe 30+ . There is no way the exhaust would do that (unless it is blocked) & reseting the ECU won't fix it either .

Maybe there is a blockage ???????
can you post a pic of what the donut connection looks like ?

Is it possible that the muffler used in this kit isn't up to the task? I would figure this problem that peter is having to be an isolated issue, however, over the last two years that I have become more and more involved in the aftermarket scene I am finding that very few people truly KNOW what the hell is going on. Mazda has no clue as to why the '04 models are having problems, the service techs are of no help, and many of the aftermarket companies are lacking in their customer service skills and technical knowledge, as well. As such, it wouldn't surprise me, at all, if the Agency system wasn't fully tested out before it was offered.

if it's true you should be able to swap back and notice the difference :dunno:

well for the next week or so i am just gonna ride my car. I am going to take my car for a flywheel and clutch installation in aobut a week or two so i'll post pictures then of my doughnut.

after hearing all of you guys try to help me out, which i am very glad for, i have concluded that it is just me. i am going to dyno my car with everyone else on the 31st and check how much i am pushing. if its a good amount, then its okay:). haha

but yea thanks to everyone. i guess i'll check my exhaust the day of my installation. if it is blocked or anything.

thanks again guys:) i'll update soon and take pics which MIGHT help you guys help me out. hahah

There you go again. If you think you lost power, wait until you install the flywheel.

Once again you will loose torque. Torque makes power. You will feel slower. It is slower.

The trade off is it rev's faster with the fly wheel and you can get a quicker 1/4 mile.

You will be slower in daily driving. The exhaust does the same thing. looses torque.

I'm still not convinced that a 3" exhaust will give you better results ans the engine is so small.

It seems like the the 3" setup is the way to go. I have a 3" in the back, but not up front with high flow cat yet.

Once again a too large exhaust diameter is slower. The AEM intake hasn't been proven to be superior to RB intake and is most likely slower. After adding the full 3" system you may have over done the system.

However, if you go FI or some sort of ECU upgrade you can take advantage of the the full exhaust system.

That's why a lot of people don't up grade. You get slower performance due to less torque which is less pulling power.

How often do you drive at 6k consistently during daily driving?

Everyday your slower, but if your on it you get results. Remember results are only obtained if your 6500 or more consistently in your driving.

That type of RPM will make you over the speed limit and attact attention due to the noise. It's a trade off.

Show me where you can consistently go over 6k in each gear and be legal.

There you go again. If you think you lost power, wait until you install the flywheel.

Once again you will loose torque. Torque makes power. You will feel slower. It is slower.

The trade off is it rev's faster with the fly wheel and you can get a quicker 1/4 mile.

You will be slower in daily driving. The exhaust does the same thing. looses torque.

I'm still not convinced that a 3" exhaust will give you better results ans the engine is so small.

It seems like the the 3" setup is the way to go. I have a 3" in the back, but not up front with high flow cat yet.

Once again a too large exhaust diameter is slower. The AEM intake hasn't been proven to be superior to RB intake and is most likely slower. After adding the full 3" system you may have over done the system.

However, if you go FI or some sort of ECU upgrade you can take advantage of the the full exhaust system.

That's why a lot of people don't up grade. You get slower performance due to less torque which is less pulling power.

How often do you drive at 6k consistently during daily driving?

Everyday your slower, but if your on it you get results. Remember results are only obtained if your 6500 or more consistently in your driving.

That type of RPM will make you over the speed limit and attact attention due to the noise. It's a trade off.

Show me where you can consistently go over 6k in each gear and be legal.

You must be joking...

http://www.rx8club.com/showthread.php?t=77560&page=7&pp=15&highlight=turboxs

Our peak trq hits at 5500rpms anyways, 500rpms is not going to make a diff.

A full three inch exhaust will not drop you trq if paired with a midpipe. As a matter of fact it increases from 3000rpm on. I will admit you will not see much of a change before 3000rpms,but to say you lose trq is wrong.

if it's true you should be able to swap back and notice the difference :dunno:

True, that would be the best way to see if another problem exist.

What's worse about doing a flywheel swap while still not being sure about what is/isn't happening with the exhaust system and any power losses is that when we change more than one variable at a time we can never be sure which change is responsible for whichever outcome we are trying to analyze. Further, there are enough of us running around with 3" catless exhaust systems and light flys to tell you, unanimously, that they provide worthwhile gains across the board.

There you go again. If you think you lost power, wait until you install the flywheel.

Once again you will loose torque. Torque makes power. You will feel slower. It is slower.

The trade off is it rev's faster with the fly wheel and you can get a quicker 1/4 mile.

You will be slower in daily driving. The exhaust does the same thing. looses torque.



That's why a lot of people don't up grade. You get slower performance due to less torque which is less pulling power.



.

:wallbash: What planet are you on ?

Ya think Razz wants to test his theory by meeting me on that Forza Challenge show?

Ask any professional drag racer. Torque makes power. They have enough HP.

They'll take an increase in Torque over HP any day.

Ya think Razz wants to test his theory by meeting me on that Forza Challenge show?

heh - only seen that once . a guy in a honda with a fake nitrous setup against a rx7 . You wouldn't do that would you charles ?

Ok, I'm up against Daddy Rat Fink.

And I will loose..........

It will be a fun show!

Ask any professional drag racer. Torque makes power. They have enough HP.

They'll take an increase in Torque over HP any day.

:wallbash: i'm getting a sore head now Razz

im getting a headache too. two sides to choose from. hahah oh well. like i said before, i am gonna trust charles cuz that guy knows a lot bout the 8(not like the others dont) but since i am looking into the same set up as he has. i will put my 8 in his hands.... hahaha

I looked at the photos on-line of the Agency system and I can't see anything inherently wrong in its design that would drastically differentiate it from other systems. There was one thing I did notice; the flange connector that bolts up to the factory exhaust manifold has a reduction in cross-section designed into it. If there were to be any obstruction that was obvious, that would be it. I know my Bonez midpipe has no such reduction in diameter. I also tend to prefer the single muffler design of my Borla system, but that's subjective.

lol i just read through this whole thing very intresting. if back presure is the issue and there is one pipe that splits in two. what would happen if you put tape over one of the mufflers. wouldnt that create more back pressure. if you get your power back then thats your problem.

ps if i just said something totaly stupid be nice "newbie"

lol i just read through this whole thing very intresting. if back presure is the issue and there is one pipe that splits in two. what would happen if you put tape over one of the mufflers. wouldnt that create more back pressure. if you get your power back then thats your problem.

ps if i just said something totaly stupid be nice "newbie"

ummm... Tape over an exhaust?

I will just be nice and say no, that will not help...

my turboXS unit came with silencers. u might try something like that and see if the car is more responsive. thatll let u know if backpressure has anything to do with it.

my turboXS unit came with silencers. u might try something like that and see if the car is more responsive. thatll let u know if backpressure has anything to do with it.


wat do silencers do as far as back pressure??

The type of silencers that cap off the exhaust tip muffle the sound somewhat by virtue of restricting exhaust flow, which is to say increasing backpressure. For a good example of that very concept as a tuning tool look up Supertrapp mufflers. They are mostly used on two-strokes and dune buggies, most for their simplicity and low weight. Gotta hand it to our new friend Ricky, at least he is thinking and asking rather than jumping in and making false statements out of ignorance. May we kick around the idea as to why it is that 99% of the time those of us who swap to a 3" catless exhaust experience impressive gains even though our engines are said to have no intake/exhaust overlap?

wat do silencers do as far as back pressure??


The silencers restrict the tips to dampen noise. Which creates some back pressure. :)

May we kick around the idea as to why it is that 99% of the time those of us who swap to a 3" catless exhaust experience impressive gains even though our engines are said to have no intake/exhaust overlap?

yeh lets . I have no idea - do you have any thoughts ?

I have three concurrent curiosities going right now; the first involves MM's assertion that the Renesis' VE drops above 7,800 rpms. The second is the lack of intake/exhaust overlap that the Renesis apparently has. If they are both related in the sense that Mazda designed the exhaust to flow enough for a linear torque curve until 7,800 that's probably why 3" catless exhausts only show noticeable gains above 8K. That's what my G-Tech showed me on repeated ocassions, anyway. The third involves whether or not it is true that the Renny was also designed to have a built-in EGR effect with the lack of overlap. I am also curious as to what the vacuum readings would be through the rpm band in 3rd and 4th gear so as to get an idea on the design of the intake side. I still have to read through Dave's porting project thread. As it stands, if all this stuff is true then the gains we see are strictly caused by reducing backpressure so that the gains are actually from reduced exhaust pumping inefficiencies and not from any overlap-induced scavenging. That's why porting on the exhaust side was/is such a interesting topic. If we induce a bit of overlap and tune accordingly, how much more beneficial will our 3" systems be?

wow so much info. hahaha im trying to process all this in. hahah

hey guys,
juss read an article in a automobile magazine and i thought it might help with some of us disputing both sides. My problem or doubt WAS that i thought i was having a loss of power due to too big of an exhaust 3". But as i read in the article, it said that when a tuner was trying to make an exhaust for a 911 turbo, he was making a bigger one than stock to DECREASE any backpressure. I'm not sure whether the article had stated that backpressure increases or decreases power, but the tone that i derived from it is that backpressure does not matter at all. so yea... juss letting you guys know. hahah :fingersx:

Charles - what were you measuring with gtech ? HP , 0-60 , 1\4 mile . Can you definately rule out technique as a factor ?

When using the G all that data is gathered at the same time. There is also a c.d. included which allows the users to upload their run data in a spreadsheet-like fashion. When spring comes I'll load that software back on my computer and maybe that'll be another thread I can host: "Getting the Most from Your G-Tech", or something like that. When you ask about ruling out technique, I am not sure that technique couldn't be ruled out in any scientific endeavor. Since each person has their own peculiar ways in which they do things I am sure mine might differ in the details as much as anyone's might. I can say with confidence that I use the G-Tech in a manner indicated in the operations manual and with a firm grasp of the concepts therein. With a strong drag racing background I understand things like "roll-out", significance of the 60' times, and etc.

Will adding a full Agency power catback including the midpipe that takes away the cat make my 04 AT rx8 a lil faster? if not should i go with a 2.5" exhaust instead? or 3" all the way?

yes it'll make your car faster.

2.5" exhausts will be more quiet.

for me, 3" all the way.

would it be better if i do an agency power midpipe with the greddy sp2? how many inches is the greddy sp2?

From what Ive read less backpressure is desireable but in a NA car a properly sized/tuned system will induce a scavenging effect by tuning exhaust pulses to line up casuing a suction effect, the pulse in front pulling the one behind it out the pipe. Quality headers have tuned length runners to line up exhasut pulses. I dont know if this is practiced or possible on the 8 bc of the shared mani pipe in the middle. Im new w/ the 8.

Ive seen plenty of 350-400 hp turbo DSMs on a 2.5" system so Im feelin a 3" system on a 250-300hp 8 is too big unless you go FI.

Who makes a 2.5" cat back and a 2.5" race pipe or race cat/pipe?

Also ive read losing this scavenging effect will result in a loss of tourqe at lower RPM and all HP gains are on the top end. I think Im a few lb/ft better than the S2000 stock and dont want to lose this bragging right:) For around town regular driving more tourqe is better imo.

http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

this has some info about exhaust gasses cooling too much becoming denser than hot exhaust as well but not sure if that counts with the high ex temps of the 8

would it be better if i do an agency power midpipe with the greddy sp2? how many inches is the greddy sp2?the greddy sp2 is 60mm or about 2.4 inches so you would want a 2.5 test pipe or a different 3" catback




https://www.wesellcarparts.com/store/scripts/prodView.asp?idProduct=3768

I'm so torn between the Agency Power vs JIC Magic Exhaust. such a HARD decision :(