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.

 

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.

 

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.

 

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