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Discussion Starter · #1 ·
hey guys, I recently had a magnaflow catback installed a few days ago; as for the sound, its awesome... however, i've noticed a significant loss of low end torque, the car just doesn't seem to accelerate as quickly as before (i was running stock exhaust with both resonators removed). i'm wondering if the larger diameter pipes eliminate too much back pressure on the exhaust.. and if so, would i be better off keeping the stock exhaust on there and just changing the mufflers?

anyone have any ideas/suggestions/experience with this?
 

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hey guys, I recently had a magnaflow catback installed a few days ago; as for the sound, its awesome... however, i've noticed a significant loss of low end torque, the car just doesn't seem to accelerate as quickly as before (i was running stock exhaust with both resonators removed). i'm wondering if the larger diameter pipes eliminate too much back pressure on the exhaust.. and if so, would i be better off keeping the stock exhaust on there and just changing the mufflers?

anyone have any ideas/suggestions/experience with this?
I know that it results in a loss of HP and torque for the 4 cylinder models. It needs back pressure. That's the trade off.
 

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Carpe Diem
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however, i've noticed a significant loss of low end torque, the car just doesn't seem to accelerate as quickly as before (i was running stock exhaust with both resonators removed).
I don't know if you have an i4 or a v6 but there are v6 guys with full 3" custom exhausts (magnaflow catbacks are 2.25/2.5") with actually dyno charts showing a good increase in hp/tq.


Butt dynos aren't very accurate...
 

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Discussion Starter · #4 ·
sorry, forgot to mention i'm v6.. also everything else is stock (ie. the intake). I have noticed a break in the intake tubing (the accordian looking tube) so maybe thats where my issue is, granted it was there before the exhaust went on and there were no issues. i have no codes either (i have seen the occasional o2 sensor code pop up but it usually just goes away after a while)..

i'm beginning to wonder if i just feel like the car is slower because of the increased sound at lower revs? lol
 

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When you install a catback exhaust, it shifts the power band. You'll gain, but it's very much up top when exhaust flow is fast. Dyno = doesn't mean s**t.

I had a 98 Accord V6, it got slow as hell when I moved up to a 2.5" diameter catback exhaust with 2 monster coffee cans in the rear. By slow I meant a stock V6 would beat me off the line QUICKLY. On a very hot day, if you turn on the A/C, the car gets even slower, just wait until summer.

In summary, when you install a catback exhaust on a naturally aspirated engine, you lose low end torque and gain top end HP. But ask yourself just how often do you hit the top end 5500rpm+? Not very often, so it's not very usable power. So I spent $500 on catback, I dumped it, went back to stock exhaust and the car got back to being "quicker". Catback exhaust is very much usable on a forced induction car, but not on a NA engine where the gains are dismal up top.
 

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well my downpipe/2.5 inch piping into dual exhaust helped with my i4 accord ALOT. the airflow is much better and the car passes on the highway much better. my low end also improved. i also have an intake, throttle body spacer and ported intake runners. and im sure those helped also. one mod compliments the other mod.
 

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These last two posts (from "tr-d" and from fLYaZZbRASilenO) highlight that improvements are not done in a "vacuum", but in the real world where they work for or against another modification. On other car forums for other cars, they have it organized into Stage 1, Stage 2, etc...each stage has a set of 3 or 4 mods that must be done at the same time.

Well written....I learned something new today. Thank you.
 

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It depends on the mufflers and how much they reduce back pressure. Back pressure helps the engine develop the low end torque you are missing. You may just need a muffler that doesn't reduce back pressure as much, totally free flowing is great for certain applications, not daily driving.
 

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Roll Tide!
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In summary, when you install a catback exhaust on a naturally aspirated engine, you lose low end torque and gain top end HP. But ask yourself just how often do you hit the top end 5500rpm+? Not very often, so it's not very usable power. So I spent $500 on catback, I dumped it, went back to stock exhaust and the car got back to being "quicker". Catback exhaust is very much usable on a forced induction car, but not on a NA engine where the gains are dismal up top.
That depends on which naturally aspirated engines we are talking about now doesn't it? Not ALL engines perform the same way as the tiny honda engines, and you know it. And not all catbacks are created equally, and even you must know that too. Putting a catback on a I4 or V6 Honda is in not way comparable to putting a catback on a choked down V8 that was de-tuned from the factory to meet the smog nazis, warranty department, and insurance industry expectations.
 

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Discussion Starter · #11 ·
thx for the replies guys... i'm considering at this point to switch back to my stock piping (either no resonator or use the magnaflow res) with the magnaflow mufflers... how do you guys think that would sound/perform?
 

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Discussion Starter · #13 ·
lol thanks for the advice.. I only payed 225 for the catback, and in addition to the power loss my gas milege has also gone down significantly.. I love the sound, but now am torn as there seems to be more cons than pros.. thats why i'm considering stock piping with magnaflow mufflers.. has anyone on here done this? i've seen a clip on youtube with a white 2003 v6 coupe which sounds great but have no idea on the performance..

*gas mileage decrease may be the result of me stepping on it to hear the exhaust and/or revving higher to get to the regular speed i'm used to in the city (now have to rev to 3000 rpm instead of 2500 rpm) lol
 

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But we aren't talking about a V8 here, i fully understand that fact. What are we driving? An I4 or V6 Accord here without a turbo or supercharger. I'm telling you from my experience and the money I needlessly wasted.

"HONDA"

- No other mods, perhaps just an intake + catback -> a slower car
- You have intake path mods like intake manifold spacer + runner, which are torque modes + catback -> OK

I had full Comptech headers + intake + 2.5" catback -> SLOWER THAN STOCK, unless I punch it and go past 5000rpm, but HOW OFTEN do I exercise that??

I spent another $300 changed back to stock piping (because I dumped the stock one the day I installed catback, I was young and dumb) with Comptech axle-back mufflers only ($500) -> WOW, back to the way it was, way quicker off the line.

So I wasted a total of $1300 and I just about went back to stock.
 

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Discussion Starter · #15 ·
so t-rd, if i understand you, you ended up going back to stock piping with the comptech mufflers and regained the lost performance? and if so did you use resonators?
 

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Keep the resonator, you are losing nothing but gaining more sound and possible droning issue when you remove the mid resonator.
 

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Discussion Starter · #17 ·
Problem solved.

hey guys, just as an update, I finally got the exahust figured out. when I had it installed, it was welded on to my stock flange (as the magnaflow flange was cut off by the previous owner whose car was written off). my gas milage dropped drastically, the exhaust was just borderline too loud @ 2500 rpm and the car felt rediculously slow. From a red light I would need to hit around 3000 rpm just to get to normal speed (~50 - 60km/h). on the other hand if i floored it on the highway the car would FLY. Sometimes while driving the exhaust would get much louder, and at one point it stayed loud... like helicopter loud. so went back to the shop, lifted the car while running to see exhaust smoke leaking from the flange weld. turns out the [email protected]$ didn't weld it on at all. so for almost 2 weeks I've been running with basically no exhaust. luckily I didn't get a ticket for the exhaust. anyways, now the exhaust is properly installed and it sounds great, not too loud at all and next to no drone on the highway (if your radio is on you will not hear it). Performance is decent, exhaust tips stick in way too much (I have the hfp lip kit). IMHO, not worth the $600-800 plus install fees that some people would pay for it (granted I payed $225 for the cat back exhaust and $80 for the install).

I'm happy with it, however, I find that just removing both resonators on the stock exhaust is extremely comparable and sounds nice (almost g35-ish, vs. a very slightly deeper sound with the magnaflow) and that only cost me $60. Also, you keep a bit more low-end torque.

Just an FYI for anyone considering the magnaflow exhaust. Thanks again for the replies,

Cheers
 
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