i have a 95 auto with a injen cai. about a month ago i had my exhaust and piping(2.5) changed up to the cat. every since i have noticed a significant power loss. my acceleration, the pick up time is slowwww, it feels lazy. i have since spoken to many mechanics and they advised that the prob is the exhaust, it's causing too much backpressure which results in the power loss. so i'm thinking about changing the exhaust.
i don't want to spend too much money on an entire catback so i'v decided to go with a magnaflow exhaust, the ones SWA sells.
my question is those running automatics with the magnaflow, have you guys experienced the power loss or the lazy acceleration as i have. i don't want to buy it and have have the same prob, b/c if so i would go back to stock. so help guys!

 

My only mods were Y-pipe and 2.5 in catback (magnaflow)and it works great other then still not having the correct hangars mailed to me but that is another problem I ahve to fix.

One piece of advice would be to reset teh ecu cuz when I got a new muffler put on my car did similar things till it did that. Took it a little to learn. This was on my 3rd gen VG though.

 

That makes absolutely no sense. How can your mechanics say you have too much backpressure? In that case you would've been even slower with your stock exhaust. It sounds like you have some other issue with your car. And by the way if your looking into aftermarket exhausts, most of them are in 2.25" piping which is the same as stock. Going any larger than 2.5 will be doing more harm than good.

 

i think my mechanic ment that the aftermarket exhaust was the cause of the backpressure. furthermore after a month with it i noticed a reasonable power loss in my acceleration. the pick up was very slow. when it was stock i never had such a prob.

 

I'm having a hard time understanding some of the information you have received. So let me see if I have got this straight. You replaced your exhaust from the cat back with 2-1/2" pipe & you upgraded to an aftermarket muffler with a 2-1/2" inlet & outlet to replace your stock muffler? When you upgraded to the larger diameter exhaust pipe did you remove the factory 2-1/4" resonator or leave it on? If you kept the factory resonator intact then the resonator is suspect because it has a smaller diameter then your 2-1/2" exhaust pipe and it could be producing unwanted back pressure in the exhaust system.

If what I have mentioned above is the case I am having a hard time accepting that your aftermarket muffler is more restrictive then the factory muffler. What brand is your aftermarket muffler? Is it a straight through design?

Another thing I would not listen to is the information (Ant96GLE) has given you about your 2-1/2" exhaust pipe doing more harm then good. First off any backpressure in any exhaust system is a bad thing. You do not want back pressure, I don't care what mods you have done to your car. "You do not want back pressure". Smaller exhaust pipe equals more back pressure, end of subject!!!

What I would do is find out if your aftermarket muffler is a straight through design. If it isn't then I would purchase a muffler that is. I would also remove the resonator if it is still on the car, or purchase a resonator that has 2-1/2" diameter to match the diameter of your exhaust pipe. If that doesn't cure your problem then there is something else going on with your vehicle. Another item I suggest purchasing is a Y-pipe. Most of the back pressure in the exhaust system is being produced by the factory Y-pipe. That is why an aftermarket Y-pipe gives such tremendous HP gains on a dyno, it lowers the amount of back pressure.

If anyone wants to debate that larger exhaust pipe will harm performance, I suggest you go to the supercharger/turbo forum & read the thread about 3" exhaust creating more power on the dyno...

 

no power loss or acceleration at all for me

 

Read again, I said anything LARGER than 2.5. I have 2.5 piping all the way back and I havent had a problem. My point is if hes going to buy an aftermarket exhaust, most of them are 2.25 inches in diameter. You can talk about 3" diameter piping on boosted and sprayed cars, thats fine, but remember they're churning out more exhaust gases than a N/A car. So you cant compare the two.

 

 

first off u'r post was very helpful. my question is where is the "factory 2-1/4" resonator " because we changet the piping all the way up the big round thing that's before the cat.
i'm using this pic to show where the piping was changed up to. http://custommaxima.com/CattmanCatBackExhaust.php
in this pic we changet it after the big round thing where the words bpipe are under.
so mabe u can tell me where is the "factory 2-1/4" resonator ".
ths in advance

 

that big round thing is the resonator

 

are you sure

 

There is no way a 2.5" cat back, which from how you describe it is most likely a resonator back, could hurt performance. The reason why a 3" is hurtfull is not because lack of back pressure but because the gasses would travel too slow. The gasses need to travel fast so the engine can breathe better. Anyway I belive you have a bad knock sensor.....cus there is no way in he11 that your 1 month old "cat back" is the problem.

 

Hmm, sounds like you have other problems.

I have a Budget Y-Pipe that is wrapped. Before I wrapped it I noticed a nasty hesitation around 2,500 RPM. After wrapping it, it got better, but every once in a while there is still a slight hesitation. I think it's because I am still running a stock bpipe and muffler, too much back pressure. Flows great through the ypipe and when it reaches the bpipe it probably backs up a little bit, that's my guess.

All I can say is try resetting the ECU. I do plan to get a Magnaflow though, they sound great.

 

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Ant is right....you don't want any larger than 2.5" on N/A car. It will just do you more harm than good. However, on blown...you want that large of piping. Like he said, two totally different things.

Also, you cannot possibly tell me that with 2.5" exhaust except for the 2.25" resonator, that this 1/4" piece for only about a foot and a half is causing the problem. I mean, I kept the 2.25" resonator(stock) on, replaced the rest of the b-pipe with 2.5" pipe, and got 5th gen dual pipe muffler. I saw a pretty significant increase in power....enough to tell(5 or so hp at the crank)....and that is before I got my y-pipe on. When I got my y-pipe on, I could really tell that it was breathing better.

Anyway, I also think it might be a knock sensor or something, but not your muffler or your exhaust causing the problem.

 

well all this talk about the knock sensor being the prob is making me wonder if that's the case. about two weeks ago my CEL came on, but after a few days with it, i had to disconnect my battery, and when i connected it back the CEL came off. Do u guys think that it was the knock sensor or one of the O2 sensors?