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Cat back exhaust question.

2280 Views 24 Replies 7 Participants Last post by  Marvin
Hi all, have a problem and hope I can get some help.

I want to get a Cat-back exhaust but don't know which one to pick up.

They have ones from Greedy, Nismo (a tad on the expensive side), Magnaflow, Vibrant (Duel tipped, three inch outlets, not bad, looks stock from afar).

Anybody have any suggestions which would give me the most gains? I am kind of pushing towards Magnaflow but still am undecided.

Any help would be great and thanks in advance!
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NickZac said:
No. If anything, 2.25 is too small. When tested on a 2.4 liter engine, the 2.5 yielded much higher gains than the 2.25. Especially if you are building your engine, 2.5 is a must. If you are turbocharging, then you should go 3.
Who tested this? I ask because on a DSM, a 2.5" exhaust is good for 11s 1/4s. 3" is going to be overkill on a 4cyl street aplication turbo or not. A lot of people do it, but it isn't really needed. It is generally only needed for track use and large turbo's. The larger the exhaust, the more low end you will loose.

I just can't see a na 2.5l needing all that exhaust. I think it would be interesting to see a dyno with the stock exhaust compared to the stock exhaust with a high flow cat and streight through magnaflow muffler. The stock muffler looks like a huge truck muffler. Anyone see a cutout? I bet the exhaust is bounced back 3 times before it exits the muffler.
all star hybrid said:
The system (part# 15764) that MagnaFlow offers is infact a 2.25" setup, not 2.5" as mentioned.
That's more like it.

Also, unless you are going to do head work and a cam, you might never get all the use out of that larger exhaust. Even on a larger displacement mustang and exhaust it not a huge power gain. It is a setup for intake manifold, heads, and cam.

If all you are going to do is a CAI, header, and exhaust, you might just want to stick with the stock exhaust size and get a high flow cat and a free flowing muffler. If you are going to do some more work, then ya, you will want that larger exhaust, but your engine is going to have to pump out more gas then stock to need a larger exhaust.
NickZac said:
2.4 liter Cavileer and gains were about 4 WHP difference. I'll see if I can find the dyno sheets. I dont know any DSM guys running 11s with a 2.5 inch exhaust. My buddy was running around 400WHP and he was 3 inch piping all the way. DSMs need to get rid of back pressure. Some Supras run 5 inch piping. We do not lose low end on a 2.5 inch piping IIRC. The Magnaflow is 2.25, the VRS I was referring to with the Magnaflow muffler is whatever size you choose.
11s might have been pushing it. I'm pretty sure I read about a new record on 2.5" exhaust, but I can't find the link. mid 12s are comon tho.

Also, DSMs don't need to get rid of back pressure. Larger exhaust are needed for more boost. I tuned a low budget talon once and used the stock exhaust with a test pipe and magnaflow turbo muffler. At 13psi and a junk yard IC upgrade, I was able to break the tires free from a roll and spin all the way through 2nd. The car was way faster then stock and it didn't take a larger exhaust. I took it to the track once before the IC install against a 13s mustang. I lost due to FWD traction and mustang hookup. I couldn't catch up in time, but I started to pull readly hard before the end of the 1/4. The 1/4 time was embarasing so I'll leave that out, but it was at 99MPH and I had a LOUSY 0-60'. The IC prolly gave another 30HP, but also a much wider power band. It was a blast on the street, I could just never hook up with the non lsd FWD crap. Point being, the car was way-way faster then stock, and it didn't take a larger exhaust.

As far as not loosing torque on low end with a larger exhaust. It is comon with every other 4cyl car out there. Not sure why the spec v would be any different. Unless a driver likes hanging out at higher RPMs all day long to stay in the power zone, a header with no cat, high flow main cat, and high flow muffler would prolly be better the a larger cat back with the stock cat in place. The muffler and high flow cat will cost less if ya shop around.

Look, the auto after market was a 5 billion dollar buisness last year. A LOT of products get pushed and too many people think that CAIs and larger exhaust are the be all of must have performance parts. Like I said before, the engine needs to be pushing way more gas then stock to really get a full benifit from a larger exhaust. The only way to do that on the spec v is forced induction or head work and cam.

When you read that a cat back gives 4hp on a caviler or any car for that matter, you gotta ask yourself something. How much of that is having a much better flowing muffler and how much is due to the size of the exhaust and then how does the dyno look compared to a stock run? Just because a part gives 4HP doesn't mean that something was lost to get it and peak HP is not always a gain and that's what race shops advertize. Peak HP gains. So out of that 4HP, is it worth to spend $350 or more on a cat back when you can just go to a exhaust shop and get a nicer muffler installed for around $100. Maybe you only get 2-3HP out of it, but how much is that extra 1-2HP worth? You could prolly spend another 150 for a high flow cat and get more gain then just the cat back because stock cats are very restrictive.

I'm not saying, don't buy cat backs, it's not worth it, but when you tune a car, any car. You gotta have a game plan. You gotta know what your budget is, you gotta know what you want to get out of the car and what you want to do with the car.

All I see on this list is buy a CAI and cat back first thing. It's a must. Well, if your going to autox, it would be better to spend your money on suspention and if your going to drag race, tires and motor mounts and a clutch. It just seems like the first thing people wanna do on any car first thing is to get a CAI and exhaust. On any forum, not just this one.

I was talking with a mustang buddy of mine today. We've both been around the block and we both learned a LOT over the years. Anyway, the topic of CAIs came out some how and he had a LOT of trouble with the one that came on his car. It screwed with his maf, and then he tried to have it calibrated right. It cost him a lot of money and he never got it working right. I guess Fords mafs are touchty to the air not comming in just perfect. He put a drop in K&N using the stock air box and his car ran a lot better. He then told me people are running 11s 1/4 with the stock air box.

I got a lot of crap on this list telling me a K&N in the stock air box didn't do much if anything on the spec v. I noticed a nice gain with just a K&N. More then I expected. The surface area of the stock filter is large, the car has a large non restrictive and short intake path to the TB. The only extra gain from a CAI is going to come from a cone filter having more surface area then the stock air filter. Depending on who you ask (I've asked engineers), a metal intake is going to heat up while plastic keeps the intake charge cooler. Also, if it isn't a real CAI system, it pulls hot air from the engine bay.

This turned in to a huge rant, but just think before you jump on the CAI and catback wagon. Ask yourself is it really woth the money. Will it give more HP then a just a K&N and new muffler? Maybe a few, but is it worth the hundreds of extra dollars when you could buy real mods. The header with no cat is the best mod I've seen for this car yet. I don't doubt for a second that it can give 12HP without giving anything up. You could prolly get another 5-8HP by replacing the main cat with a magnaflow high flow cat and they only cost about $100. Maybe $150 installed. If you can find a shop to do it for ya. Cause there are laws about replacing cats. If your factory one some how gets dammaged tho, you can get a replacement legaly. Other then that your car has to be old enough and have enough miles on it to just be able to replace the cat. It's common enough for a rock or sledge hammer to dammage a exhaust system tho.

Anyway, I don't want to start a huge fight, just tring to educate and maybe help out with why you do or don't want to just run out and buy parts just because you can. I've seen it many times. Too many parts and not enough tunning. If you really want to tune a spec v, talk with a old shool tunner. There has to be at least one in your family. Listen to what they have to say. They might have 30+ years under their belt and they could tell you a thing or two about what will work and what won't work. Things have changed over the years, but engines do the exact same thing the did since they were invented. They are just better now days. I also recomend watching the old guys on speed. Two guys garage. They don't talk all gay and they are the most realistic car show on TV. I still learn new stuff from them. Some days they work on older cars and other days they are working on brand new cars. Either way, you should learn something new every time you watch the show.
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Common NickZak, you can't say 2.5" is best for any 4cyl. I've personly seen low end loss from larger exhaust. My brother n law installed a larger exhaust on a escort GT. I drove it afterwards and it bogged for a bit before it started to pick up. I got a little bit of low end loss on my turbo car with a full 2.5". The loss is so short and the overall gain is much more, that it doesn't matter, but the loss is so short because the turbo spools. It would be longer if it were NA.

I'm not saying that a larger exhaust is never the right choice, because it can be. I wasn't suggesting that you don't get a larger exhaust or telling you how to tune your car. However, like you said yourself, you gotta be working on a real build up. Not every spec V owner on this list is going to be doing major build ups. Most of them will probably be doing bolt on mods. They are worth doing too. They free up some HP and raise the MPG. I was just suggesting that the cost to HP ratio would probably be better to get a K&N drop in, header with no cat, high flow main cat, and muffler for a bolt on build up only. If you arn't going to touch the engine, then what's the point on going with a larger exhaust size? I would personly spend the rest of the money on other things cause for bolt ons only, the extra few possible HP is gonna cost hundreds. You could save it for new tires cause everyone is bitching about the stockers. That and the stereo. Or hell, buy your date something.

Last but not least, if your build up and car cost get close to the cost of a srt-4, then um, you must really love Nissan.

To answer the original question, I really like magnaflow for a 4cyl car. They look and sound great and they last.
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No one could have been working on DSMs for 3 decades. They are only 15 years old.

I'm going to bed.
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