Cat back exhaust question.

2267 Views 24 Replies 7 Participants Last post by Marvin, Jan 21, 2005

Maxwell31

Discussion Starter · Jan 16, 2005

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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Zac

· #3 · Jan 16, 2005

if your more serious about gains go for 2.5 inch piping. i like the stromung best for sound. i have a 2.5 inch vrs with magnaflow muffer and i am very happy with the split between cost, sound and performance.

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Zac

· #6 · Jan 17, 2005

Maxwell31 said:
How much did that set-up cost you and thanks for the input!

VRS sells the 2.5 for $320...I got mine a good bit less from Stemar Motorsports though.

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Zac

· #9 · Jan 18, 2005

2.5sentra03 said:
wow 2.5? isnt that a lil too big? i thought 2.25 would be perfect.

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.

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Zac

· #13 · Jan 19, 2005

caveman said:
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.

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.

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Zac

· #15 · Jan 20, 2005 (Edited)

I understand what you are saying and I had a K&N. Dyno gains are seen with a K&N and especially with the removal of many of the silencers in the (edit: not exhaust, airbox

). The Spec V has a decently well flowing exhaust, but for a real build, bigger piping all around is what is needed. The AEBS header I am going for and 2.5 inch catback will work in harmony. CAIs do give a dyno gain but not as much so as many people are led to believe.

On the 2.4 Cavileer:
*The Iperformance cat back exhaust system outperformed the RK Sport cat back exhaust system by a rather healthy margin.

*The Iperformance system picked up more than 1 1/2 times more peak horsepower and nearly double the peak torque as compared to the RK Sport system.

*The Iperformance system shows almost double the increase in average HP and 1 1/2 times the increase in average torque as compared to the RK Sport system.

*Comparing the two on the basis of dollars spent per peak horsepower gained, the RK Sport system costs $81 per horsepower, while the Iperformance system costs $51 per horsepower.

*The design of both systems is nearly identical, both using mandrel bent pipe and both using Magnaflow brand straight through mufflers. The performance difference being that the 2 1/4 inch pipe can not keep up with the flow requirements of the engine and can not match the results of the 2 1/2 inch pipe.

*Yet again, our testing has shown that 2 1/2 inch is the proper size for any naturally aspirated four cylinder engines and 2 1/4 inch is too small.

*We have demonstrated once more, that there is no loss of mid or low range torque or horsepower when comparing 2 1/4 inch exhaust systems to 2 1/2 inch exhaust systems.

Sadley, I am having problems locating the dyno sheet.

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Zac

· #16 · Jan 20, 2005

I many times reccomend a CAI and catback as much for sound as I do performance. A budget tuner may get a high flow muffler, a header (this would sound horrible), remove the stock air flow silencers, add a high flow cat or downpipe and that would make a huge difference on flow. This is not my goal though. My goal is not autoxing and right now I am in the engine part of my build. Once I am done the engine aspect, I will have the CAI, AEBS header w/ high flow cat which is a huge asset to our cars considering the massive secondaries of the AEBS vs other brands (not to mention dyno sheets have a much nicer curve with this header), a 2.5 inch catback exhaust, balancer shaft removed, crank pulley, jwt stage 1 billet cams, safc2 and dyno tuning, a full auto tranny rebuild from a company called IPT as well as nitrous and a few other mickey mouse odds and ends.

Steve Stemar of Stemar Motorsports has been in the business of working DSMs for about 3 decades and is highly respected; respected enough that I went to him although he is a DSM specialist over Nissan specialists. They are damned good when it comes to making cars fast and reliable and have shown their ability to build and tune cars over the last decade. He was pushing for me to do a 3 inch catback and a T3/T4 turbo system. When I decided against turbocharging, for the build up I wanted he pushed a 2.5 over a 2.25 (especially since they cost the same). I have never been able to dyno a car with the same mods and same exhaust in 2.25 and 2.5 so I have no numbers on our specefic car. IIRC the NISMO is actually 2.36 piping and not 2.25 as many sites claim. I dont know if that information is helpful at all though.

One thing I can say for almost sure is the 2.5 inch piping sounds a lot meaner. A CAI will add a tone to a car that is highly grand. If I had a 2.25 inch exhaust, I would try to get dyno tunes on both. With the time allocation I have though, I highly doubt this will happen.

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Zac

· #20 · Jan 20, 2005

caveman said:
No one could have been working on DSMs for 3 decades. They are only 15 years old.

I'm going to bed.

I suppose I worded that poorly and should have said cars in general.

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Zac

· #21 · Jan 20, 2005

caveman said:
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.

Without a dyno sheet, I cant say how much if any low end is lost. I will on our engine trade some low end for more mid and top for what I am looking for. And considering I got the car 13.9 new, I got a little leeway until my pocketbook meets up with an SRT.

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Zac

· #22 · Jan 20, 2005

Mark said:
Ok, i'm going to just skip over the subject of diameter and ask a good one.....

Is there a huge gain differnece between a custom job and buying a prefabbed one (except for mandrel bends)?

I can't see there being a huge difference.

Do you mean like a name brand vs custom piping? Crush vs Mandrel?

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Zac

· #24 · Jan 20, 2005

Mark said:
I mean I ordered my resonator and muffler off of the web, took it to my local muffler shop (who has done work for me and a fellow 3rd Gen) and he put in custom, non mandrel bent pipe. It goes straight back to the muffler, a very slight bend, but no where to bog down at all.

I doubt their is a huge difference but mandrel bent is generally better than crush bent. The only way to tell is on a dyno. IIRC you have a header so I am going to guess your car is VERY loud, even with the resonator.

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