Gibson Exhaust. Torque loss?

[GreenEyez]

Hey guys I've been around the website for awhile before I finally became a member and now I've recently started becoming or trying to atleast active. I'm looking into one of 2 things for my 2003 x xlt 4x4. Either a Gibson unit I.e http://gibsonexhaustdirect.com/product.php?productid=3725 or a flowmaster 50 (just the muffler I think they don't make cat back units for the 4.0.) If I just got the muffler I was going to look at some custom tubing so I could get the side exit look I wanted with a nice tip. Now Since I've wasted enough time my actual question was. Would the big 2.5 inch gibson cat back give me significant torque loss. I'm not sure how it would lose or gain torque I'm not mech savy. Any help or ideas would be great thanks.

 

[CALDWELL]

The TQ isnt " lost "... the better phrase would be to say that the TQ is just shifted in the power band lol...

by increasing to 2.5'' exhaust, you are reducing back pressure, which helps free up the exhaust flow. The 4.0 power is really in the low end of the RPM range. by reducing the back pressure in the exhaust you lose the low end TQ grunt that the 4.0 has, but now with every action there is a reaction.

Since you have eliminated some of the back pressure in the exhaust. the real gains from the exhaust will shine in the mid to top end of the RPM range. the stock 4.0 will pull hard until about 4500-4700 RPM before the power starts to fade off. with a 2.5'' CBE ( Cat Back Exhaust ) your X will pull harder and higher in the RPM into the ball park of 5500-5700 RPM

simply put, you lose Low End TQ but you gain Top End TQ + HP... I hope this makes sense...


** numbers I posted, are from my own experience with my former 03' 4.0 - K&N INTAKE / CUSTOM FM 40 SERIES EXHAUST

 

[GreenEyez]

Hmmm I try not to rev that high all the time unless I'm messing around gas is expensive enough. If I went with a flowmaster 50 and new piping after the muffler to the tip would the tq relocation be minimized?

 

[CALDWELL]

automatically when you talk about 2.5'' pipe, your going to lose back pressure, and lose a little bit of low end TQ. It's not a drastic amount thats lost, but it is noticeable...

the best way to combat the loss of low end TQ, is to buy an Intake. I did the exhaust first on my X, then installed the intake, and i did gain a little bit of the low end grunt back.

 

[GreenEyez]

The only reason I'd run the new tubing is for the side exit but I might just bite the bullet and go with the regular exit and tip it. Yea I planned on doing an intake or at least airbox mod, Though I keep seeing all these snorkel x's and they look so damn good. A snorkel has to be good when zombie outbreak happens.

 

[CALDWELL]

right now i just have a magnaflow muffler, and a tip right now. i like the side exit ( 45 degree ) myself, and this is what mine currently looks like...

I had the very last bend of the stock exhaust cut ( where it makes the final turn to exit out the rear ) so i could have the side exit look...

this would be an exhaust upgrade option if you do not want to upgrade pipe size...

 

[GreenEyez]

That;s exactly what I want hopefully keep the pipe size down so I can keep that low end torque. How much fab work do you think it would run to get a setup like that. It seems like you needed to increase the pipe size before and after the muffler. I keep hearing flowmaster has less or a torque loss than a magnaflow muffler or is it barley noticeable and just whichever I'd rather run.

 

[CALDWELL]

i took my X to my local exhaust shop. my truck was up on the lift, and back down in 20 minutes... really easy for any exhaust shop, just depends on how much they charge, and what your willing to pay...

they did make the factory pipe bigger on both ends of the muffler yes. I bought the muffler 2.5'' inlet / outlet so that i could upgrade the piping later.

Magnaflow mufflers are a straight thru design, while the flowmasters have specific baffles within the muffler. they both flow better then stock either way. you can feel the slightest amount of TQ loss in the " low end ", but nothing like running 2.5'' pipe. after all you are freeing up the exhaust flow...

really it comes down to which muffler you like better...

 

[rhauf]

better flowing exhaust DOES NOT reduce torque. this is the stupidest myth ever.

exhaust back pressure is a bad thing, at any rpm, all the time, no matter what.

 

[CALDWELL]

I never said that you completely lose torque.

If people were to lose HP / TQ doing mods, then we would all be driving factory spec vehicles. that would just be boring lol

 

[rhauf]

I never said that you completely lose torque.

If people were to lose HP / TQ doing mods, then we would all be driving factory spec vehicles. that would just be boring lol

no, i meant that there isn't any torque lost whatsoever. as in at any rpm, there is either no change in power, or there is a gain in power.

this of course is not true with many mods, like cylinder head changes, cam changes, intake changes etc... but with exhaust, the more of it you can get out of the cylinder the better. the only thing better than a 100% free flowing exhaust system, is an exhaust system with greater than 100% flow (exhaust scavenging)..... which actually sucks the exhaust out of the next cylinder to breathe using the energy from the previous cylinder.

 

[CALDWELL]

again im not saying that there is a loss in TQ...

My thoughts, and info are from my own personal experience with my former 2003, and with my current 2005...

in overall power there absolultey is a gain in HP / TQ numbers, but with an upgraded exhaust on a 3rd gen X... My X just didnt have the same low end grunt off the line as factory, but the TQ curve lasted longer in the top end before dropping off...

i think most members will agree with me, and thats all im trying to explain to the OP...

also i would just like to comment that yes " back pressure " can be bad, but is also required for a N/A vehicle to a certain point... I think your previous statement would be better applied to a turbo application...

 

[Ronin8002]

Mostly I drive 3500 RPM and below. I didn't perceive any major shift in the torque curve of my truck when I installed the Gibson catback. I am sure it did shift a bit just due to the physics but the difference I felt as a driver was very slight. That might have been because I did the intake/throttle body gasket mods beforehand. All I know is going up hills in 5th gear/overdrive at 55-75mph used to be harder for my truck and it doesn't lug as much now.

It does sound good and definitely won't rust though...I am putting it on a lift today so I will finally have a chance to take good pics and get a video with sound

 

[GreenEyez]

i normally don't go above 2200 unless im trying to get off the line quick. Cad did you have to bring in any other parts other than the muffler and the tip when you brought it to the shop? Guess it's now just up to deciding which I'd prefer.

 

[rhauf]

again im not saying that there is a loss in TQ...

My thoughts, and info are from my own personal experience with my former 2003, and with my current 2005...

in overall power there absolultey is a gain in HP / TQ numbers, but with an upgraded exhaust on a 3rd gen X... My X just didnt have the same low end grunt off the line as factory, but the TQ curve lasted longer in the top end before dropping off...

i think most members will agree with me, and thats all im trying to explain to the OP...

also i would just like to comment that yes " back pressure " can be bad, but is also required for a N/A vehicle to a certain point... I think your previous statement would be better applied to a turbo application...

????? so you said you don't loose torque, then you say you lost low end torque? i'm trying to say that, at every RPM, there will be no change, or gain, in torque.

the only possible scenario for a loss in performance by an exhaust flow increase would be it increased the VE of the engine enough to throw off the fuel map of the ECU, in which case it would need a reprogram.

and i think a naturally aspirated vehicle is where exhaust flow is most important, since the only thing bringing air into the engine is atmospheric pressure, the more exhaust you can get out of the cylinders each cycle the better. a fresh fuel/air charge will give more power than one diluted with worthless exhaust air. and a good exhaust system will allow more to flow out (or in some cases even suck it out via scavenging)

and yes, i realize most members on this forum will agree with you that back pressure gives low rpm "grunt", however, they are all wrong. it's a very popular myth, but that doesn't make it accurate. i think some of the reason people feel like their engine is working harder at low rpm's with a free-flowing exhaust system, is an illusion created by the change in sound of the engine, it gets louder and drones more so it's more apparent that it is bogging down than it would be with quiet stock exhaust. (it just appears to be struggling more)

 

[Ronin8002]

Video clip of the gibson catback in post #9 of this thread:

http://www.explorerforum.com/forums/showthread.php?p=2492418#post2492418

If you are interested in just the muffler instead of the whole system, the gibson part number is: 788500S