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Discussion Starter · #1 ·
I originally posted this under another post, but then felt I was hijacking that post, so I made it a post of its own. I started this post to get some feedback and experiences from other members and to share my experiences thus far.

I had, at one time, an aftermarket 3" CAT Back Exhaust, CAI and TBS. I have since removed all but the TBS. The TBS didn't add any HP, but that's not what it's desiged to do. It did give a bit more low end/mid range torque, and arguably better gas mileage. I did see a noticeable increase in low end and mid range torque after installing the TBS, but it was added last and I had felt a noticeable loss in low end torque after installing the 3" exhaust system.

I originally removed the exhaust because the sound was a bit louder than I prefer, and am currently running the stock exhaust. I felt an additional increase in low end after reinstalling the stock exhaust, and also saw an increase in gas mileage, although it was minimal. I feel a 3" system is just to big for this engine and the low end suffers because of it.

Last weekend I also removed the CAI and replaced it with the stock air box because I have an appointment on Monday to have the trailer tow recall done and my dealership is a PITA about aftermarket parts. They even told me adding the K&N filter would foul the MAF Sensor because it would get lint in it with the K&N filter! So I figured I'd put most of it back to stock to get the Recall done. I'm thinking of shopping for a new service depatment as well as I'm tired of their condesending attitude toward mods! It is my truck afterall, I bought it not them!

Anyway, the point of this all is that the only mod on my truck at the moment is the TBS, which I cleverly am trying to disguise with black electrical tape. I have also seen an additional increase in MPG with replacing the CAI with the stock air box and stock Nissan Air Filter.

These increases are not great, it jumped from 16 to 16.5 mpg since replacing the aftermarket exhaust and CAI with the stock parts, and I'm sure there has been a drop in HP because of it, but that's not been that noticable either!

While I'm not an engineer, I do have a theory as to why my gas mileage increased instead of decreased with the replacement of the aftermarket parts with stock parts. All the aftermarket parts are designed to flow more air easier. With the increased amount of air, there needs to be an increase in the amount of fuel to maintain the proper fuel air mix, and being as this is controlled by the computer, I feel the computer is dumping more fuel into the mix to keep the right ratios. And we all know that more air and more fuel equals more HP, so it's pretty obvious to me why my mileage suffered with the aftermarket parts. Throw in the density of the cold winter air, and the lousy winter fuels, and it just compounds the problem.

So, I think for the rest of winter I'll be running my truck as is. This summer I may experiment a bit more and see if the aftermarket parts improve gas mileage with the warmer weather. I may also try a new aftermarket exhaust at that time as well. JBA has announced a new CAT Back system that uses the stock pipe sizes mated to a free flowing "Y" pipe and muffler. Hopefully this combination will allow a more free flowing exhaust without the inherent loss of low end torque. At the moment though I think I'll leave it as is because for the first time this winter, I'm getting consistant gas mileage above 16 mpg.

With the aftermarket parts my gas mileage never seemed very consistant. It would fluctuate between 16 and 16.5 during my daily commute to work and back, but then drop to 15.8 over the weekend when I was running errands around town. This past week, it's climbed to 16.5 and has been consistant for the past three days, even with the pure city driving I do running errands on the weekends.

Sorry for the long post, but thought I'd share my experiences with aftermarket parts and the effects I have personally seen with how they have effected my gas mileage. I have never had my truck on a dyno, so I have no idea how much power was gained with the mods, or how much was lost with their removal, but my goal was to improve gas mileage. Those who are looking for more power will definately get what they are looking for with the aftermarket parts, those (like myself) who are looking for improved economy, may be better off spending their money on fuel! Just my 2 cents!

Does anyone else have any experiences with aftermarket performance mods and the effects on their gas mileage? I'm curious if others have noticed the same type of results?
 

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i got a 05 nismo KC auto trans, i was getting crappy mpg before 4000 like around 13.5 average, after that it seemed like the mpg fairy gave more mpg i was averaging 16-17, i reciently purchased the a airraid cai and poweraid tbs,i can feel the power i gained, before i couldnt spin the tires when taking off,now i can, and now when it rains at 40 mph i can break loose, before that i couldnt, my meter is saying im getting 15 but i think its gonna take some time for the computer to relearn my driving habits. and the sound from my intake and tbs is nice you can hear it suck in the air!
 

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05 NISMO 4x4, that sucks about all the aftermarket parts. Since I'm planning on lifting the s#!t out of my truck and throwing in some taller tires, I'll need whatever extra power I can get. Hmmm, I wonder how crappy my gas mileage would be after all that!
 

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Discussion Starter · #4 ·
It wasn't all that bad! We're talking less than 1 MPG in my case! With a lift and bigger tires, you'll probably see a bit more of a loss. I think the thing to remember when going to larger tires is the change in final drive ratio. You really have to compensate for that when figuring your gas mileage, or you'll really be disappointed!
 

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hey 05_NISMO_4X4,
I got a question for you, i notice you never talk about getting headers.is there a reason, i never here of people getting headers for new vehicles, im set to get a free set of headers, but i was wonder if it messes with the longevity of the engine? what do you think? thanks for your help
 

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Discussion Starter · #6 ·
pablo,

I've often had the same question! I've never had headers on a vehicle before, so I really don't know how it would effect the longevity of the engine. I would think that if they are good quality and properly installed they should last as long as the original exhaust manifolds. Headers are getting a little to close to the heart of the vehicle for me. This is one of those things that I feel crosses the line from shade tree mechanic to the professional! I don't know that I'm confident enough in my abilities to install a set of headers myself.

Are you gettng the JBA headers? If so, I'm really looking forward to your review! Was it your truck they used as a test bed for the JBA CAT back exhaust as well? I bet the combination of the two will be awesome!

I'm very interested in the new Exhaust JBA is offereing, I heard they made a change to the muffler, any insight into what the change was? From what I understand it initially heard it was a straight through design, which kind of concerned me, especially after having a straight through muffler on the Banks exhaust I had. Hopefully they went with a nice quiet baffled muffler that retains all the low end torque while giving a nice increase in HP! That's my idea of a perfect system!
 

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yeah im gonna get a set of JBA headers and exhaust, when i dropped off my truck they were very professinal, when i picked it up all stock stuff was put back on, the guy down there just said nissan used a old type of exhaust manifold and the gains would be good, hopefully ill get these put on in the next few weeks, if u go to their website it looks like there on top of their game. but im pretty happy with just the airraid intake and the tbs, i feel alot more low end power, do you hear the sound of the intake sucking in that air? i love it
 

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Man, you guys are making me jealous. I wish I had one already. As far as headers go, I don't think anything detrimental will happen if professionally installed. I have yet to put headers on any vehicle (would have put it on my slammed Hardbody, but I'm too low!), but if they are good, which it looks like the JBAs will be, I plan on putting them on my truck.

I was afraid of them at first for the same reason that its so close to the heart, but its not like a S/C or turbo. The way I see it, its a bolt on that helps route spent gases more efficiently. I don't see how that would decrease the life of the truck any differently than an intake or exhaust.
 

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Discussion Starter · #9 ·
I have the stock air box on it at the moment, I brought it to the dealership today for the Trialer Tow recall, and they're a real PITA about aftermarket mods! They even gave me crap about the K&N Filter I had in the stock air box! I'll probably be putting the CAI back in a a couple of weeks. I'm running my own non-scientific MPG tests at the moment, and want to give it a couple of weeks with just the TBS before I add the CAI back to the mix! I missit though!
 

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The only vehicle I ever put headers on was a 1964 Ttiumph TR-4. I did not keep it long enough to tell if there were any long term effects from the header. What I did notice
was that it changed the sound of the exhaust.

I loved the TR-4 exhaust before the change, but it gave the thing a hollow (tinny??)
sound after that. I always regretted doing it. Our trucks have a kind of throaty
sound as they are, I would hate to mess that up.

OkieScot
 

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Discussion Starter · #11 ·
The only thing that would concern me with the headers was if they were not install correctly and there was a leak at the manifold it could cause damage to the exhaust valves, but as Pimp pointed out, if professionally installed, they should add to the effeciency of the engine!

Like Okie, I think my biggest concern would be what it would do to the sound. I prefer a quiet subtle sound over a loud overbearing sound! I like what the AirAid CAI did, subtle but noticiable under heavy throttle. But I regretted the Banks exhaust for waht it did. The drone in the cab was way to obtrusive. When the sound causes you to try and alter your driving habits to try and suppress the noise, that's too much. I didn't like my truck when that system was on it.

The stock exhaust already has a nice subtle rumble to it. I'd like to keep that sound while gaining a little more HP, and the JBA System sounds like it may be the system to fit my needs, but that still remains to be seen. If the headers added more noise, I'm afraid I'd be back where I was with the Banks, and not liking my truck! So, hopefully, JBA did their homework, and have a couple new products that will add to the performance while not detracting from the driving experience!
 

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I had a '70 Mustang that I set up to haul a$$. Headers, Edelbrach intake, Holley four barrel, etc, etc, etc.

The headers didn't change the sound as much as the exhaust. Dual 3 inch pipes into glass paks. AWESOME!!!

The only reason I would not put headers on my truck is if they won't pass smog inspection. Living in California, my K&N CAI won't pass visual smog inspection. They couldn't care less if it makes it run cleaner or not. Very few headers are smog legal in Cali. I'm wondering whether a TBS is smog legal here. I will find out in 3 years.
 

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Food for thought guys...

If increased airflow also increases fuel consumption, then would decreased airflow decrease fuel consumption? Such as a dirty or blocked air filter. I've always heard you want good airflow to get good gas mileage.

After reading your posts, I decided not to get a CAI now but just a K&N filter. I installed it today. First my mileage dropped to 15 and I thought I'd made a big mistake, then after a few miles it went back up 19. I reset my trip computer and then my mileage jumped up to 28, then 24, and leveled out at 21. That was around town. I was getting 18-19 before I installed it. Maybe alittle extra air helps but too much doesn't. As far as mileage goes.
 

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05_NISMO_4X4, I am in the middle of doing alittle of my on MPG work. I was thinking of getting a CAI but after reading your post I am not sure. I just would like to get a little better gas milage with my truck. Right now I am getting about 14.4-14.8 so far with my math but I am going to do a few more fill ups first.

Nismo54, you talked about just getting a K&N filter. Can someone who knows this refer me to the best filter I can get for my 05 crew cab le? If I can get a little better MGP for less money than a CAI I will jump at it. I read a few posts in other places about K&N filters being bad :?: Can someone recommend some. Thank you. (if it can be bought at any local autozone, advanced auto parts the better)
 

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Discussion Starter · #15 ·
Don't panic just yet! There are some variables that I have no control over that probably have an impact on my gas mileage! Weather being the biggest!

I'm currently running my truck with the stock air box and stock Nissan paper filter. For the past week and a half I have averaged 16.6 MPG. On wednesday I'll probably fill up again and switch to the K&N filter and run that for two tanks to see if there is any change. Then I'll switch back to the AirAid Intake and run another two tanks.

My gas mileage was very unstable with the Banks exhaust and AirAid CAI on my truck, but then the weather was fluctuating between sub freezing temps and balmy low 60's temps! I know cold air is denser then warm air (which is why warm air rises), and a cold engine will run richer than one at operating temp. My commute is less than 30 minutes in the morning and about 40 minutes in the afternoon (due to traffic) so those variable impact gas mileage quite a bit.

I think that as the weather continues to warm, I will see much better gas mileage out of the CAI than I did during the really cold temps. I know they call it a cold air intake, but I think sub frezing temps are a bit more than what they mean! Again, all this is relative, because even though my gas mileage was not as stable with the CAI and the 3" Exhaust (which I think is too big for our trucks) on the up side of the swing, I was getting 16.8 MPG! But when it dropped, it would drop a full mile per gallon to 15.8 MPG. So, at the present, I feel my stable 16.6 MPG is netting me a better return that the swings between 15.8 to 16.8 MPG!

I want to add a new exhaust (but with smaller pipes) this spring, and I think I'll see an overall increase with this combination and the warmer temps! Keep in mind, none of this has any thing to do with performance! I was modding my truck strictly in an attempt to increase gas mileage! Hope this helps some!
 

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I've been using K&N airfilters in my other vehicles for over 10 years without any problems. One problems could be if you overoil it and the oil get to the MAS. One reason I went with the filter now instead of the CAI (besides price) is my dealership is also a PITA about mods. Can switch out the filter alot easier before I go in for service. You can find the K&N and AirHog at most auto parts stores. Got mine for $36.

After looking at the Y-Pipe and that huge muffler everyone has been talking about seems like the exhaust is the biggest restriction. Hope one of those the new exhaust systems prove to help. I rather have gas mileage over HP.
 

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Discussion Starter · #17 ·
The new JBA exhaust is sounding very promising! Hopefully we'll have a review and some specs shortly. From what I've seen and heard thus far, JBA did their homework and a lot of testing, rather than just rush a big bore exhaust to the market. I'm waiting on verifications of the specs, but I was initially told the pipe size from the CATs to the Y were 2", which are the same as the stock size. Those feed a 2" in 2.5" out Y pipe and the rest of the system, including the muffler, is 2.5" with a 3" polished stainless steel tip.

The muffler is also stainless steel. The combination of stock pipe size to the Y and a free flowing Y and Muffler (stock pipe size is 2.25" after the restrictive stock Y) should increase flow which should increase HP and gas mileage, but not sacrifice the low end torque. Here's a link to a picture of the JBA system:

http://www.clubfrontier.org/modules.php?name=Forums&file=viewtopic&t=997
 

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Wow this a lot of great info. I almost ordered a CAI and still might but will probably end up with the Volant box unit. Hopefully flow better than stock but still keep the mileage somewhere near where it is at. Mine has stayed at 16.8 for over a week now with mixed driving to and from work. Mine is completely stock and I have about 1500 miles on it.

I am sure the headers will drop your gas mileage much like the Banks exhaust system stated above because the of increased flow. Stock manifolds on most cars and trucks are pretty restrictive.

The headers should increase the longevity of the engine. I had a 2003 Cobra with headers. All I ever read on Mustang forums was that the free flowing exhaust gases would reduce some of the pressures within the engine itself therefore making it last longer. I too am no engineer just stating what I read about mustangs.
 

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Discussion Starter · #19 ·
I read an article about exhaust recently and it emphisized that flow was more important than size when it comes to exhaust. The point they were trying to make was that an exhaust system with the proper size pipes (i.e. closer to that of the exhaust manifold, CATs. etc) would flow better than a system that dumped into a large diameter pipe. This makes sense in that headers are designed so that exhaust from each cylinder acts to create velocity as the gases exit the manifold. I.e. no two exhaust strokes will reach the collector at the same time, but in an equally spaced order to create a smooth flow.

The same can be said for the exhaust system's pipe size. If the outlet from the exhaust manifold and CAT is 2" and it's just being dumped into a 3" pipe, there is no flow to keep the gases moving. The increase in diameter will actually stifle the flow of exhaust gases because the velocity is lost. I feel this is why I saw a loss of gas mileage with the Banks system, especially in city driving! I do about 40% highway and 60% city driving during my daily commute. On the highway, the engine was much more effecient mainly because there was much more exhaust being created. But, during city driving it really suffered! Thus the flucuation I experienced.

The stock Frontier Exhaust system is 2" pipe to the pitifullly restrictive Y (if you can even call it that, as it's actually two 2" pipes crimped and stuffed into one 2.25" pipe!) with a 2.25" pipe going to a resctictive muffler then out the tail pipe.

Before JBA announced they were coming out with a new system, I was contemplating having a custom exhaust shop fabricate me a system that would consist of 2" pipes from the CATS to a free flowing Y (MagnaFlow makes one that's dual 2" input/Single 2.5" output) then run 2.5" pipes to a free flowing baffled muffler, and out the back to a 3" tip. I came up with these specs after consulting several knowledgeable people at local exhaust shops and doing a good bit of research on the web. I was just about to order the parts when I saw a post about the JBA system. The specs I came up with are pretty much the same specs JBA is using on their new Evol Exhaust for the Frontiers. By maintaining as close to stock pipe size with less restrictions, the exhaust should flow better because it will maintain the velocity that helps reduce back pressure and help draw the exhaust gases from the manifolds out the back. This essentially makes the engine work more effecinetly and should, in theory, increase gas mileage.

I was getting 18+ miles per gallon with my F-150 that had the Gibson CAT back exhaust on it. And that was with a 4.6L V8! It had 2.5" pipes to the Y and then 3" pipes from the Y back through the Muffler. There was no loss of low end torque and the sound was very mellow. If I can hit 18 MPG with this truck, I'd be thrilled! I also think the right exhaust system will enhance gas mileage, the goal now is to find that system!
 

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I was thinking of putting the gibson exhaust on my 2002 s/c I already have the airaid
on but reading your replys I am not sure if I should order it what do you think I should do?
 
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