Exhaust set up!

[Jeepersteve71]

Let's see your exhaust set up! Might be a good discussion for anyone looking to upgrade. We bought our Borla cat back kit for our LJ for $50 on craigslist. Fit like a glove, improved mileage and more rumble but not to much. It was exactly what we were looking for. I'm debating on cutting the pipe right over the rear axle and welding a new exhaust tip on. This would help with ground clearance and I wouldn't have to stare at the dirty pipe coming out of the back all the time lol. Has anyone ever done this, pics, pros/cons?

 

[Jeepersteve71]

This is what I was thinking. Somewhere along the lines of this.

 

[fljeeper]

That is interesting, but buying the JK that the exhaust fits might be expensive!

 

[Jeepersteve71]

That is interesting, but buying the JK that the exhaust fits might be expensive!

Ha! I don't think I'll be buying another JK anytime soon. It was more to post as an idea.

 

[Chris]

I've seen this done on TJs and I know someone here has it done, just can't remember who. Hopefully they'll see this!

I think it would look good though if you do it as you're describing and weld on a new tip.

 

[Jerry Bransford]

Great exhaust but don't believe for a second that it improved your mpg.

 

[Jeepersteve71]

Great exhaust but don't believe for a second that it improved your mpg.

The muffler is shorter than the stock one. It pushes air a lot faster. I'd like to get a cool air intake as well. It doesn't dramatically increase it but it did increase it by 1-2 mpg depending on weather conditions, how far I drive, etc.

 

[Jerry Bransford]

"1-2 mpg" would indeed be considered very dramatic. And a cold air intake won't help either. They do in theory but not in reality. Really. Don't believe all the ads for CAIs, they're written to sell product. And when you reduce exhaust restriction with a shorter or larger diameter muffler, exhaust velocity actually decreases.

It just isn't easy to improve mpg any more so long as everything is working as designed. If it were, the automotive manufacturers wouldn't be fighting for every tenth of a mpg, and they are. That's why Jeep had to give up on the 4.0L engine and go with the V6 for the JK, they had wrung all of the mpg out of the 4.0L they could.

 

[Jeepersteve71]

"1-2 mpg" would indeed be considered very dramatic. And a cold air intake won't help either. They do in theory but not in reality. Really. Don't believe all the ads for CAIs, they're written to sell product.

It just isn't easy to improve mpg any more so long as everything is working as designed. If it were, the automotive manufacturers wouldn't be fighting for every tenth of a mpg, and they are. That's why Jeep had to give up on the 4.0L engine and go with the V6, they had wrung all of the mpg out of it they could.

When I put a cool air intake and an exhaust on my JK it improved my mpg by 3. It had a 4 inch lift and was on 35's. it was a 2011 model and had the 3.8 in it.

In my opinion I believe it helps the MPG and the longevity of the motor as long as the routine maintenance is performed. Trust me when I say that I don't pay the sticker price for these items though. I don't think we would have put an exhaust on our jeep at all if it wasn't for the price of $50. I'm a craigslist nut and am in no hurry to upgrade. Just something I like to do over time when the price is right lol.

 

[Blade]

"1-2 mpg" would indeed be considered very dramatic. And a cold air intake won't help either. They do in theory but not in reality. Really. Don't believe all the ads for CAIs, they're written to sell product. And when you reduce exhaust restriction with a shorter or larger diameter muffler, exhaust velocity actually decreases.

It just isn't easy to improve mpg any more so long as everything is working as designed. If it were, the automotive manufacturers wouldn't be fighting for every tenth of a mpg, and they are. That's why Jeep had to give up on the 4.0L engine and go with the V6 for the JK, they had wrung all of the mpg out of the 4.0L they could.

I think the only way to may improve MPGs on a TJ is to improve on its aerodynamics...if you do that, is it still a TJ?

 

[Jeepersteve71]

I think the only way to may improve MPGs on a TJ is to improve on its aerodynamics...if you do that, is it still a TJ?

Right? Either way I'm happy with the $50 I spent. I don't feel that it went to waste lol.

 

[The Real Lxxtsy]

For a while I ran an K&N cone filter and got horrible gas mileage and ran like a$$ when I got on it, sounded like the engine was going to explode, lmao. I read a tread on this forum about cold air intakes posted by Chris, see below. After reading this, I put the stock air box back on and getting better gas mileage and does not sound like its going to explode when I get on it. I'll be sticking with the stock setup going forward.

Yes, please do stay with the stock airbox. Read this thread: Cold Air Intake FAQ

There is little to nothing at all to be gained from a cold air intake on these engines. Even one of the engineers who designed the Jeep Wrangler TJ said this:

"As with any "system" on the vehicle, such as the air induction system, there is a certain amount of compromise that needs to be designed into it. What I mean is that you could maximize flow, but at what cost to filtration and protection of the engine? Essentially we design the stock intake system to meet the airflow requirements of the engine while still protecting it from fine particle ingestion. Will a cold air intake possibly flow a little more? Perhaps, but it may potentially allow larger particles through that the stock paper element would not.

In the case of the TJ, the 4.0L is an engine optimized for low RPM power and torque - the potential increase in airflow that a cold air intake might offer would not really play into the typical RPM range that a 4.0L generally operates in."
So really and realistically, you have nothing to gain from a cold air intake unless you're getting it for free. Not to mention that most of the air filters (i.e. K&N) that come with cold air intakes can actually do more harm than good for your engine, due to the fact that a lot of particles bypass those filters.

 

[Blade]

A bone stock TJ will produce the best MPGs, I think most of us try to compensate or balance the equation because we upgrade just about everything (larger wheels and tires, heavy duty bumpers, all kinds of gear, etc.) on our TJ that will kill the MPGs and AND, we are tinkerers by nature, we just can't leave things how they are cuz what's the fun in that...

 

[Jerry Bransford]

For a while I ran an K&N cone filter and got horrible gas mileage and ran like a$$ when I got on it, sounded like the engine was going to explode, lmao. I read a tread on this forum about cold air intakes posted by Chris, see below. After reading this, I put the stock air box back on and getting better gas mileage and does not sound like its going to explode when I get on it. I'll be sticking with the stock setup going forward.

Yes, please do stay with the stock airbox. Read this thread: Cold Air Intake FAQ

There is little to nothing at all to be gained from a cold air intake on these engines. Even one of the engineers who designed the Jeep Wrangler TJ said this:

"As with any "system" on the vehicle, such as the air induction system, there is a certain amount of compromise that needs to be designed into it. What I mean is that you could maximize flow, but at what cost to filtration and protection of the engine? Essentially we design the stock intake system to meet the airflow requirements of the engine while still protecting it from fine particle ingestion. Will a cold air intake possibly flow a little more? Perhaps, but it may potentially allow larger particles through that the stock paper element would not.

In the case of the TJ, the 4.0L is an engine optimized for low RPM power and torque - the potential increase in airflow that a cold air intake might offer would not really play into the typical RPM range that a 4.0L generally operates in."
So really and realistically, you have nothing to gain from a cold air intake unless you're getting it for free. Not to mention that most of the air filters (i.e. K&N) that come with cold air intakes can actually do more harm than good for your engine, due to the fact that a lot of particles bypass those filters.

That sounds like what Jim Repp would have said. Jim is, if he's not retired by now, probably the most senior of all the Jeep engineers having started during the CJ days. Jim is also known as the 'father of the Jeep Rubicon', its concept and design was his baby.

 

[Jeepersteve71]

If anything I'll probably upgrade to a nicer filter in the stock box before upgrading unless someone was selling the banks intake system (my preference) for cheap lol.

So getting back on the exhaust topic.. Has anyone ever dumped their exhaust in the rear? It's not that it's a problem where it currently sits. Just don't want to keep painting the exhaust pipe with high heat engine paint and the dirty brown is an eye sore lol.

 

[Jerry Bransford]

A better air filter would be a drop-in from AC-Delco. That filter has ranked #1 in terms of air filtration and ability to flow more air than the engine can consume/ask for. What well-known air filter consistently ranks dead-last in filtration tests? K&N.

And lxxtsy, I should have included what you said sounded like what Jim Repp said because he & I had multiple phone conversations years ago about the time the Rubicon was coming out and that is exactly what he told me when I asked him about the air intake system. Jim said they purposely wanted the TJ to have a totally non-restrictive air intake system and that as designed it easily flows more air than the engine can consume at redline RPMs and wide-open throttle. Some air intake systems are purposely designed to be restrictive, like the Camaro Z-28 and Mustang 5.0, but the TJ's was not.

Edit: Here's an interesting chart from a well-known ISO lab-conducted air filter test... there are lots of charts that were generated from this test but this is one more the more telling charts. Note what the lab said underneath the chart.

"In the chart above it’s important to note the different test durations for each filter. The AC Delco filter test ran for 60 minutes before exceeding the restriction limit while the AMSOIL and K&N tests each ran for 20 and 24 minutes respectively before reaching max restriction. In 60 minutes the AC Filter accumulated 574gms of dirt and passed only 0.4gms. After only 24 minutes the K&N had accumulated 221gms of dirt but passed 7.0gms. Compared to the AC, the K&N “plugged up” nearly 3 times faster, passed 18 times more dirt and captured 37% less dirt. " Those are the lab's words, not mine.

 

[The Real Lxxtsy]

@Jerry Bransford, good to know about the air intake system. Once I put the stock box back on the performance was night and day.