Intake, Performance

[sublime600]

So im looking to get a little more HP, and some better MPG. So ive been looking at TB spacers and intakes, exhaust, etc. So my questions is what are the good ones. Ive been looking at the airaid TB Spacer. Ive been looking at the Airaid intake and the K & N intake, which is better. Also im pretty set on the Dynomax cat-back system. Any info on better products would be great. Also some sites that have what im looking for, for pretty good prices. Is there anything else i can do to get more? please no SC or turbos lol

[j99xj]

The best peformance products are the ones you make yourself.

They will save money for mods you can't make yourself (like exhaust headers, air filters, etc.)

[streetpirate]

dont use a spacer, get an intake manifold off of a '99 4.0, pacesetter header, the dynomax cat back, and make your own air intake. if you search in the street 'n performance forum, Dr. Dyno is a user who has had great success making his own performance parts on the cheap, and he has a website where he tells you how he did it.


SP

[gradon]

Get the '99+ intake manifold, a bored out TB, a header w/downpipe along with your dynomax catback and whichever intake you choose/make(I got a good deal on my FIPK)and your XJ will be breathing easier, more responsive, and will get higher MPG once you get tired of your awakened 4.0. Ditto on skipping the TB spacer.

[raypla]

Get the '99+ intake manifold, a bored out TB, a header w/downpipe along with your dynomax catback and whichever intake you choose/make(I got a good deal on my FIPK)and your XJ will be breathing easier, more responsive, and will get higher MPG once you get tired of your awakened 4.0. Ditto on skipping the TB spacer.

He already has the newer intake on his 01'. Definately nic the spacer and go for a free flowing intake w/ a bored TB. I'm not sure who makes headers for the 01', they have those funky precats in the header. Maybe you can look into eliminating all that junk and get a Borla w/the downpipe.

Here is a link for a TB http://www.thefastman.com/Throttlebodies40.asp real good price, guy to deal with.:yelclap:

[sublime600]

Thanks for the info guys. Ill def be knicking the TB spacer for the bored out TB. Sorrry that i didnt say what year i had earlier. But the Dynomax is probably the best exhaust over flowmaster right. I was always under the impression flowmaster was more for sound then performance. If anyone finds headers for an 01 please post a link thanks again!

[gradon]

I dished out $750 for the Borla setup (header w/downpipe and catback), and $50 for the magnaflow cat and I would definitely buy it again--great sound and good power, not to mention ss. My brother has the Borla header/flowmaster setup and his has a deeper and louder exhaust note On my old Jeep I had just the dynomax catback, which I was satisfied with

[XJoshua]

I still need to do a good intake, but I got a good exhaust on.

List from engine to tailpipe:
Renix 4.0
Banks Headers
Summit Racing Flex Pipe(2.5")
Custom S Pipe(Down Pipe)(2.5")
DynoMax High Flow Cat(2.5")
DynoMax Super Turbo Muffler(2.5")
Custom Muffler Back Pipe(2.5")

Total Cost(excluding motor): $210

I got the headers used, and got a discount on all the pipes which were madrel bent. So It sounds good, with the cat, without it, it sounds like poo poo when you hold a gear way to long, which you souldnt do.

[j99xj]

Why does it seem that everybody on this forum hates throttle body spacers?

I agree that you shouldn't buy a spacer with the swirls, but the smooth bore ones work for me especially because I got it dirt cheap on ebay. If you don't want an ebay account summit sells the smooth bore spacers too.

Anyway you slice it, a throttle body spacer is a worthwhile addition to your intake if you can find a cheap price. The common agreement around here is that its worth about 2-3 hp at the peak and about 4-5 lb-ft at the low end. I wouldn't pay a dime over 50 bucks for one. I got incredibly lucky when I found mine for 30 bucks, including shipping. And I'm sure its paid for itself in fuel savings by now.

[gradon]

My FIPK won't allow me to add a spacer and I installed the 99+ intake which added 1700cc's more air volume instead of the 76cc's you got with the spacer.

[Beej]

Why does it seem that everybody on this forum hates throttle body spacers?

I agree that you shouldn't buy a spacer with the swirls, but the smooth bore ones work for me especially because I got it dirt cheap on ebay. If you don't want an ebay account summit sells the smooth bore spacers too.

Anyway you slice it, a throttle body spacer is a worthwhile addition to your intake if you can find a cheap price. The common agreement around here is that its worth about 2-3 hp at the peak and about 4-5 lb-ft at the low end. I wouldn't pay a dime over 50 bucks for one. I got incredibly lucky when I found mine for 30 bucks, including shipping. And I'm sure its paid for itself in fuel savings by now. People crap on them here because they don't add anything. I don't know where you got that common agreement idea from, but I'm sure its from a butt-dyno, not the real thing. It can't hurt to add one, but they just add plenum volume, something that is done much better by utilizing a later model intake...

[RichP]

You will get better MPG improvement by running your tires at the correct pressure. I run my BFG AT/KO's at around 40psi and that upped my MPG about 2mpg on my daily commute, every day, both ways. Going to take that safari rack off too, I know that cost me 2mpg at the speeds I drive on the turnpike, 70-80mph consistantly. If maintained correctly the 4.0L 97+ XJ is capable of 23-25mpg, that includes cleaning the fuel system on a regular basis when you get gas. I usually buy valvoline fuel system cleaner at Sams club by the case so it's no big deal to add it on a regular basis which I use my 3,000mi oil changes to base it on..

[j99xj]

You will get better MPG improvement by running your tires at the correct pressure. I run my BFG AT/KO's at around 40psi and that upped my MPG about 2mpg on my daily commute, every day, both ways. Going to take that safari rack off too, I know that cost me 2mpg at the speeds I drive on the turnpike, 70-80mph consistantly. If maintained correctly the 4.0L 97+ XJ is capable of 23-25mpg, that includes cleaning the fuel system on a regular basis when you get gas. I usually buy valvoline fuel system cleaner at Sams club by the case so it's no big deal to add it on a regular basis which I use my 3,000mi oil changes to base it on..

I got 24 mpg a few times with the cruise control on at 65.

[j99xj]

People crap on them here because they don't add anything. I don't know where you got that common agreement idea from, but I'm sure its from a butt-dyno, not the real thing. It can't hurt to add one, but they just add plenum volume, something that is done much better by utilizing a later model intake...

Dr Dyno did some testing with a stopwatch some time back and his best number was 5 lb-ft around the low end.

[old_man]

Dr Dyno did some testing with a stopwatch some time back and his best number was 5 lb-ft around the low end.

OK, what is the transfer function to get from time to lb/foot????

[j99xj]

OK, what is the transfer function to get from time to lb/foot????

You'll have to ask Dr. Dyno. But I'm sure it was simple kinetics. This is where I got my info from http://www.naxja.org/forum/showthread.php?t=65212&page=3&highlight=stopwatch+spacer

[indianaXJ]

hello:

You shoulld look into a pre 98 head to take advantage of your 99+ intake. Then you could use a header for a 97/98 model. Check out the Kolak exaust kit, it uses a factory mopar header and 70 series flomaster. The mopar header is sweet and the 70 series has a nice tone, not too loud but a nice rumble. The Kolak kit is high quality plus the kit was dino developed. This setup will probably not be EPA legal but with the bored TB and FIPK will give you the most gain for bolt on type mods.

I have not tried one yeat but as I understand it a TBS will help out in the lower rpm range with the 99+ intake . I would only try this as an experiment after the mods. above though.

[Dr. Dyno]

The TB spacer DOES produce a small HP/TQ gain across the rpm range (my estimate is 2-3lbft at higher rpm, 3-5lbft at lower rpm) and a small gain in fuel economy (nearly 1.0mpg) in '91-'99 models with the older log type intake manifold. The spacer adds an extra 1.0" in length to the intake tract and slightly lowers the peak HP/TQ rpm points (by ~100rpm). Since it's sandwiched between the TB and the manifold, it raises the TB away from the manifold floor and acts like a velocity stack (especially if it's smooth bored to a 62mm diameter). A thicker spacer than 1" would be even better but there isn't enough underhood clearance for one.

[MaXJohnson]

The TB spacer DOES produce a small HP/TQ gain across the rpm range (my estimate is 2-3lbft at higher rpm, 3-5lbft at lower rpm) and a small gain in fuel economy (nearly 1.0mpg) in '91-'99 models with the older log type intake manifold. The spacer adds an extra 1.0" in length to the intake tract and slightly lowers the peak HP/TQ rpm points (by ~100rpm). Since it's sandwiched between the TB and the manifold, it raises the TB away from the manifold floor and acts like a velocity stack (especially if it's smooth bored to a 62mm diameter). A thicker spacer than 1" would be even better but there isn't enough underhood clearance for one.
Three areas to improve fuel mileage: driving habits, reduced load, increase efficiency.

Since a spacer has no effect on driver habits or load, so we can assume your quoted gains are based on an increase in efficiency.

For the typical XJ, fuel consumption is around 14 to 20 mpg, so a 1.0 mpg improvement in fuel economy represents a 5 to 7 percent improvement in volumetric efficiency. Consider your claimed torque improvement and the percentage would be even higher.

The cost per vehicle to increase the plenum volume of the intake manifold by 72cc (1" spacer) would only amount to a few pennies. I find it hard to believe that the Jeep drive-train engineering group would miss such an inexpensive way to improve their competitive advantage. We know they weren't distracted by cup holder placement.

[j99xj]

Three areas to improve fuel mileage: driving habits, reduced load, increase efficiency.

Since a spacer has no effect on driver habits or load, so we can assume your quoted gains are based on an increase in efficiency.

For the typical XJ, fuel consumption is around 14 to 20 mpg, so a 1.0 mpg improvement in fuel economy represents a 5 to 7 percent improvement in volumetric efficiency. Consider your claimed torque improvement and the percentage would be even higher.

The cost per vehicle to increase the plenum volume of the intake manifold by 72cc (1" spacer) would only amount to a few pennies. I find it hard to believe that the Jeep drive-train engineering group would miss such an inexpensive way to improve their competitive advantage. We know they weren't distracted by cup holder placement.

I'm far from a marketer, but back in the day Jeep didn't need to have competitive advantage, because I think most of their buyers were previous Jeep owners that were completely satisfied with the product. Nowadays, Jeep is trying very hard to attract new buyers with the additon of the Compass etc. 4wd minivans. But in the process they are disintegrating and softening their base of Jeep loyalists who demand capability, not a posh ride .

The only vehicles worthy of having "Jeep" on the hood in the 2007 lineup are the Wrangler and Wrangler Unlimited.

I think the 4 door Wrangler Unlimited was the best idea Jeep has had for a long time. Why do I think this? Because it attracts former XJ owners, and it fills the gap that the XJ used to fill. (a capable 4 wheel drive, 4 door vehicle with an off road oriented suspension, ie solid axles) Make no mistake, NO VEHICLE will ever be able to replace the XJ but this new Wrangler Unlimited does attract "the XJ type" of buyer.

Sorry for my rambling, but I stand by the throttle body spacer. Whatever it does doesn't matter, its the fact that it works that matters. Dr Dyno says it gained 3 -5 lb-ft of torque on the low end. So let's say for instance that he had a 50% human error in calculating those numbers (which is highly unlikely in my opinion). So that brings the numbers down to 1.5 - 2.5 lb-ft of torque. Those gains in my opinion are still gains that are worth 30 bucks. I know its not a big gain, but its 1.5-2.5 lb-ft more than the other XJ revving its engine next to you at a red light....

[MaXJohnson]

I'm far from a marketer, but back in the day Jeep didn't need to have competitive advantage, because I think most of their buyers were previous Jeep owners that were completely satisfied with the product. Nowadays, Jeep is trying very hard to attract new buyers with the additon of the Compass etc. 4wd minivans. But in the process they are disintegrating and softening their base of Jeep loyalists who demand capability, not a posh ride .

The only vehicles worthy of having "Jeep" on the hood in the 2007 lineup are the Wrangler and Wrangler Unlimited.

I think the 4 door Wrangler Unlimited was the best idea Jeep has had for a long time. Why do I think this? Because it attracts former XJ owners, and it fills the gap that the XJ used to fill. (a capable 4 wheel drive, 4 door vehicle with an off road oriented suspension, ie solid axles) Make no mistake, NO VEHICLE will ever be able to replace the XJ but this new Wrangler Unlimited does attract "the XJ type" of buyer.

Sorry for my rambling, but I stand by the throttle body spacer. Whatever it does doesn't matter, its the fact that it works that matters. Dr Dyno says it gained 3 -5 lb-ft of torque on the low end. So let's say for instance that he had a 50% human error in calculating those numbers (which is highly unlikely in my opinion). So that brings the numbers down to 1.5 - 2.5 lb-ft of torque. Those gains in my opinion are still gains that are worth 30 bucks. I know its not a big gain, but its 1.5-2.5 lb-ft more than the other XJ revving its engine next to you at a red light....
you make some compelling arguements

[Dr. Dyno]

The cost per vehicle to increase the plenum volume of the intake manifold by 72cc (1" spacer) would only amount to a few pennies. I find it hard to believe that the Jeep drive-train engineering group would miss such an inexpensive way to improve their competitive advantage. We know they weren't distracted by cup holder placement.

DC could have given the 4.0 XJ a power boost over the years to keep it ahead of the pack performance-wise but instead, they kept the power output stuck at 190hp from '91 to '01 and decided to axe the XJ instead of developing it (and the 4.0) further.
Up to 1992, the 4.0 XJ was the performance king of the SUV's (unless you count the GMC Syclone). Since then, so many SUV's have entered the market, overtaken the XJ, and by 2001 it was left begging for mercy when DC finally killed it.
My point? DC could have improved the HP/TQ of the 4.0 engine over the years and also improved the XJ in other areas to keep it ahead of its peers. I'm sure the engineers had lots of good ideas (I'm not an engineer and I could come up with a very long list) but as always, accountants and managers make the decisions and I'm sure the inclusion of more cupholders was one of them. Upgrading the powertrain definitely wasn't.

[MaXJohnson]

DC could have given the 4.0 XJ a power boost over the years to keep it ahead of the pack performance-wise but instead, they kept the power output stuck at 190hp from '91 to '01 and decided to axe the XJ instead of developing it (and the 4.0) further.
Up to 1992, the 4.0 XJ was the performance king of the SUV's (unless you count the GMC Syclone). Since then, so many SUV's have entered the market, overtaken the XJ, and by 2001 it was left begging for mercy when DC finally killed it.
My point? DC could have improved the HP/TQ of the 4.0 engine over the years and also improved the XJ in other areas to keep it ahead of its peers. I'm sure the engineers had lots of good ideas (I'm not an engineer and I could come up with a very long list) but as always, accountants and managers make the decisions and I'm sure the inclusion of more cupholders was one of them. Upgrading the powertrain definitely wasn't.
What I'm questioning is the claimed 5-7 percent increase in volumetric efficiency that a 1.0 increase in mpg represents, not a modest shift in the power band of a few hp. Of course, independent dyno runs supporting any increase in hp or torque are hard to come by as well.

Your own website documents numerous changes over the life of the XJ, starting with a V6 and moving through 3 major renditions of the 4.0 inline 6. This includes different blocks and crankshafts, heads, intakes, exhausts cams, throttle bodies, engine electronic management, etc. Lots and lots of changes, and yet they missed adding a throttle body spacer for an almost free 5-7 percent increase in volumetric efficiency. OK

[j99xj]

Lots and lots of changes, and yet they missed adding a throttle body spacer for an almost free 5-7 percent increase in volumetric efficiency. OK

I'm sure the engineers could have done so. But I think the whole idea was shot down at Jeep for two reasons:

1. It increases throttle response. Some people don't like lots of torque at low throttle settings because its somewhat harder to control in stop and go traffic. This is why I'm almost CERTAIN that the stock throttle body has that lip on it that restricts the flow, it's to smooth the throttle response. I'm pretty sure the engineers designed the HO 4.0 with a 62 mm throttle body from the begining. However after testing the Jeep had too much torque at low rpms, and was too "herky jerky" so they decided to take the throttle bodies off the lathes earlier to leave that lip on.

2. Jeep didn't have the desired to spend the money to re tool their intake manifold machinery. When your dealing with anything in mass production, once you spend millions on a machine that designs one part (in this case the intake manifold) your not going to want to change that part at all (because you would need a new machine, and all the thousands of dollars in computers and engineering techs to run the machines).

The only reason Jeep had to redesign the intake manifold for 99+ is because they had to get some more power after an emission change that likely killed a lot of power.

[MaXJohnson]

I'm sure the engineers could have done so. But I think the whole idea was shot down at Jeep for two reasons:

1. It increases throttle response. Some people don't like lots of torque at low throttle settings because its somewhat harder to control in stop and go traffic. This is why I'm almost CERTAIN that the stock throttle body has that lip on it that restricts the flow, it's to smooth the throttle response. I'm pretty sure the engineers designed the HO 4.0 with a 62 mm throttle body from the begining. However after testing the Jeep had too much torque at low rpms, and was too "herky jerky" so they decided to take the throttle bodies off the lathes earlier to leave that lip on.

2. Jeep didn't have the desired to spend the money to re tool their intake manifold machinery. When your dealing with anything in mass production, once you spend millions on a machine that designs one part (in this case the intake manifold) your not going to want to change that part at all (because you would need a new machine, and all the thousands of dollars in computers and engineering techs to run the machines).

The only reason Jeep had to redesign the intake manifold for 99+ is because they had to get some more power after an emission change that likely killed a lot of power.

1. Throttle response is inversely proportional to plenum size, so adding a spacer or using other means to increase plenum size would have a negative impact on throttle response. The restriction at the base of the throttle body increases flow velocity and helps boost the vacuum signal. If you have something besides being "pretty sure" to support this statement: "...the engineers designed the HO 4.0 with a 62 mm throttle body from the begining. However after testing the Jeep had too much torque at low rpms, and was too "herky jerky" so they decided to take the throttle bodies off the lathes", I'd love to see it.

2. See previous post. Jeep made numerous changes, including three different intake manifolds, so obviously they were willing to spend the money when the benefits were there. Of couse they also had the option of a bolt-on spacer to avoid manifold design changes.

[School Bus Man]

I have a 99 Classic

In the past three months I completely changed my exhaust, intake, and headers (this coming weekend).

I went from a stock exhaust to a 2.5" pipe on a Magnaflow muffler (don't remember which series) then I used a 3.0" Magnaflow cat and I just purchased a Gibson header which I have not installed yet.

Also I installed a K&N FIPK.

The exhaust is a bit noiser that what I would have liked. The performance increase is noticable. The FIPK I just installed and I'm noticing some performance increase but potentially not as much as I had hoped.

The headers we'll see about and I'll post later with those results.

You cannot fit a TB Spacer and K&N FIPK together - there isn't enough space beneath the hood.

I think if I were to do it again (I will later) - I would use a combination of an ARB Snorkle kit with a FIPK - but you'll have to fab it yourself.

The snorkles are great except they go into your stock exhaust box and utilize the stock filter. The FIPK is great except its still exposed to all the nasty dirty hot air. So to fab somethjing that combines the two would be a huge performance increase.

I would highly recommend a magnaflow system at the very least. It's a straight through design so no little sound flanges to break inside muffler (like the Flowmaster design). It's pretty organized and well designed.

Good Luck,
Mike

----Everything below this doesn't directly apply---

I did this all to improve power and fuel economy. So far I've noticed a huge improvement in throttle response - If I were one of those rice burner streetrace kids (I'm not - I'm a schoolbus driver and weekly offroader) I'd be thrilled because I can smoke just about anyone off the line and do really well in the 1/4 mile ( I had to play a little...)

Originally I was getting 250miles per tank which sucked - now I'm getting somewhere between 300 & 350.

I'm still trying maximize the balance between power & fuel econ.

[j99xj]

1. Throttle response is inversely proportional to plenum size, so adding a spacer or using other means to increase plenum size would have a negative impact on throttle response. The restriction at the base of the throttle body increases flow velocity and helps boost the vacuum signal. If you have something besides being "pretty sure" to support this statement: "...the engineers designed the HO 4.0 with a 62 mm throttle body from the begining. However after testing the Jeep had too much torque at low rpms, and was too "herky jerky" so they decided to take the throttle bodies off the lathes", I'd love to see it.

2. See previous post. Jeep made numerous changes, including three different intake manifolds, so obviously they were willing to spend the money when the benefits were there. Of couse they also had the option of a bolt-on spacer to avoid manifold design changes.


1. Good throttle response comes from a torque band that starts early. So if a bigger plenum reduces throttle response, then it must reduce torque. But that's been proven wrong from Dr. Dyno's testing. Yes, you are correct in that a smaller throttle body has a higher booster signal and velocity, but that shouldn't pose any problems on a fuel injected engine. (Since the pressure is higher, that would tell the computer to add more fuel, with makes sense because more air is entering the engine from the bored out lip) If it were carbureted, you would really screw up fuel atomization at low speeds causing crappy throttle response, this is precisely why there are no such things as "bored carburetors" because carbs must have a venturi to work correctly. Anyway my justification for the 62 mm throttle body as the original design is the fact that all the 91+ intake manifolds have a 62 mm opening, and that the lip on the bottom of the throttle body just looks like an afterthought. (A band aid if you will).

2. I know that. But I was talking about the 91-98 intakes. Anyway they would still have to come up with the tooling to make hundreds of thousands of spacers a year. (Unless they made a contract with Airaid or the other various aftermarket spacer companies). Either of which would cost them money which would reduce Jeep's bottom line. Businessmen tend to frown upon anything that cuts from their profit.

[Dr. Dyno]

What I'm questioning is the claimed 5-7 percent increase in volumetric efficiency that a 1.0 increase in mpg represents, not a modest shift in the power band of a few hp.

Who said that the TB spacer increases volumetric efficiency by 5-7%? On a 4.0, you'll need all the external bolt on performance mods that you can get plus a ported head to increase VE by 7%, and you'd gain roughly 25% more HP over stock in the process.
A 0.8mpg gain (in my case) doesn't represent a 5-7% increase in VE. The mpg gain caused by the spacer could be the result of increased intake air velocity and a more even distribution of air to the cylinders. DC didn't need to add a spacer; they could have just made the intake manifold plenum inlet 1" taller.

The only reason Jeep had to redesign the intake manifold for 99+ is because they had to get some more power after an emission change that likely killed a lot of power.

No. The reason they redesigned the manifold (and later added distributorless ignition) was to meet tightening emissions regulations, not to add HP. If it was to add HP, ask yourself why the HP output remained at 190.

Good throttle response comes from a torque band that starts early. So if a bigger plenum reduces throttle response, then it must reduce torque. But that's been proven wrong from Dr. Dyno's testing.

A bigger plenum DOES reduce torque at low revs and increases it at higher revs. It also weakens throttle response and reduces the vacuum signal. The newer intake manifold does have a bigger plenum but it also has smaller diameter runners to improve low rev torque. The TB spacer only adds a negligible amount of volume to the plenum so consider it insignificant. The reason for the small torque increase, I feel, is because the spacer raises the TB away from the intake manifold floor, and increases air velocity as it enters the plenum.

[j99xj]

The biggest mystery I have with my 1999 4.0 engine is whether or not I have the new emissions regulation ecu programming or not.

As far as I know the latest model and lowest emission 4.0 had the 0331 cylinder head, the bigger intake manifold, 2 seperate exhaust manifolds with a mini catalytic converters on each with the distributorless ignition system and revised ecu programming.

My 4.0 came stock with a 0630 head, the bigger intake, the old "crackable" single exhaust manifold, with the conventional distributor ignition.

If my 99 engine came with the old intake it would be identical to a 98 engine.