Intake, Performance

[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.