Bear with me while I ask a dumb question...

Basically, the engine is a big restriction in the system. In other words, what you put in (air) needs to be pushed out through the exhaust.

So, if you provide a tight turn on the air flow in, you provide a "restriction".

Now, if you lengthen the input with less of a tight turn, you relieve the restriction.

This discussion is like placing a fan in a hallway with the 90 degree turn at the end. The closer you are to the turn, does not mean you will get higher air flow through the turn. However, if you back off, you will get more air flow through the turn.

So, I can see both points. The ability of the engine to efficiently preform means that it needs to have air (and fuel) delivered at a specific rate.

If you change the rate of flow of the air, you will not be operating at peak efficiency.

Now, the point in question appears to be HOW the air flows, not HOW MUCH air flows. The spacer does not increase the quantity of air. However, it could alter the air flow characteristics to achieve a more efficient delivery of air and potential increase in horsepower.

John
HOW the air flows before entering the TB doesn't make much difference. While being pulled at 18 inches thru the Tb and then the runners it gets just about the same ending no matter what it was doing when it got into the TB.
The seeming restrictions in front of the Tb in MOST engines, regardless of make, aren't restrictions at all. For the most part they are there to absorb intake sound.
These sound absorbers are designed to NOT restrict the flow of incoming air.
I KNOW K&N has advertised "restrictive this and restrictive that" for many years. They have single handedly made the public think the auto manufactors are willing to "restrict" incoming air to their engines.. Doesn't make one bit of sense to me. Even less sense when considering these new fuelies we are running now. These thigs have so much quality engineering in them, I find it really hard to believe anything that is said against their performance.
BUT on the other hand. If one is on the strip and has OPEN exhausts and long runners to match the camshaft, and whatever else stuck under the hood. All for only one purpose. I totally understand changes in this or that. But for our low rpm streeted vehicles? Naaaa!
I do know this for sure. The WAY these systems are designed they are operating at the maximum compression just as they come from the factory. If there is a "restriction" in the system and it is taken out, which then provides more air into the chamber, bad things will happen. One will quickly find out that REALLY was a restriction. However if NOTHING happens the "restriction" was imaginery.
A loooong time ago when we were young, we took the choke plates out of our carbs...thinking they "restricted" the flow of air. We even went so far as to take our air cleaners entirely OFF of the carbs, for the same reason. Now later in life we all know that was silly!
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks for the explanation. It now makes more sense.

Specifically, the VERY short air cleaner elbow on a ZJ was due to the low, sloping hood height in the Grand Cherokee in comparison to the trucks using the same engine. The aftermarket spacers take up all the available space, usually causing the elbow to rub on the hood insulation. I suspect it helps the airflow straighten above the throttle body bores a bit.

The ZJ 5.2l exhaust system also uses more restrictive exhaust manifolds, due to the tighter package and relocated starter (passenger side on a Jeep, driver's side on a Dodge) As an aside, the '92-'93 "Magnum" truck exhaust manifolds are about the best flowing small block Mopar V8 stock manifolds, only sightly bettered by those from the old 340 six pack.

Next time you visit a junk yard, compare the differences!

BigJim, I don't have pictures of the Dodge vs. Jeep dyno readings to show the differences in the respective power curves, but I suspect they would show up more at the higher RPM range, at WOT, where the max horsepower readings are taken.

Air cleaner designs are a compromise of power/fit/Govt. sound level restrictions/filtering efficiency/cost. Sometimes the aftermarket can come up with improvements because they don't face the same limitations as the factory does. Rarely do they actually filter the air or fit better, sometimes they actually improve breathing. Usually, they add to the engine noises. Most times, the added cost isn't worth the gains.

Engine pumping losses are a serious consideration with more modern engines being designed to lower the power used to turn the engine. New designs coming out of Detroit etc. are using computer controlled cam, ignition and injection timing, and electronic throttles to lower part throttle cruise engine vacuum to lower these losses. The PCM will control a wider than needed overlap of the cams, open the throttle blade wider and using direct cylinder fuel injection make the engine run smoothly at cruise with very low engine vacuum. A new engine design may only have 5" vacuum at cruise where the old engines were efficiently cruising at 15", this increases fuel economy and power for the same amount of fuel burnt, through better efficiency.

Pumping losses can be decreased in older engines with more efficient intake and exhaust systems.

Engine pumping losses are a serious consideration with more modern engines being designed to lower the power used to turn the engine. New designs coming out of Detroit etc. are using computer controlled cam, ignition and injection timing, and electronic throttles to lower part throttle cruise engine vacuum to lower these losses. The PCM will control a wider than needed overlap of the cams, open the throttle blade wider and using direct cylinder fuel injection make the engine run smoothly at cruise with very low engine vacuum. A new engine design may only have 5" vacuum at cruise where the old engines were efficiently cruising at 15", this increases fuel economy and power for the same amount of fuel burnt, through better efficiency.


Boggles the mind don't it? Five inches at cruise! Wow, who'd a thought it?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Spacers are used to harmonically tune the length of the intake (the hype ones, not the size constraining ones), so the positive pressure pulse from the overlap in valve timing/inertia of the air charge reflects off of the throttle valve. This cause constructive interference with the incoming air charge for the subsequent cycle allowing for net positive head on the valve.

Sure, you can "tune" your intake in your jeep, but the intake manifold doesn't even have equal length runners. So you would need a non-symetric shaped spacer to accommodate for this... Or you can build a custom equal length intake manifold!! IÆve had good luck with COMSOL doing FEA for such things...

Those spacer kits may or may not add a measurable amount of HP, but they do add a heck of a lot of






The compression ratio is fixed. It is the ratio of the volume of air at BDC compared to the ratio at TDC.
Poppet valves are fairly good at small pressure changes, theyÆd be fairly quiet.
What goes up is the compression pressure, which affects the volumetric efficiency of the engine (weighted % of the cylinder at gauged Atmospheric pressure at the end of the intake stroke).
This doesn't cause valves to clatter, it causes localized spontaneous combustion in the higher pressure at TDC where there is a hot spot (and temperature PV=NRT ish but not really because the system is not quasi-static). This causes multiple flame fronts. When they hit you get knocking, which is BAD = engine damage.

BJ's pretty much right though...
The Engineers/scientists that designed the engines in your modern cars are smarter than you. By a lot. Especially if you are just slapping on aftermarket parts cause you bought the hype. Even if they some how weren't, they are WAY better funded.
And if both clauses don't satiate you, then you are Bill Gates and please don't come to my house and kill me cause I didnÆt mean your not better than them...

Race car engines can make a ton of power per liter, but they get rebuilt after VERY little miles. Do you really wanna build a race car engine (not just slap on some hype and stickers) and rebuild it, or can you live with a mediocre amount of HP for a couple hundred thousand miles and go wheeling more often?

I, for one, love going out to my jeep with 211,000 miles on it and turning the key and driving away... Sure, the mustang next to me at the stop light is going to beat me in a drag race... I bought a trusty reliable jeep.

My 2 cents

I didn't want to get into VE and tuned runners as there are few that have a clue! Since anyone may read these posts today or in the future all I wish to do is make them aware of how pointless most of these add-ons are.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

If you don't educate them how are they to learn?

But I see your point, most people just glaze over when they start readin technical stuff...

Let's go back to the particular VE of an engine...any engine. Doesn't that particular ve depend not only on cam overlap and such but also on the intake system to get the ve the engineer desires?
If that is correct then my hypothesis of anything actually changing the intake system for the better would have the effect of changing the ve from what was considered the maximum desired to more than that maximum?
Since these engines are built to be almost grenading anyway wouldn't changing that ve be highly noticeable to the driver?
Then, if so, it follows...NONE of these aftermarket gadgets do what they advertise?
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

So, if the throttle body spacers don't work, does that mean that the K&N filter systems are not worth the effort/cost???