In my thinking the TB spacer won't do one damn thing to the vehicle they are on. Good or bad, so they are about inert.
BUT the K&N may harm the vehicle. As the oil wears off the K&N allows larger particles, than a stock filter, of dirt to enter the engine. Also the oil can and does screw up the maf. Besides that harm the only gain from one is the noise they might make after the stock intake silencer is removed.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Volumetric Efficiency (VE) of an engine is governed by SO many different things. First it is an air pump. Head losses via frictional drag (length and surface roughness) and geometry (turns in the air tract, protrusions) lower the net positive pressure on the intake and raise the net positive pressure on the exhaust. This in turn makes it harder for the engine to breath in and out, lowering VE. That said, the engineers new this and compensated some with valve and ignition timing.

Usually the highest areas of loss are the sharp turns in the intake manifold, overall TB diameter, valve diameters, exhaust system(manifold) turns and sizing, CAT, ETC...
The hype plays to the idea that the most restrictive things are the muffler and your air filter.

The aftermarket gadgets do a little of what the are supposed to. but for the money to HP gain, they are a bust. Particularly if you do ONLY them.

You can Definitely increase the volumetric efficiency of the 4.0. Just starting with the intake, you can build your own manifold with equal length runners of the right harmonic length. Then of course you'd want to increase the size of the TB to make sure it is not the restriction. Now your intake valve/timing is limiting you, and you need to machine the head for a larger valve, or multiple intake valves. While your at it do the exhaust. Of course in order to make sure your not bottle necking at the head you need to enlarge and polish the ports. Next you need to build a harmonically tuned exhaust to fit this hot rod head/intake combo. But now is your bottom end strong enough? How bout light enough? Ok, so you have a great engine that can handle the HP you want, what a bout a fuel delivery system. The stock fuel/ignition curve isn't going to hack it. So you need to dyno tune your new engine. But hey now that a lot of metal is gone from all your machining/tuning, you should probably freshen it up so that you can drive it reliably. Oh hey BTW SMOG...

You see what I'm saying?
The engine is a SYSTEM, and needs to be approached as such. Jeep made a nice strong I6 that last reliably for a long time making some power. In fact it is so well engineered that it will operate outside it's designed parameters and run an exhaust/cat/TB spacer/etc... and make a little(<5%) more HP while still getting an ok mean time between failure.


I don't think the 4.0/5.2/5.9 is, but some are (look at the Mazda CX-7, ~240HP ~250Ft.lb. around 2500 RPM).

I think on a system view a 4.0 can get a better VE, but just cobbling together a bunch of random aftermarket parts and calling yourself a mechanic/engineer is just plain stupid. And for all practical reasons, yeah your just build an engine that will prematurely fail.

And K&N filters are horrible. ESPECIALLY for a jeep. Flow for a given area and a given pressure drop is determined by the diameter of the opening, and roughness of the surface it's touching (first order approximation). A K&N compared to a paper has roughly the same surface area and roughly the same surface texture. So why does one flow better than the other? The size of the openings available for air to flow through. Bigger openings = less flow restriction. The problem for a jeep with bigger openings?? Bigger holes for more dirt to get through! = less life for the engine! If you want HP spend the big bucks and make HP if you want reliability, you already have it!

Good post Sunder. Did that college time teach you to write so pretty?
Ok I've got me near $300. What can I do with it to help my 99 Wrangler? It's a six cylinder with the automatic transmission. I'm thinking I'd like bout, maybe 50 or 60 more horses.
Second thought...did ya take that sand rail up there in the far north? Have the noseeums got ya yet?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

300 Bucks ehh??

When's the last time you did a good tranny flush? How's about an OEM cap and rotor? Fuel filter and stock air filter?

Or are we talkin above and beyond the normal maintanence the car gets?

300$ sure ain't gunnu get you 50 HP...

They sell aftermarket turbo's for ~grand that'll get you pushin a few more ponies...

300$ on a sand rail, now there's a different story... Get yourself a cam, ratio rockers, and stiffer springs. Or maybe a good Trimil...

Na, I left the buggy in CA. Good thing too, there just ain't no wheelin out here. <img src="/forums/images/graemlins/scared.gif" alt="" /> <img src="/forums/images/graemlins/confused.gif" alt="" />
Thanks New York DEC, I'd hate for me to use my public land in a manner I wanted anyways. <img src="/forums/images/graemlins/nana.gif" alt="" />
I never thought I'd miss all the freedom I had in CA <img src="/forums/images/graemlins/rolleyes.gif" alt="" />
Oh Well... Gettin paid!! Can't complain there.
Noseeums sure don't like that 45% DEET I rub all over myself as lotion...

Big Jim....$300 might buy you a used nitrous system! <img src="/forums/images/graemlins/notooth.gif" alt="" />

I agree that the oiled cheesecloth type air filters do a poor job of actually filtering the air. I've seen low mile jeep engines with bores worn out from all the grit they injested through a K&N type filter. The intake manifold on one 4.0l that I replaced (at 20k miles due to only having 60 lbs compression) had 1/2" of fine oily dust inside the plenum! Improperly cleaning and over oiling these filters makes the problem worse. If you read the directions that come with the filter, you are not supposed to clean it for something like 50k miles! I suppose they want the dirt to build up and help trap the finer particles, which would probably lower the airflow back to below paper element levels, anyways. Any excess oil that is pulled through the filter also tends to collect on any mass airflow sensors (used in other brand vehicles) which throws the reading off. Any excess oil pulled through the filter into the airsteam also contains very fine grit, which acts as lapping compound on the rings and bores. Any water accidently injested in heavy rain storms or while fording will also pull grit through these filters.

You can't beat a stock type filter for actually filtering the air! The best factory filtering setup on a light duty vehicle was probably the old CJ/SJ/TJ Jeep and Chevy 6.2l diesel filters that used a oiled open cell foam wrap over a stock type paper element. The oiled foam would stop the large particles, the paper element traps the fine dust.

The stock elements on most late model Jeeps are oiled paper which works very well at filtering fine dust. AC Delco air filter elements are often factory oiled for better filtering, too.

I got the perfect "upgrade" for ya Jim, Buy Fuel. It will get you further down the trail than any upgrade will, but you already knew that. <img src="/forums/images/graemlins/pfft.gif" alt="" />

Sunder you hit the nail on the head when you said the engine works as a SYSTEM, and any modification to the engine has to be looked at with respect to the system. You can take it beyond the engine too, the vehicle works as a system, you start lifting the vehicle and putting bigger tires on it, as most of us know there are other things that are affected that donÆt come with the bigger tires or the lift kit; ie shocks, brakes to stop the additional mass, drive shafts, brake lines, power/ torque to turn those tires, gears to correct the final drive ratio and bring back the power/torque that was "lost", etc. The whole vehicle is a system and the aftermarket community has grossly taken advantage of the mail-order market and the uninformed consumer and flooded the market with crap.

my 2 cents.

<img src="/forums/images/graemlins/cheers.gif" alt="" />

Sean

Sunder having all that schooling and such I thought he had learned about how to get cheap horsepower... Maybe something the rest of us could covet.. But no! All I get is smart stuff that most of us already knew.
So I guess I'll do as Sean suggested and spend my money the way I always have.. Fuel and wiper fluid.
One thing I do want to mention here. My Wrangler is sitting out there on the Pecos River in west Texas. I go look at it every 3 or 4 months. When I get there I raise the hood and look for varmints and any damage they may have done in my absence. Then I insert the key and give it a turn.. So far the Wrangler has responded every time with a roar into life. In the old days we had to drain the carb, and disconnect the battery and even then sometimes a little wrenching was in order after a few of those type of sittings.
Even My Chevy, if I leave it in the garage at home for a month or so will need a battery charge before it will start.
I am more than happy with the new model Jeep...I am elated.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Better yet, FUEL ADDETIVES!!! <img src="/forums/images/graemlins/pfft.gif" alt="" />

For 300$ a tank you could run PURE octane boost....

That aughta make your Jeep Wheelie!!!

octane boost wont do a thing for the 4.0L unless you have increased the compression ratio, or your engine is dirty (carbon deposits) which effectively increases the compression. The Jeep 4.0L system is designed to run on basic 87 octane.

<img src="/forums/images/graemlins/cheers.gif" alt="" />

Na, I'm stickin to my story...

300$ worth of Octane boost aught to make it WHEELIE!!! <img src="/forums/images/graemlins/notooth.gif" alt="" />