hutchman

This question is asked on every Jeep forum on the net and the answers are always similar to the answers given so far in this thread. There have been some good answers, but I think you, and all of us need to ask the question - "What do I really want from my Jeep?"

My guess is that we all want better seat of the pants street/wheeling performance. A Wrangler is never going to be any good for a top speed car, and not much good for a drag car either. I know they have been raced, but that is not what they are purchased for normally. Someone stated that if you wanted a race car, buy a Vette........and that is probably good advice! So back to the seat of the pants street/wheeling performance.

What defines good street performance? I think we want decent acceleration from both a standing start and merging on the freeway. We want to be able to pull hills in high gear on the highway. And for a Jeep, we want the ability to crawl along a very slow speeds while climbing hills or crawling over obstacles. So if we can agree that these are the basic requirements of a daily driven street driven Jeep, what can we change to make them better?

If we increase torque available at low speeds, then we will improve performance in these areas. Torque is what makes the Jeep accellerate and gives it the ability to crawl over stuff. We always talk about horsepower, but in reality, horsepower is a mathematical derivative of torque and engine speed. As speed increases, so does horsepower. What we want is increased low speed torque.

So how do we increase torque at low speeds? We could add a supercharge or nitrous and these would both increase torque, but at the cost of engine reliability. These both increase cylinder pressure and could cause eventual engine failure.

We could also install low restriction intake and exhaust mods, but we have to be careful here because if we open the intake and exhaust too much, we slow down the intake and exhaust mixtures which will reduce low speed torque. These mods will definitely help make horsepower at higher rpm, as they reduce restriction somewhat, but they can kill the low speed torque we need.

So I think the real question we should ask ourselves is how can we increase low speed torque without over stressing the engine and reducing reliability..............and I believe the question can be answered in one word......gears. Gears are not an engine mod, but if we look at the purpose of gearing in the Jeep - they are torque multipliers - we find that by going to lower gears, we multiply the available torque provided by the motor for use by the Jeep. And we do this without increasing cylinder pressure which may decrease reliability.

So let's say you decided you wanted a 20% increase in available torque at a given speed, you could just install gears that are 20% lower.....If you had 3.07s, you could go to 3.73s for slightly more than a 20% increase and likewise going to 4.56s from 3.73s would also result in a similar increase.

It looks like gearing might be a pretty good choice then, but what about the downside........

Obviously, if you go to 20% lower gearing, engine speed will increase by 20% at any give road speed. This could result in the wearing out sooner than with the higher gears. This could be a concern if you plan on keeping you Jeep for 150,000 miles, but if you trade every 3 or 4 years, it should have no impact.

What about gas mileage? Common sense would tell you that you might have a 20% reduction in mileage, but maybe not. The "brake specific fuel consumption" of a gasoline engine is the least at peak torque. This is the point on the torque curve at which the engine burns the least amount of fuel per horse power produced. For the 3.8, peak torque is at approximately 3600 rpm and that is the point at which the engine operates at it's peak efficiency. This may not be the point of greatest mpg though because of other factors such as wind resistance etc.

So as we increase engine speed we approach the most efficient point on the torque curve and we might even see an increase in MPG, depending on the other conditions at the time. I have actually measured this on my 06 TJ........it got better mileage in 5th gear than it did in 6th at 70 mph. Throttle position may actually decrease for a give speed, which results in higher intake manifold vacuum and increase economy.

To sum this up, it is my opinion that if you want more/better performance from your Jeep, you should invest in gears first. They increase the available torque at any given speed without the reliability issues that might be associated with some of the other performance enhancements.

They are the single best performance enhancer you can buy, dollar for dollar. You can't beat 'em.

Octane

Apples and apples... (torque)

GM 3.6L________250.8 ft.lbs
Honda 3.5L_____245 ft.lbs
Chrysler 3.5L____250 ft.lbs
Mitsubishi 3.0L___204.8 ft.lbs
Chrysler 2.7L____189.6 ft.lbs

Jeep 3.8L_____240 ft.lbs

Torque I think is what we are really after. Jeep is more capable of applying the same tq onto the trail better. This is a bit better, but for the size of the engine, you would think our engine would be capable of more...

Famof5Jeep

HP is 100% dependent upon RPM and Torque because the HP calculation is the area beneath the torque curve. Hence the reason we all want diesels. Most of the engines described above all run at higher RPM bands and require those RPMs to produce power. A higher RPM motor will rely on a shorter stroke and larger bore to produce higher HP. While those of us interested in Torque (the low end grunt) build engines with longer strokes and smaller bores. Just look at the little 4 bangers producing 250 HP out of 2 liters. It has to run at 5500 RPM to hit it's peak torque. Who would want to crawl rocks running 5500 RPM? F1 Race cars produce gobs and gobs of power but so much of that is related to the insane RPM's they turn something around 18000 and higher in V8 engines. No I did not add an extra zero.

The bottom line is that most of think the JK is underpowered. It is, but what most of want is more torque. If you buy a JK with the intent of it being fast you've bought the wrong vehicle. If it had 20 - 30 more ft/lbs of torque we'd all be pretty happy but come on it is really that bad?

dpoelstra

You are exactly right.

I could feel the difference (really...) with the CAI and love the exhaust sound, but don't think it made a great deal of "seat of the pants like the CAI did. The Jet Stage II chip was a complete waste and is now on my workbench, and I could not tell that I took it off.

The biggest improvement I think was miles. This thing just seemed to wake up after about 4 or 5 thousand miles. Pleaseant and adequate, but not a hotrod.

I have never lacked torque off road though. I have a 6 speed and almost always go into 4 lo right away. I only wish I had a lower ratio to crawl slower, but the torque has been fine, especially once I learned how to feather the throttle just a bit.

bwiencek

Plus you're not comparing technologies... those engines listed are likey multi-valved overhead cam engines - I know the honda has 4-valves per cylinder and variable valve timing (wife's got one - it's impressive for a stock V6). The technology in the JK is more comparable to the old GM 3.8L V6 - 200HP/225 FT-LB torque (basicly 2/3 of an old SBC 305) - it's actually hard to find such an old technology engine to compare the JK's engine to - every other MFGR went with newer and more complex technology a long time ago...

You're not buying a wrangler for the HP, drag performance or engine technology that's for sure... you're buying it because it's a rugged, mod-able off-road capable machine... In this case I believe they figured simpler is better....

davebloomer

that is how i look at it... how many of them old nasty chrysler vans do u still see driving around... Way to many that is for sure. and it's not cause they have been maintained so well it's cause of that rugged ole 3.8L that don't have enough horsepower to tear itself apart.. (that's what i tell myself to keep from feeling bad about the lack of power)

avosfit

At the most basic:

Think in terms of HELPING the engine INHALE better, EXHALE better, move less weight, and move that weight more efficiently (streamline).

*CAI
*Free-flowing exhaust
*lighter wheels/ tires (rotational mass), and dropping weight instead of adding 600lbs of bumpers/ winches etc...
Not much we can do to help streamline the JK.