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Unread 09-22-2006, 05:52 AM   #16
JLH
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Quote:
Originally Posted by Sweeney
The only effect that the cylinder configuration will have is miniscule...
This is incorrect. I work with an engineer that spent 12 years at Cummins. The dynamic power vector equations for a in-line six perfectly cancel each other. You have a six cylinder engine with a 4 stroke cycle which are timed 120 degrees out of phase. Thus the in-line six has the highest energy conversion because energy is not being wasted on vibrational loses. The power vectors in the V-6 do not cancel because the shorter crank can't properly lever the other cylinders. The in-line six is inherently the better engine, but due to the new safety standards, it could not be used.

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Unread 09-22-2006, 06:42 AM   #17
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Quote:
Originally Posted by JLH
This is incorrect. I work with an engineer that spent 12 years at Cummins. The dynamic power vector equations for a in-line six perfectly cancel each other. You have a six cylinder engine with a 4 stroke cycle which are timed 120 degrees out of phase. Thus the in-line six has the highest energy conversion because energy is not being wasted on vibrational loses. The power vectors in the V-6 do not cancel because the shorter crank can't properly lever the other cylinders. The in-line six is inherently the better engine, but due to the new safety standards, it could not be used.
That is why I said it is miniscule (perhaps too strong a word) and not "non-existant". The loss due to the configuration is very small in the grand scheme and with the addition of a counter shaft the vibrations are reduced or eliminated... of course you then need to spin the counter shaft. It's not the length of the crank at issue, it's that opposing cylinders are not 180 degrees out of phase.
The point is, the difference will be nearly undetectable to the opperator.
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Unread 09-22-2006, 07:54 AM   #18
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The 3.8 is also a "narrow vee" and not a ~90 degree V like most V setups.
This makes it perform closer to an inline setup (I'm not saying it performs like one, but closer to than a 90 degree V).
Power and torque characteristics can also easily be modified with the other components of the engine that has already been mentioned.

The biggest benefit to an inline 6 in my opinion is that it is perfectly balanced and therefore tends to run smoother and quieter than oter configurations (which is why BMW still makes inline 6s). But that point is pretty moot on a jeep, at least a wrangler and if you are any familiar at all with the 4.0, you know that the last thing it was was smooth and quiet! Especially your buddy's 98, they reworked it a little bit for MY 99 to make it a bit quieter (because owners were complaining it was too noisy).
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Unread 09-22-2006, 10:39 AM   #19
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From the reports I have read about the engine choices, the V6 gets higher torque and horsepower at a higher RPM than what the I6 maxes out at a slightly lower RPM.

I would love to see a side-by-side comparison of the horse-power and torque values between the two engines with a similar maximum RPM/power value (ie: 3500rpm I6 has ### power and V6 has ### power).

Most people do not rev their engines to the absolute max unless they are hoping to blow the engine up to put a new one in anyway. I rarely push my engine over 3500RPM - no real need to.
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Unread 09-22-2006, 01:48 PM   #20
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I think i am beginning to understand and from what i'm gettin from everyone is that the inline six generally makes its torque at a slightly lower rpm than a v6. This was what i thought but i wasn't completely sure so i figured i'd ask. When i go to test drive them later on this month once the dealer gets a 2 dr jk. I will get a better idea because the dealership is right on a highway that has some pretty good hill climbs. Should provide me a good comparison but almost nething will amaze me since all i have now is a 2.4L.

and Ledfoot you are very right his 98 is really loud. Not just from the exhaust well lack there of. He's missin everything from the muffler back. He put a chery bomb muffler on and when he cut out the old muffler he just cut the pipes flush with the old one so when he went to put the new cherry bomb pipe on he didn't have enuff pipe so he just did a hack job of welding and the thing fell of when he hit a bump. ( and he calls me stupid for thinking the JK is ok) Thx for all the help guys
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Unread 09-22-2006, 08:19 PM   #21
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Yea over ~3500 the V6 will have more torque, below that the I6 will be better, as it peaks at 3200.

I know i wont need that power, i shift at 2000 rpm as it is.
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Unread 09-22-2006, 08:48 PM   #22
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Quote:
Originally Posted by JLH
This is incorrect. I work with an engineer that spent 12 years at Cummins. The dynamic power vector equations for a in-line six perfectly cancel each other. You have a six cylinder engine with a 4 stroke cycle which are timed 120 degrees out of phase. Thus the in-line six has the highest energy conversion because energy is not being wasted on vibrational loses. The power vectors in the V-6 do not cancel because the shorter crank can't properly lever the other cylinders. The in-line six is inherently the better engine, but due to the new safety standards, it could not be used.
That has effect on balance, but not on power. I6 is first order balanced. V6 needs additional balancing, but they have figured it out by now. Vibrational losses are not important.
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Unread 09-24-2006, 07:30 PM   #23
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The inline motor is naturallly balanced which helps power and torque. The valve actually determines the personality of the engine along with how long it it is held open, the overlap between the intake and exaust valves and how quickly the valve goes from fully closed at the seat to fully open is the opening ramp and who fast it slams shut is the closing ramp. Small valves with more overlap make good power and torque but are very peaky and not flat while I have found that short overlap wider lobe sepreation angles and larger valves or more valves make flatter torque.

Another factor in personality is rod to stroke ratio. Some sources say that a short rod to stroke rato lowers the power after 2500 rpm while others say that it makes the peak hp and peak torque hither with steepre curves and is not very flat at all.

I like a motor with a medium stroke, long rod, and a big bore. A wider lobe seperation angle, about 260-280 duturation, big valves and generous ports to make the torque as flat as I can from 2000-5000 rpm. Ideally!
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Unread 09-24-2006, 08:19 PM   #24
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I am not a techno nut, but I just sold a 98 TJ, and bought the 07 Unlimited. I put mine thru some fairly tuff mud, and there is enough torque I didn't need to go to low range. I think you are trying to make something out of numbers that doesn't mean anything in actual application. The 98 TJ had the 3.? gears and 5 speed, the 2007 has the auto and 4.1 gears. I am very pleased with the 2007. For comparison, for the 98 TJ to go interstate speeds in the hills with 30" tires, I had to stay in 4th to avoid downshifting on most hills. The 2007 has 32" tires and only downshifts from overdrive on the steepest hills. At 75mph the engine is turning 2500 rpm. Like my 97 Grand Cherokee with 318 engine, I have found no need to go into low range. So from this experience, I don't think there is a problem with low end torque, even for a rock crawler, but I would definately get the 4.1 gears.
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Unread 09-24-2006, 08:40 PM   #25
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OK here's my take on the I6 vs. V6. The 4.0 is tried and tested. they will easily go 200k, and are easy to work on. I personaly hate V6's i had a ZR2, great running truck, but it didn't have the petal response of the 4.0. Also, don't know if it is true, but i have been told that the 4.0 makes 80% of it's power at idle. Just a few reasons why i dont like the new motor. The only way that i will buy a JK is when the v6 has been run for a few years with no major problems or when it comes with a V8. Untill then i will stroke and build my jeep till it falls apart.
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Unread 09-24-2006, 09:53 PM   #26
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Quote:
Originally Posted by Jakemd98
The only way that i will buy a JK is when the v6 has been run for a few years with no major problems
Umm, this has already happened... It has been around in DC minivans for years.
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Unread 09-24-2006, 10:00 PM   #27
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Quote:
Originally Posted by LEDFoot
Umm, this has already happened... It has been around in DC minivans for years.
different applacation, could mean different results due to different uses of the motor, ie water, mud, weight.... (just needed some BS to cover my *****)
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Unread 09-24-2006, 10:41 PM   #28
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Quote:
Originally Posted by Jakemd98
Also, don't know if it is true, but i have been told that the 4.0 makes 80% of it's power at idle. Just a few reasons why i dont like the new motor.
What percentage of its power does the 3.8 make at idle?
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Unread 09-24-2006, 11:55 PM   #29
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Quote:
Originally Posted by cab76
What percentage of its power does the 3.8 make at idle?
It makes percentage of torque, not power. And it is irrelevant, as unlike power, torque (at the wheels, where it matters) can be increased by proper gearing. With proper gearing 3.8 will pull itself quite happily in 4Lo, and on the highway - it is the area under the torque curve that matters, as you are not dirving or passing in idle.
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Unread 09-25-2006, 03:50 AM   #30
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Quote:
Originally Posted by Laxstar46
KK guys well Ive been lookin into these JK's and Gotta say i really like them. I was a big fan of the 4.0L but i think this 3.8 will be just as good if not better. Now here's my question. I'm lookin at the jeep website they give the 4.0 L 190 hp and 237 ft lbs torque. The 3.8 has 202 hp and 240 ft lbs. they also say that the 3.8 is a better engine cuz it will have more torque available in the higher rpm range. this is what jeep states.

Now i work with a guy that has a 98 sport tj. He is tellin me that even tho this is what jeep says the 3.8 puts out he says the 4L still has way more torque. His only info to back that statement up was "well the 3.8 is a V so it stinks". which isn't very factual.
I did some reading online and what i came up with was reasoning sorta like this. If two engines that are relatively the same displacemnt and are being given a comparable fuel mixture and that most parts of the engine are similar. Then the Inline engine will have an edge in torque over the V. But i also gathered that this is not a standard across the board for all engines on the market.
So i'm figuring that the 3.8 must be designed different in someway that makes it hvae just about the same torque with more hp than the 4.0L.
I'm also looking at the ratings that jeep puts up and when looking at those the 3.8 actually has a bit of an edge over the 4.0. Can someon explain to me how inline engines compare to V styel engines with torque and why (if at all) the 4.0 is so much better an engine than the 3.8.

I'm gettin an opinion from you guys cuz when i look at jeep they support what i'm thinking and that's that the two engines are practically the same. But the guy i work with sez no the 3.8 is junk but he had not factual info to back it up. i also don't believe him cuz about three weeks ago i lost my gas cap and he told me that my jeep would blow up cuz there would be air in the gas tank. i basically told him that theres air in the tank all the time or the tank would implode under air pressure from the outside. he then got mad threw a tantrum and told me "fine don't call me when ur jeep is gone" and just acted liek a child. so i turn to the guys on this forum for my answer because i think i hvae a good understanding of it but i want some outside opinions.
I haven't read all the posts so I'm not sure whats been said.

Essentially configuration of the engine probably has little to do with power deployment, for the most part anyhow.

Now the 3.8 is a modern engine and thus has all the traits of modern engines. Thi good and bad. Generally modern engines are efficent, economical and reliable. However they generally are revvy little suckers.

Older engines like the 4.0 are longer stroke and in typcially American fashion are good on low end grunt. This means they are very responsive low down. But generally the torque PEAKS early so HP isn't great.

To understand this you need to know what HP is. Well its mearly an expression of torque at speed.

HP = torque (lb ft) x rpm / 5252

So you can make less torque at higher rpms but make more HP.

In fact making torque at high rpms is the key to high HP applications, such as modern 4 cylinder engines. Or more extreme sports bikes and Formula 1 engines. An F1 engine is capable of 800bhp from only 3.0 litres, but it needs to rev past 17,000rpm to achieve this.

Now the new engine is a OHC engine and I would guess it has been designed to take advantage of this valve train setup, this means short stroke which in turn means higher revs. So PEAK numbers and highway performance should be superb, although you will probably have to drive a it bit hard to make the most of it.

The old 4.0 was a push rod OHV engine, now generally speaking these are long stroke engines. This means the don't like revs but will make more power down low. Personally I prefer such a setup as it means you don't have to drive the engine as hard to make the power. The down side is the engine is being less efficenct in terms of specific output and also maximum HP is potentially limited.

For off roading I honestly believe the 4.0 is a better powerplant. You want lots of power/torque and engine breaking from idle. The newer V6 will not be able to deliver this. Gearing can help but not overcome. This is why diesels are often great off road, they operate in low rpms and can make massive lb ft.

A nice example is I have a 2.5 turbo diesel Discovery (111bhp), my brother recently had a 3.5 litre OHV V8 Land Rover (137bhp). Off road these are both great and in low 1st will crawl along at idle no problem and on steep rouge inclines there is plenty of power to keep it going without risk of stalling.

My mother however has a Vauxhall Frontera, a modern 4x4 which weighs less than either of the Land Rovers. It has a moder DOHC 2.2 litre 16v 4 cylinder engine and makes 136bhp. So more power than the Discovery and pretty close to the V8. However as it is a modern engine its all revs. And off road it is pretty cutless. To get up some slopes you have to ride the clutch this is because it will stall due to lack of grunt low down. As long as you are above 3000-3500rpm it's fine, but driving in such a manor off raod is not only potentially damaging but dangerous also.

However due to the incresed displacement of the new V6 I'm sure it won't be as bad, but the inherant traits of its design will still exist.

For high speed use or racing the V6 is so much better than the old 4.0, however for low end grunt and relaxed driving I'd plum for the old timer each and every time.
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