Good point. However, hate to say it, but I'd thought I'd look into injectors, etc., a little more fuel, some timing changes -- perhaps bring it into the HX35 range, but then again, maybe that's all way too much -- since the stock 3.9L is way too much in the first place.

Still thinking about it.

 

I think how much you bomb the motor will depend on what you intend to use this Jeep for. If you're going rock crawling or trail riding, the most important thing is smooth, predictable torque from idle to governor, not max HP. If you're going mud bogging or playing on sand dunes, then max HP would be a good thing and a little turbo lag would be acceptable.

 

im running one in my m715. i can help with SOME questions, if i can....

im looking at adding an intercooler to mine now...
im runnin 4.56 gears, nv4500, divorced 205, 60 front w/electrac, 14bolt rear w/detroit and a used 4bt 3.9l motor

 

Dang that's sweet!!! i love it!



Hey Tartarus, where are you located? I'd sure like to see this TJ! Make sure you take plenty of pics to share with us!

 

That 4BT looks tiny next to those tires. Awesome pic!

 

Heard fropm my cousin who works for DB here in Kenosha Wi. he says there going to put 2.7turbodiesel in Grand cherokee and Jeep Liberty for 2005 . I don't know how true that is but i do know there doing it in Europe right now. I think just Grand Cherokee.

 

First of all, what a neat vechile this is goign to be--just what a Jeep should be, in my opinoin! Glad to see someone being creative. Though this isn't probably a first priroty for this vechile, I'll be interested to know what sort of fuel economy you get with this Jeep. A friend's '99 4.0L 5-spd only will pull about 14mpg.

Seconldy, the ISB 4-cylinder is, recall, 2/3 of a 5.9. Ever notice how the Chevy 4.3 V6 vibrated quite a bit, where as the 5.7 V-8 did not? Well, same story. It's 2/3 the original engine, and in the case of the ISB, it's no longer naturally balanced, so yes, it's going to vibrate--a lot. I've worked with this engine in Case industrial equipment, that's why I reccommended against putting it into a Durango that was to be used as a daily driver in another thread. You will need to consider very good iso mounts for this engine, and some creativity will be needed. Good luck with the project!

 

Now I am not an engineer, and can only print what I have read on this subject but.... A v-8 balances, a four cylinder balances, a straight six balances, but a v-6 does not. GM changed the crank throws to split the pairs to balance the v-6. A lot of ricers would be shocked that you can't balance a four cylinder. On the other hand the more cylinders the smoother it runs, hence the rougher 3.9. How about an expert chiming in here on this...

 

Well, I am no expert, but here's my take on the engine balance issue:

Engine configuration is the largest determinant of smoothness. The smoothest engines are going to be either inline engines or horizontally opposed engines (boxers, like Subaru and Porsche use).

Why? ANY Vee-configured engine has forces that cannot be accounted for. The cylinders are not operating in the same plane, so there's going to be vibrations that can't be countered.

Consider too, the NO engine will balance perfectly. This is because the "weight" of each piston is constantly changing with the forces acting on it. On the exhaust stroke, the piston is "lighter" near TDC as it's about to make the turn to the intake stroke. On the power stroke, the piston is "heavier" as the forces of combustion act on it.

This is where torsional harmonics come from. The momentary nature of the cylinders firing causes the crankshaft to twist and then untwist at a certain frequency. This is why inline engines are rarely more than 6 cylinders-- a long crankshaft is VERY prone to cracking from torsional harmonics.

The reason the Chev 4.3 V6 is not smooth is NOT because it is a v-6. It's the wrong vee angle. It is simply because GM wanted to save money and used the same basic block as the 5700 or 350. The vee angle of a V8 should be 90 degrees. This gives you one cylinder firing every 90 degrees [two crankshaft rotations=720 degrees, divided by 8 cylinders= 90 degrees]

However, the vee angle for a V-6 should be 60 degrees. Look at V6 engines from Nissan and Toyota and Honda. They are smooth as silk. Most are 60° V6s. And that's for a reason.

But generally, NO vee configured engine can be as smooth as an inline or boxer engine can. It's the nature of the beast.

It's interesting that a Vee engine will generally rev faster than an engine of another configuration, and that's why you see them so much in racing.

Balance shaft can help a lot as far as the amount of vibration transmitted from the engine to the vehicle. They work on the principle of destructive interference. What's that, you say??

Imagine you have a graph of a sine wave on an oscilloscope. It's similar to when you crack a whip-- you send a wave down the line.

Now if you send another wave down the line, it may either cancel the first wave, or it will add to it and make it double- depending on the timing. If it's "in phase" you will have constructive interference that makes the wave bigger. If it's "out of phase" you will have destructive interference that makes that wave smaller.

So if we install a balance shaft that always generates a wave of equal amplitude, but is 180° out of phase, the destructive interference cancels the vibration almost completely.

Incidently, this is how the noise-cancelling headphones work. They listen to the background noise and generate exact destructive interference. Presto! The noise is gone.

Sorry to digress. I'll be happy to post more if there are more questions.


Justin

 

I forgot to add:

The relative size and number of the cylinders also plays a key role in engine smoothness. With smaller, lighter pistons the the vibration is less because the combustion forces are less, so you have less amplitude to your vibration waves.

The MORE cylinders, not only do you have lighter pistons and rods, but the the combustion impacts are spread out-- you have smaller combustion events occuring more often.

That's why V-12s or v16s are so smooth, even though they are vee engines. It's also why they rev so fast and are so responsive-- because you have a cylinder firing every 45 or 60 degrees as opposed to 90 or 120 degrees.

To illustrate:

4cyl: one cylinder firing every 180 degrees of crank rotation
5 cyl: every 144°
6 cyl:120°
8 cyl: 90°
10 cyl: 72°
12 cyl: 60°

So you can see how as you add cylinders, the engine will become smoother from each combustion event occuring closer together and with smaller impact.


Justin

 

Hey Tartarus, where did you get the engine and how much was it. I want one for my YJ. I've look all over my area and no one can help. I even work for dodge and these guys can't help eather. Any info will help, thanks.

 

oh yeah, this is awesome!
questions for mcinfantry:

how fast can you go?
mpg?
how is it on torque?
do you have any mods done?
is it as noisy as the 6s?

 

ok i can go 76mph. mathmatically i should do 84

i get 32mpg at 55
i get 26mpg at 70
i get 22mpg at city driving
fantastic torque
0 mods
not very noisy.

 

I love that set up. That is exactly what I've been wanting to do to my 75 Ramcharger. I already have Dana 60's front and rear.


By the way, what size tires are you running

 

, Hey, I am considering this same engine setup, using the Cummins ISB170. How much was the deal you found for the engine, and where did you get it from? Is it the newest common rail unit? Similar to the 5.9L Cummins with Common Rail injection? Does it use pre-charge technology as well, to make the engine quiet? How quiet is it? Or have you fired it up yet? Thanks in advance for you thoughts and inputs. Gene