mikewadley

Thought I would update: Just finished a 75 mile trip thru the hills of Arkansas averaging between 55-60mph. I averaged 18.2 mpg so a little better this time. I did notice at 57 mph I was running about 1900rpm.

jhol111964

Not to continue digressing, but I have seen close to 21 mpg in my sport with the 29's, - calculated, not relying on the hokey computer mpg. Putting 32" MTs on cost me about 4 mpg! That's almost 20% increase in fuel cost, which for my work commute, which means $40 a month extra. It looks anemic again, but I recently put my 29" pizza cutters back on, and enjoying the better mileage, less rolling resistance, and smoother ride. Paradoxically, it doesn't corner as well. These wimpy ST's must have jello sidewall stiffness compared to the MT's or something.

Back to the OP, at highway speeds in the 1500-2000 rpm range, the 3.6 makes the same torque as the 3.8, and only 10% more power. See the RIPP supercharger thread with the dyno test conclusive results. So, 2012 is all about proper gearing.

jhol111964

Here's the thread on the dyno tests and results:

https://www.jk-forum.com/forums/show...ight=ripp+test

AZMyke

Here's some information about my JKU and I also have a question (at the bottom)

My 2012 JKU now has 3500 miles. My commute is 44 miles round trip and so far I've been averaging 18.2 to 19.8 (depending on the traffic I had to deal with) between fill-ups (primarily inner-hwy). The majority of the time I'm stay around 65-70, but every now and then I get the urge to jump on it.

The 3.6L is nice and I do need to "step into it" for the response I want, but it gives it to me. This is either from a dead stop or whether I'm at cruising speeds. Finally getting use to it.

On the long open highway, traveling at 65-70 (6k altitude), I managed to get 22+ mpg ... this was a fairly level stretch of road.

I noticed that the gear ratio chart @ 70mph put the RPMs at:
33's @ 2288
35's @ 2426 (both green bands)

Currently I am stock and I'm getting the information above. I do want to lift approx 3 or 4" and get some 35's to wheel on and when I'm not wheeling, have the stock tires on. I have room to store the set that's not on.
It seems there's no need to regear with the 4.10s.

(I do realize I will need a ProCal unit and DSs.)

Is this making any sense to you all?

I appreciate any comments. (By the way ... this jeep rocks! Like all the rest that I've ever owned)

Enzo

Its an aluminum engine, like all the others before it will leak.....last example the cadillac North Star engine

AZMyke

BadTrainDriver,

I read the article ... pretty informative. Like yourself I'm not at 5k yet. But I will come back once I'm there and tell you what's happening with my jeep. I try to keep good tabs on it's performance

goaterguy

I don't think you can get higher rpms with a taller tire while being in the same gear, the rpms should be lower @ a specific speed.

What!? Most engines nowadays are made from aluminum. All of my 5 vehicles have aluminum engines, even my $97 Walmart lawnmower engine is aluminum and none leak.

VVTL is not related to odometer miles, it has to do with rpms and load and it is the reason a smaller displacement engine (3.6 vs. 3.8) develops more torque after 1,000 rpms and more horsepower across the band.

Blade

The northstar engine leaks because it is a split block design. The viper engine is also aluminum engine and I have seen great things from that motor.

deathboyardee

Exactly. The only problem with the Northstar was that the heads would pull from the block. After GM released the TSB repair procedure with the inserts the problem was solved. And even at that most didn't have problems until the 100K mark or later. Other than that the Northstar was an excellent motor with a lot of technology behind it!

Tuto

Please let us know how you manage to get over 24 MPG in the old 3.8 V6?