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6.4L/8-Speed or 6.2L/6-Speed

12K views 27 replies 13 participants last post by  BlackOps82 
#1 ·
So with debut of the new 6.4L/8-Speed automatic Grand Cherokee SRT... Would you rather have the LS 6.2L and 6 speed automatic or the new 6.4l/8-speed?
 
#2 ·
LS/HEMI in a JK

What year Jeep, because if you have a 2012-2013 it is easier to use the 6.4L/A580.

If you have a 2007-2011 it is eaier to use the 6.2L/6L80, we have done both. I like both, but the Aluminum Block 6.2L will probaly have less chance of over heating or getting hot.

The 6.4L is a very good engine, like the VVT Truck Hemi a lot of low end Torque. It is all about the intake manifold. We are getting better with the tuning, we are tring cams, headers.

I like the LS because the tuning is much easier and a lighter engine, they both are good choses.

I am a GM guy and always liked the Chevrolet engines, I put a LS in my Jeep, but my wife wants a HEMI so we will have both, she likes the HEMI engines better. She likes to keep the JEEP all MOPAR!
 
#4 ·
I'm saying which would you rather have? I realize that it's not available at the moment.

I guess it would be more fair to compare the new 6.4L/8-Speed auto to the new GM LS 6.2L/6-Speed auto.
 
#5 ·
I would rather have an LS. No matter how much power or how many gears a Hemi has it is heavy, susceptible to run hot, and is dependent on Chrysler software.

Vehicle dynamics are different with an LS, drive one, especially off road.

I'm sure the Gen V LS will be an awesome engine too.

The new 8 speed was designed by European's for smaller engines to keep them in their power band. Chrysler is targeting fuel economy with the 8 and 9 speed transmissions . In a large V8 I think 8 speeds will be to much shifting. I have 7 speeds in my Mercedes with a 3.5 liter engine and it works well but boarders on being annoying. Add MDS and a V8 with 8 speeds?

The original ZF was good for about 500 ft. lbs and the 6l80 about 800, interesting to see if they beef it up.

And above all else the 6l80 is like magic the way it is always in the right gear. Untold hours spent on software development on a American transmission. Chrysler is already having issues with the 8 speeds software.

In a straight line race I think the 6.4 has the advantage, but most everywhere else I'd take an LS.
 
#8 ·
I would say the reason is that there is so much aftermarket support for the GM engines. They are easy and cheaper to hot rod. In days past I rebuilt a lot of engines; Chevys were always a good bit less expensive to rebuild. I also think Chevy has more parts commonality and it is easier to find Chevy parts in a pinch. Ask Robbie about the Hemi that needed a water pump that took up residence in his shop because the part was on national back order.
 
#9 ·
Too many gears

I have a Commercial Drivers License though I haven't driven a semi for a few years now. Semi's have 10 and 13 speed transmissions so you can always keep them in a very narrow Rpm range; typically 1700 to 2100. This is needed so that you can keep the rpm in the fat of the torque curve and maximize economy when you are pulling 80,000 pounds down the freeway and so you can climb hills.

But our JK's are not Semi's and a big torquey engine like the LS engines don't have to stay in a narrow rpm range. The VVT moves the torque curve quite low and low and also makes it broad.

If I was trying to maximize a lousy engine like the Pentastar an 8 speed tranny might be helpful. He'll, the 3.8 would have done better with an 8 speed.

There is more to a vehicle than HP and number of gears. For an off road vehicle tractability is important and here the LS shines. Given it is also a smaller, lighter engine that cools better and has better aftermarket support I just don't see any excuse to put a HEMI in ANYTHING. In fact, other than into JK's to simplify wiring, does anybody put the HEMI in anything else. How many Hammers buggy's run Hemi's? The Hemi is just a big heavy old school hunk of American pig iron with no redeeming features other than the name and that it was an improvement over the Chrysler V8's that it replaced. That is not saying much. It is not a world class engine like the LS is.

Of course I may be a little pissed that my Jeep engine died at 29,000 and even though I had the supposed lifetime power train warranty Chrysler declined to warrant it.

I am recommending to one and all that if you want great JK you find an 07 or 08, shitcan the entire drivetrain and put an LS, 6L80, and 60’s in it and call it good.
 
#12 ·
just looking at options, if/when i do this it'll be a pullout deal if i can source one. def not a 25k turnkey install. i just know the 5spd in the 2012 GC was one of the worst trannys i've ever driven, and therefore curious about the 8spd
 
#13 ·
Ls motor is far better... aftermarket is 100 times stronger and tuning ability is exponentially better compared to mopar... the 6L80 trans is a monster... its perfect in stock for for 800 hp and tuning it is awesome.. I like Hemi's but the aftermarket sucks horribly.. and I it always will the tuning sucks and always will...! I'm doing a 392 swap in mine only because I have a new free motor and don't need much to swap it into my jku and I have the skills to tune and wire and fab whatever I need. if I didn't have the motor I'd do an aluminum LS3 all day long I have plenty of parts from my ZO6 to make it perk up a bit too!
 
#18 ·
I don't get the point of an 8spd trans, given how wide the powerband is on a LS or Hemi. If it was behind a high strung little 2L engine, I could understand it.

I think most of what's driving these new transmissions to be released is emissions. I can only speak for myself, but emissions doesn't even make the list of things I care about for my Jeep.
 
#20 ·
I'm not sold on the 8 speed transmission yet. We are doing a couple Gen V swaps right now and I will know more soon. I was disappointed with the Chrysler 8 speed I drove it never seemed to be happy in any gear so it was always shifting.

I think the 8 and 9 speed transmissions work best in small displacement engines to broaden their usable power as well as in diesels that like to run at a particular rpm.

An 8 speed may not show as much advantage in a large V8 with a wide torque curve. If you have a Corvette that goes 200 mph the 8 speed makes more sense, but in a JK that may go 90 mph 8 gears is a lot. The 6l80 and 8l80 low and high gears are not that different so they are shooting for efficiency through optimizing the operating range.

Direct Injection is huge, allows high compression with lower grade fuel and improved mpg. CVVT I believe will also make a difference.

We will be doing a Gen V 6.2 6 and 8 speed swap and I will be able to compare them side by side.
 
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