5.7L V8 Questions

[Kungfubhuda]

After some previous FCA lemons, RAM wasn't on my radar, but I decided to test drive the 2019 1500 while I was looking at some Silverado's. I ended up loving the truck, and got a V8 Laramie. Now I've become a little obsessed, among my random questions, I'm curious about the 5.7 V8:

Based on the wiki, it sounds like the 5.7 V8 has been around a while. From what I can tell, this gen was released in 2003, MDS and 50 hp were added in 2009, and an extra 5hp in 2013. Any other noteworthy updates? Is that accurate?

At idle, if I'm understanding MDS correctly, should the engine be running on 4 cylinders? Or is that only activated when cruising at highway?

The transmission hits 8th gear pretty early (45mph or so). Is there a reason that there isn't a 9th gear for 70+?

 

[Electrical]

I believe the update in 2009 were Eagle Apache heads, which flowed a TON better and were a large part of the power bump. This being the reason not a lot of aftermarket exists; Eagle's Apache's already have outstanding flow.

Several small updates along the way like improving the cam chain tensioner and revising valve seats to better withstand over-temperature conditions.

People call the Hemi and Pentastar long in the tooth, but the fact is they are still very competitive and that long history means improved durability.

The reason why there isn't a 9th gear is the same why there isn't a 10th gear. It simply wasn't in the cards. It's a ZF unit, used across many brands and generally considered bullet-proof. Top gear is already 0.67. So not much more to be had on top, but more intermediate gears would be beneficial.

 

[Zeronet]

The transmission hits 8th gear pretty early (45mph or so). Is there a reason that there isn't a 9th gear for 70+?

Do you have 3.21 or 3.92 rear axle ratio? The optional 3.92 ratio will reduce the speed the truck shifts into 8th gear.

It would be helpful to add your truck trim and options in your signature. Easier to answer your questions without a lot of back and forth.

 

[2019ramshortbedcrewcabguy]

MDS comes on on cruise at low load.

Doesn't do it stopped.

 

[Kungfubhuda]

Great info, very interesting. Thanks for the details. New to the forum, signature added.

I'm surprised that it's running on all 8 cylinders at idle. Seems odd.

As for the Pentastar, I loved the engine until my 2012 Jeep GC started running terribly. Ended up needing to replace the left head at only 35,000 miles. Thankfully FCA replaced it, (though they tried not to). Apparently it was a fairly common flaw for a few years. I imagine that's been long ironed out by now though.

 

[Goatmann]

Great info, very interesting. Thanks for the details. New to the forum, signature added.
I'm surprised that it's running on all 8 cylinders at idle. Seems odd.

I agree it is odd he truck drops out of ECO mode at a traffic light. Not sure what stresses are involved when the truck goes from idle to, what 2k rpm from 4 cylinders then to 8 cylinders.

 

[Electrical]

I think MDS relies on re-directing oil flow to de-activate lifters on the "dead" cylinders.

I could be convinced if someone said operating conditions at idle weren't conducive to the specifics of Hemi MDS.

 

[Jordan2929]

At idle the engine doesn't make much power, things like the ac compressor, altenator, water pump, etc need quite a bit of power to run expecially when they're all consuming power from the engine at one time. 4 cylinder mode would bog the engine to much. There may be other reasons the engineers didn't allow 4 cylinder mode at idle but that seems like a reasonable answer.

 

[Billy James]

Great info, very interesting. Thanks for the details. New to the forum, signature added.

I'm surprised that it's running on all 8 cylinders at idle. Seems odd.

As for the Pentastar, I loved the engine until my 2012 Jeep GC started running terribly. Ended up needing to replace the left head at only 35,000 miles. Thankfully FCA replaced it, (though they tried not to). Apparently it was a fairly common flaw for a few years. I imagine that's been long ironed out by now though.

A lot of 2012 Pentastar heads were defective. FCA voluntarily extended the warranty on suspect vehicles to 150,000 miles. They sent me a letter for my JK extending the warranty. I thought the Pentastar was a great engine; I had one in my JK and one in my Journey.

 

[Rich]

My thoughts are that it turns off MDS at a stop because it knows you will need to start moving from a standstill, and they want to allow for a smooth acceleration. I think 4 cyls wouldn't feel smooth from a standstill.