MDS, CAFE, Emissions, and a 392 Powered RAM

[StickyLifter]

So I don't know how you guy's trucks run, but my RCSB 2wd 5.7/65RFE/3.92/31" tire Tradesman runs in MDS a lot since I went to the 3.92:1 final. I like MDS because it saves gas and is non intrusive. It's a pretty slick setup and I think it's cool.

Assume that Chrysler's durability testing works abd that the "hemi tick" is really a "warped cast iron truck manifold tick" for most occurrences and has nothing to do with the valvetrain.

When I swap out the turdly 65RFE for an 8HP70, I'm expecting to be able to spend even more time in MDS mode, which you would think Chrysler would like for their CAFE and emissions compliance. So here is what I'm wondering:

If the factory had offered a 6.4L/485hp MDS version, wouldn't it have helped their CAFE? I don't see how it would fail emissions, and I'm pretty sure that the added power from the displacement increase would help the truck stay in MDS mode EVEN EVEN MORE. I could them offering it as an option on the R/T models that already have the 8spd and 3.92 final. I don't see how it would burn more gas at light load, and with 40 extra cubes it's bound to pull hills in MDS and stay in more often. How can a 3.2L running on four NOT get better mileage and emissions than a 5.7 running on all eight under those conditions?

 

[DILLIGAF]

MDS, What's that ?

 

[Burla]

The decision was made, hemi is going byby following the Ford ecoboost route. I wonder if Pentastar will be far behind, maybe all v8's going away for ram.

 

[StickyLifter]

The decision was made, hemi is going byby following the Ford ecoboost route. I wonder if Pentastar will be far behind, maybe all v8's going away for ram.

:*(
Yep so I'll drive mine, and my rowdy Corvette, till I die. I hope I never have to buy a new vehicle.

 

[StickyLifter]

MDS, What's that ?

The fact that the lifters don't loft right off the cam lobes is wicked hot tuna to me. Watching the mpg meter bury itself above 30 while going down the interstate produces petrified wood in the seat. Do try it, it's rather remarkable.

 

[DILLIGAF]

Hellcat Lifters sound cooler. MPG is for soccer moms

 

[fernandok]

^^^

 

[retired]

i can verify that on a 6.4 i do not see any difference in mpg when mds is kicked in at 65 mph or when it is not kicked in.

 

[kurek]

The top gear ratio is almost the same on the 6 and 8 speed transmission so I think it's unlikely either gearbox would produce a meaningfully different outcome at a constant highway speed.

I'm in a 4x4 and get the eco indicator most of the time at cruise, can't tell when MDS is active because mine is seamless but if I try at all I can get the mpg-o-meter to claim 20+ mpg on extended trips.

I haven't calculated by hand in ages, not worth worrying about. But on my truck MDS has no drawbacks so I really have no clue what people find so offensive about it.

 

[Wahrsuul]

A lot of the people that don't like MDS blame it for "hemi-tick", or have modified exhausts. To be fair, I test drove a truck with a custom exhaust and it sounds ... weird when MDS kicks in.

I've had mine over four years now and I can tell when MDS kicks in sometimes, but not often. I've run the same section of I-95 both with it on and off and for my use it does save some gas, but only in specific situations. Running around town, it seems better with MDS off.

But for the most part, I like it.

 

[Travis8352]

The top gear ratio is almost the same on the 6 and 8 speed transmission so I think it's unlikely either gearbox would produce a meaningfully different outcome at a constant highway speed.

I'm in a 4x4 and get the eco indicator most of the time at cruise, can't tell when MDS is active because mine is seamless but if I try at all I can get the mpg-o-meter to claim 20+ mpg on extended trips.

I haven't calculated by hand in ages, not worth worrying about. But on my truck MDS has no drawbacks so I really have no clue what people find so offensive about it.

It seems those with aftermarket exhausts hate mds. Mds funtions flawlessly in mine and if it saves me even a miniscule amount of gas on a long trip ill welcome it

 

[StickyLifter]

Hellcat Lifters sound cooler. MPG is for soccer moms

Lifters make it sound cooler?? How dat work?

The same tricks that improve MPG will also improve 1/4 mile performance.

 

[kurek]

I think it's interesting how frequently the "if i wanted mpg i wouldn't have a truck" demographic also intersects with the "dang gas prices I'm gonna make it political!" demographic

I put different rockers & pushrods on my car last week... they're probably going to change the sound of the car a tiny bit going from 1.6 to 1.72 ratio but I left the stock lifters in there.



This engine doesn't have MDS but it also doesn't have VCT or variable intake tuning so it's only rated 215 horsepower from a 5 liter V8

 

[StickyLifter]

I don't think you guys are getting what I'm laying down here.

I'm not talking about just on the highway, I'm saying it should run in MDS nearly constantly once your accelerated to whatever speed you are driving at. Mine goes into MDS at all speeds when I let out of the pedal, meaning light load. If I am on level ground cruising at ANY speed, I'm in MDS mode and getting between 27 and 30+ MPG. The only time my truck drops out of MDS is when I get to a hill or want to accelerate. This is a function of load on the engine, which decreses as gearing is shortened. The truck will run in MDS mode MORE OFTEN with the 8 spd.

Since increased load is overcome by more diplacement, in theory MDS should stay engaged even longer (like when climbing a hill) with a 6.4 than it does with a 5.7 because a 3.2L four cylinder makes more power under a given set of conditions than a 2.8L four cylinder. So why didn't we see a 6.4L R/T? Was it the load that a federal emissions dyno puts on the truck during testing? Did it keep kicking out of MDS during testing, and thus not pass? I just can't imagine why a 6.4L/485hp/8HP70 RAM R/T wasn't a thing from 2013 to 2022.

Y'all need to quit TL: DRing, you might learn something.

If you don't think that MDS saves you gas then you don't understand how an engine works.

 

[StickyLifter]

I think it's interesting how frequently the "if i wanted mpg i wouldn't have a truck" demographic also intersects with the "dang gas prices I'm gonna make it political!" demographic

I put different rockers & pushrods on my car last week... they're probably going to change the sound of the car a tiny bit going from 1.6 to 1.72 ratio but I left the stock lifters in there.

View attachment 482380

This engine doesn't have MDS but it also doesn't have VCT or variable intake tuning so it's only rated 215 horsepower from a 5 liter V8

Increasing rocker ratio will give you more lift at the valve and just a tad more duration. It may change the idle just a bit.

No need to apologize for lower output per displacement, that's a cam and head package away from being a 400hp 5L and you still have good area under the curve with 300+ ftlbs of torque from a very small and light engine.

 

[StickyLifter]

And another thing; This thread is really me asking about CAFE and emissions testing and associated reasoning, not whether my hypothesis is correct.

 

[Wild one]

Increasing rocker ratio will give you more lift at the valve and just a tad more duration. It may change the idle just a bit.

No need to apologize for lower output per displacement, that's a cam and head package away from being a 400hp 5L and you still have good area under the curve with 300+ ftlbs of torque from a very small and light engine.

400 hp out of a 302 smallblock is going to take a bunch of rpm /a very good set of heads,and alot bigger cam,plus a differant set of headers,as 1 5/8" headers are a touch small to generate 400hp even on a little 302. That's just over 1.3hp per cube,which is do-able on a smallblock Ford,but it's starting to get a bit radical,and will need a fair bit of gear and convertor to be livable on the street,even in a 3300 lb Mustang etc.

 

[kurek]

I might be looking at the high side of 230.. it's still on stock heads and there's no budget this year for new ones. This thing's just a rescue with a quarter million miles that I picked up last summer for a few hundred bucks so I'd have something to do in the garage when I'm bored.

I only brought up my old winter project because it's an example of how far we've come - 395 horsepower on a half ton gardener's truck ain't bad. People don't like MDS but variable cam timing and variable intake geometry doesn't suck

 

[Wild one]

I might be looking at the high side of 230.. it's still on stock heads and there's no budget this year for new ones. This thing's just a rescue with a quarter million miles that I picked up last summer for a few hundred bucks so I'd have something to do in the garage when I'm bored.

I only brought up my old winter project because it's an example of how far we've come - 395 horsepower on a half ton gardener's truck ain't bad. People don't like MDS but variable cam timing and variable intake geometry doesn't suck

The later 302's with the hyperutic pistons were tough little motors.I seen lots of them drug out of 1/2tons/Mustangs etc,with 150,000 miles on the motor,and guys would throw a 150 shot of nitrous at them,and they'd swallow it all day long,lol

 

[StickyLifter]

400 hp out of a 302 smallblock is going to take a bunch of rpm /a very good set of heads,and alot bigger cam,plus a differant set of headers,as 1 5/8" headers are a touch small to generate 400hp even on a little 302. That's just over 1.3hp per cube,which is do-able on a smallblock Ford,but it's starting to get a bit radical,and will need a fair bit of gear and convertor to be livable on the street,even in a 3300 lb Mustang etc.

Yep! Gears, converter, shift kit, subframe connectors, shocks, bushings, and slicks are first, then a set of Twisted Wedge heads, 220/230ish roller cam, long tubes, and a Vic Jr aught to get it done. If you have to spin over 6500 to get close something is wrong.

Old motors are the best. For sure don't have to worry about ring ends butting together or spinning a rod bearing when you got huge blow-by and 10psi at idle on 20w50.

*but*

Why do you think RAM team never offered a 6.4L R/T model?