ib516 wrote:
Comparing apples to apples, the 6.4L Hemi is the clear performance winner. LINK
I have towed my 11 - 12k 5er through the Canadian Rockies, and not once have had the RPM limiting that is shown on the "Ike" video. I'm just guessing here, but it may have something to do with the elevation? I've never had my truck at 11,000' above sea level when towing either. I have also searched the other 6.4L Hemi forums I frequent and have never rear of another owner experiencing the RPM limiting seen in the video.
The point I'm trying to make is that I don't think it's sensible to judge a powertrain's towing merits based on it's performance on the one highway in the whole country where it struggles. Check out the "Davis Dam" portion of the above link. That is an uphill grade as well, and involves towing, yet no RPM limiting. That and the fact that I haven't had mine do that is why I think it is the elevation that makes the computer do what it did. They likely designed it that way for a reason (why I have no idea?).
On the longevity of the 6.4L Hemi, it is a new engine as of 2014 (in trucks anyway) so there's no data out there to judge that on. It is designed to be robust however, as can be seen in this newsletter sent out to the dealers when it came out:
Also -
"6.4-L Hemi developed for truck duty
Though it debuted in the 2011 Dodge Challenger SRT8 (and is used in other Chrysler, Dodge, and Jeep SRT8 models), the 6.4-L was originally designed as a truck engine, according to Mets. Its components were optimized to satisfy tough durability and market requirements.
โAn active runner intake system [helps to] provide that low-end torque that is required in a heavy-duty truck, but without sacrificing that high-end power,โ Mets said. โIf you look at the torque curves between this engine and our competition as well as the 5.7-L Hemi, the 6.4-L generates as much torque as the others but at 800 to 1000 rpm less.โ
Another truck-specific feature is an optional dual-alternator setup for chassis-cab applications. This marks the first time Chrysler has offered a gasoline application in the 4500 and 5500 chassis cabs, according to Mets.
โDesigned as a truck engine, we were able to do things like packaging an optional dual alternator; so straight out of the factory, a dual alternator with 380-A [220 and 160 A] outputโฆwhich is very significant for those electric applications [customers] put on the back of a chassis cab,โ he said.
The 6.4-L Hemi shares the basic iron block/aluminum heads architecture of the 5.7-L Hemi, as well as its manufacturing process. It also borrows Chryslerโs fuel-saving cylinder-deactivation system, which shuts down four cylinders when in steady-state operation. This is Chryslerโs first application of cylinder deactivation to the heavy-duty pickup truck and chassis-cab markets, according to Gary Rogers, Chief Engineer for Engines.
While fuel-economy figures for the 6.4-L trucks are not yet available, engineers placed a great deal of emphasis during development on features to improve fuel economy, Rogers said.
โWeโve put a lot of hardware in the engine for that purpose, like the cylinder deactivation, the cooled EGR [exhaust gas recirculation], the active intake, variable valve timing, and the active thermostatโthose are all fuel-economy features,โ he said.
To better manage high temperatures and improve durability, engineers specified โpremium" materials for the 6.4-L application, Mets shared. These include stainless steel exhaust manifolds, steel gaskets, and fasteners as well as sodium-filled exhaust valves and an upgraded valve-seat material.
โWe also have a robust high-volume oil cooler and oil jets for cooling the pistons. These are all key things to keep this engine running at a good temperature for long engine durability and longevity,โ he said."
And -
"The 6.4-liter engine develops 410 horsepower and 429 foot-pounds of peak torque. Designed as a truck engine from the ground up, it features an active runner intake system that enables the block to generate as much torque as competitive models at 800- 1000 rpm lower engine speeds. As a result, engineers were able to add a cylinder deactivation feature that cuts out half the cylinders when engine loads are low to extend gas mileage.
Construction consists of a cast iron engine block with aluminum heads, a heavy-duty forged steel crankcase, stainless steel exhaust and sodium-filled exhaust valves. A positive crank ventilation valve integrated into the intake system and cool exhaust gas recirculation make these emissions components more efficient. Oil jets cool the pistons under extreme temperatures or when the engine is working hard hauling heavy loads."
I'm going with the 6.4 Hemi. Thanks for your insights. Saw your YouTube video just now and I'm certain I will have no issues pulling a 6-7k lb Airstream after seeing you get up to speed with your 5th wheeler that doubles my weight. Thanks. I will spend that $11k on beer, firewood, and marshmallows for the kids. Hah.
Dan
