Ram 1500 diesel review

bimbert84 wrote:


It's not a deficiency. It's a difference in the way the engines operate.

I simply don't understand the compulsion to compare these engines at the same RPM. It's like comparing a running back to a wide receiver but never throwing a pass. That's not a deficiency of the wide receiver -- it's a misuse of his abilities. The same is true with running a gas engine at low RPMs when power is needed. Why would you do that?

The entire purpose of the transmission is to put the engine's power to the ground, yet so many people choose to ignore this. A better spreadsheet would be one that shows maximum available power at any given road speed. Do this and you'll find the diesel and gas engines will be running different RPMs (because they'll be using different gears) at the same road speed.

-- Rob

Maybe deficiency wasn't the best word choice. All I was doing was showing that the two different engine types have a different delivery of horsepower (I just noted the 1:1 ratio to make comparisons even on power delivery). Such as when 200 HP is needed to move a load, the diesels will have it at 1500 RPM, and the gassers will be either at 2500 RPM or 3100 RPM depending on which engine in the spreadsheet. I think Wilbert was trying to express why many diesel fans find a diesel more satisfying to drive with that lower end power. Not saying that one or the other is superior power wise when it comes to pulling a load.

In the case of Ford Superduties, the Diesel and Gas engines use the same exact transmission and the only differences are rear gears (gas motors typically have 3.73 or 4.10 rear ratios while diesels get 3.31 or 3.55). So you get different behaviors out of these two trucks. The gas motors have far more operation range (6,000 rpm redline or there abouts) than the diesels (roughly 3100 rpm) and can dig down all the way to 2nd gear at freeway speeds if they need more power to pull a load up. This allows a Gas Motor to multiply their output to the ground more when they get into their power band. Sure they'll be revving pretty hard, but they're designed for that. This is typically the reason why a gasser will out-accelerate and pass a diesel with similar horsepower figures on a flat road (once the gasser gets to its powerband). Diesels with their narrow power band don't have this flexibility, so they "feel" like they lose a bit of steam when they can't downshift to 2nd gear on the freeway and accelerate hard, instead they have to remain in a higher gear and lose the advantage of output multiplication from the transmission.

Unfortunately all gassers in heavy duty trucks (F-250/2500's) are naturally aspirated and lose a lot of power high in the mountains. Now if they were turbocharged like the Ecoboost motor from Ford, I'm pretty sure the truck would have no problem going up a mountain since the turbo's will ensure the engine gets close to the same amount of oxygen as it did at sea floor. If a diesel didn't have a turbo, you would experience the same power loss in the mountains as well, then you would be the one holding up traffic in the slow lane.

As to the spreadsheet, it's easy to add another modifier line to it and chart out available power for given tire size, axle and transmission gear ratios. In the end, the transmission and differential are going to be multiplying the output from those base horsepower charts on the spreadsheet.