Hoo boy. For a second there, I thought that was a photo of our 2009 Dodge Ram 1500 on -- get this -- a chassis dyno.
<rubs eyes>
Wait, what?
Call it a Mopar kind of day. Photographer extraordinaire Kurt Niebuhr had driven the Ram to the dyno on the day we dyno-tested the Viper. Things wrapped up with the Viper and before we knew it, the Ram's 5.7-liter V8 was singing a full-throttle song while spinning the rollers. The explanation eludes us. Maybe it was the exhaust fumes. Maybe the Starbucks lady slipped a little something-something in our Pike Place that morning, who knows.
Whatever the root cause, it happened, and this is the result. Dodge's pushrod "Hemi" V8 is rated at 390 horsepower at 5600 rpm and 407 lb-ft of torque at 4000 rpm. The chassis dyno measures output at the wheels, and the Dynojet 248 inertia dyno we typically use had this to say about that (click chart for a larger image):
A 3% SAE weather correction has been applied.
You'll notice that the data starts at a relatively high 3,750 rpm, a direct result of the automatic transmission's tendency to downshift even in manual mode. Hitting wide-open throttle at anything less than 3,750 rpm triggered a downshift, which caused revs to soar and aborted the run.
Fortunately, this is low enough in the rev range to capture the torque peak. We measured 328 hp at 5,700 rpm and 336 lb-ft at 4,050 rpm to the wheels.
We haven't dyno-tested many trucks recently but a few years back I wrote a pickup comparison test of the 2007 Tundra, Silverado and Titan that included a trip to this very dyno. Unfortunately the raw data is long gone but this image of each truck's horsepower remains, and is duplicated below, alongside a similarly scaled version of the Ram's run. I realize it's not an ideal way to compare the trucks but please bear with me:
Disclaimer: All the usual disclaimers pertaining to dyno testing on different days (years, even) apply here. Still, it's worth noting that the 5.7-liter V8 in the Ram is remarkably akin to the Tundra's 381-hp 5.7-liter V8 in the magnitude and character of its power delivery, as it continues making power all the way to its 5,750 rpm fuel cut.
Also worth noting, however, that the Ram recommends 89 octane (which is what we had in the tank) whereas these other trucks here were tested on 87 octane.
On a more personal level, this time spent on the dyno with the Ram was perhaps my final opportunity to wheel -- er, throttle -- the big truck. And I'm gonna miss it. It's been a terrific truck.
Jason Kavanagh, Engineering Editor
jdbosmaus says:
03:35 PM, 06/17/10
I have a question about the operation of the dyno.
I know it works by measuring the acceleration of the drum, which has a known inertia. With that you can estimate the power applied at the driving wheels.
My question is this: is there a correction factor that is applied to account for the inertia of the drivetrain? That is probably a lot higher for a truck like this than for a typical car, which would lead to a greater error in the power estimate.
half_ton says:
04:23 PM, 06/17/10
328HP at the wheels . . . would the outcome have been different with a 6-speed tranny?
church123 says:
05:56 PM, 06/17/10
If I may chime in to answer your question jdbosmaus,
The dynojet dyno in this case does not have any correction factor for the inertia of the drivetrain. With a chassis dyno, all you can really expect is to be able to measure what is left after all the drivetrain losses (friction, inertia, etc.) are accounted for.
As long as this inertia does not change, then the dyno remains useful for calculating differences in power due to changes in parts, tuning, etc. And if you're comparing similar vehicles (all large pickups for example), then the small variances in wheel/tire inertia, etc. aren't too big a deal.
As you've probably already guessed, chassis dynos are not useful for comparing vastly different vehicles. Some manufacturers, notably Mustang, Dyno Dynamics and Dynalog do try to offer a compensation factor for driveline drag and wheel/tire inertia, but since it is impossible to measure these things accurately on the dyno (which is a whole nother discussion), and no dyno shop I know of is sporting a Moment of Inertia measuring device for wheels/tires, they often tend to be more of a source of error than a tool for improving accuracy.
Summary - no compensation for wheel/tire inertia on Dynojet, but astute of you to notice.
yellowmiata says:
05:16 AM, 06/18/10
Great for the Ram - good truck. Now what is that yellow car to the right? A lotus elise?
kevm14 says:
07:47 AM, 06/18/10
Man that is kind of uneven power delivery.
hybris says:
09:38 AM, 06/18/10
The torque curve seems a bit high in the RPMs even for a gas pickup.
What sort of rear diff gear does the Ram have?
yellowmiata says:
12:18 PM, 06/18/10
FWIW - The ram-boxes still seem gimmicky. Besides busting a hole in one, have there been any other mishaps? Are the lids still closing correctly?
half_ton says:
02:58 PM, 06/18/10
@hybris
The diff is either 3.77 or 3.71 depending on the options.
half_ton says:
02:59 PM, 06/18/10
CORRECTION!!
Either 3.55 or 3.71
threemopars says:
05:48 PM, 06/18/10
@half_ton
Ram HEMI's have either: 3.55, 3.92, or 4.10 (Sport R/T model)
colorado1974 says:
05:49 PM, 06/18/10
Correction, 3.55 or 3.92 (limited slip only).
my09 says:
10:52 PM, 06/18/10
@colorado1974
Don't forget the 3.21 gears either :) The Laramie model being tested most likely has the 3.55 gears, followed in likelihood by the 3.21 gears... 3.92 gears, in general, aren't put into Rams unless if specifically requested from the factory via dealer or customer. Also (correct me if i'm wrong) but to the best of my knowledge the 3.92 gears are the only one's with Limited slip. All others have an open differential.
threemopars says:
09:45 PM, 06/19/10
Correct 3.92 and the 4.10 gears are limited slip.
bimmerjay says:
01:16 PM, 06/20/10
After 4900 RPM it appears the Tundra opens up a can of whoop-ass whereas the Titan closes up and goes home.
rodger_victor says:
02:32 AM, 06/21/10
At 4900 rpm's the Toyota Tundra would be blowing its cracked camshafts all over the floor. Trust me. I have first hand experience on the matter.
colorado1974 says:
06:04 PM, 06/21/10
2009 Ram Crew Cab Laramies were only available with 3.55's or 3.92's. No 4.10's or 3.21's were offered in 2009. The 3.92 is only available if you want the Limited Slip and if you wanted the Limited Slip, you are forced into the 3.92.
With 20" wheels, the 3.92 is more like a 3.73 ratio.