Stock '09 hemi results

[v8440]

I figured I'd better start a new thread for this to make it more recognizable if someone is looking for it. I don't know if anyone else has dynoed their '09, but here's what mine did.

I think we need to ignore the 326 ft/lb result on one pull, that looks like a fluke caused by the transmission downshifting and confusing the dyno. So, in my book the official results are 307 hp and 313 ft/lbs.

Like I said in another thread, this particular dyno is widely known to be too conservative, but I'm only gonna claim what it actually said. For reference, there was another hemi truck there, an '05 rumblebee. For mods he has a flowmaster muffler, and he posted 259 hp. So, I think we can safely say that the '09 hemis are getting us roughly 50 more hp at the wheels. If that is the case, they're making more than 45 hp over the '08 and back motors.

[Daniel08]

nice numbers

i cant belive there is close to 25% drivetrain loss on 3g rams i mean WOW.

I dont guess there is anyway to close that gap either.

[v8440]

The only practical thing I can think of for the average owner to do to reduce drivetrain loss is to reduce the weight of their wheel/tire combo. Not getting 20's is the first and obvious way to start.

The dyno you run on will have a lot to do with drivetrain losses in the sense of how they affect the results. The dyno can't affect frictional drag or the rotational inertia of truck components of course, but it can affect how much the rotational inertia hurts the results. A dyno with a light drum will accelerate faster. This won't artificially boost the results since the dyno software will know how heavy the drum is and scale things accordingly. But, what a light drum WILL do is cause the rotational inertia of your drivetrain components to sap more power between your engine and wheels. This is because the more quickly the drum accelerates the more power is spent also speeding your engine and drivetrain up.

To clarify, lemme give you an example. Let's say it takes 30 horsepower to accelerate your engine and drivetrain from 30 to 60 mph road speed in 3 seconds. I'm not talking about accelerating your truck, just speeding up the drivetrain components. Now, you run your truck on a dyno who's drum your truck can accelerate at that rate. Just in rotational inertia, 30 hp will disappear from your results. This is power taken over and above the frictional losses that your drivetrain also imposes. Now, let's say that you put the same truck under exactly the same conditions, but instead run it on a dyno that has a very heavy drum. Now, for the sake of this example, your truck takes 12 seconds to accelerate the drum from 30 to 60 mph, 4 times as long. Guess what? Your truck will post higher numbers because it didn't have to spend as much of it's power accelerating it's drivetrain.

You may be wondering which numbers are accurate. The truthful answer would be that both are. In each case, the numbers are a reflection of how much power was available to turn the drum after all frictional and rotational inertia losses were overcome. The inertial losses were different because of different drum weights.

So, which is a better reflection of how your truck will actually perform? I'd say the dyno with a drum weight that provides a resistance closest to what your truck's weight does. After all, the power you actually get to the ground depends in part on how much inertial losses take away. If you run your truck on a dyno, pay attention to how fast it gains speed in whatever gear you make your pull in. Now, take it somewhere and run it at wot in the same gear through the same speed range. The closer the 2 rates of acceleration are, the more realistic your dyno results are likely to be.

[Lead Head]

Just to bad there are not many electrical or hydraulic dynos around. They actually tell you exactly how much HP you are generating at any given time and funky gear ratios/tire sizes can't mess them up. Another big benefit of Electric/Hydraulic dynos is that they can load the engine up and bring it any RPM you want, so you can see how different mods effect low end torque or high end power, etc..etc..

308 RWHP isn't to bad, works out to about 21% drive train loss. Which seems a tad excessive. Any way to verify the torque converter was locked during the run? Would be interesting to see what it would do with a 6 speed manual.

[v8440]

I have no idea whether the converter was locked or not. However, the loss may not actually be 21%. I'm certain that this particular dyno is way pessimistic. I guess that's better than optimistic, but this one frequently gives power numbers that would not allow cars of known weight and trap speed to trap the speeds they do.

[am3gross]

you say that this dyno is a bit shy on the numbers..... what do you think the number really is? 325? 330? more?

[v8440]

Well, I dunno. The online guestimators all say right at 340, based on trap speed and weight. I have trouble believing it's that much, but it's kind of hard to imagine it's running 96.75 mph weighing 4800 lbs with 307 hp at the wheels. There's a list of other examples of cars posting impossibly low numbers on that dyno.

My buddy's grand national, runs 142 in the quarter mile, weighs about 3900 with him in it. This dyno said 720 hp. That's retarded-it's not even in the ballpark. Furthermore, other guys with turbo buicks that he beats dyno around or over 800-on other dynos.

My '91 mustang-went 137 mph with a weight of 3200 lbs. According to this dyno, it made 546 hp.

My '98 dually-weighs 7200 lbs with me in it. It ran 98 mph. This dyno? Again, I worked a miracle-I did that with only 450 hp at the wheels.


It happens again and again and again with this dyno.

[chirp08]

you say that this dyno is a bit shy on the numbers..... what do you think the number really is? 325? 330? more?

E/T calculator with his numbers puts it at 330-339hp. Coming up 20hp off in either direction doesn't seem that odd for all I've read about Dynojet's. We really need more guys to run their trucks before we'll know for sure.

[v8440]

E/T calculator with his numbers puts it at 330-339hp. Coming up 20hp off in either direction doesn't seem that odd for all I've read about Dynojet's.

Yeah, but it's sure strange it's always a surprise in the same direction. I don't mean a surprise to Billy Bob who thought his 1980 camaro with a clapped out 350 made 400 hp, I mean a surprise to people who have quick cars and have a realistic view of what it takes to run what kind of numbers.

[Bubba_Hemi]

I just made an appointment at the closest dyno round me (at a diesel performance shop) for tomorrow afternoon so we'll see how that goes.

[seth505]

nice man, thanks for sharing the info

[jrod82]

I just made an appointment at the closest dyno round me (at a diesel performance shop) for tomorrow afternoon so we'll see how that goes.

sweet!! :tup:

I can't seem to locate one in my neck of the woods. What do they charge to let you dyno?

[Bubba_Hemi]

Looks like I had just a little bit better results than you. Not sure why the difference, but I know there are at least these differences between our trucks:

You / Me
3.92 / 3.55
2wd / 4wd
17s / 20s

Those are the things I can point out right now... besides my exhaust cutout. But I think your 2wd with 17s would get a better number than my 4wd with 20s. The gears... I think a higher gear will show better as I remember someone thinking they had lost power with 4.56s but it's actually better. Anyhow...

I had 3 runs: 1) 316.7 / 337.1 2) 322.2 / 335.6 3) 322.2 / 334.0

And yea... don't forget to unhook the ABS sensors from the front wheels. lol

[v8440]

Your results are more like what I think these trucks actually make. My truck would almost certainly post better results on the dyno you used than the one I was on. Likewise, your truck would probably show lower results on our dyno here than the one you were on.

From a mathematical standpoint, your numbers are much more likely to be correct than mine, since our dyno is stingy to the point of being unbelievable.

[Bubba_Hemi]

I just figured you were talking about a DynoJet compared to a Mustang... not that specific DynoJet machine (which is what mine was as well).

[hemi1569]

Damn i wish i had money i would be all over a quad cab 2wd hemi

[v8440]

No, I mean this particular dynojet machine.

[Bubba_Hemi]

Here are some pix of mine

Have a video too... but it's not the best quality. Will upload and then post here.

[Bubba_Hemi]

K, here's the vid... kinda crappy though as it was taken with my cell phone. Have another with actual camera and with a camcorder... but no way to get it on the computer yet.

http://www.youtube.com/watch?v=2ioVQAojpsA

[wyat72]

what gear you all pulling in? Does the speed limiter screw up the numbers? Or can you pull in a different gear these days?

[Bubba_Hemi]

Well I thought about talking to the guy about that on my way down... but of course didn't think about it till after I was leaving. lol But he did say he did the runs in 3rd... so I'm assuming he used the AutoShift to put it in 3rd. You can kinda hear it in mine were it hits 4th on it's own to protect it from the high RPMs. But otherwise in 4th it'd hit the speedlimiter before the RPMs got high enough to give it a good number.

[v8440]

The pulls were probably done in 2nd prime. Remember, that's 3rd in manual mode.