[rob-2]

I wonder if my 470 at the crank is under rated?

After reading an article by edmunds where the 6.4 put down 443 HP and the 2015 got bumped to 485 without any engine modifications I got wondering.

What do you think? Is dodge under rating these motors? Are we really driving around with a little over 500 hp?

 

[tacamo01]

Edmunds uses a dyno that are always high compared to stock dyno's. They report outrageous numbers for Mustangs, Camaro's and Chargers.

However, IMO from looking at stock SRT dyno's 2012-2014 Dodge did underrate the 6.4L. Most stock SRT Chargers with the NAG 1 will dyno right around 415 rwhp. I have seen a few a little higher and some a little lower but not by much. The track numbers tell the same story and back up the average 415 rwhp. Torque average is around 420 lb-ft. Torque is definitely around 500 at the engine. Taking a correction factor of 1.19 for the NAG1, a 415 rwhp equates to 495 hp at the engine. Some experts like Modern Muscle put the correction factor at 20% loss. (1.20 x 415 = 498)

It will be interesting to see what the new 2015's look like when they hit the dyno with the 8 speed and only a 10% drivetrain loss. The 2015 Challengers are putting up time slips showing 3.9 0-60 and 12.2, 12.3 1/4's with just increasing the size of the rear tires from stock. (The 3.9 sec 0-60 came off the Evic. The evic was spot on with 1/8, and 1/4 mile times compared to the track slip)

Here is Maryland Speeds dyno when they just got the 2012 SRT.

 

[Sammy123]

I think they're underrated on purpose for insurance purposes.

Even at a conservative 15% drivetrain loss, and taking 410whp as a low number, that's 410/.85 = 482hp.

We do need all the power we can get to move this 4300lb vehicle though, so no complaints here.

 

[Ddaddy]

The whole "under-rated engine" thing in the modern world is pure myth. In todays world, manufacturers are held to the SAE standards for HP rating and simply cannot underrate their engines HP.

SAE HP testing has strict requirements and the variance allowed is only 1%. An engine is pulled randomly from the production line and tested per the strict SAE requirements with an SAE official observer present. The manufacturer then has the option of rating the engine +/- 1% from the measured value.

For example, any Hellcat coming off the factory production line will range from 693-721 hp per the SAE requirements and giving 2 standard deviations to the measurement (SAE creates that range by the way they test and allow manufacturers to rate their HP). The same applies to the 6.4L engine.

The 6.4L engine bump in HP came from changes in the intake airbox, active intake tuning, ECM tuning, and exhaust configurations. Remember that the 6.4L was originally shown to be capable of 500 HP during the early development and was detuned a bit to take a conservative approach for longevity. After a few years of experience with the engine, they bumped it back up again.

 

[Sammy123]

I don't know what went on with the old Neon SRT4's, but it was pretty well known those cars were often dynoing MORE than the advertised crank hp at the wheels, with the lower end at least equal or within 5hp between crank and whp. This was especially true for the 215hp 2003 model where nearly every dyno was turning out 220+ at the wheels.

These tests were done by major auto outlets like Motortrend (full list on the SRT4 wikipedia page).

I'm not sure of the actual specifics of SAE testing, but if a standard ambient temp isn't part of the specs, then Dodge can rate their engines as if it were running in the dead heat of summer and use those numbers.

I think it was especially important for the SRT4 market, as a high insurance rate would have killed sales for what was supposed to be an affordable $20k performance car for a younger generation.

This is what I recall with the SRT4. If Dodge was able to get away with claiming only 215hp (230 for 03/04 models) and dynos were routinely exceeding that number at the wheels, I wouldn't be surprised if similar "tactics" were employed for the Hemi, though not nearly as dramatic.

 

[Ddaddy]

I don't know what went on with the old Neon SRT4's, but it was pretty well known those cars were often dynoing MORE than the advertised crank hp at the wheels, with the lower end at least equal or within 5hp between crank and whp. This was especially true for the 215hp 2003 model where nearly every dyno was turning out 220+ at the wheels.

These tests were done by major auto outlets like Motortrend (full list on the SRT4 wikipedia page).

I'm not sure of the actual specifics of SAE testing, but if a standard ambient temp isn't part of the specs, then Dodge can rate their engines as if it were running in the dead heat of summer and use those numbers.

I think it was especially important for the SRT4 market, as a high insurance rate would have killed sales for what was supposed to be an affordable $20k performance car for a younger generation.

This is what I recall with the SRT4. If Dodge was able to get away with claiming only 215hp (230 for 03/04 models) and dynos were routinely exceeding that number at the wheels, I wouldn't be surprised if similar "tactics" were employed for the Hemi, though not nearly as dramatic.

SAE testing is conducted under well controlled and defined conditions. 2003 was 12 years ago...a lot has changed since then.

 

[rob-2]

SAE testing is conducted under well controlled and defined conditions. 2003 was 12 years ago...a lot has changed since then.

Well here is an interesting one.

SAE tested 2001 S2000, rated at 240hp crank, test between 180-195RWHP
SAE tested 2008 S2000, rated 237hp crank (with note that reduction due to SAE standards change, when 240 prior), test between 205-220rwhp.

I'm not so certain the SAE results are now without fault. I would like to better understand why the HP figures have changed, the tranny 'improved' and yet the times remain exactly the same.

 

[tacamo01]

The difference may be how they calculate drive train loss. That coupled with what Ddaddy said about a 1% allowable variance adds up to a lot of hp. I have seen folks use anywhere from 15% up to 20% drive train loss. The new 8 speed is estimated at only 10 - 12% from the early Challenger dyno's.

What is the difference I wonder between pulling an engine off the assembly line (Engine dyno) and a real world dyno where we measure hp to the wheels?

 

[KStryker]

A lot of these are based on calculated formulas. I'm sure there is a +/- 1% variation which they can't calculate for.