So what does this all mean for what really matters: acceleration?
Luckily, I've written some code to process torque curve data, along with other key specs about a vehicle (weight, gear ratios, tire size, aerodynamic drag, etc.) and simulate how they would accelerate under full throttle.
For all my acceleration simulations, I assume the following (based mostly on my Jeep):
- Base model 2-door Wrangler with 3.21 axles and stock 29" tires.
- Weight for 6.4 Hemi: 4249 lbs = 3849 lbs (base model curb weight) + 400 lbs (AEV's claim of added weight)
- Weight for all others: 3960 lbs (my actual weight; assuming all bolt-on kits are close enough in weight to not have a big impact on results)
- Weight of driver: 140 lbs (my weight)
- Stock 6-speed manual transmission. THIS IS NOT CORRECT FOR THE HEMI. Unfortunately, my code can only simulate a manual transmission. This is the best I can do for this comparison. It's still at least an interesting comparison of the differences in torque curves (and weight), with ALL ELSE being equal.
- For simulated races, launch at 2500 rpms, perfectly slipping the clutch (holding 2500 rpm during the entire launch) at full throttle, and executing gear changes in 0.6s each.
- 11 inches of "roll-out" before the race officially begins for the 1/4 mile races. This simulates how cars are "staged" for a drag race, and how they trigger the timing system to start.
NOTE: I'm not claiming that my simulation will perfectly simulate the real world and make perfect predictions. Real world results depend on so many variable factors, human imperfection, etc. The goal of the simulation is not to accurately predict real-world results, but to compare relative real-world *potential* between different vehicles/configurations, using computerized perfection to remove the uncontrollable variables of the real world. This allows us to objectively/relatively compare stuff without arguing about whether the results were simply due to difference in driver skill, a bad launch, a poorly timed shift, bad weather conditions for traction, etc.
Now on to some fun results...
First up is a chart showing for any given road speed, what is the fastest the Jeep could accelerate at that speed if you're in the best transmission gear for max acceleration. Due to the torque curve shapes, the best gear for acceleration in this case is always the lowest gear you can possibly be in at that speed (upshift as close to the rev limiter as you can), but this is not true of all vehicles/engines.
click for full size
Where the end of each line hits the bottom of the chart (0 acceleration) represents the predicted top speed.
That's interesting data, but it doesn't really clearly show how quickly each Jeep will be able to accelerate up to speed over time. For that, I can simulate a 1/4 mile drag race for each and graph speed vs time:
click for full size
The end of each line indicates the time and speed at which the Jeep passes the finish line. Here's the numeric results:
Stock:
15.89s @ 85.79 mph
Magnuson:
14.05s @ 97.87 mph
RIPP:
13.89s @ 98.05 mph
6.4 Hemi:
13.27s @ 101.53 mph
Prodigy:
13.18s @ 106.62 mph
Another interesting aspect is how quickly does each Jeep actually move down the track? The most interesting and clearest way of presenting this that I found was to show how much of a lead each modded Jeep has over a stock Jeep throughout the race. This gives a pretty good visual of how much they all leave the stock Jeep in the dust, and also how they "jockey for position" with each other throughout the race:
click for full size
I think this is the best visualization of how the different power mods actually compare to each other in acceleration. The 6.4 Hemi clearly destroys both superchargers. The turbo clearly has an early disadvantage due to its minimal low RPM gains, but more than makes up for it by the end with his upper RPM power.
Keep in mind, though, that this is a race from a complete stop to a 1/4 mile distance. Not quite a typical real-world scenario. For example, cross-reference the two drag race charts to compare how each Jeep would perform when accelerating up to various legal road speeds. You may find that one Jeep (Prodigy) will reach a target speed in a shorter amount of time, but a different Jeep (6.4 Hemi) is actually further ahead by distance, despite requiring more time to get up to speed.
Also keep in mind that a 2500 rpm launch was arbitrarily chosen because it seems reasonable and minimally abusive to the clutch. Launching at higher rpms would produce very different results for the turbo, while having relatively limited impact on the results of all the other Jeeps, but is not a very good representation of how you would most likely drive it on the streets.
On the other hand, if you begin the acceleration from a rolling start at some higher speed, like executing a pass on a highway for example, differences in low end torque won't matter because you can downshift for maximum acceleration (see the first chart in this post).
The actual results of any "race" between these different Jeeps will vary quite a bit depending on the starting speed, and whether it is a race to a particular speed, a race to see who covers a given amount of distance first, or a race to see who is furthest ahead after a given amount of time.
I think it is safe to say, though, that the 6.4 Hemi should be a rocket with the best balance of torque/acceleration available at any time.
(if you want to skip past a couple pages of bickering and see more analysis, click here)
Reply With Quote
Connect With Us