The Lotus Cars Community banner

1 - 7 of 7 Posts

·
Banned
Joined
·
6,941 Posts
Discussion Starter #1 (Edited)
As we know our cars accelerate the fastest when in "Lift" or "V V" or (cringe) "VTEC" or when "on the cam", etc. This means that for max accel you need to stay in Lift at each upshift. And for twisty stuff you'd hope to be near the bottom of lift coming out of a turn to avoid the jump when it kicks in and be ready for a burst of accel before the next shift.

We have an 8000 RPM steady state redline. And a momentary redline for about 1.5 seconds at up to 8600 RPMs. I think 8500 is claimed, but it actually seems to be 8600. In the chart below I put in the 8600 RPM column for each gear but it will only hit that for sure in 1-2. I suppose that the higher gears can briefly exceed 8000 but how much depends on how much speed they can gain during that roughly 1.5 second period. Note that our shift lights are coordinated with this transient limit and this can help you out.

In a given gear from low revs, you hit Lift at about 6200 RPMs. Once you are in lift, it will stay on as long as you are over 5800 RPMs. For best acceleration you'd generally want to shift such that when in the next gear you are at or above Lift. There is more to the shift point RPM than that but the step-up in torque during Lift is the main thing to retain.

Here is a chart I made using the data from the Road & Track article in the Articles and Reviews section.

Gear__8000__8600__6200__5800___SHIFT-AT-RPM:LIFT
1____42MPH_45MPH_33MPH_30MPH___8600
2____64_____69____50_____46______8600
3____89_____96____69_____65______7300
4___112____120____87_____81______7400
5___142____153___110____103______6500
6___160____172___124____116_______N/A

Now these numbers are rounded off and so forth but you can see that when upshifting into 4,5 and 6 it is easy to stay at or above 5800 RPMs. For example when shifting from 3 to 4 you need to be at a road speed above 81 MPH, looking at the 5800 RPM column for 4th gear. In 3rd gear that would be when you shift at or above 7300 RPMs, the rightmost column for 3rd gear. The right most column is the RPM you need to be at or above in order to stay in lift when you upshift to the next higher gear. This is not necessarily the same as the best shift point at all times. You can see that the gear ratios close up in the higher gears.

So in first gear the strongest part of the powerband is not hit until you are a bit over 30 MPH. Cars like the BMW M-Coupe have to shift up to second at the point our cars are just getting to the sweet stuff! An early M coupe hits the meat of it's band by about 12-15 MPH or so. It would be interesting to see how fast the M-coupe can accelerate from say 30-45 MPH compared to our cars! You can be doing 30 MPH by the time you cross an intersection so the M-coupe has an advantage for the first 50-100 feet if both are launched off idle.
 

·
Registered
Joined
·
2,308 Posts
Good thread Stan. As a previous Audi TT driver (285hp) I have been relearning how to drive without electronics or quattro. This chart is very helpful.
 

·
shay2nak
Joined
·
24,910 Posts
Stan said:
It would be interesting to see how fast the M-coupe can accelerate from say 30-45 MPH compared to our cars! You can be doing 30 MPH by the time you cross an intersection so the M-coupe has an advantage for the first 50-100 feet if both are launched off idle.
I was comparing the R&T acceleration numbers with other cars, EVO, STi, 911, C5 Z06, M3 and others, and I found that the Elise was the fastest to 50mph. So I can understand what you're talking about.
 

·
Banned
Joined
·
6,941 Posts
Discussion Starter #4
>>>I was comparing the R&T acceleration numbers with other cars, EVO, STi, 911, C5 Z06, M3 and others, and I found that the Elise was the fastest to 50mph. So I can understand what you're talking about.<<<

Keep in mind that the magazines test the Elise with an all-out 8000 RPM clutch drop start. This really perks up the off the line acceleration! When you just floor it in 1st from say a 5 MPH roll it's a different experience.
 

·
Registered
Joined
·
79 Posts
Once I get my new clutch in and new tires I'll try perfecting the 8k drop. I wonder if you guys will get the same wheel hop I did once. Perhaps I'll get solid motor mounts.

At 9k I'm guessing:

1 47 mph
2 72.3 mph
3 100.67 mph
4 125.33 mph
5 160.33 mph
6 180 mph
 

·
Registered
Joined
·
803 Posts
calculating shift points

I have not gotten around to doing this calculation for the Elise yet. (I am spending too much time driving it, about to leave for the Pacific Northwest...)

But I did it for the NSX when it first came out. I calculated the torque curves in each gear as that is what accelerates the car. Horsepower does not enter into the calculation (yes, horsepower is directly calculated from torque...)

Taking the torque and multiplying by the gear ratio of each selected gear ratio results in the actual torque at each rpm in each gear. You can then plot these curves, and the shift points are where each of the curves cross. (see example torque curves below) Our Toyota motor complicates things because the curves "curve" as it were, as the lifters step up onto the next cam lobe.

The SAE Technical Paper Series 2000-01-0671, Development of the High Speed 2ZZ-GE Engine, has a series of torque vs rpm corves, and it shows a subtantial dip before the cam arrives. While the curves illustrate the problem, Lotus has smoothed the transition and so additional data is needed.

I have several power curves for the 2ZZ-GE but it would be really nice to get some actual dyno runs from the Lotus controlled engine.

Michael

http://www.sandsmuseum.com/cars/nsx/nsxmine.html
 

Attachments

·
Registered
Joined
·
803 Posts
finally got the Elise shift chart

I did some of the calculations. I have a degree in Math and I still cannot remember what I did for my NSX back in 1998 and how to get the right results now.

http://www.sandsmuseum.com/cars/elise/thecar/modifications/shiftpoints.html

The chart of RPM, Torque, and torque multiplied by the gear ratio, along with the speed in gears is on my website and provides the basis for the following chart. I used data collected on the Dynojet Model 248C from the Primedia Tech Center. It shows Torque and Horsepower for the 2005 Elise compared to the Toyota Celica GT-S.

My calculations show the torque after the final drive but not as applied to the ground so my numbers will not match. I will do that as soon as I can measure the wheels on my car. I also need to check the data against the SAE article.

The shift points are where the top curve drops and crosses the bottom curve. Since the data points are every 500 rpm, you will need to count back from 9000 rpm. I will leave it as an exercise for the reader to decide exactly where you are going to shift.
 

Attachments

1 - 7 of 7 Posts
Top