Lexus IS Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
591 Posts
Discussion Starter #1
I've just read the New October Car&Driver spill on the IS.

It says the car is GOVERNED at 144mph.
Not Drag Limited.
And I might add that to their Somewhat Surprise the car DID EVERY BIT of that 144mph.
(Surprise I say because they were surprised they didn't get the 7.1 0-60 times. (Only 1750 miles on the test car)
But overall they gave the Car a Good Recommendation.
 

·
Registered
Joined
·
1,991 Posts
Well, here is a way to check. If anyone can measure the frontal cross section of the car, and then use the CD=D/0.5*ro*v^2*A to figure out D. You then put use the equation P=DV, and you will be able to find out approxmiately how much horsepower is required to overcome drag at 144mph. If the HP is less than what the wheel is outputing, then it means the top speed is electronic governed, but if the HP is greater than the actual output, then you know you are drag limited.
 

·
Registered
Joined
·
4,250 Posts
nono, here's the best way to check. find an open road, no cars arond, take it to the top speed, if its at redline, its redline limited but if you're near redline and the car won't go faster..its drag limited, simple yeah?
 

·
Registered
Joined
·
49 Posts
WTF is this:
CD=D/0.5*ro*v^2*A to figure out D

is this a joke or a real equation? urgh math makes my head hurt.
 

·
Registered
Joined
·
1,991 Posts
it is a real suggestion. It is not that difficult. Just take a tape measure, find out the exact width, height of the car, and then find the area. Get the density of air and plug them into the equation. Take less than 5 minutes to do this. I just don't have anything to measure my car right now since I am at work, but I may do that once I get home.
BTW, remember all your units has to be consistent.
 

·
Registered
Joined
·
195 Posts
According to the Lexus website, it says the top speed in "143.7 mph." Now, if it were governed, don't you think they would chose a nice round number, like 144? It appears that it's drag limited.
 

·
Registered
Joined
·
1,991 Posts
Ok, here you go.
ro= air density = 1.184kg/m^3
v = 144 mph = 63.37 m/s
A = W * H = 67.7" * 54.9" = 2.29m^2
Cd=0.29

So here we go.

Cd=D/0.5*ro*A*v^2 => D = 1578.78 N
P=DV=100047.52 watt = 134.17 hp

This means at 144 mph, the car needs approximately 134.17 hp to over come the drag. I know the least amount of rear wheel horsepower we have seen is 156 or so, so this most likely means the IS is electronic governed at 144mph.
Note: there are many general assumptions used in this calculation, but the error should be within a +/- 10hp.
 

·
Registered
Joined
·
162 Posts
hmm... I read that it was drag limited @ 144mph. BUT, there were a few posts where someone had the car "dyno'd" and they claimed that it ran right up to 143-144. If this is the case, then it must be electronically limited. There's no wind resistance when you "dyno" a car, right??
Any ideas on this??
 

·
Registered
Joined
·
1,991 Posts
well, people can say it is drag limited because they see the rpm stopped before the redline, so they thought they have ran off the power. You are right, there is no aerodynamic drag applied to most dyno, so if the IS is able to go up to 144mph on a dyno, then it means it is electronically limited at that. There are only about 4 or 5 dynos I know in the world that can simulate a real life driving situations, and I highly doubt any of the consumer car manufacturers will use those to test their cars.
 

·
Registered
Joined
·
109 Posts
forget all that equation crap. I took in on the road and hit exactly 144mph, and then the car like gave me a halt.
and no it wasn't an open road.
NY state Thruway baby!!!
 

·
Registered
Joined
·
90 Posts
I hope the IS300 is putting more than 156 hp at the rear wheels, because that is quite low for 215 hp at the crank. :|

I've seen dyno sheets for a 323i, and it puts 152-155 hp at the wheels, while a 328i puts 167-170 hp at the wheels.

Are you sure about the IS300 numbers??? Even though the automatic sheds an extra 10% power loss, it should be putting close to 165-170 rwhp. Any way, just curious...
 

·
Registered
Joined
·
395 Posts
Not that this proves anything, but for calculations like these I use a nifty little program called Car Test. From what I've found, it is actually pretty accurate in estimating 0-60 times and top speeds. It uses similar equations and finds the IS to be drag limited at 145 mph. I tend to agree with it, although I think webmaster owes it to us to take it to 144 and see if there's any punch left =). Interestingly enough, car test estimates 0-60 times of 6.6 or so, which would be more representative of a car with these numbers. I've always wondered if the transmission eats away power to make the car so smooth... even in power mode. Anyway, you can download car test from

here, it is 479k

I have the IS300 stored under "IS300" instead of "Lexus IS300". Apologies in advance for my laziness not to change it.

[This message has been edited by Nate (edited September 30, 2000).]
 

·
Registered
Joined
·
591 Posts
Discussion Starter #16
Also, the IS300 reaches that 144mph at 6000rpm not 6200 like the Top Speeds of the other gears.

Can everyone say "Electronically Governed"

Im sure the car would hit at Least 150mph
at "6200rpm" in 5th gear.
 

·
Registered
Joined
·
4,250 Posts
smra, even if the chip is removed it does not mean that it can hit 6200 rpm in 5th gear. the car may not have enough hp to do so.
 

·
Registered
Joined
·
626 Posts
Question. And why do we care? Are you really driving this fast. If so, please tell me where you all live so I can remind myself to avoid those areas.

GEEZ, I have never seen so much conversation about such an unsafe activity. Here is an equation for ya.

E = the coefficient of x over m(144 -0) divided by the negative G force of Tree= 6 feet under.


Can you all figure that one out?

[This message has been edited by ISFAN (edited September 30, 2000).]
 

·
Registered
Joined
·
1,991 Posts
I just tried the Car Test software. I changed a few parameters for the IS, including the weight (now is at 3400lb) and the launch rpm (1500rpm). I think these are more realistic numbers because you need to include the weight of a driver and most people do not power brake their car when they launch for 0-60mph.
The 0-60 time I got was 7.3, which is closer to what everyone claims right now.
I do have to say that all the numbers for other cars I have seen so far look a bit slower. It showed 2G Eclipse GSX goes from 0-60 in 7.1 sec, but I have in fact done 6.9s using G-Tech and many magazines have able to get somwhere between 6.5 to 7.0 times. Also, the Supra number is so of low, so maybe there is a parameter in there that is not optimized?
 
1 - 20 of 20 Posts
Top