Just to clarify that, I reposted/posted that teams/driver stuff because Tyr asked if there was an option to change the strength of all computer controlled cars. Obviously, the opposite of doing that would be just tuning your own car up like you're saying, but I ruled that out as a likely reason here because the modern carsets I've seen all have the car settings set to "use selected team power", and per default, GP2edit should export these settings when you export the carset. I assume that if you're using one of these current sets, you should have a reasonable, team-dependent performance of your player car and that shouldn't be the primary reason why you'd be significantly slower than a lot of AI drivers.
What I did was that I compared the original carset with some modern ones and one difference I immediately saw was that a lof of the AI drivers' performance values in the original carset are significantly lower than in the modern ones. I think that's what could most likely create the impression that the unpatched game is easy to play, while in a 2007 carset, even driving a Ferrari or McLaren you could be far behind the lead.
That being said, I still made a tutorial for changing the car settings.
This screenshot shows the "car settings" window, which can be accessed from GP2Edit's main window by clicking the button "car settings" at the bottom left. Alternatively, it can be accessed via the menu: Performance > Car settings.
I've numbered the relevant fields so it might be a bit easier to see and illustrate (assuming the general buttons at the bottom should speak well for themselves):
Players Car
[1] Power (Race/Practice)
This value shows the current power value of the player car that will be applied for all practice seessions and the race on Sunday. You can adjust it by moving the scroll bar element left or right.
[2] Power (Qualification)
With this value, you can specifically adjust the power of your car in qualifying. (Reference to a time in F1 when teams had engines with more power especially for qualifying)
[3] Use Selected Team Power
Case 1: Unchecked
If you don't check this box (as seen in the screenshot), the values set under [1] and [2] will universally apply to *any* car you might select in the game. Whether you select a Ferrari, a Red Bull, a Spyker or any other car, you will always have the same engine power (in the screenshot: 790/780 bhp).
Possible consequence: Your car's power might not be accurate in relation to other cars - you could easily win races with a Spyker if your settings here are set to a value that's at the top of the other teams' performances in the carset, or you could hopelessly drag behind with a Ferrari if, say, you have the values indicated in the screenshot and you're driving a 2004/2005 carset where basically all regular cars have performance values of 800 or higher.
Case 2: Checked
If you check this box, any car you might select in the game will have the performance specified for it in the carset (see the red frame in my "altering performance" post). Whatever values might be set under [1] and [2] do *not* apply to your car (the scroll bars will go grey/unusable).
Effectively, your car's power will always be in what's the intended balance to the other cars in the carset, i.e. a current McLaren will have a lot of power and a Spyker will have significantly less.
[4] Random Power Variation
Case 1: Unchecked
If you leave this box unchecked (unlike the screenshot), your car's power in the game will always be exactly the same, according to the values either specified in [1] and [2] or in the teams' power settings (if you checked "Use Selcted Team Power").
Case 2: Checked
If you check this, your car's power in the game will randomly vary the values specified, so you won't always have the exact same power.
Note: I don't know how much the power differs if you check this.
[5] Grip Factor
With this scroll bar, you can adjust your car's tyre grip. Values range from 0 to 1000. Low values give high grip, high values give low grip.
[6] Weight
Here, you can adjust your player car's weight (range: 182-1815 kg).
[7.1] Pit Speed Limit
You can use this scroll bar to adjust the speed limit in the pit lane (range: 1-321 kph).
Note: This seems to have an effect on your car only. The AI will always abide by a speed limit specified elsewhere, but I don't know where - in the track's .dat files maybe?
[7.2] No Speed Limit
Case 1: Unchecked
The pit lane speed limit for your car will be as specified under [7].
Case 2: Checked
You can accelerate as much as you want in the pitlane, as the value from [7] will have no effect.
Computer Controlled Cars
[8] Weight
With this scroll bar, you can adjust the computer controlled cars' weight (range again: 182-1815 kg).
[9] Performance
(These are the same three options you can also select from a menu in the GP2 options in the game.)
Case 1: All The Same
All computer controlled cars will have the same performance values, completely disregarding any specifications in the carset.
Case 2: Use GP2edit Values
All computer controlled cars will have the performance values specified in the carset.
Case 3: Random
All computer controlled cars will have random performance values that are set internally at the start of a session (practice/qualifying/race).
Global
[10] Show Driver [1] as [0]
If you check this box, the driver with the number 1 will have the number 0 in the game instead, simulating seasons like 1994 where the previous year's world champion didn't race.
Now, I could've just copied that from the GP2Edit help, but I didn't. I only looked there when I was about done with this. 
](./images/smilies/eusa_wall.gif "Brick wall"){kind=small}
) that's why i don't know what the other levels do...
