on the GTA source page, it gives the performance as such:
1990 GTA 0-60 was 6.5 seconds
1991 GTA 0-60 was 7.1 seconds
Don't they both have the same engine and HP ratings? why such a huge difference..

 

Depends on how each one is speced out. One of the 91 GTA's has 5 less HP compared to the 90 model. There are a few different versions of GTA. 305/350, M5/A4 and each also has different gear ratios. In 91, all the L98 cars also got dual catalytic converters.

Do both cars have the same size engine? Do both cars have the same transmission? Do both cars have the same diff gears? Do both cars have the same weight? When you start adding or removing options such as power seats, AC etc, the cars are not considered the same even if they have the same engine.

Real world results never equal published tests.

0-60 isn't much of a performance guideline. Very few people will go 0-60 at WOT on the street and chances are you'll spin off the line if you try.

How much power gets to the wheels? What does it run in the 1/4 mile? What's it's top speed? Those tell more information about performance but for the average consumer, they'll never use that data.

 

I totally agree, but one would want to believe they would publish accurate performance data for all to see. It does show 350 engine 3:23 gear and I assume automatics for 90-91 comparison. Then it is also strange that the 92 with a 305 engine is just a tick slower than the 91 350. A clarification of how they came up with those numbers would have been beneficial.

This is a copy from their web page:

1990 Trans Am GTA with 5.7L V8 and 3.23 : 1 rear axle
0 - 60 mph: 6.5 seconds
Lateral Acceleration: 0.89 g

1991 Trans Am GTA with 5.7L V8 and 3.23 : 1 rear axle:
0 - 60 mph: 7.1 seconds
Lateral Acceleration: 0.90 g

1992 Trans Am GTA with 5.0L V8 and 3.42 : 1 rear axle:
0 - 60 mph: 7.3 seconds
Lateral Acceleration: 0.90 g

 

Don't use the Internet or a magazine for definitive performance info.

The fact is there are so many variables the same exact car can run a 14.0 and a 15.2. Take good/bad driving into account and the same car can run 13s vs 15s.

Don't use internet data for anything.

 

You also need to take into account where and when testing was done. The exact same car tested in may will perform differently than if tested in August. Same goes for location. Take the same car to Florida, Kansas and Denver and it will perform differently at all 3 locations.

Magazine and web articles should only be used as guidelines. It's real world results from people like owners here on TGO that will have the most accurate results and will also vary a lot depending on where they are.

 

Most good running L98 cars are closer to 5.5 seconds anyways.

And if you hit the strip its easy to drop .5 seconds off the 0-60 time if its prepped. Because you can put down the power much better.

My GTA was closer to low 4's on the drag strip according to the data logs. But more like 5's on the street.