YELLOWGSLSE

iTrader: (7)

I have an 84 gsl-se with around 30,000 miles on a factory rebuild. It has a Racing Beat Streetport exhaust, but it's a stock ported motor. The 6 ports are oparated via the air pump so they always open at 4000 rpm. My issue is that the car seems to have a lot more power during the first 5-10 mins. of driving than it does after. For example, on the way home from work last weekend, I pulled away from my job with enough power to pin me to my seat and slightly spin the rear tires. This level of thrust lasted me a good 15 mins. I was even able to outrun a friend's '99 Eclipse GSX on the highway. ( Suprised the hell out of both of us!!) However, a few hours later, my car seemed to be down about 15 horses. It wasn't slow, It just didn't pin me to my seat the way it did hours earlier when I left work. The same friend with the GSX tried me again later that night on the same highway and got me by about 2 car lenghts. he even asked me how my car "went from Superman to Clark Kent is such a short time?" This is rather normal for the car, the initial thrust is intense then it changes to just kind of average after 10-15 mins. of driving. Any ideas as to what it could be??? The car has no o2 sensor since the exhaust was installed but it was doing the same thing when it it just had an o2 sensor with the cat- replacement pipe. Any help would be greatly apprieciated.