The stock springs are weak from the factory.If it was ME,I would first change out the stock springs.Second thing I would do,is,not shift the car at such high rpm.The best way to find the optinum shift point,is goto a track and run the car and record your shift points and your ET times,you'll find the best rpm range to be shifting at on your lowest ET's..
Also the cobra intake,which uses the same lower intake as the GT-40, levels off at around 5500RPM,so there's no point in running it up to the rev limiter @ 6250 cause your not gonna be making any power then.
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Paxton Blown 87GT
ICQ#112698436