why is 87 vette slower than 84-86?

I read in Car and Driver May 1988 test of the then-new 88 Vette that the 87 vette(which my grandpa owns) was slower than the 85 and 86 vettes. That doesn't make sense, because the 87 had aluminum heads and the 85-86 didn't. also the 87 had roller lifters and 240 hp as opposed to 230-235 with the earlier ones and 345 lb/ft of torque as opposed to 330 or so.
Am I wrong or is the 87 just a junker. I also found out in Consumer Guide book about corvette published in 1988 that it said the top speed is 135 instead of 140 like the 84-86 vettes but 150 in overdrive. Does that mean the sticks, once again, have taller top ends than the automatics? Why is the 87 vette slow?
thanks,
jecht

ps: was the lotus turbo esprit and porsche 928 faster than the vette back then? the 1980s weren't fast compared to today but back then a 14 second quarter mile was supercar territory. Now we have Accord V6 running 14.8 and Altima/Maximas running 14.0 or 13.9...

one of my friends has an 87, he just got it. Is the 87's heavier than the 85 and 86's?

It could be heavier
They used low compression cast pistons in all those years
87 may have been lower compression

want to make it scream?

put flat top forged pistons in at zero deck height
add a SLP cam and smooth port the heads
pro flow cut back stem valves

car flies

If you want it too be really fast, Build up the engine, and do a gear swap in the rear axle. Slap some lower gears in there and you'll really feel a difference !!!! :evillol: