The big portion of the HP jump from 225 to 260 was due to new heads on the 99-00 compared to the 98. From what I've read, a gain of around 30 horses can be had by going to the SVO heads or the 99-00 heads. Taking into account the price of 96-98 SVO heads, some are taking a somewhat cheaper route and strapping on heads from 99-00 models....
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1998 Mustang GT
13.97@103
"Traction Impaired" or "Nitto Needy"
Pilot Proverb:
If all you can see out of the window is ground that's going round and round and all you can hear is commotion coming from the passenger compartment, things are not at all as they should be.