stick with the 65mm. its all you need and throttle response will be much better, which you will want for autocrossing.
Ive had both, a 70mm BBK and a 65mm Ford motorsport, and I speak from personal experience.
the difference in power between a 65 and 70mm on a combo like yours is non-existent, but again, throttle response is much better
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2002 GT
1993 GT (SOLD)
'93 Mustang GT
RHC member #142
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