I have a friend that put a 70mm throttle body on his mustang and he said it killed his low end power and he said he can not feel a difference up higher either.
I would get the 65mm throttle body until you are a lot more modifyed than you are right now.
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James Cox
nochevy@hotmail.com
1991 Mustang LX
12.565 @109.38mph 1.764 60ft