yes it can make a big difference. Many people make the mistake of thinking they need the biggest throttle body using the rational that bigger must be better. WRONG! In most cases of a bolt on engine setup you will not see much improvement and possibly even a loss with a larger throttle body. In the case of a larger build, ie: increased compression, cams, good header, tuning you could possibly use a larger TB. For an all motor setup, unless you are just running a balls out race setup a 65mm TB is as big as you need. I have made some good NA hp on both of my builds and I am still running the stock Civic Si TB. I could probably use to go up to a 65mm but it will be one of the last things I do. you can make plenty of power using stock Honda/Acura TB's. Make sure the rest of your setup is where it needs to be before worrying about a tB.