performance-wise, is there a big difference between the 70mm and 75mm throttle body/plenum's, like from this site and others. in the long run, does it really matter which one you get?

 

The 75 mm will give you about 2 more hp when match witht he correct plenum. Also, if you have plans for a blower down the road, the 75 will be better. I tend to think that the 70 mm idle a little better, though.

 

Normal rule of thumb is that if you dont have a power adder nor plan to put one in your car, than stick with 70mm.

other wise go with 75mm.

 

I have a 75mm Ford Racing TB and #1 is right, idle is rougher. I even had a small problem with it killing when coming to a quick stop, but I fixed it by adjusting the TPS.

 

I have an Accufab 75 mm and plenum installed and I see no idle problems at all.

 

Understand. I also have a 75mm. I merely made this point because I have heard more complaints from folks with the 75 than the 70 in regards to idle. Regardless, the issue can be addressed and corrected.

 

I called Accufab today with the same question (70vs75) Accufab told me that there 70mm flows almost the same as the 75mm and they recommend that if you have a stock car with just a few bolt on's such as mufflers and air filter go with the 70mm and If you have a very free breathing engine such as headers and o/r pipe and perhaps cams and or ported heads go with the 75mm. I also asked them about idle quality and throtle response differences and they said there wouldn't be a noticeable difference between the two. I ordered The 75mm just so I don't regret it later if I ever go ahead with cams and headwork.