For the Accufab plenum, we only offer it with a 70 MM tb. For the C&L, go with what they recommend. As for why the Accufab is sold 70 MM only is because that's what yields the best results. I get tired of answering the question, BUT I'll try again.
The objective in making a throttle body and plenum work efficiently is to get the maximum amount of air through the smallest hole possible. Just like when porting cylinder heads. When you have done that then you have the best product that you can make. When you have to go larger to obtain the same results, you lose low end efficiency.
Now the C&L and the Dragon appear to yield better results with a 75 MM tb. I am friends with the owner of C&L and do not wish to elaborate further. He has his customer following and so does Accufab. I think you should purchase the plenum that fits your style and budget.
It is very rare in this industry that you will find competitors who suggest each others products much less put dyno numbers on their web site. C&L did dyno testing using our throttle bodies on their plenums against the
BBK and Ford Motorsport and put the information on their website.
As for why you are seeing testing done using the 70 MM tb, it follows simple dyno strategy of one change at a time. If you make two changes at once, then you do not know what contributed to the power gains (or losses). However, if you really want to know the difference, look on the C&L website. They have done the test and I agree with their results.
Thanks,
John Mihovetz