I know that the V-AFC controls the VTEC engaugement point but I have seen some people with GSR's and Si's that have the S-AFC. Why, is there a reason for this or not, just preference?

 

S-AFC's are a lil lower in price...not a big diff, about $20-$30. Depending on the turbo setup, it may or may not be that important on where VTEC engages. On an NA setup, however, different cams like different engagement points and power can suffer dramatically if VTEC doesn't engage at the right time. This effect is less pronounced on most FI setups. Also, maybe they got them used from a friend for cheap. For a honda, I'd always want VTEC control if I had the option, whether FI or NA. Fields SFC-VTEC is a lower cost alternative to look into, tho I've heard of some problems with it running on certain setups. never had experience with the Fields units, so I can't say much aside from what I've read/heard. HTH.

 

I have experience w/ both VAFC is better.