what does the si have for transmission

6- Speed close syncro manual transmission

let's not forget LSD

the si have this product update on there 6-speed tranny's, if you have on, the third gear may pop out of gear, you need to go the dealership and they will replace the entire main shaft.

It depends on which Si you're talking about. the EP Si and newer have 6 speed transmissions with a factory LSD. Previously in the EK Si's they came with the y80/s80 5speed tranny's. In the JDM market, they had an optional LSD. so some have it, some are open diff boxes. But if you aren't gangster enough to go JDM, the USDM codes for the B16 tranny's are S4C/Y21 (neither had LSD). The EG Si's came with a sohc d-series motor with the P20/B000 tranny (5-speed manual). Hope this helps