I bought a used transmission for my honda and the mechanic who installed called me tonight and said that it is a 4 speed that i bought does anyone know anything about what i had installed and what the difference drivability is or should i have it pulled back out and returned

 

you accidentally had a 4-speed manual tranny installed into your Si? I'd have that bastard yanked back out, but thats just my opinion. I dont know much about EF's but this post will be a nice bump for you and hopefully someone with more EF knowledge can help you out.

 

I would swap it back out. The 4 speeds came in Non-Si models. Nothing bad will happen IMO, however, I would definitely miss that 5th gear.

 

I think it might turn the CEL on with a code 17 when the ECU discovers the road speed doesn't match rpm with the expected ratio. Also the engine will rev higher in top gear leading to reduced highway mpg.