I have a 99 SI motor in my 96 hatch. The kid before me destroyed the factory SI trans and installed a LS trans so the car was driveable. I am currently getting 35 mpg mixed highway/city, and have gotten 43 all highway (driving about 75 entire time with windows down). The car is completely gutted, so it's pretty light. Went for a ride in my buddy's 94, same motor, SI trans. Pulls MUCH harder, but he has less engine work done. He is only getting 27-30 mpg. I drive about 80 miles a day, so gas mileage is important. I was thinking about getting a 1st-4th gear setup from a SI trans, and keeping my 5th. I have a trans guy who said he could do it for me IF I got the right parts. Which brings me to my question...

What all do I need? Can I just get the 4 individual gears? Do I need the entire mainshaft? Does the final drive have to change? I know most people start with a SI trans and put a LS trans 5th in...but I'd like to avoid buying a 2nd trans if possible. I recently started building a forged motor, so don't want to spend TOO much on the trans. Hoping to pick up a used LSD and the necessary parts to have my LS rebuilt. I really think 3rd is the main problem with the LS trans. 1st/2nd don't seem TOO bad, but it just falls on it's face in 3rd (even with me staying in vtec on the shifts)

I was also debating going with a more extreme aftermarket gear set 1-4...but there seems to be a lot of horror stories on this site about them failing.

 

OR would I be better off just changing my final gear? (though that would obviously hurt gas mileage, even in 5th)

 

You are better off getting another transmission. I can't even imagine how slow a B16A2 is with a LS transmission! Also no LSD, might as well be a Geo Metro or Cavalier.

 

wow, i know mind the gas mpg....

 

I have a 75 shot. 1st and 2nd go pretty fast....3rd sucks

 

I can get the main/countershaft assemblies from a SI for 350ish...is this all I'll need? Rather not buy a whole trans if I don't NEED to. No reason to have 2 casings laying around.