This is assuming stock motor/tranny.

Can anyone who drives their rex on the highway a lot verify these stats? I did a bunch of searching and found these... but it was just a post by some random guy on another forum.

with 185/60/14 - 5th gear (si)
70 mph = 3,390
75 mph = 3,632
80 mph = 3,874

with 185/60/14 - 5th gear (dx)
70 mph - 3,101
75 mph - 3,323
80 mph - 3,544

with 185/60/14 - 5th gear (hf)
70 mph - 2,121
75 mph - 2,272
80 mph - 2,424

 

The Si stats match pretty close to what I get. 80% of my miles are highway.

 

The HF stats are close to what mine were before the swap.

 

Sounds about right. I've had all those set ups lol hf trans was ridiculous long gearing.

 

Would an HF tranny bolt up to a D16a6? Or if not, could the gears be switched over? I'm looking for the best way to tame the highway RPMs on my SI build.

 

Yes and yes. I don't know off the top of my head but you may want to play with a gear speed calculator and see if it'd be worth it to run the HF 5th and final drive with Si/DX 1-4 gears (Si and DX gears are the same, only final drive makes the Si accelerate faster). I know from experience that running a tall gear set may actually hurt your performance. I converted my 94 CX (8valve essentially a newer HF) into a DX but didn't change the transmission. I could only take it for 4-5 days before I swapped transmissions. Every time I shifted it would drop it below the power band and I have to downshift one more gear than normal to make it up a hill even though I just added like 20hp with the DX conversion. The reason why it worked on the HF and later the CX models is because the 8 valve engine produce more torque down low in the rpm range.

 

Yes it will bolt up just fine. I ran a sohc zc with the hf trans. Even with the zc (mpfi as well) doing 40 around town in 5th would bog lol. I did get a good laugh though after I hit 90 mph in 2nd gear at around 7200 rpm.

 

I did the same the first time I hit the freeway. I remember thinking "Man it feels like 2nd gear is never ever going to end!"

 

thats the whole reason i loved my hf ....i swapped in a d16a6 and it was like driving inside a motorcycle 90 in second was awesome ....it is a very livable setup if youre hard on your car anyways.... if i remember correctly we swapped in a dx final drive when that trans went into my buddys car and that was pretty damn fast through the first 3 gears just got "hf'ish" mileage when you werent getting on it