I want to replace my 89 si's trans with an hf to push better mpg. What's needed, obviously the trans, do I need half shafts. Which clutch/input shafts are compatible?

 

it's all compatible, take out old transmission, put in new one.

 

thanks, I've been reading this post and wondering if it's worth it. I have this car for 100 miles of highway commute. Little to no hills, so I'm thinking of taking a gamble and trying it or maybe the dx trans. I know the 3500rpms at 65mph is a little over kill from this si trans

https://honda-tech.com/zerothread?id=2201838

 

First, hello to another Mainer!

I'd take the time to find an HF tranny if you're interested in . It was designed for high fuel efficiency.

Unfortunately I recently sold the HF tranny that I had. I was planning to do the swap in my 88 CRX DX that was an auto but I ended up getting a 91 CRX DX (manual) from Arizona.

Granted it needed a bit of work but has a completely rust free body so I decided to sell the auto and get the 91.

 

im kinda new but i think if u were to use a hf tranny on a si, you would need hf axles... hubs too? just thought that might be useful to know

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by neozero999 &raquo;</TD></TR><TR><TD CLASS="quote">im kinda new but i think if u were to use a hf tranny on a si, you would need hf axles... hubs too? just thought that might be useful to know </TD></TR></TABLE>

No as long as your tranny and axles have the same amount of splines it will work.
I know this first hand because had i have a SI tranny with HF axles then i later put SI axles and hubs on it.

 

what about the hf 5th gear, is it possible to swap the 5th out of the si trans with one from an hf?

 

I my dx has squeezed out 53 mpg hwy only when in peak tune. But that was 2yrs ago, it has had about 28 states of travel added since the best mpg
I get 37-40mpg city/hwy now and am disappointed

see my barely altered setup below. still has orig dx tranny w/ 300k on it.
It neeeeds rebuild/replace.
I think the wear may be hurting the mileage. I know it has bad seals and/or bushings

My goal is to have a si-1st dx 2-4 and hf 5th, or other option for perf-eco

 

SI and DX have same gears 1-5, the final drive is the difference. In 5th gear an SI transmission with an HF 5th gear set will come out close to a DX 5th, but with better performance in 1st - 4th. I am doing this hybrid transmission build to go in with my JDM D15B VTEC swap with hopes that it does as good as my DX trans and DPFI-MPFI swap, 90 mile daily commute averaging 40-42 MPG.