Alright bros, here's the deal. 1990 EF Civic DX that runs like a wet dream.


Spare motor being rebuilt needs a transmission. Why not mate an HF transmission for better MPG's? (when current motor blows up, I can swap in a fresh set up)


HF trans are hard to find, found one on EBay. Transmission is from a wrecked 86 CRX HF.


Noob question- WILL it mount up in my 1990 EF?


OR will someone point me in the right direction to find out for myself


thanks guys!

 

Yes, all 88-91 cable d series transmissions are interchangeable.


Edit: Not sure about 86 hf, but you might as well just get the 90' STD 4 spd for economy.

 

you wouldn't recommend going the HF route for longer gears?

 

Yes, but a STD transmission has longer more economy gears.

 

I did basically the same thing in my 94 Civic CX. It didn't work out the way you would think. Longer gears by themselves don't automatically equate to better gas mileage. In my case the gear spacing dropped completely out of the power band with each shift. Combine that with where a DX generates max torque and where an HF generates max torque you will find yourself giving it more throttle to maintain the same speed essentially lugging the engine along.

 

it will not - not even close

 

wow, im glad I asked. that will make sourcing parts much easier then.


Just so I understand gooder, can you go into more detail about how DX works, versus HF? If they are both powered by the same engine, why wouldn't the HF trans work?


Thanks again, guys!

 

You specified two different generations of engine and transmissions (they are not the same).

 

d15a won't fit d15b

 

I actually did mate an HF tranny to my DX engine just to see what would happen, and yes the gearing was WAY out of the power band and was just miserable to drive.

I ended up swapping the HF 4th and 5th gears into the DX tranny, and I noticed a 4-5 mpg gain while still feeling peppy at the same time.

 

DX and HF engines are NOT the same actually.
The engineers at Honda are pretty smart with all their degrees, experience and calculations. They usually try and match the transmission gearing to the engine output to keep the vehicle reasonable to drive. They do have to balance a lot of factors, economy, power output, reliability and making at it reasonable to drive.
If you want to transmission swap you are best sticking with the 89-91 transmissions since 88 has a one year spline difference on the input shaft. the 87 and back transmissions will require custom work to go in. If you have a 4 spd transmission a 5 speed from an SI or DX model would be a decent upgrade, however the best way to control fuel economy is through your right foot.

 

this has been super helpful.

I had no idea how many differences there were between HF and DX

If i ever swap an engine, i will really have to do my research.

Thanks guys!