crx hf 5th gear swap? - Fuel Economy, Hypermiling, EcoModding News and Forum

arcosine · 07-11-2011, 10:28 PM

Is it it possible to replace the Honda crx hf .694 ratio 5th gear with a .605 Saturn 5th gear? Anyone in the know? .694/.605 = 1.15 = 1677 rpm@60 mph

some_other_dave · 07-12-2011, 02:30 AM

Chances are really really really really high that the answer is "no". Pretty much everything has to be identical between the two except for the number of teeth, and I'd be surprised if there weren't one or two things that were different.

-soD

arcosine · 07-12-2011, 07:58 AM

Yes, but has anyone tried. I have both transmissions, Saturn 5th gear pair is already out from a previous swap. Honda tranny is stored 30 miles away. Its funny, they both have identical first gear ratios.

Ryland · 07-12-2011, 09:21 AM

Why not just swap the entire transmission? oh yeah, because not only were they made for different vehicles but they were made in different countries so the chances of getting it to fit even with heavy modifications are slim to non.

some_other_dave · 07-12-2011, 03:22 PM

If the Saturn 5th gear pair is out of the box, then measure the diameter of the drive gear and the driven gear. Then measure the inner diameter of the bore through the center. Count the splines on the bore, and measure the width of the splines and the width of the space between them. Measure how thick each of the gears is, too.

Oh, and don't forget the dog teeth where the sliders engage the gear as well.

Then talk to someone who knows D-series transmissions really well (like "Mista Bone" on the various Honda/Civic/CRX BBSes) and see if all of those match perfectly. If any one is off, then your answer is "no it won't work".

Oh, and even if all of the numbers match, there may still be other problems that prevent it from working correctly.

....You can see why we're a little dubious....

-soD

arcosine · 07-12-2011, 04:29 PM

Quote:

Originally Posted by Ryland

Why not just swap the entire transmission? oh yeah, because not only were they made for different vehicles but they were made in different countries so the chances of getting it to fit even with heavy modifications are slim to non.

Because the HF has a 3.25 final drive ratio, that's why.

Ryland · 07-13-2011, 01:45 AM

Quote:

Originally Posted by arcosine

Because the HF has a 3.25 final drive ratio, that's why.

My point was, finding gears that swap from one year to another is hard enough in the same brand but you are hoping that auto engineers on the other side of the world made parts that can be swapped, by chance.

arcosine · 07-13-2011, 08:09 AM

You don't think that Saturn reversed engineered their transmission from Honda? Anyway my other idea was to reverse second gear, which would give 1/1.89 = .529 fifth gear, that would give 1466 rpm at 60 mph. With this case at least the gear pitch diameters are the same.

Ryland · 07-13-2011, 08:21 AM

Quote:

Originally Posted by arcosine

You don't think that Saturn reversed engineered their transmission from Honda?

If they did then they didn't learn anything, Saturns remind me much more of Toyota's and Toyota has a different line of thinking from Honda and I've toyed with ideas of swapping parts from a Toyota to a Honda and failed due to major design differences, but you seem pretty stuck on this idea, so go for it.

some_other_dave · 07-18-2011, 04:29 PM

Quote:

Originally Posted by arcosine

Anyway my other idea was to reverse second gear, which would give 1/1.89 = .529 fifth gear, that would give 1466 rpm at 60 mph. With this case at least the gear pitch diameters are the same.

Now this I have specifically asked about. It is definitely a no-go, either the spline count is different from drive to driven shaft, or the shaft diameter is different. I had thought it would be a clever way to drop my revs on the freeway, but Mista Bone shot that down in a hurry.

-soD