I just finished my HF transmission swap - Fuelly Forums

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Old 01-29-2007, 08:16 AM   #1
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I just finished my HF transmission swap

I just replaced the stock 5 speed trans in my 87 Civic 1.5 liter cvcc, with a trans from an 84 crx 1.3 (the crx that was rated for 50-60 mpg on the highway).

The swap took about 6 hours total with no surprises other than the last person to put the bell housing bolts on must have thought they were tightening down semi truck lug nuts. I was impressed that the engine block is aluminum- that must save quite a few pounds in the car's overall weight.

My 60 mph 5th gear rpms have been dropped from 2600rpm to 2100rpm. Strangely enough, the 4th gear of this new trans is geared higher than the 5th gear of my original transmission.

Thanks to Ryland for sharing the carpart.com website info where I found my transmission. It was only $75 but I had to drive 4.5 hours one way to pick it up. It has a moderate whine in 2nd gear and a small whine in 3rd that I am a little concerned about, but no growling noises.

Metrompg's assesment of the trans swap on his webpage is a good one- the drivebility is definitely lower (or at least uncomfortably different at the present). I have to rev the engine much farther in 1st and 2nd before I can upshift and I wonder if it will actually hurt my city mpg figures. I also have a small 4X6 trailer that I haul things on every few months or so, and the higher 1st gear will definitely shorten my clutch life when getting that rolling.

I am hoping for at least a 10% improvement in highway mpg. If its much less, lets say 4%, I may even put my old trans back in and just swap out the 5th gear sets.

I have to thank 3gencivic on the redpepperracing website for the gear ratio data below. I assume that my stock 87 1.5 dx transmission ratio was pretty close to the 86 data shown here.

86 dx 1.5 crx
1 2.916
2 1.764
3 1.181
4 0.846
5 0.714
r 2.916

for a 84 1.3
1 2.916
2 1.526
3 0.960
4 0.750
5 0.655
r 2.916
final 3.473

Side note- By the way, if anyone ever needs a left side transmission output seal for these transmissions (84-87), most autoparts stores have the wrong seal number listed in their books. It took days to finally find the correct seal.

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Old 01-29-2007, 08:56 AM   #2
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Old 01-29-2007, 09:10 AM   #3
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Congrats! It takes some getting used to, but you'll love it.

You will not get the expected MPG if you rev very high. It's taken some time, but I typically shift at 1750 RPM now and almost never surpass 2250 unless I'm really cruising down the highway. Getting used to people passing you all the time and riding your *** takes a while, but the savings are wonderful.
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Old 01-29-2007, 12:43 PM   #4
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whining gears is really annoying, in attemps to extend the life of my tranny while on a road trip right befor I replaced it, I put in some thicker motor oil, and that helped.
$75 was a great price, altho you had a longer drive then some people would have been willing to make to get it.
you shouldn't have to rev it way up... unless you were shifting really early befor, I think the HF engines put out peek touqe at around 3,000 rpm, insted of over 4,000rpm like the normal civics and crx's did.

so I assume that the 1.3L bell houseing is the same? I've never found a 1.3 crx, they only made them for one year, and information on them seems pretty rare.
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Old 01-29-2007, 03:07 PM   #5
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Erik, Your engine may not have very much torque, my 1991 4g hf tranny swap did the same thing, I have to really rev it high to get any REAL power. My d15b1 engine has no torque, and I've been thinking of an hf 8 valve d15b6 headswap for this very reason, plus it'd give much better mpg than the d15b1/hf tranny. Maybe if you found a torque-er cylinder head to give more power. dunno the 3g civic engines, but i assume there was also an 8 valve hf engine that you could use in place of your current stock 16 valve (i assume it's 16).
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Old 01-30-2007, 09:15 AM   #6
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Low rpm torque

I was looking at my tach today and I have to rev it to 2800 rpm in 1st to get 1700 rpm in 2nd when I let off on the clutch.

I think my engine has a fair amount of low rpm torque at 1700 rpms, but not much at all at 1500 or below.

I am going to do a little 120 mile highway trip this afternoon so I can get a sense of how much it will increase my mpg.

Ryland- yes the bellhousings are the same, it bolted up without a problem. Starters/flywheels must be the same too.
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Old 01-30-2007, 09:59 AM   #7
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It's odd, because my ratios are even lower, and I don't need to rev so much...Hmm.
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Old 01-30-2007, 12:51 PM   #8
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I don't think it's as odd as it sounds. The 87 engine is a CVCC design, with a carburater (that's not spelled right, but I can't remember what's right). The 87 has quite a bit less torque and power, compared to the 89-91 engines. The 87 DX my daughter drives has probably 20%-25% less power, than my 89 wagon.

I wonder if you might be able to do something with changing the cam timing, that might get you back some of your lower end power?

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