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I have a 87 CRX HF with 210,000 miles. I need to replace the throw-out bearing, so a new clutch, resurface of flywheel will also be done. I was thinking of swapping the transmission for a SI unit. My question is how much will this affect the MPG and performance. I am looking for a little more performance without sacrificing all of my MPG. Any thoughts?
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Hf-si Transmission Swap....
Started by GTI-CRX, Feb 19 2012 01:03 PM
9 replies to this topic
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#2
Posted 19 February 2012 - 07:52 PM
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- Mr.Ididntseeyousittingthereofficer
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- Group: 2009 Contributing Member
- Location:Hickory, North Carolina
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Drives: 74'vert Blazer, 84redrexHF (RIP), 87blackrexSI, 91STDhatch(resurrected for beater)(RIP again)
you are better off swapping a whole engine trans combo IMO.
QUOTE (kjeffery @ Apr 17 2009, 06:17 PM) <{POST_SNAPBACK}>
Yet again Scott, you have all the answers
QUOTE (cbstdscott @ Apr 17 2009, 07:31 PM) <{POST_SNAPBACK}>
No. All the answers are in the Kakabox build thread.
QUOTE (Lymitliss @ May 26 2009, 08:06 PM) <{POST_SNAPBACK}>
Ohh yeah I guess that makes sense. King Kaymo has all the answers 
#3
Posted 19 February 2012 - 09:49 PM
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- Swap in HF drums, check your cam timing
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- Group: 2015 Contributor
- Location:CRX Heaven, Los Angeles
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Drives: '87 CRX Si, '07 Civic Si Sedan, '15 Scion FRS
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QUOTE (GTI-CRX @ Feb 19 2012, 10:03 AM) <{POST_SNAPBACK}>
I have a 87 CRX HF with 210,000 miles. I need to replace the throw-out bearing, so a new clutch, resurface of flywheel will also be done. I was thinking of swapping the transmission for a SI unit. My question is how much will this affect the MPG and performance. I am looking for a little more performance without sacrificing all of my MPG. Any thoughts?
The Hf has wider spaced gears and a higher final gear ratio, the Si is geared for more "fun." The best set up is to use the HF's fifth gear in the Si transmission.
Form Follows Function
#4
Posted 20 February 2012 - 12:08 PM
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- Leadfoot
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- Group: 2013 Contributor
- Location:Youngsville, NC
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Drives: 87 CRX Si, bought new, no rice. 07 MCa w/sport, no kraut.
Can you buy that 5th gear alone some place reasonable?
That seems to be the optimal setup for an Si. 1-4 set up to move out, and
a taller 5th for the mpg on the highway.
That seems to be the optimal setup for an Si. 1-4 set up to move out, and
a taller 5th for the mpg on the highway.
#5
Posted 20 February 2012 - 12:10 PM
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- Leadfoot
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- Group: 2013 Contributor
- Location:Youngsville, NC
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Drives: 87 CRX Si, bought new, no rice. 07 MCa w/sport, no kraut.
BTW check on the flywheel costs.
Here they want $65 to resurface it and rockauto had them on closeout for a lot less
than that it has been a while but $45 shipped.
Here they want $65 to resurface it and rockauto had them on closeout for a lot less
than that it has been a while but $45 shipped.
#6
Posted 20 February 2012 - 09:33 PM
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- Slowpoke
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- Group: Members
- Location:Minnesota
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Drives: '88 Iroc Camaro, 2001 Silverado, '86 CRX si
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Is the final drive ratio on the HF trans also different from the SI trans? I was thinking of swapping 5th gear in my SI but I thought I read somewhere the final drive is also different, so you wouldn't be turning as low of rpms without the entire HF trans. If anyone wants to trade an HF trans for an SI one let me know. I have a spare SI trans I wouldn't mind trading.
#7
Posted 21 February 2012 - 06:26 AM
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- tinker, tinker....BOOOOOOM!!!! then I run around
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- Group: Contributing Mod
- Location:Hurst, Texas
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Drives: Don't, because they don't run and I am a crappy mechanic.
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QUOTE (cbstdscott @ Feb 19 2012, 09:49 PM) <{POST_SNAPBACK}>
The Hf has wider spaced gears and a higher final gear ratio, the Si is geared for more "fun." The best set up is to use the HF's fifth gear in the Si transmission.
That is if he didn't have to rev rediculously high, in order to use the hf 5th. I would just go with a dx trans, keep the HF flywheel and starter. Mild reduction in MPG, but enough to keep it peppy, with a 35 to 40 MPG with proper tuning.
Honda, because it's hard to look baller in your mom's Volvo.
The entire tool selection at Sears or the contents of a Snap-On truck will do you no good if you do not know how to use them.
The entire tool selection at Sears or the contents of a Snap-On truck will do you no good if you do not know how to use them.
#8
Posted 21 February 2012 - 07:35 AM
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- The Beach....The only place where salt LOWERS your blood pressur
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- Group: 2009 Contributing Member
- Location:Florida
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Drives: 2017 Camaro 1LE and 2001 F250 SD
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QUOTE (Ryguy440 @ Feb 20 2012, 09:33 PM) <{POST_SNAPBACK}>
Is the final drive ratio on the HF trans also different from the SI trans?
Yes, they are quite a bit different, not to mention there are three different ratios that came in the HFs depending on what market area they were sold in.
US, 49 states had a 2.95:1 FD ratio
California only HFs had 3.55:1
US, Hi Alt (mountain areas) came with 4.06:1
This is according to the FSMs that I have.
If you love the Elise, drive a Se7en - Caterham or whatever...
It has even less content than the Elise, is less graceful looking
...and changes direction like a ping pong ball whacked by Thor.
#9
Posted 21 February 2012 - 10:26 AM
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- Leadfoot
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- Group: 2011 Contributing Member
- Location:Akron , Ohio 44305
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Drives: 1986 CRX si
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Well according to the FSMs that I have, the California and Hi-alt HF trans are the only 5th gears that are different than the Si 5th.
So I think that I agree with badpenny "I would just go with a dx trans" depending on what HF trans you have.
Good information Jay.
Jeff
So I think that I agree with badpenny "I would just go with a dx trans" depending on what HF trans you have.
Good information Jay.
Jeff
#10
Posted 21 February 2012 - 09:03 PM
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- Slowpoke
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- Group: 2012 Contributor
- Location:Billings, MT
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Drives: 86 CRX HF, 85 CRX SI, 84 CRX D16A1 swap, 76 Scirocco, 90 Firebird, 70 Charger R/T, 87 V8 S10
I put a Si trans into my HF which had already had a DX engine swapped and I still get 42 in town, about 38 cruising at 70, and 35 on the interstate at 80. It made the car so much more fun to drive that it was hard to beleive it was the same engine. You will not be dissapointed with this swap. If you dropped the good HF fifth into it then it would be better yet. I have the parts for mine, but have been too lazy to get the swap done.
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