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Tach w/ suby motors: Occams razor strikes again!
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ProvoCyclist
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PostPosted: Thu May 27, 2010 9:25 am    Post subject: Tach w/ suby motors: Occams razor strikes again! Reply with quote

Yeah, ill prolly get yelled at, but whatever. "suby motor! damn the infidel!"

So for about 10 months now ive been driving with a tach that reads pretty much whatever it wants, with the 8k tach face from smallcar.com i think it was reading 2x the true rpms. "this is dumb!" i thought, but resigned myself to the idea that there was no easy (read: cheap) fix. I was wrong.

I was at the junkyard the other day and pulled an 85 GTI instrument cluster with the 7k tach (oooh!). I swapped the units, and lo and behold, theres a little potentiometer on the back.

With the new unit installed, let your beloved get up to operating temps so the idle is stable, and turn the pot with a little screwdriver. Easy. Redline is spot on, idle is spot on.

A dislaimer: i have no idea if this will work with the "later style" tachs, but it works with the GTI units for sure.
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Clark
Current: 1986 Tintop GL 2wd, stock 2.1L, manual trans, Flash Silver LP7Y.

Past: 1985 Sunroof GL, 2wd, Subaru 3.3L, manual trans, resprayed to Diamond Silver L97A
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Wellington
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PostPosted: Thu May 27, 2010 9:31 am    Post subject: Reply with quote

Can you clarify a couple of things please:
Are you using the tach signal directly from the Subaru ECU or the diode method?
The SVX being a 6 cylinder and the GTI being a 4, is that why you adjusted the pot?
You swapped in the entire GTI tach as stock or swapped faces?
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ProvoCyclist
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PostPosted: Thu May 27, 2010 9:42 am    Post subject: Reply with quote

Wellington wrote:
Can you clarify a couple of things please:
Are you using the tach signal directly from the Subaru ECU or the diode method?
The SVX being a 6 cylinder and the GTI being a 4, is that why you adjusted the pot?
You swapped in the entire GTI tach as stock or swapped faces?


Oh yeah, sorry about that! Embarassed
1) The tach signal is directly from the ECU, no diodes. Ive heard mixed reviews about that method, and decided not to do it.
2) Yes, thats why i adjusted the pot.
3) I put in the entire GTI unit, although both units (van vs. GTI) look the same. Id guess the early van unit could be adjusted just as easily, and just use a 7k tach face. Honesty, i think the 8k face is overkill when your redline is 6400 rpm :p
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Current: 1986 Tintop GL 2wd, stock 2.1L, manual trans, Flash Silver LP7Y.

Past: 1985 Sunroof GL, 2wd, Subaru 3.3L, manual trans, resprayed to Diamond Silver L97A
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izzydog
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PostPosted: Thu May 27, 2010 3:58 pm    Post subject: Reply with quote

I used the resistor mod in my tach for my Subie 2.2 and it worked great. The tach on my 87 has an adjustment screw on the back as well. I plugged in my old crappy PC running B10 Scantool and with the tach laying on the dash and the computer running on the passenger seat, I was able to sync up the ECU rpms to the tach rpms.

I'm going to be dropping an SVX in soon and wondered how you know what your ECU rpms are? I didn't think that B10 worked on SVXs...
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ProvoCyclist
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PostPosted: Thu May 27, 2010 10:14 pm    Post subject: Reply with quote

I'd thought about doing the resistor mod, but i only heard about it for 4 cyl swaps.

As for setting the rpm, i knew it idled at 6-700ish rpm, and hit redline at 66-6700, so i kinda fudged it Embarassed but its pretty darn close. I think i need to raise the indicated idle (and consequent redline) just a hair, but for now its close enough.

A note on the GTI tach: it doesnt start to read til 300 rpm, then its graduated at 200 rpm to 7k. Woo!
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Clark
Current: 1986 Tintop GL 2wd, stock 2.1L, manual trans, Flash Silver LP7Y.

Past: 1985 Sunroof GL, 2wd, Subaru 3.3L, manual trans, resprayed to Diamond Silver L97A
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Wildthings
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PostPosted: Fri May 28, 2010 6:16 am    Post subject: Re: Tach w/ suby motors: Occams razor strikes again! Reply with quote

ProvoCyclist wrote:


I was at the junkyard the other day and pulled an 85 GTI instrument cluster with the 7k tach (oooh!). I swapped the units, and lo and behold, theres a little potentiometer on the back.



So you are saying that the GTI tach will fit into the Vanagon dash cluster?
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ProvoCyclist
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PostPosted: Fri May 28, 2010 8:06 am    Post subject: Reply with quote

yup, you have to reuse the part that the tach is mounted to (the black plastic part), but the gauge face diameters are the same.
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Clark
Current: 1986 Tintop GL 2wd, stock 2.1L, manual trans, Flash Silver LP7Y.

Past: 1985 Sunroof GL, 2wd, Subaru 3.3L, manual trans, resprayed to Diamond Silver L97A
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Wildthings
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PostPosted: Fri May 28, 2010 2:30 pm    Post subject: Reply with quote

ProvoCyclist wrote:
yup, you have to reuse the part that the tach is mounted to (the black plastic part), but the gauge face diameters are the same.


Cool thanks, I am going to give it a try. Any help with years and models I should be looking for.

Our local yard just did a crush. Only a couple of Subies on the lot right now, may have to wait a couple of weeks for the inventory to build up. Confused
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ProvoCyclist
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PostPosted: Fri May 28, 2010 8:27 pm    Post subject: Reply with quote

I pulled mine from an 85 GTI, id think any mark 2 golf or jetta with the 7k tach and the gas/temp gauges in the same spot as ours.
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Clark
Current: 1986 Tintop GL 2wd, stock 2.1L, manual trans, Flash Silver LP7Y.

Past: 1985 Sunroof GL, 2wd, Subaru 3.3L, manual trans, resprayed to Diamond Silver L97A
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syncrodoka
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PostPosted: Fri May 28, 2010 11:37 pm    Post subject: Reply with quote

You need one of these- http://cgi.ebay.com/ebaymotors/VW-Vanagon-Subaru-C...19bc8e6957
They have been putting them in subaru conversions for many years. There are 2 problems with this tach. The tach face needs to be slightly modded at the bottom to completely fill in the vanagon cluster because the jetta tach has a flat section at the bottom where the vanagon tach is round. The second bigger problem is that people have a hard time determining which ones work. I tested 6 tachs and only 2 worked with my EJ22 conversions and they all came from the same year range jettas.
Supposedly 16V sciroccos have 8K tachs that will work with subaru conversions as well.
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