10Krpm / 6-cyl chrome dot tach build, DIY conversion from early -4 donor tach Options

[Retroracer]

So this post builds on, and references Tim’s (timothy_nd28) awesome post here:

http://www.914world.com/bbs2/index.php?sho...719&hl=tach

…which details the steps necessary to improve the original VDO tach performance and provide better transient and damping response, coupled with a more universal input. If you’re not familiar with this DIY tach upgrade, best read that first.

Given the flexibility and performance upgrade of retrofitting the SunPro/Bosch innards into the VDO casing, I took on the challenge of seeing if a 10K racing tach could be constructed around an early 914-4 tach housing – with a target cost of $100. Read on if this piques your interest; move on if you don’t think this sort of thing is necessary or sensible.

A 10K tachometer was an essential part of the GT cars (and other Porsche race cars too), which typically had no redline area indicated under the glass, such that the actual redline could be indicated with a marker or tape, to suit the particular engine build being run for that event. Original 10K VDO units appear for sale occasionally, but the prices are usually prohibitive.



I ordered the Bosch version of the SunPro via Amazon, and disassembled it using Tim's post as suggested:





There is some metal fabrication necessary to get the donor VDO fascia to mate up to the new core. This is not difficult, the only thing you may not have around is the M2 tap.



Getting the right fascia: So I toyed with idea of using a drawing or graphics package to replicate the 10K tach face, then somehow print a design on to vinyl, trim it, then glue that over the existing -4 face. Then I realized that I was never going to get round to doing that, so looked at other options.

I ended up buying a printed and finished insert fascia from these guys:

https://www.heiler-tachodesign.de/Tachomete...ithout-red-Area

Not a cheap way to get a result, but they a) offer multiple choices to match various Porsche VDO tachs and other gauges, b) the quality of the fit, paint and graphics are exemplary and c) without the talent and tools for “rolling your own”, there are very few other options. They also allow you to pick custom colors and lettering if you so desire. It took about 2 weeks to arrive, I also ordered a 914-6 style temp gauge replacement at the same time, total cost for both gauge faces including shipping was about $93.



So, $100 target blown already - the tach core is around $35 - but still in the ball park.

[914forme]

(IMG:style_emoticons/default/lol-2.gif) You really want to know how easy it is (IMG:style_emoticons/default/av-943.gif)

You rotate the needle on the shaft to the proper new location. VDO tach have stops "rests" the Sunpro / Bosch do not, they will travel 360 degrees.

More detailed version, many sets of step by steps have been written.

Okay here it goes do not get to (IMG:style_emoticons/default/icon8.gif) knowing how it is done.

1. Remove bezel - write-ups can be found on how to do this.
2. Remove needle - well documented
3. Remove face - 2 screws removes the face
If changing the guts to a "Modren" (IMG:style_emoticons/default/laugh.gif) tach then follow the write-ups
3a remove guts
3b install new guts - This thread, but Timothy did an excellent writeup on this process.
4. Install your new artwork with numbers in proper orientation
5. Install needles
6. Calibrate tach using a single generator, or tach tester, you can also connect the wires and fire up the car and gently put the needle on it where you digital tach says it goes. Analog tach are just a reference, something that sweeps to make people go wow I can rev and engine. VDO should not be used as a scientific instrument, (IMG:style_emoticons/default/av-943.gif)
7. Clean up and install glass and trim
8. Crimp trim to lock it onto the gauge.

Done....

Install in the dash hook up the wires correctly and you're off and running again.

Where this gets harder, but not impossible. If you are adding an extra gauge ala 930 style unit. Moving warning lights around, building a custom gauge like a triple, or a quad to the right of the tach. clocking the gauges or painting them, making custom colors and getting all the markings right. Installing a rebuilt speedo - the old mechanical ones can get tricky to setup right. No gauge work is beyond the scope of a reasonably skilled DIYer. Maybe I am not reasonably skilled (IMG:style_emoticons/default/confused24.gif)

Custom artwork has all ways been the hardest part of gauge work for me. Old days we had to do it via a silk screen, then we got Alps printers, made life a bit better. Now I am working on two methods that show promise for getting these done, and making them easier to customize for various configurations.

[djway]

(IMG:style_emoticons/default/lol-2.gif) You really want to know how easy it is (IMG:style_emoticons/default/av-943.gif)

You rotate the needle on the shaft to the proper new location. VDO tach have stops "rests" the Sunpro / Bosch do not, they will travel 360 degrees.

More detailed version, many sets of step by steps have been written.

Okay here it goes do not get to (IMG:style_emoticons/default/icon8.gif) knowing how it is done.

1. Remove bezel - write-ups can be found on how to do this.
2. Remove needle - well documented
3. Remove face - 2 screws removes the face
If changing the guts to a "Modren" (IMG:style_emoticons/default/laugh.gif) tach then follow the write-ups
3a remove guts
3b install new guts - This thread, but Timothy did an excellent writeup on this process.
4. Install your new artwork with numbers in proper orientation
5. Install needles
6. Calibrate tach using a single generator, or tach tester, you can also connect the wires and fire up the car and gently put the needle on it where you digital tach says it goes. Analog tach are just a reference, something that sweeps to make people go wow I can rev and engine. VDO should not be used as a scientific instrument, (IMG:style_emoticons/default/av-943.gif)
7. Clean up and install glass and trim
8. Crimp trim to lock it onto the gauge.

Done....

Install in the dash hook up the wires correctly and you're off and running again.

Where this gets harder, but not impossible. If you are adding an extra gauge ala 930 style unit. Moving warning lights around, building a custom gauge like a triple, or a quad to the right of the tach. clocking the gauges or painting them, making custom colors and getting all the markings right. Installing a rebuilt speedo - the old mechanical ones can get tricky to setup right. No gauge work is beyond the scope of a reasonably skilled DIYer. Maybe I am not reasonably skilled (IMG:style_emoticons/default/confused24.gif)

Custom artwork has all ways been the hardest part of gauge work for me. Old days we had to do it via a silk screen, then we got Alps printers, made life a bit better. Now I am working on two methods that show promise for getting these done, and making them easier to customize for various configurations.

I miss my Alps