944Hybrids: 924/944/968 and 928 V8 Conversions
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HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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How do I mod an early tach for a V8 signal?

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944convert
haroldk
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How do I mod an early tach for a V8 signal? Empty How do I mod an early tach for a V8 signal?

Post  haroldk Fri Feb 15, 2013 6:35 pm

I've got an early car and will be running Ford EDIS which outputs a normal V8 tach signal. I searched an found a few references to info on Porsche Hybrids, but the links go nowhere useful. Anybody know what's up? I could take care of it externally with some diodes, but I'd rather take care of it inside the tach itself.

Edit: I've got this working. See my post farther down the page for more info.


Last edited by haroldk on Mon Oct 07, 2013 11:25 am; edited 2 times in total
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Post  944convert Sun Feb 17, 2013 1:56 pm

Is this the commonly used 'voltage pull-up' circuit that you are looking for? (from LT1swap.com website).

How do I mod an early tach for a V8 signal? Tach_p10

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Post  haroldk Sun Feb 17, 2013 5:48 pm

That won't modify the frequency of the signal, just the voltage. What I'm looking for is something to modify the tach itself to display correctly with a traditional 8-cyl tach signal. I can get a 4-cyl tach signal by using a couple diodes on the coil packs, but I'd prefer to make the tach work with the signal I'll have instead.
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Post  HorizonblueDK Mon Mar 11, 2013 3:26 pm

You need a tachometer converter. One of these two might work.

http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=127/prd127.htm

http://www.ashlocktech.com/Home.php

If your original tachometer gets the signal from the original ECU, you probably need the Dakota. Haven't checked, but I believe all 944's do that.

If the original tachometer is conected to the negative terminal on the coil, then it's the last one. I need that one for my project ('76 924 straight six swap)

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Post  haroldk Mon Mar 11, 2013 4:05 pm

Again, I'm trying to mod the tach internally. I'm not paying $50-90 for a box that I can build for under $10. I would prefer to just change the way the tach displays to messing with the signal at all. What I'm looking for is information like what exists for the late tachs.
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Post  944convert Mon Mar 11, 2013 5:07 pm

I've never opened a late 944 tach...any chance it uses the ever popular 555 IC as a pulse counter?

There is a ton of info around if it does. Starting here:

http://www.electronicecircuits.com/electronic-circuits/analog-frequency-meter-circuit

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Post  haroldk Mon Mar 11, 2013 5:12 pm

944convert wrote:I've never opened a late 944 tach...any chance it uses the ever popular 555 IC as a pulse counter?

That's a good question for somebody who has a late tach. I can't help you with that one.

All I know is I've seen specific instructions on which resistor to replace with what value in the late tach to make it read correctly for a V8 signal. I'm sure it's after any signal processing and before the movement. I'm asking if anybody here has that same sort of info for an early tach. I'm not looking for external solutions because I can make one of those on my own. I'm not looking for how to modify a late tach because I don't have one of those.
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Post  944convert Mon Mar 11, 2013 5:20 pm

haroldk wrote:What I'm looking for is information like what exists for the late tachs.
oops...I misread this bit Embarassed

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Post  v8carreragts Fri Mar 22, 2013 12:47 pm

If you are still interested i have a write-up on how to do this. I did it to mine.
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Post  haroldk Fri Mar 22, 2013 3:14 pm

v8carreragts wrote:If you are still interested i have a write-up on how to do this. I did it to mine.

Yes, please.
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Post  v8carreragts Fri Mar 22, 2013 3:24 pm

It's in WORD format so I can't post it here. Send me a PM with your e-mail.
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Post  admiralkhole Sat Mar 23, 2013 5:12 pm

I would like to know as well, but I have too low of a post count to be able to send PMs. If you e mail me at admiralkhole @ gmail. com I would really appreciate it! Thank you.

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Post  haroldk Mon Oct 07, 2013 11:24 am

Alright, I've got this working. The relevant resister to replace is by the adjustment pot on the left side of the tach (as you're looking at the face). There's a 16k ohm resister inboard of the pot in between another resister and a diode. Pull the face off Make sure you note the position of the needles before you remove them and use a twisting motion to pull them off. You don't want to snap the shaft. Unsolder the 16k resister and replace it with a 931 ohm to 951 ohm resister. Replace the face and the needles.

Here's the part that made me thing I broke it: you'll need to turn the pot a good deal counter-clockwise before you attempt to calibrate it. I actually drilled a hole in the case where the pot is so I could adjust it while it's assembled since the ground is a lot easier to attach to when it's assembled.

Thanks to Peter for the info on this.
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How do I mod an early tach for a V8 signal? Empty Early tach and LS3 question

Post  johntorg Thu Apr 13, 2017 7:49 am

I just bought an a 924S with an LS3. It has the early dash and I want to connect it. I understand that the LS1 ouputs a 4 Cyl signal. Does the LS3 do the same? Also, where can I pick up the tach signal on the LS3 wiring? Any info on modifying the tach if the signal is 8 cyl, if necessary, would also be appreciated.
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