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Posted by: amfab Dec 28 2018, 07:07 PM

Hanging with family over the holidays so I cannot really get to the garage to do anything substantive, so I I was looking at parts for my 3.2 conversion and was thinking I will need a tach. Aside from a matching 84–89 3.2 tach, what other tachs are a good option? Would a 3.6 964 tach work? Other options?

Thanks in advance

-Andrew

Posted by: IronHillRestorations Dec 28 2018, 07:21 PM

Pretty sure you have to get a 3.2 tach

Posted by: TravisNeff Dec 28 2018, 07:32 PM

There was a thread on pelican where someone was suspecting that using a non 3.2 tach would smoke the motronic unit.

Posted by: Steve Dec 28 2018, 07:34 PM

The 964 and 993 tach have a connection to the computer. I don’t think it will work without it. I’m runnng a 3.2 tach with my 3.2, but the same 3.2 tach worked with my previous 2.7 engine.

Posted by: mepstein Dec 28 2018, 08:36 PM

I’m running an SC tach in my 3.2. Works well. At our shop, we do a lot of 3.2 and 3.6 installs and use tachs from earlier cars. No problems. You just want to tie off the wire for the shift light. I was previously told that using an early tach on a 3.2 would cause problems but that is not true.

Posted by: amfab Dec 28 2018, 09:24 PM

Mark How do you know when to shift?!
(jk, that arrow was the only thing I didn't like about my old 84 Carrera)

Good to know that the SC tach works—they seem to show up cheaper used.
I was surprised about the 3.6 not working.

-Andrew

Posted by: mepstein Dec 28 2018, 09:34 PM

The 3.6 tach is ugly...and probably pricey. I don’t like the shift light either.

Posted by: Steve Dec 29 2018, 11:23 AM

I couldn’t get the 3.6 tach to work with my 3.2, but it might just be a bad tach. I thought it would be cool to get the OBD to work in my car. It has outside temp and digital speedometer. There are a bunch of articles on how to fix them. I’m prepping my car for paint, so it will be awhile before I can screw around with it again.

Posted by: naro914 Dec 31 2018, 01:24 PM

I have an Autometer tach that will probably be available if you're interested.

Posted by: larryM Jan 1 2019, 10:55 PM

http://www.914world.com/bbs2/index.php?showtopic=298758&st=0


mepstein wrote:

We have 20 bad ecu's (3.2 engine computers) in the shop. I sent a couple to Steve Wong / 911 Chips for repair. He asked if they were from a 914-6 conversion car since they had a particular defective part. They weren't but most of our cars are 3.2's into early 911's so sort of the same idea. Steve said the reason we were blowing ecu's is because we were mixing the ecu's with a non 3.2 tach. It's very common for a 914 conversion to either modify their 4 tach with an electronic unit or modify an early tach to work with the 3.2. Steve said it may work for a short time, sometimes longer but failure often happens at high rpm. Go to the track, ralley or just some spirited driving and the higher rpm's kill the ecu's. I have to believe him since we have a pile of them to prove it. We had one burn out after 1.5 miles. Even hooking up the shift light wire on the 3.2 tach incorrectly will burn up the ecu's. Not right away but over time. A rebuilt ecu runs $900 and the burnt core is worthless. It's a known problem so it isn't accepted by most, if not all of the ecu rebuilders. You also must use a coil for a 3.2. No substitutes.

https://www.pca.org/tech/32-dme-vs-tach-compatibility

12.01.2016 Asked by Larry Moeller [GG]
"a post recently appeared on 914World suggesting that a 3.2 DME can (and probably will) be irreparably damaged (fried) if hooked up to an older 911 tach (i.e., anything other than '84-89) or any converted 914-4 tach

I have a 914/6-GT with a 3.2 & Wong chipped 082 DME, and have been running a 911 tach (OEM to my car, 901.741.302.04) for past 3 yrs (albeit not more than a few thousand miles & no racing nor prolonged high-rpm)

when i did the 3.2 conversion, Palo Alto Speedometer checked/refurbished my old Tach & said it was compatible with the 3.2

nevertheless, the 914World story scared me enuf to buy a 3.2 tach as "insurance", (which i am installing tomorrow)

but, i am wondering: (1) if there is really any validity to this, and (2) secondly if SC tachs are exempt from the worry, since there seems to be controversy on that point??

the post link is: http://www.914world.com/bbs2/index.php?showtopic=298758

ALSO SEE

- http://forums.pelicanparts.com/porsche-911-technical-forum/280714-tachometer-compatibility-chart-3.html

http://forums.pelicanparts.com/porsche-911-technical-forum/334338-tachometer-tap-3-2-a.html#post3972081

http://forums.pelicanparts.com/porsche-911-technical-forum/240252-help-tach-died-i-need-know-what-can-replace.html

Posted by: amfab Jan 2 2019, 09:39 AM

Good info,

Mark what was it specifically that changed your mind on the Tach not being the issue with all those fried ECUs?

-Andrew