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Posted by: hedfurst Feb 23 2018, 09:25 AM

Rebuilding a track-car I haven't used for 10 years, it has 2 VDO head temp gauges and was set up for #s 1 and 3. I'd like to be able to watch all four.
Has anybody ever set any thing up for this before? I'd like a switch to change from 1 & 3 to 2 & 4?

Posted by: brant Feb 23 2018, 09:52 AM

a lot of people have done it
check the air craft suppliers for the gauges like that
spruce is one...


but you probably would be better off monitoring EGT on each cylinder than 4x- headtemps.....


the EGT is going to be more money but more useful
I think a single CHT on #3 is adequate if you know your mixture and your EGT

brant

Posted by: hedfurst Feb 23 2018, 10:39 AM

Hey, appreciate it but what I was wondering was if there was a way to rig up a switch for an extra two sending units to use the gauges I have!

Posted by: brant Feb 23 2018, 11:56 AM

probably....


but why..
again CHT on #3 is going to tell you the whole story
and you can't use CHT to judge mixture

EGT will not only tell you mixture
but will give you real time info about what is going to happen to head temps before there is a problem
much better info
info available to prevent a problem
plus perfect mixture and max performance

not sure there is a benefit what so ever to adding 4 CHT readings.

I don't even run CHT on my race car at all
I use innovate wide band O2 for mixture
but in order to cut weight no CHT what so ever


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Posted by: jd74914 Feb 23 2018, 01:43 PM

Just buy a thermocouple selector switch.

Cheap surplus one with 4 channels:
https://obtainsurplus.com/electrical/components/omega-4-position-selector-switch-for-thermocouple-000090917024jj17store

Posted by: jd74914 Feb 23 2018, 01:53 PM

The less costly and more space saving way is to buy any double-pole, double-throw (DPDT) switch and wire each side of the TC to it's respective pole.

CAVEAT: IF YOU GO THIS WAY YOU NEED THE SWITCH TO BE NEAR THE GAUGE.

The reason is that by using a generic switch (without special Nickel-Chromium amd Nickel-Alumel wires, assuming you're using Type K), you introduce cold junction error which puts a bias on your measurement. As long as the switch and your gauge are at the same temperature you're good to go because the compensation is the same.

See the picture for a wiring example. For some reason you need to click on it, it's not displaying all of the test otherwise.


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Posted by: hedfurst Feb 23 2018, 04:26 PM

Thanks to you all! Appreciate your expertise.
Obviously some things to think about.