Ok, here's my dilema and question.

I have one of these VDO Head Temp Sensors and 6 leads. I want to be able to monitor each head's temp. I'm running webers and thought this would be a handy thing to help figure out if/which one were running too lean.

They work off impedance or resistance, don't have the part here or I'd go into detail.

What kind of switch, etc. would work without giving unreliable results? ( I don't want 6 guages)

Any thoughts, comments, experience?

EGT would be a much better parameter to monitor.

Try Spruce Aircraft

Take a look at the 6 position switch: http://www.frostalarm.com/cat/p37.html

Not sure if the switch would work with the VDO gauge and leads, but in my experience these folks are very helpful and would be able to answer the question

Garry

I didn't wanna drill holes in my pretty jh coated header.

I just emailed westach, I'll pass along their response.
thanks for the lead!

This is their response:

Dear Sir: In reply to your request, your gauge should operate correctly using our 6 position switch. We trust this is helpful.

Very truly yours
WESTBERG MFG. INC.

R. R. Westberg
Admin. VP

BTW, the thermocouple senders (that's what those are, thermocouples) send a voltage. They do not change resistance with temperature, they actually put out a voltage difference depending on the temperature of the sender. I hear that it is very very critical to have zero (or as close as is practical) resistance in the wiring from the gauge to the sender. That's supposedly why VDO tells you not to shorten those wires.

--DD

Dave,

Your avatar scares me almost as much as Zois' old one did.

Alfred

dave, there is no wire, no matter how long (or short) that has 0 resistance, unless you cool it down to absolute 0 and use a special meterial, effectively turning it into a supra-conducter. the reason why VDO does not want you to shorten (OR lengthen!) the wire is because their sender and gauge are calibrated for the exact resitance their wire adds to the circuit (sp?). using different wire, even with the same length will also throw off the results ...

Andy

seanery,
if you're really anal you should get the 6-switch, measure the resistance for each of the 6 switch leads, then cut just as much out of each wire to match the switch resistance on that lead.

Andy

Andy,

That's a little above my head.

How do I know how much to cut off?

easy (well, sort of)
you need to cut the wires anyways to get the switch inbetween.
so what you do is:

1 - measure the resistance of the switch for each lead on the switch.
write them down.

2 - take a complete wire, measure the length and the resistance for that wire,
then cut out a small piece, let's say half an inch long, measure the resistance
of that piece, then use the "rule of proportion" (sometimes also called "rule of three") to calculate the correct length of the piece of wire you actually have to cut out. hopefully that will be more than the half inch you just removed

3 - repeat 2 for each of the 6 wires/switch positions ...

voila! won't be scientifically perfect but close enough
Andy

oh, also, remember that electrical resistance changes dramatically if you have large temperature fluctuations. make sure the wires a routed in a way so that they don't be exposed to large temperature changes ...

Andy

ahhh, the engineer in me speaking.
i had physics and math as my majors ...

Me thinks Meuller is right. Head temps are not going to take you where you want to go....too many variables with no base line.

EGT will get you closer, if there was a baseline. O2 sensors would be better.

Being a non-techno-geek, I just read plugs.

OK JP & Mike,

Is your theory because the heads will be a heatsink and not show the change in temps as quickly as the EGT?

You will not tune a engine using head temps. Plug readings, EGT or 02. EGT will give you individual cylinders as well as plug readings. 02 will give you all 6 unless you run 6 O2's.

Just being honest: I think your heading down the wrong path for what you want to do.

B

What Brad said....I got's to get to wurk....shit.
I'll elucidate (?) when I get back home....if there's a need.

Aaaaahndy sez: dave, there is no wire, no matter how long (or short) that has 0 resistance

Sorry, I meant "as close to 0 extra resistance as is practical".


JP sez: EGT will get you closer, if there was a baseline. O2 sensors would be better.

EGT will only get you to some known spot. To find what the "correct" EGT is for you, you need to go to a dyno first. Tune the car for max power, and see what the EGTs are there. Then, when you go elsewhere (so air temps/pressures/humidity/etc. change) or make some very small mod to the motor, you can re-tune the engine to hit those "target" EGTs--and you'll be at max power.

At least, this is according to a couple of racers that I have talked to that use EGT to tune.

A narrow-band O2 sensor will tell you "richer than 14.7:1", or "leaner than 14.7:1". It will not tell you how much richer or how much leaner... At least, not reliably or repeatably. A wide-band O2 sensor will, but those are not cheap and non-trivial to install properly.


Alfred sez: Your avatar scares me almost as much as Zois' old one did.

Why, thank you! I'm glad that you like it. Some friends of mine bought it to hang on their wall, and I discovered that it actually fit me pretty well also...

Grrr! Argh!

--DD

How long did you wear it, and did you ask them to take your pic because you knew it would look good as an avatar ?? LOL


B

Only a few minutes--they were just going to get the ladder when I decided to try it on. Kinda sucked as a useable mask, though, as the eye- and nose-holes weren't lined up so I could see through any of them, and my glasses didn't fit under it anyway so what little I saw was a big blur.

I did ask them to take a pic, but I didn't think about using it as an avatar until later.

--DD