Getting probed!

[Chris Wire]

In shopping for EGT gauges, I am torn between which style probe to use; band-type or screw-in.

According to RPW,

STREET PERFORMANCE PROBE: (band type)
This probe has less shielding than the street probe so it will react to temperature changes quicker but may not last as long.

HIGH PERFORMANCE PROBE: (screw-in)
The hard core racer that has a car that is raced often and is rarely or never street driven will want the high performance probe. - This probe has an exposed thermocouple junction (no shielding) which gives the ultimate reaction time to temperature change but has no protection and it's life will be short.

The car is an ITS RX7. But I welcome all opinions.

Thanks.

[C. Ludwig]

I'd do the screw in for a permanent installation. You just have to weld a bung (supplied) in the header. I wouldn't want to have a band clamp holding everything together for long. Might not be anything wrong with it but it's just hokie IMO.

They also have a "race" probe. Difference between the three is in how much shielding there is around the thermocouple. More shielding lasts longer but responds slower. For tuning you want something that responds as quickly as possible. And then again IMO for tuning toss the pyrometer and use a wideband and a load bearing dyno. $.02

[ddewhurst]

***Getting probed!, Not whatchyer thinkin....***

Side track............... Some years ago while at a gas station there was this nice Ford Probe for which there was a really nice looking lady pumping her gas. Her personalized licence plate was "Probe Me". being that the nice looking lady was on the young side I felt compeled to question what her mother thought of her licence plate.

I used the ban type mounting in my Karting & in my 1st gen RX-7. Didn't know anything special about the probes except the J or K type (whatever Alpha) thermocouple type.

[tdw6974]

We have used the "clamp" on type K Westach Ran it 4 years in 1st Gen. Over the off season have added gauge to the 2nd gen and now Aim system will be loging the temps these probes have the clamp and/or the weld on Nut. Maybe we will get to test the gauge within a couple weeks doesn't come up at idle damn cold weather. T

[John Herman]

Don't shop for an EGT, shop for thermocouple meters and thermocouples. Anything with "race" or "high-performance" in the description is probably going to cost more than some boring piece of scientific instrumentation. There is a company called Omega which has all kinds of stuff. My experience with the exposed thermocouples is they will burn out pretty fast when right near the head, but you can buy replacements for $10 a piece. Shielded ones last longer. They also come in all sorts of sizes and configurations to "fine-tune" them to your application. The other advantage to the thermocouples and meter is, you'll start figuring out all sorts of things to measure. Want to know what your air intake temp is, install a thermocouple. Brake pads, same thing. A simple rotary switch allows you to change between the thermocouples. All the meters are digital readout as well.

[Chris Wire]

Very interesting site, John. Most of the stuff is WAY over my head, but I did find a K-type thermocouple with NPT fitting for $34!

I'm hoping it would be compatible with the SW temp gauges the I'm using. With the cost being that cheap, it's much easier to get the fastest reacting sensor even if the longevity isn't so great.

I looked at the digital temp displays on the site but they were all around $200 or more.

Thanks for the info.

[David Ferguson]

A great source for EGT Probes for all types of systems is Exhaust Gas Technologies. http://exhaustgas.com/

[Mike Guenther]

Chris, a thermocouple is a junction of two wires of dissimilar metals. Any two dissimilar metals will generate a tiny current when they are connected. The current will vary in relation to the temperature and what the two metals are.

Thermocouples are designated by letters like type J or K to indicate exactly what the two metals are and their known useful temperature range of linear output versus temperature. Thermocouple grade wire is more closely monitored for purity of the metal to insure the output is in the known linear range. That's important if you need to add extension wires between the thermocouple leads and the instrument measuring the current (the gauge). When extensions are added they make additional connections and therefore induce an additional error, so it is best to order the thermocouple with the length wire leads you need and not add extension wire. If you do use an extension wire it is important to use thermocouple grade wire of the same type as the thermocouple or the error will be significant. (Significant is a relative word).

The connection to the instrument also is another junction (cold reference junction) but is usually calibrated out by the instrument manufacturer to compensate. There should be a letter stamped into the instrument to indicate what type T/C it is made to measure. Use the wrong type and you might get a reading but it will have a significant error.

The band type is measuring the surface temperature where it is connected. The temp of the outside of the header is not as important as the gas temp inside the header. The temps inside and outside will be very close but there will be a loss of heat radiating off the surface making it slightly cooler than the gas inside. And there is also a time lag induced by the mass of the header wall.

As for sheeth versus bare junction, the sheeth is relatively little mass and will induce negligable time lag especially when inserted directly into the hot gas you are measuring. (Negligable is another relative word). I would use the sheeth type as it will read virtually the exact same temps, will last much longer and only costs a little more than a bare junction.

[John Herman]

Chris, do you have a tire temp gage? If not, keep that in mind when you are evaluating costs. I know they have a probe for measuring temp's under the surface (i.e. in the tire), so now there are two uses for the standard gage. However, if you have a tire temp gage, it might just be an inexpensive K-type thermocouple digital readout. Turns out the one I had was. Just some more thoughts.

[Chris Wire]

I'm assuming that the SW gauges (don't have them yet) will have some markings or documentation that will help determine which probes will be best to use.

Omega seems to have infinite choices of probes, so I hope that I can determine exactly what I need and save $80 or so per probe on the cost.

Thanks for all the help.

[Chris Wire]

Well the issue appears to be resolved, but with a twist and some compromise.

I originally wanted a 2 5/8" gauge. Not happening since I also want it to match my existing AutoMeter Ultra-Lite gauges. So I guess 2 1/16" it is.

Then I came here looking for an alternative to the normal $100+ probes, and to whether it is better to use an band type or screw in model. The information shared has been helpful.

By accident, stumbled across an AutoMeter 'kit', that includes both the gauge and screw-in probe on HRPworld.com. All for just $153. That's just about the price I was looking for to start with, so although I don't ultimately get my 2 5/8" gauges, I guess everything else worked out.

Thanks for all the replies.