CHT probe placement

[Randy Webb]

Tcpl is an abbreviation for thermocouple - they use a special wire and the wire type for each type (e.g. type K or type T) is different. Get them from Omega Instruments, which will do you well for any general needs.

Ron - you misunderstand -- the gauge itself is temperature sensitive -- that's my bet.

[RoninLB]

Originally posted by Randy Webb


Ron - you misunderstand -- the gauge itself is temperature sensitive -- that's my bet.

ok, I got that part.. I was trying to say that you could watch the needle drop as it was placed into the console.

[Randy Webb]

OK, I've got no explanation for that. I don't see why there would be RF up there. What happens if you move the gauge translationally in various directions?

[RoninLB]

Originally posted by Randy Webb
What happens if you move the gauge translationally in various directions?

it was either placed in the lower console specific area, where the left ga would move to a lower temp than the right ga, or removed where the left ga would = the right ga. [All connections always attached]

I'm not using it anymore. I upgraded.

[RoninLB]

Originally posted by Grady Clay
I have compared the under-sparkplug thermistors to planted-in-the-head thermocouples and the latter is far better.


If it is OK with you (hijack), I would propose a data acquisition preference.
1) Head temperatures at the intake and exhaust on all six heads.
2) Exhaust gas temperatures for each cylinder.

There is a lot to be gained with good data acquisition. These days it is widely available and relatively inexpensive.

ok.. I wanted to add my experiences with some book info. I'm late.

The planted thermocouple is complicated without pro experience in finding the correct probe placement. Cooling air could affect the temp ga reading so that has to be an educated placement. I couldn't do it.

The spark plug washer/thermistors is an area of spark plug heat dissapation. It can be 100deg hotter than true head temp at times because of this. I have the thermistor probe. I do notice a brief CHT increase when I peg the EGTs. It only lasts as long as the EGT's are high. [high EGT's are not a prob as long as CHTs are ok.] Anyway I never connected the dots of scattered spikes of 25-50deg higher CHTs with Higher EGTs till this thread. An analog gauge never notices these brief spikes. I don't race the engine so I'm ok. and I know the profile. I like being able to open the engine comp and going right to the clogged jet.

I always wondered what the max CHT is for our engines till they seize or blow up. I would guess between 350-400deg. I run between 240-260deg @3.5-3.8k consistantly in 5th @70deg ambiant.

[SCWDP911]

sub'd for future

[RoninLB]

[SCWDP911]

Originally posted by RoninLB

Ronin,

I would love more info that CHT display. I have been on the drawing board with an analog idea similar to yours using a selector switch for each channel and then also a channel that would read highest. I really like the idea the the mulitple display and greatest delta at the bottom.

Nice work. Now go clean your console up!

[RoninLB]

Originally posted by v8_ranch

I would love more info that CHT display.
---------- My bar display shows only an EGT reading between 1,000F & 1,500F. The CHT bars only come on at 300F and i run below that. The EGT & CHT numerics scroll every 7sec and then scroll thru voltage, "Dif", + options.

"Dif"/differential is the difference between coldest EGT and hottest EGT. [EGT is a reflection of piston power]. A power plant consisting of 6 equal engines that has the ability to have all EGTs in sync means all are producing equal piston power on the crank.
The notorious carb induction is the crudest according to text where "Dif" greater that 100F is considered good and 125F not out of the ballpark. Basic FI is better with a "Dif" range around 75F-90F. High end electronic FI may be around 60F.

My 50F "Dif" is somewhere around 75mph in 5th. Very rarely do i see 45F and routinely read between 50-60F. I took that pic because it's more of a painting than providing just info. PMOs are a carb enthusist's dream come true and i can prove it.



I really like the idea the the mulitple display and greatest delta at the bottom.
-------- you gotta love it but you have to be an engine nut to install it. You don't have to have it and it costs over $2.3k. Install time is over 20hrs for a decent install and over 30hrs for a trick install. Just alligning the EGT probes to flow into a smooth harness takes hours. If you asked a shop to copy my install they'd call the funny farm on you.

Grady posted a list of data aquisition mfg that should be more cost efficent and prices are dropping as technology advances. You should explore that.


btw.. tuning is a kick as you're looking into combustion with every adjust. I even tuned to a bad degree just to watch what happens inside this little universe. Needless to say i can watch acceleration cool combustion and watch a partially clogged idle jet raise its EGT. The only thing i didn't try is an induced misfire.
btw.. i run regular gas confidently. Less additives per gallon means more fuel per gallon.

Nice work. Now go clean your console up!
---------- lol.. i blow cigs but the unit can be FAA certified so it's a wash.



the below pic shows the lower bars as CHT. My non pro opinion is that EGTs around 1,300-1,375F are really nice. 1,200-1,250F are close to plug fouling. These units are not just a plug and play as there is a learning curve to understanding your data. If i had to comment on best bang for the buck i'd say a single digital numeric EGT & CHT on #5.

[JohnJL]

Hi Guys,
I received my Westach gauge, 6-position switch and 6 plug thermistors. The gauge is OK, not great looking. The silkscreened numbers aren't as crisp as I'd hoped. The thermisters, leads, connectors and shields do look of high quality.

Its a single 3" gauge that fits directly into my clock hole. I mounted the switch into a blank I made frm fiberboard and leftover leather frm one of the old door panels. It looks pretty good and fits the old stereo hole perfectly.

The thermisters are 14mm ring terminals that fit around the sparkplugs. I put them on the "lower" plugs as its a twin-plugged engine and the exhaust side runs hotter. They are a bit of a PIA to fit as they are a tight fit into the plug holes and my plug wrench got stuck in every one of them. I couldn't fit the #4 plug yet as I need to grind the case back a but to get a straight shot at the plug hole...a universal-joint wrench extension just won't work.

I was surprised to find the gauge doesnt require any power! I don't understand the workings of how it measures resistance without any external current supply.

I took some pics but I'd like to finish the install so hopefully will do that and post them tomorrow.

Any opinions/real world observations about what temps are too high? Engine is race-only 3L twin-plugged EFI.

Thanks all!

[Porsche virgin]

Originally posted by Grady Clay
I have compared the under-sparkplug thermistors to planted-in-the-head thermocouples and the latter is far better.

Could someone explain "planted-in-the-head thermocouples"? I want to put a Westach dual CHT gauge in my car, and I was just planning to use the under-sparkplug type. I have a pretty stock '84 911.

Thanks.

[mede8er]

Well...I'm resurrecting this thread as I don't see what I'm looking for....

New to me 1986 Turbo...CHT thermocouple is attached to #6 exhaust stud....

Getting reading of 450 degrees and I've got it rich, on the verge of oscillation....

Is this within range??? Wouldn't the exhaust temps read higher than the cylinder head temps???

TIA

[mede8er]

BTW...a meat thermometer placed directly on #6 cyl reads 180 when the VDO CHT reads 250.....