Pre-post intercooler temps? What is going on!!

Ok here's the deal.

Just a review of the setup. (BTW thanks for the ignition help earlier! EGT's are now in the low 1400 range)

Quad4 LO block, 753 head, 226 degree cams (exhaust advanced 7 degrees to reduce overlap), Garret T3-60 turbo with .48 or .43 exhaust housing from an 84 or so Ford Turbocoupe, intercooler from later year Turbocoupe (so I am told). All of this twists and turns through different sized pipes between 2.5 and 2 inch depending on location. Hey it was made with scrap parts, ok.

I have installed two thermocouples for my Omega Engineering digital thermocouple reader (reads J-type thermocouples to 1300 degrees) on my car. These are high quality devices and I know that they are accurate. They also react very quickly because the thermocouple tip is exposed to the air (not like exhaust probes)

Today before I left with the car to take a spin they both said 91F and my IAT and CLT sensors also said 91F. So everybody agrees that it is 91F outside today.

One of them is installed post-compressor on the turbo about 6 inches from the outlet of the compressor. The tip is slipped into a hose connection and turned down into the air stream (they are about 1/16 of an inch thick so they seal well). At peak temperature I am seeing about 170F. I expected up to 200F so things are better than I perhaps had thought on the efficiency of the compressor vs flow.

Ok now here is the part I don't understand.

The second thermocouple is installed in a similar manner post-intercooler near the throttle body (before it makes a 90 degree turn into the TB). During cruise times it reads about right. Somewhere between 100-110 degrees. Here's the kicker! During full boost runs the temperature drops to 65-70 degrees F! What is going on! How can I be getting better than 100% efficiency from an intercooler (it isn't possible is it!)

So what is going on? Is there a pressure drop in that hose near this location, or what else could be causing this? I really don't understand. How could the temperature be colder than the outside air temp?

There is nothing wrong with this thermocouple that I know of, but I guess I could try another one or another location.

Man I need an answer for this one.. ;^)


Rex Weatherford rex@beretta.net
92 Beretta GTZ <- SUPER INTERCOOLED
Best 1/4 ET = 14.092 @ 99.74 mph
Best 1/4 MPH = 14.115 @ 102.69 mph

http://www.beretta.net/behind_the_wheel/

 

I retried this experiment yesterday.

Ambient Temp was 84 degrees.

Pre-IC temps ranged from 110F at cruise to 140-200F at WOT and peaked at 220-230F when I let off the gas (air has nowhere to go so it heats up!)

Post IC temps are still sometimes baffling! I changed sensors and retried in the same location. I saw temps near 88-92F during cruise and 90-95F during WOT. I moved to another location about 4 inches away and saw weird things again. Temps all the way down to 45-50F under full boost, so I give up.

 

[NickB]

Is your gauge cold junction compensated? The heat from the engine bay can make the measured temperature appear lower than it actually is without cold junction compensation. Also make sure all your thrmocouple connections are done properly. Use the supplied nuts and bolts. Don't solder thermocouples.

A cheaper/easier solution would be to use a standard air temp sensor. The one used in the early 90's GM fwd cars works well. It's a standard pipe thread, and the sensor is exposed to the airstream, not encased in a housing. My friend is using one on his eclipse, and he gets the post cooler temps within a few degrees of ambient. His intercooler is ENORMOUS though.

 

[BeechBonanza]

Rex,
I've seen temps vary based on changes in conduit shape and direction. The pressure is usually not the same across the conduit near any shape or direction change. Nor is the velocity the same across the conduit.Pressure and velocity are relational in a conduit. Lower pressure/Lower temp.

 

Rex,

If you have the Omega temp. gauge that has provisions for two thermocouples, try unplugging one thermocouple and reading ONLY the post charge-cooler temps. I have heard that the dual probe Omega units have been known to have some problems with reading both probes accurately in a T1/T2 (delta T) configuration.

Andrew Slater

http://www.hangar18fabrication.com

 

I am pretty sure that your temp sensor is calibrated for stnadard temp and pressure. The temp you are reading is at a higher than standard pressure. Maybe this is why ???

 

OOps. Not standard temerature. I meant standard pressure.