There are already MAT and MAT relocation discussions but none so specific to this topic so thats why its a new post


People relocate the MAT due to 2 reasons IMO
1.) ECM "Trickery" for non tuners(?)
2.) More Accurate reading of true air temps entering the engine

My question is about 'heat soak' with the MAT mounted in the plenum, if the plenum is hotter that will obviously heat up the passing air, the question is how much? What is truely more accurate information at the valve/combustion chamber, the ambiant air temp drawn into the engine (at the snorkle) or the stock MAT location air temp that is a mixture of air temp and plenum heat soak?

Has anybody ever seen data of the differences of air temp as close as possible to the valve (Without the heat soak variable) as to what it was when drawn into the engine?

Any input would be appreciated especially with data

 

NO?. I was sure Iv'e mentioned it a few times....

1) Advertising sells, no doubt.
2) Yep.

You mount the sensor in the air stream, and it quickly reflects the MAT. The GM sensors are well designed, and the sensing bulb is well isolated from the housing. I installed one using a large nylon insulator, and it made no difference in readings.

Typically my MATs run 40dF less then coolant temp., other then in boost or in stop and go traffic. In none boost worse case situations, it can run up to coolant temp..

A large variable in all this is what is the code using the info for?. While some cars use a IAT/MAT not always is it used for fueling and timing corrections.

With just the differences in gasolines from tank to tank IMO rules out getting too extreme with MAT corrections, BUT, some correction is a LOT better then none.

Knowing the MAT is going to lag the CT by some amount, then at the higher CTs you can correct for it.

And if you toss in EGR then it complicates the whole mix a little.

 

Its been a brushed topic in previous posts but I did'nt find anything direct enough to engine dynamics to answer how much impact the heat of a manifold will have on the actual air making it into the combustion chamber. With the sensor output lag aside, you feel they're insulated well enough to give acurate air readings then?

My application is an EGRless 730 setup (where the MAT was said by glenn to have impact on fueling from his observations) and supposedly no EGR impact (which doesnt' matter for me anyways). The question isn't specific to my setup anyways, I'm more currious if the air is in the intake long enough to get 'heat soaked' or if its only a couple ° difference from the plastic to the intake valve

 

This is the condensed version:

I've found that using an IAT works better, on both dry and wet flow manifolds. The IAT value is then blended with the CTS to come up with the inverse T term for the BPW calculation (unless using ideal gas law equations, then the IAT is used a little differently).

As far as manifold heating of the incoming air: at low airflows the air picks up more heat then at the higher airflows. At idle the incoming air slowly heats up more and more until it reaches an equilibrium.

As the airflow continues to increase there will be a point where the manifold heating of the airstream increases. This is due to friction.

A MAT sensor picks up heat from three items: incoming air, radiated heat, and reversion. The closer to the intake valve the greater the pickup of heat from reversion. This is also cam timing specific.

A MAT sensor on a wet flow manifold is about useless for AFR/BPW calculations. The swings in temperature over varying airflows and fuel flows is tremendous. So much so that I found the car to be undriveable.

As far as using an IAT on the TPI w/$8D (ideal gas law BPW calc) Glenn found that it worked very well. He has posted the new IAT(MAT) table values and stated that it worked through wide ambient temperature changes with very little change in the BLMs.

The above is what I have found through primary & secondary research, YMMV.

RBob.

P.S. Great topic.

 

RBob

Great response



I failed to consider reversion and I suppose in that case getting a sensor super close to the intake valve could possibly be just as inaccurate as anywhere else. I guess there are just too many variables to hope for too much programming depending on MAT/IAT values. Besides the heat from reversion not being present on an Intake charge, the sensor would still hold the heat from the reversion. I see the main usefulnes in a 730 scenerio for relocation into the intake boot/plastic as basically a source of minimizing the temp range of the sensor helping to reduce one more variable for trying to tighten down VE tables.

In a naturally aspirated scnerio do you think airspeeds reach a high enough point for friction heat to become measurable?

Compressed air would obviously show up on a MAT even if it was completely isolated from the manifolds temp (boosted aplications), but is friction as evident?

 

The heating of the intake air from friction was from secondary research. On an engine this would be difficult to measure (all the other factors involved). How much does friction affect air temperature? I don't really know.

At the moment I do not take it into account. I think to do so I'd need to setup a tube with airflow. Get the proper length tube at the airflow to what it would be at high RPMs and measure the increase in temperature.

Apparently the increase is enough where it is taken into account in certain applications. A long runner with small diameter (TPI) would heat the air more then a single plane (Victor/Torker) with larger runners.

RBob.

P.S. Wet flow runners can/will drop below the ambient temperature.

 

I'm running a LT1 intake so i think I can pretty much assume that its going to enter the CC at not much higher temps than what it will be measured at just before the TB. I dont have EGR so that wont influence, I dont think friction will be any form of a factor at all and would be extremely intersted to see any data of aircreating heat on anything other than a bullet/space shuttle. (not that i disagree, i just dont think it might be a living animal in an engine). Compressed air however WOULD be a consideration if i was fortunate enough to have any form of boost, then again a shot of nitrous might just cool that right back off </tangent >

Anywho I think in such a short runner de-tuned application that the air temps may gain 10-20° in hot conditions but I dont see anything more really possible.

I fully see your point on TPI. it being the most likely candidate for creating friction, moreover with the long distance it has to travel there is MUCH more hot surface area for the air to cover, and maybe a MAT would be more accurate than an IAT if heat soak was solved (or is solved with as insulated as grumpy says the sensor is)

Then there is the variable of the sensor lag time


Oh the variables :lala:

I guess its just fun to wonder

 

A while back I posed my idea of using a different sensor in the stock location that is not subject to heat soak from the plenum. After some research, I found a sensor that has a metal base to screw into the plenum but the actual sensor itself is surrounded by plastic and is not biased by the temperature of the plenum. This sensor has the same resistance values and screws right into the stock sensor location in the plenum. You have to change the plug though.

Here is my post about it: https://www.thirdgen.org/techbb2/sho...hreadid=136007

Here’s a picture of it:

 

Wow thanks for the link

I find it incredibly odd that the sensor designed to be mounted in plastic, is plastic insulated and the sensor designed to be in metal (TPI, MAT sensor) isn't (?) as well insulated. Either way I believe the LT1 sensor is faster in response to temps thus more accurate, combined with mounting it in the air filter lid and my short runner LT1 intake I think in my own application that will be as accurate as I'll ever need.

My curriosity was just more one of engine dynamics, air flow, air friction, compression, maybe laminar flow, all the ways it can pick up or resist heat on its long but fast venture through the intake

 

If you look inside the sensor I posted and the LT1 sensor, they have what looks the same sensor element inside (I have both sensors). Thus, they would respond at the same speed and be just as accurate as each other. I like the idea of the sensor I posted more because it can be mounted in the plenum and be exposited to the air a close as possible to the cylinders (without modifying the intake).

 

The Packard Wiring catalog gives the response times to the various sensors. The fastest two they list never made it into production, or so it seems.

There comes a time, when close enough is close enough.

IMO, just mount the sensor a couple inches behind the throttle body so it sees good airflow and calibrate as necessary.

If your really worried about the surface friction heating reading a few books on WWII aircraft design might help. The flow stays sub sonic so it would seem that would be a good resource.

 

I believe my post was on how unworried I was, even if it was a factor (which i'd find hard to believe) It wouldnt' be a measurable one and would be a very difficult one to take into consideration.

Yes close enough is close enough for an air temp sensor, I was only tossing around ideas and theory. Thinking of the possibilities should (sensor provided) it be possible to get extremely accurate with it.

Maybe we can even take fuel temperature into consideration

 

Here is a link to an interesting paper on a portion of the intake air heating:

http://naca.larc.nasa.gov/reports/1942/naca-tn-839/

RBob.

And a blub from the summary:

 

RBob,
That write up you posted is about an air-cooled aircraft engine. Wouldn’t that be a completely different scenario from a water-cooled SBC?

 

Not really. The information is applicable to most IC engines. Note that the blurb states 30% of the temperature rise is from the intake valve opening restriction. This is because of the friction.

The funny thing is getting used to a 'high-speed' engine being 2,600 RPM. Then bores of 6" with 5" strokes. And 4,000 CI engines.

Another good paper:

The charging process in a high-speed, single-cylinder, four-stroke engine
Reynolds, Blake (Massachusetts Institute of Technology) Schecter, Harry (Massachusetts Institute of Technology) Taylor, E S (Massachusetts Institute of Technology)
NACA TN-675
February 1939


And this one:

Air-consumption parameters for automatic mixture control of aircraft engines
Shames, Sidney J
NACA Report 804
1945

All good stuff. Now I do have to warn you, if you look around and find that you are spending waayyy too much time reading. . . I did warn you

There are a lot of papers on ION detection and knock characteristics, and just all kinds of neat stuff. Can really bulk up the CD library there.

RBob.

 

But you'd not be able to measure this heating with an IAT/MAT, because it happens on the way past the valve (ie, due to a kv^2/2g energy loss), not in the intake manifold itself?

Interesting stuff thanks RBob.

John

 

Yes, along with the heating of the charge from the chamber/cylinder and residue gases. This may be why it is so difficult to use an IAT or a MAT to access the inlet charge temperature.

In the tn-675 paper it is stated that the cylinder pressure at BDC was very close to atmospheric and that the volumetric defficiency was most likely due to thermal effects.

That finding led to the other research on the effect the intake valve has on the inlet charge heating.

RBob.