There's two possible ways to read that question.  The first is: "Does the temperature of the engine effect how efficiently it burns fuel?"  The answer to that is definitely yes.  The hotter the better.  Actually the hotter you can get the fuel the better.  I won't go into it here, but check out the Hot Vapor Engine Smokey Yunick designed.  Utterly amazing how much power per cubic inch it made and how efficient it was.  The fuel was several hundred degrees going into the chambers in that engine. 

The second way is: "Does the temperature of the sensor effect the reading you get from a wideband O2 sensor reading A/F ratio?"  The answer to that is, not entirely sure, but my guess is that it would depend on how much of a variation from the intended operating range of the sensor you got.  All widebands are heated, so they need to be at a certain temp to read accurately, but this happens within a short period of time at start up.  After that I think they read accurately over the typical operating temperature of the exhaust system.  If it were to get super hot from being super lean, hard to say, but at some point the engine will just stop running because you'll cross the lean burn threshold.  I would suppose the engineers who designed the sensors took that into consideration.  Usually the LBT is in the 15.5:1-16:1 range. 

The thing is, I know they make wideband sensors for Diesels now, and Diesel exhaust temperature can vary tremendously (from say 300 at idle to maybe 1,500 or more at WOT).  Apparently they still read accurately though.  A gas engine has nowhere near this level of variation. 

GM systems used a 9th injector to help with warm up.  That's how bad their EFI was compared to Ford!

Alessandro wrote:

Since i have afr gauge ( month ) i haven't seen noticeable variation between hot & cold . The biggest issue is the speed of readings that makes it very difficult to understand . Only few times i had steady numbers ..
too much dependable from right foot .  keep asking myself if really is so necessary 

Keep in mind that depending on placement it can take the wideband O2 (I am assuming you're using a wideband) sensor a little while to warm up itself.


 

Raymond_B wrote:

Alessandro wrote:

Since i have afr gauge ( month ) i haven't seen noticeable variation between hot & cold . The biggest issue is the speed of readings that makes it very difficult to understand . Only few times i had steady numbers ..
too much dependable from right foot .  keep asking myself if really is so necessary 

Keep in mind that depending on placement it can take the wideband O2 (I am assuming you're using a wideband) sensor a little while to warm up itself.


 

from Aem gauges e mails , they told me 4 inch after collector flange 4 into 1  on my long tubes . Impossible was in the single pipe for each cylinder . 
My gauge is a wideband heated lambda afr 
 

Rudi wrote:

With an engine that does not go above 180 degrees ever my AFR shows slightly rich at cruise, it rarely shows lean under any driving conditions. The engine starts, runs and performs very well and gets great MPG considering it's carbed and automatic. It runs so well that I am very hesitant to make any changes to the Holley 670.
 My question was posed to see if operating the engine 10-15 hotter would show a leaner reading on the AFR gauge.
 The O2 sensor is non heated and unfortunately not mounted above 15 degrees horizontal.
 The gauge is a narrow band instrument, no digital read out just green,yellow and red LED's.

To be 100% honest Rudi a narrow band does not provide you anything. Stock narrow bands have a very specific range (hence the name) and purpose. Neither of which are for performance or tuning.

Sounds like everything's good so "if it aint broke, don't fix it". But if you do decide you'd like to tune then investing in a wideband would be good. 

Hit submit too soon, yes a 15 deg temp difference probably could make a bit of difference, but honestly in my opinion it's not worth the trouble. Especially after you take in to account heat soak in the carb, intake and etc. Also the way you are pulling in air can have an effect as well as whether the car is moving etc etc.

Last edited by Raymond_B (6/18/2020 5:14 PM)

Kinda like dad usta say....if it ain’t broke; don’t fix it!!!

Like I ever listened. 😂

Raymond_B wrote:

Rudi wrote:

With an engine that does not go above 180 degrees ever my AFR shows slightly rich at cruise, it rarely shows lean under any driving conditions. The engine starts, runs and performs very well and gets great MPG considering it's carbed and automatic. It runs so well that I am very hesitant to make any changes to the Holley 670.
 My question was posed to see if operating the engine 10-15 hotter would show a leaner reading on the AFR gauge.
 The O2 sensor is non heated and unfortunately not mounted above 15 degrees horizontal.
 The gauge is a narrow band instrument, no digital read out just green,yellow and red LED's.

To be 100% honest Rudi a narrow band does not provide you anything. Stock narrow bands have a very specific range (hence the name) and purpose. Neither of which are for performance or tuning.

Sounds like everything's good so "if it aint broke, don't fix it". But if you do decide you'd like to tune then investing in a wideband would be good. 

Hit submit too soon, yes a 15 deg temp difference probably could make a bit of difference, but honestly in my opinion it's not worth the trouble. Especially after you take in to account heat soak in the carb, intake and etc. Also the way you are pulling in air can have an effect as well as whether the car is moving etc etc.

Think of a narrow band O2 like a three position switch.  It reads rich, stoich, and lean.  Used in OEM applications they don't ever give the ECU an actual A/F ratio.  Instead they basically tell the ECU that, depending on other parameters, it needs to adjust the fueling to achieve one of the other two positions on the switch.  Let's say its lean on acceleration, engine is at operating temperature, and everything else agrees it should be reading "rich".  The ECU will adjust fueling until the O2 tells it that it is now rich.  This only works in closed loop operating conditions.  You see the limitations of this system, especially if you are trying to calibrate the ECU for a non stock application.  NB sensors only tell you one of three things, but a WB tells you HOW rich or HOW lean, which allows you to make pretty accurate changes to the system using some equations. 

Say you were reading 14:1 on acceleration and you should be reading 12.5:1.  You can figure out how much fuel is actually being supplied to achieve 14:1 by taking pulsewidth and fuel pressure into account.  Then you can figure the percentage you need to increase pulsewidth to achieve 12.5:1.  Most tuning programs have a scaling function where you can change either individual cells or the entire curve (or map) up or down by a percentage. 

If the cooling system is up to snuff there's both power and reduced fuel consumption to be gained by going from a 180 to a 195.  I wouldn't think it will be a dramatic difference.  Maybe 5HP and a 1-1.5MPG improvement in highway economy.