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Old 09-23-2009, 01:50 PM   #1
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question regarding A/F theory

so this may sound random, but optimally, we would want our cars running 1 lamda throughout the RPM band, but the reason we can't is because of heat? so if (theoretically) we could utilize all heat and it wasn't an issue, could we run our cars at 14.7:1 through all throttle?

IF my logic is right, then a DI car can run a bit higher A/F ratio cause they can keep the temps cooler?


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Old 09-23-2009, 02:32 PM   #2
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I am not sure what your asking ????

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Old 09-23-2009, 04:02 PM   #3
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Basically, if we could cool the block/engine better, could a/f of 14.7 be run from idle to WOT and everything in between?
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Old 09-23-2009, 06:23 PM   #4
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No , To cool of an engine wont make good power and will get very crappy MPG

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Old 09-23-2009, 11:33 PM   #5
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well, then i guess i'm asking, why do the A/F ratio's drop below 14.7 under WOT? i mean, i was thinking if the motor could stay maybe say at 100* F (just throwing a low number out there), or even less, then it could stay at 14.7 because the motor wouldn't get too hot, no timing would be pulled and no predetination. I've always thought that the most power would be made at 1.0 Lamda. (in an ideal state) but do to real world factors, motors really can't be run at 14.7:1 under load. so do to heat, we have to run the motors richer to keep them cooler.

the reason i was thinking this is because of all the new Ecoboost engines. they are turbo'd and direcet injected and i think they have some sort of VCT or whatever solenoid based valve control . DI motors have much higher fuel PSI and are sprayed directly over the piston crown much more evenly than in the zetec. thus helping to cool the piston and in return giving a more complete combustion. but since the fuel is helping to keep the motor cooler, i'm thinking they can run the motor a bit leaner safer.

I dunno, do u follow my logic?? I'm just curious and as i'm learing more about direct injection, it intriuges me. and i was just thinking that they can squeeze a bit more power out of them because they are able to keep them a bit cooler. even if only by a few degrees. but i think the theory still holds up, i'm not sure.

like i said, just curious!!
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Old 09-23-2009, 11:59 PM   #6
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I think your getting Cyl Temp and engine coolent temp confused , mixed , crossed

As you know you have 2 temps , engine coolent that cools the heat from the Cyl and Cyl temp , the more work (load) and engine does the more fuel it needs to keep doing it idle 14.7 , NA 13.0 , FI 11.5 big boost 10.5 all depending on the engine , It needs this fuel to help keep the cyl charge cool and to feed the demand for power/load , more air going in needs more fuel added

Actually the cooler the engine (engine coolent temp) is the less efficient it is to a point

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Old 09-24-2009, 12:05 AM   #7
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makes sense, so if cylinder temp could stay at an ideal temperature, it would be safer to run a bit leaner?? i guess thats actually the gist of what i'm asking.
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Old 09-24-2009, 01:12 AM   #8
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Quote:
Originally Posted by mlbbaseball View Post

IF my logic is right, then a DI car can run a bit higher A/F ratio cause they can keep the temps cooler?
your logic is right, MS3's are often tuned to about 12.6 even at 22+psi...

start googling there is a LOT of info about the ideal max torque afr of different types of engines.

And then there is the real world which usually differs from that info, where single cam mustangs love to run at 12.6 but the NA 4v motors can get up above 13, and where turbo zetecs can be under 11.5 and still be happy.

bottom line is you have to either get on the dyno and figure out what works, or beg for the experienced opinion of a nice gentleman (sometimes named Tom)
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Old 09-24-2009, 08:49 AM   #9
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Quote:
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makes sense, so if cylinder temp could stay at an ideal temperature, it would be safer to run a bit leaner?? i guess thats actually the gist of what i'm asking.
Yes , If that is what your asking then yes , If you could controle Cyl temp in another way other then adding more fuel then you could run it leaner

The MS3 guys are learning the hard way that 12.6 isnt the safe AF as I told them that a few years ago , I build a few engines for the MS guys as well and play in them some

Just because you inject the fuel directly into the Cyl under high psi does not change the AF ratio needed to keep it safe , Direct Cyl injection is more for emmissions and MPG more then anything

Tom
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Old 09-24-2009, 11:38 AM   #10
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ok, cool, that answers my question then, thanks!
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