AFR numbers

[Rocco]

Hi there friends

today i was testing my new RS2 dark green injectors + 7A FPR +RS2 turbo,etc etc

and the AFR numbers was always between starting 10´9 like the "richest" to 11´5 or lower 12´s as the "leanest" mixtures.


the car ran perfect and looks like a earth to earth missile


these AFR numbers using 98ron fuel will be dangerous for our cylinder heads??

i have a very small cracks between the sparks holes and valve seats in some places... and some people said that it is not so dangerous while they are not between valve to valve

My cylinder head has the ARP head stud bolts with a thicker metalic head gasket that drops compression to 8´8:1CR...aniway my cylinder head was skimed 2 times... and then i think that my CR will be around 9:1 or something smilar...


thanks a lot



-Tomas-

[A80Avant]

did you calibrate the lamda sensor before starting to use it?

[Rocco]

did you calibrate the lamda sensor before starting to use it?

yes of course, time time ago hehehe. just while we were installed it in the exhaust.

IT HEATS A LOT¡¡

[Rocco]

i forgot to say that the AFR numbers was under full acceleration with the foot down ,because cruising has other numbers like 14

[A80Avant]

that detail was very important.

that sounds about right. Erdal's map was somewhat the same. On WOT 5th and 6th gear, car would go all the way to 0.70 lamda. on 4th and below it would go no more than 0.74lamda

[Rusty]

Sounds about the same as mine. 14s on light throttle, 11-12 on full throttle, perhaps a bit less if the EGTs are getting dangerous. If you're worried then get an EGT probe and gauge to monitor things for real.

[A80Avant]

i know that everyone says the ideal is no lower than 12,but really how many of our cars can do that? i think EGTs are climbing really high up with 12 after 6000rpm or so

[Rocco]

and EGT are higher always with more rpm´s and uper 12´s or lower 12´s??

i think that 12 it is a decent rich mixture under WOT... but unfortunately i dont know nothing about the EGT problems with it

[A80Avant]

upper 12,which is why sometimes you need to take it down to 11 or 10.8 to be safe

[Rocco]

hehe a rich mixture goes cooler and a lean mixture heater

because the fuel it is cooler than the air


thanks for all, now i know that i am in a decent AFR numbers for hit my car hard


-Tomas-

[GazzaG60]

timing is as good at cooling as fuel.

10.8 will loose you a bit of power

[A80Avant]

Gary, what is the best equation? more timing and more fuel or less of both,keeping in mind that less timing will raise the egts a bit as well...?

[GazzaG60]

theres no hard and fast rule that i have found and it depends on engine types too.

not sure what changes you have made vas but you used to have a mapped RS2 turbo. now that drops off earlier than say for instance what you have now. potentially your map before never needed higher RPM timing tuning as the turbo never got there. it may be that you have a slight hole in the map there that needs some tweaking. high RPM tuning can be tricky too.

instead of adding fuel try adding a degree of timing and re-run the DATALOG. id set her safe on the juice first at say 11:1 look for reductiin on EGT and balance out to previous by removing fuel

now this is nthe time compression ratio affects performance moreso. with lower compression you can add more timing. high compression and big turbos dont go hand in hand. so where you may only be able to get say 20 degrees in on the standard compression you may be able to get say 25 in with an 8:1 ratio giving better top end performance where the turbo is working. the lowering of compression is in essence preparing the engine for boost up top. this is why i skimmed the pistons as i dont see much boost below 4k.

high comp and small blower makes for good drivability and economy.

[A80Avant]

you are absolutelly right Gary.
in current setup on motronic i had 21.50deg of advance dialed in on all high rpm/load values.That was the lowest timing i had there, although on lowering the IATs(colder weather, methanol injection etc) i could get as much as +4deg advance on the map.However, when i plugged the wideband to check the fueling, it was going as low as 0.70 on high gears,without ever stuttering from being too rich!! This is amazing cause once i started using vems, it would always do that when mixture gets below 0.72 for more than seconds!!

however on vems, im on 17.50deg on 2bar and 20deg on 1.8bar which as you know are the max they can go as there is no IAT advance feature. These are for safety reasons and with those values and mixtures of no less than 0.73 (mostly 0.75) on high rpms i get slightly better EGTs or about the same as the motronic. feelingwise, i would say that the car is about the same,but without doing runs under the same conditions i can never know.dyno session might give me an answer to that.
my compression is 9:1 roughly but i may decrease it in the future.

[EspenW]

Low 12's will probably be OK, even though mid 11's is usually the target on boost.
I run high 12's, sometimes into low 13's, but that is on the proper fuel for a turbo car.