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lean a/f ratio...

10w30

10w30

Member
Joined
Jan 28, 2010
Location
SD/PDX/Singapore
What is considered dangerously lean under full boost?
I have a 85 745 on stock efi with a .60 turbonetics turbo set at 15psi,meth injection opening at full throttle etc etc

what should my UEGO wideband be reading at 10psi and 15psi.
thanks
 
Ummmmm ok, lean is any thing above stoichiometric 14.7 :1 ratio that is the idea behind lean. Any thing below stoichiometric of 14.7:1 can be considered rich. This is based on Gasoline. Notice how i did not say too rich or too lean. This 14.7 is based around allot of chemistry, I'm not sure you want to know about. If you do me and other brickers that know way more than me wold love to get into it with you, but to keep it simple if you burn at a ratio of lets say 12:1 AFR then some of the gas is not burnt and just goes out the valves as incomplete combustion ( all forms of hydrocarbons ). This is good because at 15psi and under this huge combustion event you got allot of cooling from the extra gas AFR and you did get some burn from the extra gas. Meaning your shooting for actual peak power event rather than complete combustion.

you stated "At 15psi I was lean at 10.4, is that blow up my engine lean?" this would be considered too rich not lean. What ever your experiencing its because you have too much gas to get complete combustion and your robing yourself of power at this point. You most likely will not blow up your motor but build up quite a good amount of carbon and even can wash your cylinders if at to rich for too long. No oil on piston rings because the gas washed it all away. Mostly your going to be having a hell of a time getting it to rev up. shoot for 11 AFR or higher.
 
Ah yes thanks for the help had the lean and rich switched in my mind.

Is this "cylinder washing" a common thing if you are constantly running rich?
 
My car is tuned for 11.5:1 in heavy boost (30psi), and drops into the flat 11's above 30...10-15 (which is much more with my holset than you with your .60) is around 12.5-12.7.

In my experience rich with more timing is generally more consistent than lean with less...

BUT...to answer your question low 10's is stupid rich for that low of boost...how sure of your o2 calibration are you? does it read 22% or 22:1 in open air?
 
Whatever o2 sensor/gauge setup you have should have a calibration procedure...read the manual and perform the operations until your readout is correct before using it to tune.
 
Hi, i have also 15psi, fredchips, 012amm, 3" and 630ccm injectors.. my deepest value was 10.3 on full throttle... for about 10 seconds... this means to me... boost increasing :D
 
MadDog_945 said:
Hi, i have also 15psi, fredchips, 012amm, 3" and 630ccm injectors.. my deepest value was 10.3 on full throttle... for about 10 seconds... this means to me... boost increasing :D
Click to expand...

on gasoline: yes, you can raise boost. But if you are still using the stock tdo4-13C turbo that will not help much. @15psi it will be operating at the upper limit of it's design. Try installing a td04-15G from a 850-T5. with some twisting of the compressor housing this is a nice upgrade for your engine.

10.3:1 is a bit to rich in my view. The cathaliser will not like it (gets red hot on long highspeed autobahn runs)
you can also go the other way and bring the fuel pressure down a bit. Not the stock 3 bar but maybe the 2.5bar regulator (of the B230F , B200F ??)
Then the AFR's will get a bit better at full throttle and you might even pick up some extra power. (aim for 12.5:1)

yet another approach: you are in Germany, right? Why not use E85 at stock fuelpressure? your injectors a big enough. You will like the way it runs: Very smooth, very clean, very fast !
( my car using E85 440cc/min@5bar, small stock AMM and a T3 turbo: 245km/h with still some more to come but i ran out of space, AFR's were still rich!)
 
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Hi Jan,

im already using pure e85 ;) and my 15G is also getting too small.. im looking forward to install a 18T with angled flange (70mm) or KKK24

BTW e85 costs up here in Hamburg 90?cents how much in the netherlands ?

But the idea with lowering the fuelpress is a good start.. but i think this will make my idle crappy? or halfduty?
 
last time i filled up on E85 it was €1.24/L ... still alot cheaper then gasoline (€1.50++/L)
but E85 availability is still bad in NL (in NL only Tamoil has a network of E85 filling stations.)

about the car:
full power =/= clossed loop operation. Fuel is injected directly of the mapping and the AMM signal. When you lower FP the amount of fuel injected @full power gets less = leaner.

But the idle speed and the low rev/ part-load operation = closed loop operation.
The ECU will adapt to the lambda feedback and always aim for lambda = 1Volt. It will store the new learned values and use them next time you start and drive. It will be just fine.

That said...in your first posting you did not mention your car used E85! It leads to totally different conclusions!
In the case of E85, AFR of 10.2:1 is not extremely rich. in fact for max power you can even go a bit richer.

AFR's get confusing real quick when talking about different fuels.
rich on gasoline can be lean on E85 , very very VERY rich on gasoline can be just right for E85-full-power...
Better to talk about target Lambda-voltage. And offcourse always mention what kind of fuel is used.
 
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