Date: Sun, 27 Dec 1998 18:01:43 -0800 From: Paul Grimshaw <Paul_Grimshawnopsamympatico.ca> Subject: Re: Why do you want to go 12.1??
An air/fuel ration of 13:1 will generally yield the most power, whereas 15:1 will lower brake mean fuel consumption. Neither of these ratios are, however, particularly kind to emission control systems as most 3-way converters require a near stiochiometric mixture to scrub NOx (highest at lean mixtures) and CO/HC (highest at rich mixtures). Enrichment beyond 13:1 is usually done to make up for an unresolved default, such as inadequate intercooling, poorly mapped fuel trim or bad combustion chamber distribution. The best way to increase power without incurring penalty in a street machine is to improve the intercooling. An there are more benefits than power with this approach too! Paul Grimshaw Author Volvo Performance Handbook A4 quattro wrote: > > I understand the 'safety factor', but 14.1 is plenty safe on a o2 equipped > car, since it will (within the limits of the fuel system) maintain that > ratio.... I think perhaps you are thinking back to the old days of turbo, > where it could go lean, and you wanted a 'cushion' just in case... If you > get your a/f down to 12.1, you will lose GET and HP due to being so rich... > We have discovered this in tuning my 1.8L 5 valve turbo motor on my Audi. > > I'd say best bet is to get an EGT gauge (expensive I know), and watch > it...if it stays below about 925-950, you're fine..... if not, THEN I'd > worry about making the a/f more rich. > > -- > Rich Quinlan > '97 A4 1.8tqms in Pearl, > More mods than I can shake a wastegate rod at... > > **** To reply, remove the 'nospam' after the **** > > "If it ain't broke, make it faster!!" > http://home.att.net/~richquinlan <--- Quinland--my own little world.. > > Firestarter <NOSPAMnopsamAM.com> wrote in message > news:368a7bbb.270432769nopsam.preferred.com... > >This is a continuation from my earlier post entitlted "Turbocharged > >engine pings under boost". > > > >I have a theory. I first thought that the O2 sensor would benefit my > >turbo system, but now I am thinking it may actually be causing my fuel > >enrichment problem. > > > >Here's the reason. > > > >The oxygen sensor's job is to keep the mixture within an acceptable > >range (for emmision purposes). I came to the conclusion that the O2 > >sensor's goal is to make up any deviation caused by wearing > >components, changes in altitude, temperature, etc. > > > >The system has a set of known variables it goes by but relies on the > >reading from the O2 sensor to keep these in range in case something > >changes. > > > >That's the problem with carburators. You set them to run at a given > >temperature, humidity and altitute but when you stray away from those > >conditions, the mixture changes. > > > >On my X 1/9 which has almost 200,000 miles on it, a new oxygen sensor > >made a world of difference because the engine was running way too > >rich. I even got an extra 10 miles per gallon! > > > >But on the Spider which has a new air flow meter and half as many > >miles on the componetns, a new oxygen sensor made no difference. > > > >Some earlier L-jetronic systems like the ones used on Datsun Z cars up > >until 1979 did not use an O2 sensor but the system was otherwise the > >same. Actually this system was a clone built by Nippon Denson under > >licence from Bosch. > > > >When I hit boost, I want to mixture to be at around 12.1. As of now, > >the richest it get's is 14.1. Just like it before I installed the > >turbo under WOT. > > > >I keep cranking up the fuel regualtor but it does not have any effect > >on the mixture under boost. > > > >It did not occur to me until now, but the oxygen sensor is doing what > >it is supposed to do. My original theory was that when the turbo > >started forcing air into the engine, the O2 sensor would pick up the > >lean mixture and add more fuel which would keep the mixture from > >leaning out. It seems to be doing this, however it also seems to be > >limiting the fuel mixture to 14.1 under boost. > > > >Under wide open throttle, the contacts close in the throttle position > >switch and bypass' the control loop. This is one of the tricks used by > >Legend industries. At 1 pound, a pressure switch closed the WOT > >contacts which bypassed the closed loop allowing the other two > >switches to trick the coolant temperature switch into thinking the > >engine was running colder which enrichened the fuel mixture. > > > >Without tricking the TPS, the lambda system would override the first > >two switches and try to keep the mixture from getting any richer than > >14.1 . > > > >That's why I suspect my fuel pressure regulator is not doing it's job. > > > >I think it's as simple as disconnecting the oxygen sensor from the > >computer. > > > >In one of my experiments, I found that by doing this caused the engine > >to run lean and not cycle. Some say by doing this causes the engine to > >run rich. But if you look in the shop manual, it says to disconnect > >the O2 sensor and set the mixture by turning the screw in the air flow > >meter. > > > >Or I can rig up the same sort of switch to close the WOT throttle > >contacts under boost like LI did, but I see no reason to because by > >unplugging the O2 sensor will do the same. > > > >Or install the pressure switch to break the circuit between the > >computer and O2 sensor under boost. > > > >So here is what I need to do, unplug the O2 sensor, set the mixture to > >14.1, leave the sensor unplugged and see what the mixture is under > >boost. > > > >As boost increases, the fuel pressure should also rise and get richer. > >Then I can adjust the fuel pressure regulator to what I want the > >mixture to be. > > > >The control loops seems to be defeating the purpose of the rising rate > >fuel pressure regulator. > > > >However there is always the fact that the mixture may actaully go the > >other way under boost. I will just have to wait and see. > > > > > >Due to the overwhelming amount of SPAM I receive, send replies > >via email to mailto:firestarternopsamcron.com > > -- ****************************************************** As Reviewed in EuropeanCar Magazine! "The Volvo Performance Handbook" is the Latest in Literature for your Swedish car! Check out this and other publications at: http://www3.bc.sympatico.ca/Volvo_Books/ ******************************************************
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