AFR / RPM graph
Turbo Mini Forums

Hi,
is it possible to get a graph comparing AFR and RPM using AEM wideband gauge and an engine management software using a distributor ?
How would the laptop get the RPM from ?

i would have thought load not rpm would have a bigger bearing on the numbers

I understand,
so it maybe better to take the readings on cruise / wide open throttle and adjust the mixture from it ?

it sounds like you dont know what your doing so the only advise i could give is find some one who does

Yes i moved to the darkside

Instagram @jdm_brett

Your probably right, I'm totally new in the subject but I like to learn and find informations.
I'll take your advice and try to find someone to help me.
When I was saying "adjust the mixture" I was thinking about finding the right needle not turning the screw...

I have an AEM gauge that logs boost, afr and rpm. It comes with a usb cable so that you can download the logs and check out all your data. It does everything you seem to want, all you need it someone who knows what all this stuff means to help you understand it and figure out what to do with the data.

You could post your info on here and someone who's feeling useful may help or you could try a tech savvy rolling road.

http://www.ebay.co.uk/itm/AEM-30-4900-DIGI...=item43b1354fe3

Thanks for your answer,
the reason why I need to learn basics of fueling is that I can't get access to a rolling road where I live.
I've had some fueling problems with my rebuilt engine so I've been advise to get a good wideband gauge.
Someone proposed me his help if I could give him my AFR readings, so I was thinking a graph would be perfect for that. My gauge is only the wideband, not sure if I can download any data...

I run about 14-15 on normal driving, it goes up to 16 off boost on a steep incline.
motorway cruise is about 15.
on max throttle max load max boost mine runs between 11-12. even seen it hit 10 a few times, would rather it a tad rich at this stage! in all im really happy with how it drives and the afrs at different areas/loads. a bit of scope to up the boost when im back on my feet (broke my foot on the bank holiday weekend unfortunately!)

Idle you should aim for 14.7:1

part throttle/ cruise aim for 14.7:1 to 16:1

full throttle for Normally Aspirated engine aim for 12.6:1 and no richer

Full throttle for forced induction same as normally aspirated but depending on boost level you can go richer still but there is no real need to go lower than 12:1 and anything beyond 11.5:1 is un necessary unless you realy are pushing the boundaries of mega boost levels.

Thise are general rules on steady load conditions, expect rich and lean spikes as the throttle position is changed, as that causes the volume of air to change one way or the other making the carburetter react accordingly. Under quick throttle chang conditions you will see this the most.

As for RPM, generally anything lower than 4000rpm and less than 50% throttle should be considered cruise and a near stoichiometric fuel ratio (14.7:1). Above 4000rpm and less than 50% throttle, start to richen things up a little, say 14:1.

above 50% throttle start to richen up towards the 12.5:1 at full throttle.

I say this as if it were fuel injection where you can easilly achieve these figures in specific areas of throttle and rpm, but with a carb, you might only be able to achieve the cruise 'lean' areas and the full throttle areas, everywhere else might be a compromise.

Remember that momentary rich and lean spikes are OK so long as they do not cause any adverse results, rapid throttle position changes will create these tyoes of conditions so when trying to tune anything regarding fueling, avoid that type of throttle condition.

Hope that helps.

This are the informations I was looking for.
I'll try different needles / timing curves to approach those readings,
should be enough to keep my n/a engine safe.
Thank you very much !

helpful info Sprocket cheers
brett (although i think it was a borrowed idea) also made a neat piston lift indicator to show what station your on the needle
that way to can see where your rich/lean and go from that to get it sorted good and proper
i believe if you where to put the time in you will get a dam near perfect needle

Finally installed the gauge/sensor
and after trying different needles I found one which is very close the the informations given above under cruise/part throttle conditions, but it doesn' t want to richen more than 13.5 under full throttle.
Is it dangerous for the engine or just good enough for economy (N/A engine)?
I need to order a few of this needle to start locating the weak part and do the filling job, how many would you advise me to buy ? How many did you wreck before getting the right one ?!!

Try thicker oil in the dashpot.


Nial.

Thanks for your reply, I was using automatic transmission oil then have changed for 20w50 and used a stronger spring, should I try an even thicker oil like manual gearbox oil ?
But even if I keep it wide open It doesn't richen more so was thinking the only solution is changing/ modifying the needle.
Is 13.5 AFR on WOT dangerous ?

Just buy a few spare needles similar to the one you have now and file them in the lower 3rd region to richen things up....

http://www.bobs-services.de/pdf/2003_12_nadel_en.pdf

Is 13.5 dangerous on a N/A engine? No not really, although when measured at 30C ambient it might go a bit on the lean side during a cold winters night if such thing exists in your part of the world

Yes will try the filing, looks so interesting !

I remember that winter night in 2001 when it was 18c ... had to wear gloves...

Great post Colin, what about overrun esp on FI cars

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Overrun on an FI engine should see at least 20% oxygen above 2500rpm (fuel cut) and aim for 14.7 bellow that. Remember though that the transition period from fuel cut can cause massive lean then massive rich spikes, and takes a little time to tune out when using closed loop fuel control. The thing to do there is apply a delay on the closed loop control after the fuel has first been re applied. It's all about the datalogging

Incidently, running massively rich on overrun and reasonibly retarded ignition tends to cause backfire in the exhaust. Its not dissimilar to certain types of Antilag

A stronger spring has the effect of a richer mixture.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!