Disabled Account

Having trouble getting my head round AFR values and what IS safe or NOT safe........

Am I right in thinking that the figures within the green lines denote the actual problem And that if this problem was not corrected it would have melted/badly damaged Stu's engine?

bud-weis

correct

although those figures aren't excessively lean, if left unmonitored with a dying pump then eventually it only gets worse until it gets to leaner and leaner then melts.

Disabled Account

Main reason for asking is because the dyno AFR figures (below) are almost the same
throughout the rev range My old 8 x greens engine:

Paul Eggleton

And to add another question.......

despite the boost being pretty much 34-35psi and the AFR 12-12.4 does the danger increase with revs?. i.e is it far more dangerous for the engine at 5700, than 3700 despite the boost and afr being the same(ish) at both speeds?

slowpoke

at one point tho the AFR drops to 11.4

surely this is even more dangerous ?

ie getting leaner and leaner ?

Steven_RW

Slowpoke.. the higher the figure the leaner the engine.

My understanding is that we are talking AIR to FUEL ratios

14:1 being lamda 1.

It means a ratio of 14 air to 1 fuel ( in terms of weight not volume )

So if you had 15 to 1 it is even leaner as for the same weight of fuel ( 1 ) you have more air (15)

Hope that helps in some way

RW

Disabled Account

OK....so an AFR of 11.4 means: 11.4 units of air mixed with one unit of fuel.....

And an AFR of 12.4 means: 12.4 units of air mixed with one unit of fuel...therefore more air and less fuel = lean/weeker mixture

slowpoke

ok cheers rw,

i knew lambda was 14:1 so why is the 12 bit so dangerous ?

doesnt that mean theres more fuel in there ie running richer and maybe cooling the pistons a little ?

slowpoke

ok fair point but if 14:1 is lambda ie the most economical mixture then isnt that even more lean that the 12 bit ?

yes 14:1 is considered perfect ?

just trying to getmy head around it thats all as the 12 bit looks safer than the 14 bit lol

matt

Anonymous

Thats RICHER

DaveEscos

good post doug... my dyno shows the same afr

i was / am concerned too!!

or does stu just map his a lot richer than harv.ahmed

Steven_RW

Doug,

Not sure what the " " is for as you have it on the head!

Lambda 1 is a cruise setting. Most cars with a lambda sensor set the fueling to 14:1 under cruise for efficiency however under load this needs to richen up to keep it safe.

As said, Stu can pop on and make sure this accurate as nowhere has anyone actually stated that the numbers they are quoting "12.5" etc are air fuel ratios. I've just assumed.

I dont have that much experience with them just that my father has been selling gas analysers for EVER and this sorta crap has been discussed over the dinner table till my mother wanted to kill us both

Slowpoke, just imagine the larger number is more air. More air without extra fuel = lean mixture. Simple as that.

RW

Anonymous

Your timing advance is different, and so is your CR.


Det / excess heat are brought about as a result of an interaction of factors:

Timing / CR / Fuel quality / Boost / RPM


ALL of those are in the equation, so the values for Stu's high compression engine which is probably running nearly as much advance as your low compression engine (it gets to the stage on low comp engines that you end up running maximum timing a lot sooner) means that the same AFR will give a different amount of heat.

Its not the specific value that matters, its the change in them.

The alarms on your car would be set in a different place, and on the 325 N/A im driving around in at the moment would be set in the high 13s probably for example.


Its VERY application specific.

Damo V

Thats the answer I / Dave was looking for on the other thread,

Doug As you probably noticed, Dave and I posted our charts also, on the other thread ..

Anonymous

Damo, also remeber that in car and on dyno figures are likely to be slightly different too, things need to be a little safer when they are handed back to the customer, just in case.

Damo V

Yeah, I will observe with interest when incar setup

Considering my biref was over 340-350brake SAFE SAFE SAFE not, make it over 375 brake.. I am fairly confident it will be

Anonymous

Yep im sure you will get your 340+ once all installed in the car and setup properly, so everyones a winner.

In some ways ive always questioned the logic in letting the customer see dyno AFR's the way that SCS and some others do, i would say thats a little more information than the average customer needs anyway.

Still its cool that they are prepared to share it like that i guess, just dont take it as gospel that its identical once in the car is all you need to be a little cautious about.

Damo V

aye i appreciate dyno igures are a tad higher than in car

Anonymous

Hi...on a dyno you get more of a MAX balls out map...done to the edge of destruction..for the road it will be detuned for safety.

Stus 044 column is a perfect running engine ...i would never wanna see stus 941 column on a Cossie flat out!

Fiecos Dan

11.4 :1 is bit rich really. (unless the engine runs hot at 11.8:1) EDITED cos read wrong


on the dyno 12.3-12.6 is safe, as the operator will know its not dettin, and knows the fuel he's runnin is good and fresh.
(12.6:1 bein best for power but too hot for a turbo car runnin on pump fuel for road use)

11.8 is really wot you want to be seein thro the rev range on full chatter on a engine in the car,

12.6 wont normally do any damage, as long as cyclinder temps are safe (EGT's) and there's no det. But tuners wont leave it like that as if you change different fuel, or the fuel you use is age'in (been in car for a few weeks) the octane will be lower and cause DET = melt down time OR ACT's change/ boost rises a 1-2 psi the fuelin will change and can put the engine in danger.
so a safe AFR will be 11.8 (different tuners on different engines run different AFR, but normally between 11.6:1 to 12.2:1)

for light cruise and idle 14.0-15.0 is fine, lambda 1 bein 14.7, and best fuel ecomonly bein 15.2:1

on half accelaration (not full boost or throttle) 12.6 is fine.

15.2:1 = LEAN
10.5:1 = Rich

if that helps, i'm not a tuner, but do my own mappin, and know abit about this.

Anonymous

Fiesta Cossie Note the boost that AFR figure is from...surely a tad richer is best and keeping things cooler?

Anonymous

The 11.4 at the very top end is commonplace, its often used to gentley drop the power off slightly just before the limiter and also give a little bit of extra cooling.

Agree though, you wouldnt want 11.4 in the mid range really, but then as you can see from above, stu doesnt

Fiecos Dan

Yeah i agree that some cars 11.4:1 might be needed @ top rpm's if EGT's are high, or even if det is a problem.

But i wouldn't like to see 11.4:1 at top end if there is no reason to run rich.

But also comp ratio plays apart in the fuelin, as if high CR, less ign advance = higher chamber temps = needs more fuel.

ALSO i dont know the spec of the car the above is from, so not for me to say if its runnin to rich.


But i run 12.2 before on my cossie and no problems, but run 11.8 ish normally

Anonymous

Stu's car is indeed fairly high CR.

As ive already mentioned on the other thread, its very application dependandt, what works for you could be dangerous to someone else.


Just one thing to clarify (not to you as im sure you know this, but to others)


STU WASNT POSTING ABOUT THE ACTUAL VALUES SAYING THEY WERE A PROBLEM GENERALLY ON CARS, STU WAS POSTING TO SAY THAT HIS FUEL PUMP WAS FAILING TO MEET DEMANDS AND AS SUCH HIS CAR WAS RUNNING LEANER THAN IT WAS MAPPED FOR

Thats the key thing, not what the numbes were, but that they had changed since mapping purely because of the fuel pump.

For others a normal figure might be 11.5 or 13.5 or whatever, the key thing is that if that figure then changes after mapping, YOU HAVE A PROBLEM

markk

iTrader: (2)

i wouldnt say so myself

Rs Gus

iTrader: (2)

dont forget why the afr is left a bit rich on a yb mainly because of the crap inlet design or no3 runs lean and pop

Stu @ M Developments

iTrader: (12)

And the EGT of my own YB from 6500rpm - 7300rpm in 5th is what at 11.8:1?

Love it when blind people jump over walls... its such an odd thing to do


And that ends the rest of what i was going to say, congratulations Gus, great to see your mapping tuition out with me wasnt wasted pal

Stu @ M Developments

iTrader: (12)

Indeed it is pal

Fiecos Dan

i guess of 900 oC at the down pipe .

So why do you run 11.4:1 at 6200rpm then stu?