16 replies to this topic

[new_zealand _minis]

just got a aem gauge from the us . as said was the best bet to get .. im going to put it in the next few days .. question is

what afr shuld i aim for ??


motor is

1293cc

276 cam
std rockers .
vmax eaton 45 with std boost and hif44

[Guess-Works.com]

The stoichiometric figure of petrol is approximately 14.7:1 ( depends mainly on the grade of fuel used ) commonly referred to as lambda where 1.00 = ideal...

I learnt something off Mythbusters....

[Turbo Phil]

You should be looking for 12 to 12.5 on boost, off boost anything around 14-15 is fine.

[new_zealand _minis]

sounds good .im using 95 octane ... they took 98 from all the stations round me .. ill get some 105 octane soon just for fun

so im thinking that ... 12 is richer than 14 ... ?

[mini13]

yes, 12 is richer than 14

[HUBBA.HUBBA]

just got a aem gauge from the us . as said was the best bet to get .. im going to put it in the next few days .. question is

what afr shuld i aim for ??


motor is

1293cc

276 cam
std rockers .
vmax eaton 45 with std boost and hif44

Just gone through the same process as you. As near to 12.5 on Idle as possible, but it does jump around abit( which is normal, apparently).

[Turbo Nick]

12.5 is way too rich @ idle imo. mine idles at about 14.5:1 and is around 12.3:1 on full throttle.

[benb12]

The stoichiometric figure of petrol is approximately 14.7:1 ( depends mainly on the grade of fuel used ) commonly referred to as lambda where 1.00 = ideal...

I learnt something off Mythbusters....

I believe that's only at idle (or so I have been taught anyway). At full chat it can richen up to 10:1 and when cruising lean off to about 16:1. Don't take it for gospel but it's what's in my college notes!

[Turbo Phil]

10-1 is far to rich, you'll just end up with bore washing. As I said earlier, 12-12.5 on boost and anything around 15-1 on idle.

[Ethel]

14.7:1 is the only stoichiometric value for petrol, it means there's the right amount of oxygen for the fuel's complete combustion anything leaner is asking for trouble with no real advantage. Richer mixtures (like the 12.5 suggested) are a compromise, using the excess fuel for cooling so you can cram in more air without blowing up your engine.

[R1minimagic]

One other thing to consider, and I am not sure what applies in NZ, are any emissions regulations.

If you run too rich you are likely to fail on HC and CO and also your catalyst will not work as there is too little oxygen in the exhaust gas....

Of course, you could just be using it as a track car, in which case it doesn't apply!!!

[new_zealand _minis]

na here in nz no one cares about emissions

will be road car . i have had the gauge in . seems to run about around 10-12 from idle to the point of boost and from them on it is running about 12.5 to about 13 .2

i might lean it off with mixture screw then profile the needle from the point of boost to make it rich again

any tips hints will be very grate full as i will be tuning it myself as we have no rolling road with anyone that has knowlage of a thing called a carb !!!

[moke123]

the book by Des Hammill on tuning SU carbs is good for profiling needles. I have seen threads that say use yellow spring and 20/50 oil in dashpot for SC

[HUBBA.HUBBA]

On the back of the dash pot suggestion. Fyi - I went to the rolling road at Aldon last week and they took off the c clip and that part of that collar part of the dash pot piston as it was causing some lag. The spring is a light one. They also suggested may be a small hole drilled in the cap. HIF44 by the way.

Edited by HUBBA.HUBBA, 26 June 2011 - 08:27 PM.

[new_zealand _minis]

that sounds right . because you want the dashpot to jump up to make it rich when you boot it