LM-2 A/F Ratio Guidance for a Rookie Please

[rockhouse66]

I just bought an Innovate LM-2 and am playing with it on my '69 428 CJ car.  I now realize how little I know about this.  I could use some general guidance from members please.

My car has smog, which is air injection downstream of the exhaust port but upstream of my O2 sensor.  I assume I should disconnect this or it will cause the a/f to read leaner than it actually is?

Steady state cruise shows a/f around 14.2-14.5 which is close to stoichiometric but perhaps it should be much leaner at cruise?  Like 16?

I get a little "dip" at tip in where it goes momentarily lean, then shows around 13.4 during accel.  Is this normal or can it be tuned out with perhaps a power valve change or just don't worry about it?  It doesn't feel like anything driving the car - no bog.

Thanks for any suggestions!

[jayb]

Good luck with the tuning, you will be able to really dial the engine in with the LM-2.  I agree that you should disconnect the air injection system prior to tuning the engine.  I wonder how much of a difference that will make?  If you get some results before and after that change, please post them.

I would shoot for 14.7:1 at cruise, so it sounds like you are really close.  For the lean response you are seeing at tip-in, I would be looking at tuning the accelerator pump circuit.  A bigger pump cam or bigger shooters would be a good start.

Have you tried a WOT blast yet?  Put the car in a lower gear on the freeway, and record the data as you accelerate from 3000 RPM to 5000 RPM or so.  You are looking for somewhere in the range of 12.5:1 to 13:1 for most engines.  Change the main jets to get there.  Once you change the main jets, your cruise A/F may also change, so you will have to decide what is more important, cruise or WOT.  I know what I think is more important 

[rockhouse66]

Good luck with the tuning, you will be able to really dial the engine in with the LM-2.  I agree that you should disconnect the air injection system prior to tuning the engine.  I wonder how much of a difference that will make?  If you get some results before and after that change, please post them.

Jay - thanks for the reply.  I did a quick run with and without the smog pump belt and I think it only made about a .2-.4 difference in cruise a/f (dropped from 14.5-14.6 or so to 14.2-14.3.  I should have been more patient and done it with the record feature before and after so I could actually study the results.

I am seeing a/f in the 13.3-13.5 range at WOT so it must already be close.  I was hoping maybe it wasn't and I could pick up about a zillion HP with tuning!

I'll give the accel pump change a try and thanks for the tip.

[bartlett]

Mine likes richer than that .... I would try jetting up 2 sizes on the mains just to see if it likes it ...

[jayb]

+1 on that.  Most of the engines I dyno will want 12.7:1 or so for peak power...

[rockhouse66]

OK, I'll try a little richer on the mains.

BTW, I recall that the smog system includes a diverter valve that modulates how much air the pump delivers downstream of the exhaust.  My understanding how it works is that it modulates a lower flow of air to the manifolds at idle, no flow at light loads (high vacuum) and high flow when you step on the gas.  If correct, that means that there isn't much air delivered at constant throttle/cruise anyway, which is why it didn't make much difference whether the pump was working or not.  Keeping the air pump in operation might mess with the a/f a lot more under load than at cruise.

[bartlett]

 " I could pick up about a zillion HP with tuning!"If  a zillion hp is 20-30hp you might find that in a richer jet and maybe adding in some timing if it's set conservative.