More wideband O2 tuning...

[Gpuller]

Just got the Innovative Motorsports MTX-L meter I got from ColoradoDave installed the other day. Haven't had any chance to do any tuning, mostly just driving and observing.
Low compression 440 with old MP 284/484 cam, headers, Performer RPM and 750 Holley mech secondary carb.
At cruise 2800-3000 RPM readings of in the 14.2-14.9.
That RPM range it has a surge which would think it was lean. Just for grins I pulled the choke out just a tiny bit while cruising. That brought readings to 13.2-13.9 and the surge went away.
Could it be that with the cam duration and overlap and lower compression it would like to be richer? Or is that cam giving me false readings? Thinking of jumping up a couple jet sizes and see what it does.
I can get close to 14.7 at idle, it does go lean for a split second but some accelerator pump adjustment that will fix that.

 

[69 GTX]

I'd make a jet change up 1 size and see what that does. I'd think you'd want 13.5-13.75

 

[Gpuller]

It definitely was happier at 13.2-13.9.
I'll check my jet selection and bump one and see.
Was really surprised to see that I was in the ballpark. Figured the way it always smells it would have have been pig rich. Old cam design is the reason for that I guess.

 

[dla4567]

Mine ran much better around 13- 13.5. I also have the Innovate motorsports gauge and find I need to calibrate it more often than I should.

 

[Gpuller]

That's good to hear. Figured it was "its just you" kind of things.
From what I've read the richer you run the more often it needs to be calibrated.
What are the signs that it needs calibration?

 

[hangn0ut]

Actually at a steady cruise/high manifold vacuum state you would like as lean as possible and still responsive,driveable. 15-1. The surge could be timing. Do you have vacuum advance? Power valve? At cruise how far is the throttle open? You would like to be running off the transition slot. Pick up'super tuning holley carbs' by david vizard. That explains it far better than I can.

 

[cdr]

changing main jets will not change light throttle cruise afr. as said in the above post get the holley tuning book.

 

[dla4567]

There are some good videos on youtube about tuning as well. I believe from Holley and Summit, can't remember. As far as recalibration, sometimes it just reads real lean, (20-22) I recalibrate it before making any changes. I do notice around town it is 13 to 13.5 and runs great, on the highway it does seam to run leaner. Im no expert and am not done tuning yet, these are just some things I've noticed. The problem with the O2 gauge is your always watching it and making changes, even the gas you use will give you different readings.

 

[hangn0ut]

An o2 sensor 'looks'for oxygen in the exhaust. O2=lean,more O2=leaner. A misfire leaves a lot of O2 in the exhaust.

 

[hangn0ut]

You cant beat a open book right there next to you as you work on something. Even if you just watched the video 2 minutes earlier.....

 

[MT_Mopar]

What does the A/F read when you floor it?

 

[HEMI-ITIS]

What carb you dealing with??

 

[hangn0ut]

What does the A/F read when you floor it?

Dont remember that part. But it gets rather technical. Something to do with temp? Richer runs cooler....

 

[Gpuller]

Thanks for the replies guys.
Just been observing at different driving situations.
Interesting on how ambient temp affects the tune. A person could go crazy trying to get a tune. Lol
I'm gonna get the book.

 

[Gpuller]

What carb you dealing with??

750 Holley mechanical secondaries.

 

[Gpuller]

What does the A/F read when you floor it?

At WOT its un the 12.5 range. Spikes up richer at first but then leans out.

 

[HEMI-ITIS]

When you first floor it,it will go rich for a split second as it reacts to the accelerator pump shot. 12.5 # WOT is good.

 

[MT_Mopar]

That is good to know, just in case I ever floor mine.

 

[HEMI-ITIS]

They all jump around,,,,,,,,,

 

[Hemirunner]

It definitely was happier at 13.2-13.9.
I'll check my jet selection and bump one and see.
Was really surprised to see that I was in the ballpark. Figured the way it always smells it would have have been pig rich. Old cam design is the reason for that I guess.

My experience has been that the smelly ones are lean rather than rich.