Air/Fuel Ratio Gauge?

[truckster]

I have an L31 Vortec running around 9.7:1 compression ratio, HT383 cam, Progression ignition HEI distributor, and 2.5" rams horn manifolds into 2.5" dual exhaust with a crossover. The whole thing sits under a Quadrajet carburetor.

I had a very experienced tuner build the carb for me last summer. He's a friend of mine who builds engines professionally. The problem is that he likes the carb a little "fat" - he likes them to run a little rich. I'm not sure how rich it's running, but I can smell that it's at least a bit rich.

I'm considering buying an AFR gauge. I'd like something that records the values, but the Bluetooth versions I've seen are really pricey, and I'm not planning on hooking up a computer for data logging. When I put together my exhaust system last year I welded in the bungs, knowing I might want to go this route.

So, any recommendations for an AFR gauge or how to use it to tune my Quadrajet?

And, please, don't tell me to go with fuel injection. If I wanted to do that, I would have already done it. I like the Quadrajet and I plan to keep it.

Thanks in advance.

[Ziegelsteinfaust]

I have the AEM afr guage in my 73 C10 powered by a 10-1 gen2 LT1 with a Corvette cam, and 1.6 rockers. Up top I am using the gmpp intake with a 1904 Edelbrock Q-jet.

First start with 91 or 92 octane to get your combo right then test at partial tanks to verify you can run lower octane.

The below is assuming you have a light truck like mine with noting in the bed. A heavy truck or drag inducing items like heavy tires or a camper shell can move numbers around fast. Either way it's a good baseline to play from.

I have my idle set at 13.5 to 14 afr which is a good balance. Between easy start ups, and not burning your eyes.

As far as driving afr quadrajets can keep a engine comfortably in the 16-1 or 17-1 afr no problem. Mine loves 17-1~ roughly and cruise it there. This is under light load high vacuum situations like cruising the highway with no one in front of you.

On the primary you have rods, and jets. Myself I prefer a tapered rod to improve power. The factory used stepped rods for mpg/emissions. So if you have a fat rod in the jet you can swap in a thinner rod to get more fuel or vise versa. Or swap a jet to keep you preferred rod.

Jets have a bigger impact on the APT or adjustable part throttle screw. The APT will block the vacuum signal from pulling the primary rods to far down or closing off your fuel to the engine. I adjust mine till I am in the higher 16's to low 17's cruising to maximize mpg.

What really matters in part throttle cruising is if you hit a hill, and the afr drops to high 14's low 15's roughly.

As far as full throttle. For this we will assume your secondary spring is correctly set. You have rods, and hangers. Rods make big afr changes, and hangers are fine tuning afr adjustments. So hypothetically your first full throttle run you getb15-1 afr. I would go with a smaller rod. Now let's say your at 13-1 over many passes, and you wanna dip a little into the 12's afr wise. So you will choose a hanger that has a higher letter designation. A's lift the hanger less the M's.

As for the air door spring. You tension or detention it till the bog or hesitation goes away.

[MySons68C20]

I use this one https://www.summitracing.com/parts/AVM-30-0300
It reacts very fast and the real time data is very useful.
Hope this helps!

[truckster]

Thanks. That's some good information. The AEM is the one I've been looking at. I just wish it could record without having to hook it up to a computer.

[AcampoDave]

https://67-72chevytrucks.com/vboard/....php?p=9129708 I made a thread using this one. In short....it was a great thing. Did just what I wanted, and left no trace when I was done. Yes it is Bluetooth, yes it costs a bit more, but you can move it from one vehicle to another with ease and pop it right back in again any ol' time.

[truckster]

Originally Posted by AcampoDave

https://67-72chevytrucks.com/vboard/....php?p=9129708 I made a thread using this one. In short....it was a great thing. Did just what I wanted, and left no trace when I was done. Yes it is Bluetooth, yes it costs a bit more, but you can move it from one vehicle to another with ease and pop it right back in again any ol' time.

I hadn't seen that one. It looks like it might be exactly what I'm looking for. I read the literature and it mentioned "history" - I assume that means it's capable of doing some recording, right? I like to keep my eyes on the road when I'm driving.

[AcampoDave]

Originally Posted by truckster

I hadn't seen that one. It looks like it might be exactly what I'm looking for. I read the literature and it mentioned "history" - I assume that means it's capable of doing some recording, right? I like to keep my eyes on the road when I'm driving.

Looking at the pic on post #25in my thread, that linear heartbeat looking readout below the real-time afr is the history from the last several seconds prior. Mine was set for the previous 20 seconds.