Chuck Harmon

After reading posts by ZL1Power, I also bought a Innovate Motorsports digital exhaust analyzer. Seeing how the a/f changes up and down over the entire rpm range and different throttle settings I don't know how I ever got a carb setup correctly before. An amazing tool! I don't think I could set a carb again without one.
I was running at only 11:1 a/f from idle to about 2500rpm. 13.5:1 above that. This was using #65 jets in my 950HP Holley and having completely removed the idle air bleeds! Changing the high speed air bleeds from #32 to #35's brought the a/f to 14.5:1, but makes for very lean running above 2500rpm. I ran out of time to try more combinations. I expect that I will need to increase the jets by at least 4#'s and perhaps drop the air bleeds to #34's.

The unit is great in that you can see exactly what the a/f is doing in real time. It will also connect to the MSD tach output and record 43 minutes of data while driving to be played back on my laptop.

This hasn't been cheap, $450 for the analyzer with rpm converter, plus $175 for the Holley air bleed kit. But the results have been very gratifying giving the engine a much greater smoothness and response than ever before. I was making great power with the setup before. Full throttle dyno runs showed 13.6:1 a/f making 483rwhp; but, the part throttle operation was never what I thought it should be. I thought changing to the solid roller cam would make the difference. Quite honestly, it wasn't that much smoother than the factory L88 cam that made the 483rwhp and also got 15mpg on the highway using 6th gear. The vacuum was a bit higher, 12hg vs. 7.5hg, but the engine didn't feel any smoother. I now believe that I would have probably made huge improvements even with the factory L88 cam had I had this digital analyzer earlier. Well, no going back now!

When I think of all the guys thinking that single digit mileage is all you can expect with a Vette. This shouldn't be! I believe my L88 will actually get darn close to 20mpg on the highway using 2.54:1 overall gearing once I'm done. The car is not used for mileage, but it is a good indication of the state of tune making the car much more crisp and responsive along with more power compared to an eye burning rich setup.

It's amazing how my clothes didn't smell of gas after my tweaking session today. My goal is to have the a/f around 15:1 for cruising and 13.5:1 for power. I know I can now get it just right!

Chuck

turtlevette

whats wrong with the 60 buck version from autozone?

zwede

Yeah, the widebands are amazing tools. One question though: 13.5:1 at WOT? That sounds dangerously lean. Most naturally aspirated engines want about 12.8:1 at WOT. Turbo/supercharged are set to 11.6:1-12.2:1 @ WOT.

Your cruise goal of 15:1 is about right. Depends on cam overlap if you will be able to get that lean or not without chugging. At low rpm (under 2000) you have reversion so you will probably find that you'll need about 13.5:1-14.0:1.

I'm running a techedge wideband permanently mounted and love it.

Chuck Harmon

You are right Zwede, my ZO6 is at either 12.6 or 12.8 at WOT. But I wasn't thinking that 13.5 would be bad when I am getting into the secondaries under modest power use.

Chuck

AlwaysWave

:cool: :cheers:

I've been using an Autometer a/f gauge (where the clock used to be), and although not as accurate and user frindly as yours, I have been able to tune my setup and saw improvements in performance and mileage.

I wonder if the wideband sensor can be used with the Auometer gauge? The wide band reads over a 2 volt range, whereas the normal reads at a 1 volt range.....is that right? Can a resister be put in line to make the wide band useful?

cardo0

Whats wrong with just a LED narrow band? The LEDs are supposed to give a more honest indication since the gain curve is so steep near 14.2 A/F (stociometric) and the gauge scales (at least for narrow bands) are not as accurate or reliable (maybe its readable ).
I've bought 2 Edlebrock LED units and have a O-fitting (bung) welded in each collector. Had hoped to install in radio slot but dosen't look like enough room for 2 LED boxes. So my question is one A/F monitor enough? Do I need to monitor both cyl banks? Could you guys running them now use one in each bank any better than one? Or is one enough. :confused:

zwede

Narrowband only reads correctly right at stoich which is 14.7:1. The further away from stoich, the less accurate. If you have a perf cam you usually won't be able to run stoich below 2000 rpm. You have to run 13.5 or maybe 14.0. Now the NB is just showing rich, while a WB is showing you the 13.5 or 14.0.

Then at WOT you don't want stoich, you want about 12.8. Again, a NB will just show rich.

Shark Racer

Chuck neglected to give you guys a visual of his new toy in action:



Quite the showman he is!

-Steve

lostpatrolman

lol... where did the hood go?

Shark Racer

That L-88 is FAST. :eek:

PatG

I have been doing a lot of research on the A/F measuring technology. Essentially all of the cheap versions use what is called a lambda O2 sensor that has a very non linear output. This is the same type of O2 sensor used on modern cars. The output signal has a very steep slope over the desired operating range and then is nearly linear at lean or rich conditions. This makes them useless for tuning a carb. They can work in modern cars because the computer can adjust the fuel injection quickly across the rich/lean boundary and average out to a good mixure. For real tuning use a wideband O2 sensor (that is much more expensive). The wideband produces a much smoother signal over a very wide range of A/F ratios. I have been thinking about building one similar to what is discussed at the following link.

http://www.diy-wb.com/info.htm

Desertdawg

In the fuel injected world, 14.1 is the perfect AF ratio.
Is there that much difference with a carb??????

zwede

14.7:1, not 14.1... You can tune a carb to 14.7 using an inexpensive O2 sensor but with the same issues as I described above. A performance cam causes reversion which requires a richer mixture to run right.

cardo0

Thanks for that link Pat. But that looks like a big effort while my Edlebrock LED units where less than $150 - plug and play. Now I got my books out and that milli-volt gain curve is only really steep (nearly verticle) near 14.7 A/F (where all the O2 gets used up). But fairly flat on each side. What I'm trying to say is that for WOT 12-13 A/F should be no problem to see and for lean I have one red LED for a danger warning at 15 A/F. The LED unit has a LED for each 0.5 increment of A/F from 12 to 15. Yes 7 LEDs in different colors so I can just glance at them and know what my mixture is. And for a carb, how close can you get. Everytime the coolant water temp, atmospheric temp and press changes are you going to change jets and rods - I don't think so.
Okay I can see how a WB would be great for a homebuilt EFI but I think its overkill for a carb.
BTW anyone using two A/Fs? One in each bank for comparision. Is it worth it? :skep:

Matt Gruber

i'm glad to see guys doing some tuning. :cheers: Some NB tips in my sig.
i must be the only one checking each cyl. :eek:

Kid Vette

This thread is very interesting. :thumbs:

I'm planning to install a vacuum gauge and A/F sensor and start dialing in my carb. Keep the good info coming! :hurray:

cardo0

Nice shark Kid! I have a Auto-Meter 2&5/8" vacuum gauge to install somewhere too. Any ideas? Radio slot next to A/F or on column? :rolleyes: I was able to calibrate mine at work and expect it helpful in setting the vacuum advance and monitoring engine perfrmance.
BTW how's driving without ps & pb? I think I would save a ton of headaches and a few pounds of wieght off the front end too. But how hard is it to park and stop? I'll geting tired of that pb booster in the way every time I reach for something over there. :banghead:

Desertdawg

My bad Mark, funny how the brain fades at 1am... :banghead:

Chuck Harmon

What's a couple numbers behind a decimal point among friends?

:cheers:

Chuck

Kid Vette

I was thinking maybe I could mount the gauge on the left windshield pillar at about eye level but I'm not sure how I'm going to accomplish that yet.

I don't miss the pb or ps. If I had to do a lot of parallel parking I would probably want ps. However right now I have the tie rod ends on the inner holes for the quicker ratio steering. I could always move them to the outside holes for the more leverage if I get tired of cranking it.

Thanks again to everybody for the good info. Still not sure which A/F setup I'm going to go with. Frankly at this point I don't know much about any of them or how they work.