How to install an A/F ratio meter on a multi-carb setup...?

[ww]

I want to install an Air/Fuel ratio meter but am looking for suggestions on the best method to install the sending unit.

 

<Stupid Question Snipped>

 

DOH! I've been reading so much AFM to MAF conversion stuff I got my head turned around.

 

I apologize for wasting everyone's time. Obviously, the sensor measures the exhaust gas AFTER the combustion chamber!

 

Cheers,

Wade

[DaleMX]

The only type of A/F meters that I am aware of run off of the exhaust. It's a wideband O2 sensor and only works well when heated up to operating temp. See the link below.

 

http://www.innovatemotorsports.com/products/lm1.php

[technicalninja]

As triples are actually two single barrel units per casting you actually have 6 separate carbs. This is the beauty of the 3/2 set up. It allows accurate tuning per cylinder. To be truly (labortory grade) accurate you will need 6 WB 02 sensors located in each header runner before any collectors. This is both cost prohibitive and complex. Unnecessary for street cars. As long as your engine is in good shape (ie all cylinders running same compression/leak down rates) a single wb 02 sensor located aft of where the 6 tubes come together will provide good tuning info. I place the sensor in the collector flange (exhaust system side) pointed upwards along transmission and run the wiring harness throught the tranny tunnel near the HVAC system. This keeps wiring harnesses to a minimum.

WB (wide band) is the only way to go.

I am not aware of any A/F meters that sense the intake charge but they may well exist. I would expect a direct sensing system to be very expensive.

[JMortensen]

While tuning per cylinder is possible, I know of no one who has actually done it. 99.999999999999% of people running triples run the same jets in all 6 barrels totally eliminating the need to try and figure out how #4 should be jetted vs #2 and so on. Even with much more accurate FI I know of only one person who has each cylinder tuned individually, and that is John Coffey. To most of us that last 1/2 horsepower just isn't worth it.

 

Don't put your A/F sensor in the intake Wade. It goes into the exhaust and measures either the temperature of the exhaust gasses (EGT) or the oxygen in the exhaust (O2). I used a narrowband O2 sensor which cost me $30 hooked up to a voltmeter which was another $6 to figure out what was going on. If you want to make it easy, and you're cheap like me, you can get an A/F meter from Summit Racing and install that. Wideband O2 is expensive. Much more accurate, but much more expensive. Again, how finely tuned do you need to be?

 

You might want to read up on Mikunis and Webers before you get too far into this. There is some good info in the "How to Modify Your Nissan Datsun OHC Engine" and there are numerous books on Webers that you can use to get an idea of what you're up against. Mikunis are easier to tune since they only have 4 sets of jets, where Webers have something like 8 or 10 per barrel. The downside is that the Mikunis can't be fine tuned like the Webers.

[technicalninja]

Mikunis can be tuned every bit as closely as Webers, Mikunis tend to hold their settings and balance better than Webers. 95% of fuel curve is controled by the three same parts in both brands: fuel main jet, emulsion tube, and air correction jet.

Narrow band O2 sensors are better that nothing but only slightly better. They may be able to show you if your rich, stoicometric (sp?), or lean. They cannot tell you how much lean or how much rich. A little bit lean shows same reading as disastrously lean and vice versus for richness. The range that they work over is solely designed for emissions- not fuel economy or power production. Their readings can vary dramatically with temp changes. This would not be a problem with a car that was always driven hard but could affect a street car that alllowed the sensor to cool during low cruise and idle phases. I use a heated O2 when installing a NB to solve this issue. Last NB I installed came to about $150 after all needed stuff was obtained (Bosch heated sensor, Auto Meter gauge, Bosch relay,O2 sensor pigtail, wiring, and connectors). I have seen WB stuff available in the $400 dollar range and the dif of $250 is worth it. I do not have one yet but it is on the to-buy list. As I tune other peoples cars as well as my own I will set mine up as a tool and not wire it in to any car. It can be used to tune any car with an O2 sensor bung. After tuning I will remove it and cap sensor bung (or install a NB sensor as a monitoring device- any change in readings from the NB stuff would then be checked with the WB).

The $30 sensor and voltmeter will work just not as well as I would like. Depending on the volt gauge it may be hard to read at speed- I always had trouble seeing the DVOM hand held in my lap when I first started playing with A/F gauges. I like the round bar graph in the Autometer as it is self-lit and very easy to read. it also mounts nicely to the upper steering column cover as it is not very deep. A swept hand style gauge is far easier to read at a glance than a digital display. All of the NB stuff I have seen has a digital read out which is more accurate but may be an annoyance. Some of the NB stuff has datalogging capabilities which would be nice information to have.

I see NB stuff as an oil pressure light and WB stuff as an oil pressure gauge.

Quite a bit of info about the dif between NB and WB is to be had with the search function- do research before you buy anything. Grass Roots magazine recently had a eye opening write up about this and comparisons between some of the systems available.

 

John Coffey tuning each cylinder sperately does not surpise me at all. It is to be expected at his level of competance.

 

Rick

[Guest 240zJake]

If you wanted to tune each carb individually, could you put the bungs on three or all of the primarys, then plug them when your not tuning?

[JMortensen]

Mikunis can be tuned every bit as closely as Webers, Mikunis tend to hold their settings and balance better than Webers. 95% of fuel curve is controled by the three same parts in both brands: fuel main jet, emulsion tube, and air correction jet.

 

Both of these statements are wrong IME. How many emulsion tube choices do you have for Mikunis??? 3? OA, 8, and OB (and I don't think OB fits in the smaller carbs, but I could be wrong on that one). How many choices do you have for Webers? 10? 20? Webers are more tunable, even if you only consider high rpm tunability. As to the mains and airs controlling 95% of the fuel curve I've found that the pilot jet has a much bigger effect than is stated in any of the books I've read and is making a difference up to about 3500 or 4000 rpm on my car.

 

As to the narrow band criticism, if that's your experience fine. I know my stance on NB vs WB is not the most popular, but I have my own experience to back it up. I took the advice of a friend and installed a NB. It helped enormously. Several guys I know have now had their NB on the dyno and had a chance to check it against the WB. They've all had the same results: the NB was accurate compared to the WB, and it is always a shock to the dyno operator as well. I know the NB is not AS accurate, but that doesn't mean it is useless as you hear so often. The people who told you that NB is useless are probably the same people that want to sell you a WB for $300. My Bosch non heated one wire O2 was $30, my voltmeter $6, and I had some wire laying around to connect the 2. I made more progress in 3 weeks with the NB installed than I had in a couple months trying to read plugs.

 

Jake, yes you could do that, but if you have the same jetting in every carb then you can just run one O2 and have 1/6th the equipment to buy. Plus I don't think you can run them right up next to the flange, and getting 6 sensors onto the primaries down by the collectors is going to be hard to do. Again I think the amount of hp you're going to free up by tuning each cylinder individually is going to be fairly negligable unless you're really trying to squeeze EVERY LAST HP OUT, in which case you probably shouldn't be using carburetors at all.

[ww]

Jon,

 

Thanks, I do have the Modifying your D/N OHC Engine and it's been very helpful.

 

I did get the narrow band O2 sensor since that's the one the AutoMeter 2675 calls for.

 

I'm curious if anyone has any experience with the Innovative Motorsports LM series, PLX Devices or any of the other A/F tuning tools?

 

http://www.innovatemotorsports.com/products/lm1.php

 

http://www.plxdevices.com/onlinestore_domestic.htm

[DaleMX]

I'm going with the LM. Over on the LS1tech board it is a popular device. They are working on a gauge that eliminates the box for permanent installation and I want to see how well that works before purchasing it. I understand that there have been mixed results using their RPM monitor and the LS1. Personally I plan on making my logs using EFI Live.

[Pop N Wood]

Grumpyvette once posted this article. Absolutely excellent information about using O2 sensors to tune carbs.

 

http://www.bob2000.com/carb.htm

[Hugh]

I own the Innovate LM1.

 

It is awesome. I would reccomend it to anyone.

 

You can output it to any gauge you like, even some cheapo Autometer if you want. It has two programmable outputs.

 

I send one output signal to my Electromotive Tec3 for datalogging the air/fuel ratio.

 

I send the second output to my Apexi Turbo timer because it has an O2 sensor voltage display. I then set the output voltage to read 1 volt at 10:1 A/F, and 2 volts at 20:1 A/F. This means my turbo timer will display with dead-on accuracy what the A/F is.

 

I didn't have to add any more gauges in my situation... but if I had, I might just use some sort of simple digital voltage display like the one built into my little turbo timer. Otherwise, I'd get an autometer which is very innacurate, forgo the sensor and tie my output into that... then tweak the output until the display on the gauge reads exactly what it says on the box.

 

My box rides quietly in the glove compartment, all the while telling the two other devices an accurate Air/Fuel ratio.

 

 

I also have the Aux-2 cable with RPM sensing. I use this to tune other cars. It's not perfect on the RPM sense, but very close... definitely close enough for tuning within a hundred RPM or so. This cable is $100, but hooks up to all the existing sensors on a modern EFI car.

 

I tune using RPM, boost, A/F, and throttle position with this device. Throttle position is the one thats not necessary... but it makes reading logs easier to see when the throttle is mashed and how good response is.

 

 

I seriously stand behind this LM1. I don't work for the guy... but I do own one, as well as several of my friends. We all love it.

[Guest racerbob]

I have 6 exhaust gas temp probes on the GT-2 car with 3 dual guages because at 8000rpm on a 13:1 engine you can't "be close". Overkill for the street.A good tuner can do a street car from experience.Where is John Coffey? BobMaggio