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Carb tuning w/O2 sensor
Here is a very good article on Holley carb tuning w/ a wide band O2 sensor.
http://www.innovatemotorsports.com/r...s/Stan1.php#t1 We have the Powerdex AFX Air Fuel Monitor and it is very good. http://www.ngksparkplugs.com/product...000&country=US Anybody ever use the Innovative Motorsports LM-1? The data logging feature looks very handy. http://www.innovatemotorsports.com/products/lm1.php |
How come in the
Sub-Forums : Engine Building, Tuning, and Induction there is not a forum for tuning Holley carbs? |
Have no direct experience with LM-1's, but a couple of local guys use them and swear by them. The key for us Cobra lovers is to have an O2 bung welded into the collector rigth before the muffler, for the LM-1 to read as accurately as possible.
There's a local carb tuner (Henry Olsen) who not only uses an LM-1, but also a 5 gas analyzer to do carb/ignition tuning. He tuned mine, and it runs like a champ! Here's a link to an article he wrote on using a 5 gas analyzer to tune a Roush 427R - http://www.automotiveu.com/tuningperformance.htm The key is to tune both iginition and carb together. Regards, Randy R... |
Thomas,
The local Lotus guys use them on Elans with DCOE Webers. Same circuits as an IDA, only sidedraft. They swear by the LM-1. One of the local guys was pretty active on the the Innovate Forum. Haven't been there for awhile. You do want a throttle position sensor and RPM to know where you are when you are analyzing data. A general note for all. You MUST have no leaks in your exhaust system when using this tool. Bert |
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With slip fit headers there will be leaks... But if you are rich with slip fits then you KNOW you are rich. Still lots better than guessing. Of course there needs to be no leaks to get the engine really dialed in. |
Tom,
What you need is a really good computer controlled chassis dyno as tuning a carb without a load on the engine is similar in nature to beating an aluminum quarter panel in to shape with an unevenly shaped sharp rock. Also, the placement of the O2 sensor plays a critical role in how accurate your readings will be. Mismeasurements by as little as one half and inch in either direction can mess up your readings by as much as +/- 10-15%. Either of which could be fatal to your engine in question. Bill S. |
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NGK says http://www.ngksparkplugs.com/pdf/AFX...ual_REV_06.pdf "The AFR sensor should be located between 12” and 48” from the engine, upstream of any catalyst device if so equipped. The closer the sensor is to the engine, the more likely it will be overheated, possibly shortening its life. The further it is from the engine, the more likely condensed water will get into the sensor and thermally shock it, again possibly shortening its life. The sensor should be mounted at least ten exhaust diameters upstream of the exhaust exit (ex. for a 3” exhaust pipe, that is 30”). If the sensor is mounted between one and ten exhaust diameters from the exhaust exit, the AFR measured will be leaner than the actual AFR by as much as 2 AFR at low engine speeds (i.e. less than 3000 rpm)." |
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Placement up or down stream, just as placement in one header tube vs another will cause readings that are not accurate. NGK, Bosch, and several other sellers of these aftermarket "inexpensive" aftermarket O2 sensors will tell you differently, but having had access (while still living in NJ) to a computerized chassis dyno with an operator who was properly trained show me the error of my ways. Where we would want a air/fuel ratio of 12-14 in a reading, the O2 sensor (mounted in a bung in the proper place according to the manufacturer showed one reading, while the O2 sensor in the end of the header (actually 2 feet in just after the 4X4 collector dumped into the muffler assembly showed another. Tuning with the original O2 (bunged) showed me to be running rich, when in fact I was running lean. Again, being able to set an RPM or a speed on the chassis dyno so that we could tweak any carb I had installed (4 on one particular 427 side oiler engine one weekend) was the most beneficial thing that I could have happen. Trying to tune without that load on the engine (drivetrain load vs engine rpm only) turned out to be my downfall for one over the other. Bill S. |
Bill, the placement is only critical for a factory HEGO with an EFI system, because it needs to know the pulse delay from the head to the sensor. For reading A/F, it does not matter where the sensor is in the exhaust, as long as there are no leaks.
Tom, the LM-1 is neat, but I have found them to be "off" in their readins from actual A/F. But if you can compare it to a known good setup, the mis-reading is linear, so if you know how much it's off (as much as .5 A/F in some cases), then you can still use it. I like the Dynojet Wideband Commander, because it's a good price and comes with many features that cost way more on most systems. |
Randy's right, The best place is in the collector. Two bungs are needed, one in each side for each bank. The LM1 is a great tool. first calibrate the sensor in free air...Easy to do. Then do one bank at a time. First test at idle. DO NOT use the clamps at the end of the exhast pipe as there is too much "free air" and the reading will be way too lean, probably 20 or more ( 20 parts air to 1 part fuel). Adjust your needle valves till the meter reads approx 14.2-14.5AFR. Next step is to go drive the car under load. The recording of the LM1 is great at this point as you can concentrate on driving instead of watching the meter. The number to shoot for is 13.5 AFR. My car was around 12(TOO RICH). I went down two jet sizes in the primaries and drove the car again. Bingo, 13.5!. Now WOT (wide open throttle). Find somewhere that is SAFE and open her up. The number to shoot for is around 12.5. You will be and should be on the rich side as you want to dump gas in. I was at 11. Down two jet sizes in the secondaries and right on 12.5!. Test the other bank the same way. Now I get better gas milage and unbeliavabley better performance with no stumble. There are alot of great features on the LM1. Rpm and graphing make it easy to use. Hope this helps for basic info.
Greg |
Sal,
How did you tune your car? What did you do about the slip fit connectors on the headers? I found this on Google (5th one down) about the Wide Band Commander ;) http://www.powersurgeperformance.net...products_id=28 |
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NGK and Bosch are hardly at the beginning of the oxygen sensor learning curve - they've been OE on them for 30 years now. I would venture to say that any info they provide on usage or location would be reasonably accurate.
I use O2 just like any other tuning tool. It lets you quantify where you are, and then you can find out what the motor likes from there - irregardless of the numbers you are reading. |
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