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Author Topic: AFM how lean is to lean.
Little Bill Verified Driver
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While tuning my AFM on the Dyno the dyno tech made an interesting statement. As I was getting the car to what I felt was good stoich. numbers, I was told, that there are alot of guys that are tuning their cars to the lean side, knowing that with the heat soak the car is going to go rich. So when tuned to the lean side you end up pretty close to perfect stoich. numbers at the top of the rpm range.

This seems like a time bomb to me. I would rather be just a hair on the safe side of the equation. Any one else care to comment on this? [boggled]

Rich Verified Driver
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When we tuned my AFM, the A/F ratio at around 4500 rpm is getting in to the mid-14's and still drops down to the high 12's by redline. The factory adjustment was much richer at redline. I'm wondering if this could be a result of using a tailpipe sniffer as opposed to an in-car wideband? It's hard to believe but I guess it's possible that there isn't enough exhaust moving to get an accurate reading from a tailpipe sniffer ~4500 rpm at WOT.

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Rich Wiese

Spec Wrecker Ford

disquek Verified Driver Made Donation to Website
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Racing cars are never tuned to stoich. Ever.

You want the AFR to be around 12.5-13:1. Everyone has their magic number. But they're all around that.

If she's at 14.7:1 at full boggie, she will not be happy.

-Kyle

Karl Verified Driver Made Donation to Website
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There are lots of dynos with poorly calibrated sniffers. The curves may be shaped properly, but the absolute numbers can be off. I found that they typically show leaner than the car is really running.

Plot the torque curve with the A/F curve. We have shipped many AFMs that customers tell me show 14s in the 4000 range but only a few are really there. The ones that really are there will show a dip in torque until the A/F ratio gets back into the 13s. If the dyno shows 14s (or I've even seen 15s) with no dip in the torque curve, you should ask the dyno operator / owner to recalibrate the sniffer.

Rich,

Our sniffer matches readings with installed wideband O2 sensors even at 2000. Many of our customers have AFX widebands and I always compare those numbers to our dyno's sniffer numbers. Once I see the match I pull the sniffer. The sniffer is expensive, it will wear out and it's in the way of the exhaust gasses. [Smile]

HTH!

Little Bill Verified Driver
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Sorry Kyle,

I should have clarified that when I was refering to perfect stoich. I was refering to race setting, which I consider to be 13:1

John Wymore
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quote:
Originally posted by Karl:
There are lots of dynos with poorly calibrated sniffers. The curves may be shaped properly, but the absolute numbers can be off. I found that they typically show leaner than the car is really running.

Plot the torque curve with the A/F curve. We have shipped many AFMs that customers tell me show 14s in the 4000 range but only a few are really there. The ones that really are there will show a dip in torque until the A/F ratio gets back into the 13s. If the dyno shows 14s (or I've even seen 15s) with no dip in the torque curve, you should ask the dyno operator / owner to recalibrate the sniffer.

Rich,

Our sniffer matches readings with installed wideband O2 sensors even at 2000. Many of our customers have AFX widebands and I always compare those numbers to our dyno's sniffer numbers. Once I see the match I pull the sniffer. The sniffer is expensive, it will wear out and it's in the way of the exhaust gasses. [Smile]

HTH!

Just a little plug for Karl here. I sent my AFM to him and had it calibrated last spring thinking that it would save some time and get me in the ballpark until I could get on the dyno.

This spring when I finally got on the dyno the A/F ratios were right on the money all through the range, I didn't have to adjust at all. Nice job!!

Andy Bettencourt Verified Driver
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My ITA car loves 12.8:1. My wideband in the header read almost exactly 1 point lower than the tailpipe sniffer.

YMMV.

--------------------
Andy Bettencourt
Flatout Motorsports
www.flatout-motorsports.com

pat slattery Verified Driver Made Donation to Website
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Bennett [Big Grin]

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keeping the faith for the 1.6

Arrow Karts

Rich Verified Driver
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quote:
Originally posted by Karl:
There are lots of dynos with poorly calibrated sniffers. The curves may be shaped properly, but the absolute numbers can be off. I found that they typically show leaner than the car is really running.

Plot the torque curve with the A/F curve. We have shipped many AFMs that customers tell me show 14s in the 4000 range but only a few are really there. The ones that really are there will show a dip in torque until the A/F ratio gets back into the 13s. If the dyno shows 14s (or I've even seen 15s) with no dip in the torque curve, you should ask the dyno operator / owner to recalibrate the sniffer.

Rich,

Our sniffer matches readings with installed wideband O2 sensors even at 2000. Many of our customers have AFX widebands and I always compare those numbers to our dyno's sniffer numbers. Once I see the match I pull the sniffer. The sniffer is expensive, it will wear out and it's in the way of the exhaust gasses. [Smile]

HTH!

That's good to hear. My car's torque curve is nice and smooth with no dips, it just looks a little scary being that lean in a rev range that actually sees quite a bit of action where I race due to a lot of between-gear corners.

FWIW, taking the sniffer out yields about 1hp on my car! That's cheap power right there. I just need to find the other 10 sniffers hidden in my exhaust...

--------------------
Rich Wiese

Spec Wrecker Ford

Dwayne Hoover Verified Driver Made Donation to Website
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quote:
Originally posted by pat slattery:
Bennett [Big Grin]

Hey, you and Fireball Neal are the ones that burned down motors last year .... [flamed] [flamed] [flamed] [Big Grin]

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