Mounting A/F sensor, Dyno

Chipg56

Member
Curious how everybody mounts the fairly large A/F sensor for dyno usage. Directly into a muffler? Has anyone ever tried extending the muffler with a piece of pipe and mounting in the extension?
 

RCJ

Member
I tried the extension and it doesn't work that good. Exhaust reversion pulls fresh Air back in to the pipe and throws the reading off. I've been thinking of making an adapter that bolts to the head and mounts the sensor then the pipe bolts to it. Because these carbs idle so rich the sensors have a short life. Performance Trends sells a remote sampling setup, but it is not cheap.
 

1fasttiller

Member
Sensor needs to be pretty close to the port to get an accurate reading and to keep the sensor hot. Take them out every so many pulls and clean with a propane torch to extend the life. Are you using the Bosch UEGO or NTK ?
 

alvin l nunley

Premium User
Just wonder what kind of information you're hoping to get? From what I understand, they are almost useless in an open throttle environment i.e. racing. I could be wrong.
 

1fasttiller

Member
Wide band air fuel gauges are excellent tuning tools if you know how to use them. If you know the stoichimetric ratio for the fuel type you can tune jetting to be spot on. For gasoline most engines run best at 13.5-14.0:1. Just slightly richer than perfect which is 14.7:1
 

alvin l nunley

Premium User
It is for a Dyno, Al.
It will be very interesting to see the torque curve, compared to others when not using it, to when you get the A/F optimized. How about posting a chart when not using it. Let us see how it changes when you're using it and getting the ratio right.
 

Chipg56

Member
It will be very interesting to see the torque curve, compared to others when not using it, to when you get the A/F optimized. How about posting a chart when not using it. Let us see how it changes when you're using it and getting the ratio right.
I would be happy to share with you Al. It will not be real soon as I am just building the dyno........By the way it will have EGT as well. I have been using EGT rather then head temp as long as we have been in karting, roughly 20 years. One of the many things you are right about.
 
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alvin l nunley

Premium User
I would be happy to share with you Al. It will not be real soon as I am just building the dyno........By the way it will have EGT as well. I have been using EGT rather then head temp as long as we have been in karting, roughly 20 years. One of the many things you are right about.
I'm real glad to hear that! It's going to be very interesting to see if the ideal A/F ratio matches up against the optimum EGT readings. I'm betting they won't, but I could be wrong. Knowing is going to be great.
 

RCJ

Member
You are not really trying to get an ideal a/f number. On the first pull ,let say you get an average a/f of 12.9. Take some jet out, second pull average 13.7 , hp is up. Now is when the work starts. At 4000 rpm you are 14.4 ,but it goes to 13 .0 at 6500. You know from experience for max torque at 4000 you want to be around 12.7 to 13.0 . For max hp you are looking for 13.9 to 14.3. You get the drill bits out and start adjusting high speed bleeds ,idle jets etc... For me if it makes more hp and torque I don’t care if it’s 12.5 or15 .5 . I was crew on a drag car that had 1 in each header pipe. To balance all 8 cylinders was above my pay grade.
 

alvin l nunley

Premium User
You are not really trying to get an ideal a/f number.
Sounds like you have a pretty good handle on it.

What do you think, a little lean on the low (14.4) and a little rich on the top (13.0). What happens to the A/F ratio when you get detonation? With the EGT, the temperature goes down. I'm just wondering if that top end number is because of too rich or too lean. How do you tell. And what effect does air density have on your readings.
 
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