Breaking traction and AFRs

[gmh304]

Was wondering what others experiences are with the mentioned topic. I have done a site search and haven't found anything specific.

Lets say you are at the drag strip on street tyres using pump gas. You have your tune pretty close and the AFRs in your logs are predictable. If you are logging a run and get a little aggressive with the throttle and break traction for a few seconds, do you see the AFR show richer or leaner than normal?

I only have my car to go by. My logs show that if the loss of traction is below approx 5000rpm (around peak torque) I usually see a leaner condition but if its above 5000rpm the logs show richer than normal. At that point the AFR might not be indicative of what fuel mixture the engine is actually seeing, but not sure.

I have given it some thought and have some ideas but don't know if that's just a result of my combination of parts. For those that have tuned different applications is there a trend in AFRs recorded during a loss of traction? Be interested if anyone wants to share their observations, thanks.

[antus]

Loosing traction shouldnt make a difference. Your car is measuring load, and with an ideal tune measured vs target AFRs should match. The exception is when power enrichment comes on, or decel enleanment. Perhaps your tune just hits different load areas under those conditions and you might need to tweak the VEs there a little (assuming 12P).

[vlad01]

maybe decrease in load? do you see your map readings change as well?

[VL400]

If your hitting the fuel cut (or a spark cut if you have it) there will be lean spikes in the logs due to excess oxygen.

[gmh304]

Thanks for all the responses. Antus your explanation has gotten straight to the point and makes perfect sense, thanks. As Vlad01 has also mentioned, I can picture the engine under load during aggressive acceleration, then all of a sudden the wheels skate or break traction and the load is diminished by whatever percentage, putting the engine in an area I rarely see in the VE table during normal driving.

Now it should be simple to cross reference the rpm and kpa value but it buzzes through that area so fast once it spins that I only get a couple of data points to work with. The important thing to know and what I was worried about was that I couldn't trust the data during that event. But as Antus said "your car is measuring load" and this of course will fluctuate depending on traction. Not to mention the copious amounts of AE.

VL400 I don't think I am hitting a fuel or spark cut, the engine sounds on song and smooth, but worth checking thanks.

I should add my engine is a VR V8 with a COME twin throttle body manifold and I was concerned that the manifold could be contributing to some unusual AFR readings, if posts on this forum and others are anything to go by. Now that I am using VL400s ALDL Logger, its increased recording rate should give me a few more data points to work with. You guys are the best.