How crucial is a lambda sensor?

I race X30 and it seems everyone in my class has the lambda sensor. There doesn’t seem to be many existing threads about it or how it works, what do y’all think?

It’s just an exhaust temp sensor. Not crucial on a hobby level IMO

Assuming you’re referring to people measuring AFR (Air fuel ratio), if so it’s an incredibly useful tool. I use it on my X30 and it can tell you a lot about both your engine tune and throttle inputs. Especially if you’re having issues existing certain corners, you can look at the AFR data to see if its leaning out too much, running too rich and or if you’re accelerating too early. If you want to optimize pace I’d highly recommend one.

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Thanks. Yeah the lambda sensor measuring the AFR.

What would I be looking for in the data that would indicate I’m accelerating too early? In the opening laps of a race I’m quite sluggish exiting hairpins. In the middle to later stages of the race I’m doing lap times on pace with the fastest, but the time I’ve lost in those first few laps is unattainable.

It felt like a tuning/engine issue, so I’ve done my first practise day with my new Lambda sensor and the data shows in the opening laps I’m very rich on acceleration out of corners. And as the session wears on it gets better and better. Would this mean I’m too rich on the Low jet? And if so, would it require leaning off the Low jet on the roll up laps of a race and then bumping it back open as the laps wear on?

I’m definitely curious to hear more about meaningful AFR data on a two stroke due to the presence of oxygen at partial throttle and gas reversion in other cases.

If you get a baseline on a dyno then you have a reference point for the actual ideal AFR values at given loads. Partial throttle will usually show “lean”. The tuning is generally not done with AFR. Rather the engine is tuned based on how it responds to changes, then the logged AFR becomes a datapoint for reference.

In short I’d be very cautious of chasing AFR values based on someone else’s data as it may not apply to your specific setup.

There’s not much info out there, but I’ve found this video helpful.

From 4:30 onwards he talks Lambda Value and Lambda AFR, explaining he looks for Lambda Value between 0.92 and 1.00, and will tune his high/low jets according to what his track map lambda data shows.

I’m still new to this so looking for as many opinions/as much advice as possible.

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Recently fitted a lambda to my KA100. While I haven’t made huge changes as of yet, it has so far been helpful with tuning the carbie depending on weather conditions/atmospheric conditons. Definitely worth getting one in the long run I think.

If you’re not getting the engine warmed up on the stand that may cause it to under perform until it gets to temp. But if you’re warming it up on the stand chances are its a tyre temperature issue and maybe also getting into the groove. I understand the frustration in that regard where it feels like everyone can get the tyres working quicker. The fuel mix shouldn’t really change like that due to a bad tune. If I had to guess it’d be the kart not coming off the corners like it should and that can affect the tune.

It’s hard to tell without any gopro footage and not seeing the data, you also have to have an idea of where to take the AFR into account in the corners.

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I start the engine on the stand before I head to the grid for a race, but nothing methodical in the way of running it to reach a certain temp. Usually only 20 seconds or so, mainly to make sure it’ll start lol.

What’s your usual routine in the way of warming up the engine on the stand before a race/session?

20-30 seconds won’t warm up an engine. Need to fire it up and vary the throttle with no load for minute or two, then use the brakes to put some load on and bring the throttle up and down for a minute or two. You don’t need to rev it out like a madman. You also don’t want to overdo it on the brake and throttle like you may hear some others do. You won’t achieve track temps, you can’t load it long enough. But you should be able to feel the block noticeably warmer with your hand.

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No doubt Lambda is a valuable tool to get the carb settings accurate, but if your engine tuner has set the carb from the dyno, it should be thereabouts.

I honestly think some people are getting way too caught up on what is happening on their dash, that they are losing more time in the driving element.


Thanks for the reply David. I was a big fan of yours in the 2000’s as a youngster watching you win all those state and aus titles, it’s good to see you still have such a big impact on the sport through your driver training and sharing your knowledge.

I’m in a weird position where I raced for over a decade in J’s and Clubman, but have been out of the sport for over 10 years. A lot has changed in that time and while I’m not a total newbie, I have a lot to learn about the modern chassis/tyres/engines.

While I quali’d well in my 4th race meeting back in restricted light, I lack speed in the opening laps compared to those around me, although my lap times lap 3-4 onwards are generally on par with the winning few. I only ask about lambda because I noticed most guys on the grid have it and wanted to optimise my tuning and learn more about reading data. I actually watched your videos on it the other day which were very helpful.

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On a side note, my engine hasn’t been looked at by an engine tuner yet. After 10 hours I will look to get the top end rebuilt, but I was told to run in my new X30 out of the box and race with it as is.