I’m gearing up for the Stars and Stripes trophy in two weeks, up in Lafayette. Haven’t been in in a race since January, but I’ve been trying to keep myself sharp. My only concern is that I’ve not really driven the Rotax package before. I’ve pretty much only raced on Leopards and X30s since I started a few years ago, so you can imagine I have a pretty heavy right foot. What, if any, are some things I should keep in the back of my mind while driving? What are some elements to this package that I really didn’t need to think about on X30 that I have to think about now?
The Rotax takes off once it gets “on the pipe”, and you always want to keep it in that power range. So learning to really roll into the throttle and learning throttle modulation is an important thing to master. It takes some getting used to, because the engine drives and feels a bit different than most karting engines.
I only ran Rotax for a couple years, but we did pretty well in it, and one thing everyone always told me was that you want to keep a tiny bit of maintenance throttle on almost all the time. Just enough to keep the engine revving below the clutch engagement. Something about keeping pressure going through the power valve. So even at minimum speed at apex in a hairpin, you’ve got a small amount of throttle in it, keeping it under the clutch lock up.
And as usual, smoothness is key. The engine will bog and fall on it’s face if you aren’t smooth with throttle and on the wheel.
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Tj is pretty much spot on here except for the bit about the maintenance throttle.
Now with the evo package the PV is operated/triggered electronically based on engine rpm… that is, it will stay 100% shut then open at the trigger point to 100% open.
The main thing is being progressive and smooth on throttle input, the power delivery is really non-linear and to get the best out of the engine it requires some discipline on the throttle. Bottom line is, don’t snap the throttle open like an on/off switch.
Focus on gearing it such that your average revs per lap is around 9650rpm…for a senior at least.
Keep tuning the chassis and working on your driving so that you can keep dropping teeth while maintaining 9650 average revs and you’ll see your lap times keep dropping.
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Listen to Chris on this one, I haven’t driven the Evo, he knows that better than I do.
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My pal Andre made the switch to rotax from x30 and struggled a bit at first. He might have thoughts: @AndreLafond
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I’ll be at Lafayette as well, can’t wait. A rotax is a trickier engine to drive than a comparable x30 in that you have to be so smooth. Rolling speed is critical to keeping the rpms high enough for the exit. And the bigger a gear you can push the faster you’ll go.
The midrange power of the rotax is where it’s strength lies, the longer you can stay in it the better. but a bigger gear is a bit tougher to drive as it won’t be as forgiving. The throttle takes a bit of getting used to. The way you roll onto the throttle isn’t quite linear, and if you just mash the gas the engine will bog down. It’s also a bit tougher to pass with it, as if your rpms drop slightly they will outdrag you on the exit of the corner if there’s a gap.
But something to note is that with a rotax you can really steer the kart with your feet, as the midrange power lets you rotate the kart, which when utilized correctly lets you get the kart straighter sooner and get on the power a bit earlier. It’s something I’ve really enjoyed.
I am interested to see how the mojos will drive as I’ve never run them before. From what I’ve heard you have to really drive on the top of the tire, instead of leaning on the sidewall. In theory it would make it easier to rotate the kart. But at this point I still don’t know exactly what they’ll be like when they hit the track.
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Excited to see how you guys do. Please keep us updated. We don’t hear much about Rotax in the US anymore.
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I appreciate all the insight on this one, guys. Definitely want to steal a podium or win next week if I can help it. Should be a fun one. I’ll definitely post an update when the time comes!
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Thanks, and will do.
You’ll do fine. You have a smooth driving style. Just roll on the throttle like the guys say. Evo has a fair bit of oomph down low so you need to modulate the power a bit more than an X30.
I gotta try to get whatever edge I can on these kids, I don’t want to get completely embarrassed! 
Not sure I agree with the bigger a gear the faster you’d go. This has not been my experience with rotax albeit I’ve only driven pre-evo. Tuning my chassis, working on my driving line to roll as much speed, being disciplined and smoothe on the throttle all while running smaller gear has always proved to be quickest for me. Both evo and pre-evo have a rpm limiter which the engine will not go beyond…getting there with less teeth should be the aim
By big gear I meant a more top speed oriented gear, sorry for the lack of clarification.
Ah ok, well yea more top speed would actually be a smaller physical gear on the axle at least… this would also be running “longer” gearing.
We run the throttle cable lower on the gas pedal with a Rotax to give more throw or stroke on the pedal, this helps to apply throttle more smoothly.
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Pretty tough weekend. I was top three pace wise in almost every practice session. Then in quali my front left wheel fell off and I slammed into the barrier. I got one lap in and qualified 8th. In the prefinal and Final top end speed was 10mph slower than everyone, me and my teammate were on the exact same gear and he was 10mph up. It wasn’t a great weekend as far as results go but I learned a lot and improved a fair bit.
Sounds like your excursion may have done some damage. If the kart is bound up from something bent, I will definitely affect your speed/times. Might want to have one of your local shops check it out to be sure.
that’s a very interesting point, I run mine on the top (third one, Freeline pedals) will definitely consider this as an option to try in the future.
Drive it like the F1 drivers do, keep it in the middle of the peak torque curve. Don’t let it rev much past the top of the curve while shifting. I don’t know where that is exactly, but if you post a picture of the curve I can tell you where the shift point should be.
What are you talking about shifting for? This is about a single-speed motor, not a shifter.
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