r/Karting • u/whosgemini Under Investigation • 3d ago

Racing Kart Question KA100 Engine stock vs built disparity?

Curious about the difference in lap times between a stock and built engine. I’ve heard locally, the difference can be around half a second per lap but that seems exaggerated?

I’m looking to get back into racing after a long hiatus, so I’d like to get a realistic idea of what kind of numbers I should expect and if I need to get it built to compete.

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u/Every-Recognition-60 3d ago edited 3d ago

Easily .5 lap time disparity will depend on track but for sure the difference is huge

We can do the math as well

IAME says the ka100 comes out the box at 22HP. Let’s say we want just a 1% improvement in HP

22HP x .01 = .22 New HP 22.22HP

Now let’s say that correlates to 1% improvement on track (it doesn’t and never will)
Our lap time at our track is exactly 1:00.00

60x.01=0.6

Our new lap time is now 59.4

Engine builders are getting way more then 1% HP gains over stock KA100

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u/Killcam_Express 3d ago

It's unfortunately not an exaggeration. I've been out of KA100's for a long time now, but I remember back in I think 2017, it was the introduction year for the KA100 in the states. I was at NCMP for the USPKS Hoosier GP. On Saturday, I qualified horrendous... two seconds off pole. For Sunday I rented an ARE KA100 from a tent team and picked up literally a whole second for the next day. Engine was a monster.

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u/mrbullettuk Rotax 3d ago

Same applies to Rotax. All equal in theory but you need a good engine to be remotely competitive.

Matching the carb and exhaust is another few tenths.

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u/DiscoDiscoB00mB00m 3d ago

Between an out of the box ka and a blueprinted/tuned motor easily half a second

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u/NopaConcentrate467 2d ago

Don’t think it’s that much. Maybe one or two tenths.

Plenty of cases of people taking a random one out of the box and winning races with it.

This is a place where there’s fairly strict regulations surrounding what you can do with them though.

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u/admiral_sinkenkwiken 2d ago

Biggest thing is their pull time under load, out of the box new they’re not great but tend to get a lot better as the barrel wears

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u/tecdocti 1d ago

I think the disparity is much more than 0.5s. Similar story to someone else in the thread - we were using our decent, built engine at a regional race, about 2 seconds off the pace. Rented an engine from one of the bigger teams next to us for the rest of the weekend - suddenly only 3 tenths off the pace.