Thinking out loud or maybe I’m just venting here, but It would appear that KA100 has established itself as the nation’s top tier class next to TAG125. Especially when you are seeing names that run TAG 125 having a go at 100cc. Having owned and raced one for a few years I can see why. They are reliable, fairly consistent, and plenty fast. However, has it become a victim of its success? Since they are so consistent what does it take to be competitive at a national event when there are 30-40 karts in one class? It would appear that. gone are the days of box stock for sure and from what I gather you need a freshly done motor just to have a chance. Even for club racing, these motors seem to lose that very top performance after 5-6 hours. Do you need a motor done by the likes of Comet or Woltjer just to be competitive? I’m told there isn’t a whole lot that can be done but I know there are builders stating 1-2hp gain (5% - 10%) which seems significant.
You can’t get that much from a KZ engine, let alone a KA so take the engine tuning out. In my opinion, as far as engine goes, getting the jetting right the day of and adjusting as conditions change comes first in terms of importance, followed by racing on a fresh rebuild. Tuners are great if they are supporting you the day of the race to dial things in on their specific engine they gave you, but I highly doubt anybody can squeeze that much extra hp out of a KA with a tuning, while staying within the rules. A different topic is engine parity, not sure if KA has differences that can be exploited
I had two engines on hand this weekend, and my “practice” engine with no “special sauce” and probably 6 hours on it was about the same pace as my “race” engine which was fresh and dyno’d really well.
Still isn’t a ton to squeeze out of them, but like Andy said, the advantage of a “built” KA is that you get the builder’s insight into what is going to optimize your carb settings and gearing to get the most out of your specific package.
You’re definitely not seeing 1-2 hp difference from a builder. Our practice engine to our race engine dyno .4 hp apart and that was only 3 or 4 tenths when they were both fresh from the builder. One or two hp would be looking at over a second of advantage over the field.
Regarding longevity, if you’re running competitively you’ll want a rebuild after 8 hours or so just to be safe. Our race engine made 8.5 with no noticeable drop in top end. For club racing, you can definitely push 10 or more on a top end without issue. You may notice you’re not pulling a draft as well as when the engine was fresh but it isn’t that bad.
Last year my practice engine ended up with probably 12 hours on it, and its performance went from 4 tenths off to 7 tenths, so 3 tenths off in wear over 12 hours.
Then what Andy and TJ said, when you get an engine from a builder, you should be getting their support as well. Carb tuning at the track, troubleshooting, etc.
I wonder if you could pep the engine up with a fresh ring vs doing the complete piston every x hours. Being mindful of the total time on the piston, bore condition and small end bearing condition of course.
Since they don’t turn very high RPM I’m inclined to think that the ring might be a little clattered out while the rest of the parts still have some useful life in them.
A ring buys you about an hour and a half, so you can use it in a pinch if you get to a weekend and feel like something is wrong, but I wouldn’t rely on it to go longer on a build consistently.
How they are put together defiantly seems to make a difference but it seems like you can detune them from factory rather than make massive gains. ive seen guys take off blueprinted engines that were fresh put an out of the box engine on and go faster.
Some motors are slightly better than others like any mass produced product. But the parity seems to be very very good in KA3 (i think that is the same as senior in the US) . most of the time if it looks like someone has a heap of HP over everyone their kart is just getting of the turn better.
Carby settings are paramount though, slighty off will cost you tenths