A professor Blair, Belfast University, did some interesting stuff that was published in SAE. My first Mayko pipes, in 1973, used his design theories. Hard to believe that was almost 50 years ago. How time flies when you’re having fun.
Is that for Jr or Sr? If Jr, would Sr be slightly higher due to added weight?
Lots to reply to here…
@mtbikerbob at 6200 minimum RPM, you’re just not carrying enough speed I would imagine. I never see anything below 7.5k, on any track. So that’s not a gearing issue, more a driving/chassis issue.
Top RPMs probably will never be below 15k. I think 15.2k or so is generally the lowest we go before the negatives start to outweigh the positives. Don’t be afraid to rev the thing either. I’ve mentioned before, but we ran up to almost 17k at SuperNats with no problem. Making lots of noise on the top end, but the tight infield made it necessary.
Regarding gearing, I don’t think I said “6 teeth” but definitely you see a range of about 3 teeth among the top guys. I definitely see differences in 1-2 teeth changes, and I don’t feel I need to change 3-4 to see a difference. 4 teeth is a big jump.
In summary, run the max RPM between 15-16k and you’ll be in the ballpark.
Best of luck, I’ve never been able to move the peak, torque or horsepower, by that much.
The path for air to travel through an engine, face of the carburetor, to the end of the pipe, is pretty much fixed. There are multiple to lengths, and when all those lengths (there are several) complement each other the most efficiently, that’s where you reach peak torque.
It would be for both.
@tjkoyen, I think that might have been said 2 or 3 years ago when the motor first started making it’s appearance. Obviously, more about it is known now, and probably wouldn’t be true today.
However, I’ve heard everything from lug the motor, to spin it. I tend to lean more towards letting it spin so my daughter can get out of the corners.
I found the original post, and you are right it wasn’t you. It was from a post in August 2018.
Not sure what you are referring to here. The X30 is 125cc and the KA100 is, well 100cc. My comparison in values was more about the Shape and Duration of the Curve itself than the delta of Peaks. The manufacturer stated the Peaks. Being the same manufacturer and similar design characteristics other that Water vs Air Cooling, they both operate in the same RPM ranges and they both run a Factory Tuned Pipe. One could draw the conclusion that the two engines could share similar Torque and Hp Curves across their respective bands. Only way to know for sure would be to overlay the two graphs.
Completely depends on the track. Dousman we spin it. New Castle or GoPro we lug it.
As others are mentioning in this thread, figure out how to keep the engine in that window where it is making peak torque for the longest.
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If you are using a Mychron 4 or 5 the power curve data is in your device. You have to use some factors to output the data that are difficult to get exactly right but if you ignore the accuracy of the output numbers you can still form an accurate shaped graph of RPM points for evaluation.
KA should be peak torque around 9500 and peak power around 10,500. Power curve will show you why over-rev is beneficial…how much depends on how fast the track is and how many RPM you turn in the slowest section of the track.
“Power under the curve”, always.
Lots of tight stuff? Long straightaway? A very stupid way to build a track for karting!! Lubbock Texas is a good example of a bad track design. Still, spend as much time as you can in the peak HP part of the curve. If you have to over rev it, then you have to over rev it, what else can you do? I’ll leave it up to you what “over rev it” means. I’m sure others will follow that idea and if you want to keep up, you’ll have to too! Seems to me it would be a big mistake to set a 15,000 rev limit while others are exceeding that. I wonder if the track would set a “not to exceed” gear ratio limit, would that help? It would keep people from over revving!
“Torque the motor” sounds like a good scheme, but all the motors are the same! If you’re following the rules! Read the first line!
Thank you to everyone for the replies on this topic…
TJ I have attached an overhead pic of our track. While I don’t have measurements, the hairpin is tight and we run the track in a counterclockwise configuration and is about 4/10 of a mile. I don’t think finding another 1000rpm would be possible with gear ratio or driving. Those running a gps in the KA class are seeing low 20’s mph at the apex in this corner. I have been reluctant to rev much above the 15.7k that I am seeing now, however I am only seeing this for less than 2 seconds from the start finish line to the braking point into the hairpin. Might try more.
Just out of curiosity, which way do you run this? Counterclockwise?
I currently race 4-stroke karts, which the budget side of karting but I was wondering how much the costs would change if I switched to KA. Is it at all popular in the North East (Maine to new york)
The cost could depend on some of what you run currently. Just the motor would be around $2,500. If you’re not already running 219 chains, you would need to switch over to that. That’s really about it unless your chassis is a 4 stroke specific chassis.
I can’t answer about the popularity in the North East, but in Texas it has taken off this year.
Rebuild intervals and cost roughly?
Complete rebuild? Maintenance rebuild?
The crankshaft and the rod will go for a long time, no maintenance rebuild.
Seals, every 2 to 3 maintenance rebuilds
Piston and rings?? I’m going to guess, maximum 3 or 4 races. Best case scenario, probably more. Check the compression pressure regularly, that will give you a clue.
When you replace the rod you replaced bearings and wrist pin and crank pin.
That’s it.
It’s probably been discussed further up in this long thread, but I ran all of 2017 on a stock engine without rebuilding it once. That was 4 national weekends, a couple regional and club days and some testing. Was 2nd at the final national, so performance loss was non-existent. I know some guys who have put “50 hours” on a piston just pounding practice laps. So the engine maintenance isn’t bad at all. Clutch is bulletproof, starters and electronics are pretty good too.
One thing to consider when you move up to something faster, is you will go through other consumables faster. Tires, brake pads, chains, sprockets etc. all wear out quicker with more power. KA is not bananas powerful so it doesn’t burn up equipment as bad as an X30 or something, but it is worth noting.
Same tire life as x30? Basically reds instead of whites or equivalent? One set per weekend?
It all depends on what you want out of it. I think the for best performance, you can easily go 10-15 hours minimum before needing a top end. However, you should still pull the head and clean the combustion chamber every few race days. The cost is mostly parts, and will depend on what builder you go to, but they can cost anywhere from $500-$700.
A full bottom end, you can easily get 40+ hrs. The manual states replacing the main bearings at 30 hours, but with proper oil mixture you should be able to go a little longer. That would run more, and since I haven’t had a complete bottom end, I am not sure of the cost, but would estimate between $800-$1200.
For tires, I have the experience with Evinco Blues (MG Red equivalent). They easily last more than a single weekend, especially the new compound. Obviously the track will dictate tire life, but for the most part they last multiple race weekends. For our bigger races, we’ll qualify on new tires, run the event, and then any club races and next big event practice on that one set.
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Thanks! Useful perspective. Much appreciated.
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