Looking for some info on the KA torque curve and EGT vs rpm. Of course, generic info won’t match our motor exactly, but it gives an idea.
I know that carb and motor tuning can be done to change the curves, but is there any generic information out there?
I am looking to do a better job of selecting correct gear and help dial the carb based on track layout and would love to have a better handle of where and how much the torque curve peaks and falls and what EGT to expect based on RPM.
For example, a tight track with a straight may require end of straight RPMs up around 17k to optimize the corners, but a flowing track may allow a gear ratio that allows peak strait RPMs at 15k. Knowing that that general curve would be helpful.
On the EGT, we have run a couple tight tracks where we turn upper 16s to 17k and see 1050-1100 EGT as expected when we tune correctly. But what should we see if peak RPM is 16k even, or 15.5k, or 15.3k?
I guess while I am asking about carb adjustments, how do you guys determine LSN vs HSN adjustments, and what adjustments do you make on the fly while on track? Trying to teach my son what to listen or feel for when on track besides just EGT.
No need to really overthink it. KA carb tuning is pretty straightforward. Your peak ideal EGT won’t change much from max RPM of 15k or 17k.
Very rarely do I make low speed adjustments on the KA. Only time would be when I feel it bogging on the low-end off tight corners. Your high-speed needle is your main adjustment for controlling max EGTs and making the kart run best throughout the range.
Tweak in 5 min increments to achieve the EGT you’re looking for. That’s basically it.
We were at a new track for the first time this weekend and struggled on the long straights. By the end of the weekend it had us scratching our watch and winding our ass.
Pretty fast flowy layout. 900 foot long uphill straight and a 750 foot long swoopy open downhill. All the corners seemed pretty easy to keep corner speed.
On the end of the straight we were seeing 900-960 EGT at 15300-16500k. By himself low 15s was all he could pull too, corners were 8000-8500. But he was being consistently top ended by a driver that we are usually faster than and that he had been faster than all weekend.
We ran 10/72 most of weekend. Tried 10/69 for prefinal, went back to 10/72 for final. He ran faster in the final, but was clearly getting smoked by the top 3 on the big end. Was about 0.1-0.3 off the pace depending on lap. And motor was on its first weekend out after top end and break in. The 10/69 was 900-930 temps, the 10/72 was 930-960 temps.
After looking at data, I was wondering if we shouldn’t have stayed on the 10/69 or even gone 10/68 and leaned it out a bit.
Only our third race on the KA, so still figuring it out. You don’t notice the subtle differences until you are on track vs others.
Why change 3 teeth at a time? I feel like there’s some room within that for fine tuning, and you may have missed the sweet spot vs. if you had made a 1-2 tooth change?
@Muskabeatz we weren’t prepared to go that low. Our standard gear sets are 72-82. So we had a borrowed 69 and then our 72. I think the winner was on a 10/68. The long uphill makes it odd. Seems like the speed plateaued it you geared too short and got up in the rpms. The combination of uphill and wind resistance?
We will have a 67, 68, 70, and 71 to add to the gear stack when we head back for a test weekend in 10 days.
Engine wasn’t broken in or dyno tuned by shop. Top end was redone and we broke it in Friday running 6-10k for two sessions. Work was done at Dallas Karting Complex. They have several people running their stuff in the regional TSRS and are closest to me. Will look at other options next season, as we will have 2 motors to run.
Going to be following up with them this week/weekend.
Also, we are running Mychron with old style straight TC with jam nut still on it.
Take the nut off and get the sensor all the way into the pipe for most accurate and consistent readings. You’ll notice temp readings go up from that change alone. On the smaller threaded sensor shoot for 1100 EGT max and 900 min as a general target.
Every KA dyno I’ve seen they make peak power around 10,500rpm and then it’s a slow taper from there as RPM goes up. However, power on the low end below 7500-8k drops off a cliff. So I often find myself managing gearing via minimum RPM for the slowest corners to keep it from bogging off those slow corners and then dealing with whatever RPM it ends up with up top (within reason).
On a fast flowing track like you described it was likely faster to have the taller gear to take better advantage of more power on the straights as long as it was getting out of the slow corners appropriately. If I was turning 8500 min RPM I would have gone taller in gear.
If I remember correctly this style EGT is about 100 colder than other EGT probes.
Personally, I never had much luck leaning to get the EGT up and still have good performance. The general starting point of 1 full turn on both H nd L I think is on the lean side. I usually have the H at 1 turn and 10-15 min and adjust from there.
On the EGT you want to see the temp continue to go up on the straights. If it goes down at the end of the straight when still on the gas you are likely running lean.
Don’t want to highjack the thread but what is the go to sensor for the KAs? I’ve read that the “heavy duty” right angle one reads 100 degrees hotter so what should target EGTs be?
I just got back from Dixon and I had a peak EGT of 1265.
The new probes do read higher. I wasn’t told about this and in Vegas my first session I was at 1250 and was panic richening the needle the whole session.
Eric, I believe this is the unit that reads about 100 higher, which would make your 1265 a little more normal. It is unclear to me why they read higher. I would be curious if you were able to swap your pipe with another racer that has a straight unit to do a comparison.
