The last time I crwed for a team, using an EGT, we saw a high of 1050°. This was at Sears Point Raceway in Sonoma County. I think it’s about 2.5 miles in length. That was with regular leaded gas. We led the Sprint sit up class almost every lap. On my dyno, the best I ever saw was 1200°. That was with 110 octane race gas.
I’m pretty sure you’re go to see a wide variety of numbers. There’s so many things that can make that number change. Compression ratio, fuel octane, air density and let us not forget the very important item, the location of the EGT sensor. On the Yamaha I always placed the sensor at 3 1/2 inches from the piston face, with the tip of the probe in the center of the exhaust flow.
but i’m guessing that the poster is looking for specifics on the ROK shifter engine as the placement of the EGT is standardized, and different from the Yamaha, as are many other parts and conditions. Ignition timing plays a huge role in EGTs.
I never ran an EGT sensor on my Rok Shifter, and I can’t say I know many people that do. I would tune the main based on throttle response and ADR relative to baseline. Going very aggressive with the main didn’t seem to provide any noticeable gains, so I would always jet rather conservatively, as well as run P2.5-P4 on the needle depending on the conditions.
Assuming that you’re using an Aim data logger, keep in mind that the two EGT leads they supply vary in temperature ranges. The angled “heavy duty” lead will read ~150* F higher than the straight “standard” lead (for whatever reason). Something you’ll want to pay attention to if you are comparing data with others.
I’d think the ideal approach would be to establish your control on the dyno. I don’t have one though, so I just relied on on-track data and anecdotes. This seems relatively easy to hit the ideal window with this motor given the restrictive nature of the ROK rules. If we were talking KZ jetting/setup I think it would be more complex.
The hotter a fuel/air mixture gets, the more it expands. There is a limit. If it gets too hot, the pressure in the cylinder reaches a point where the fuel begins to detonate. The cause of detonation is excessive heat and/or pressure. When the fuel starts detonating, the exhaust gas temperature goes down. When this happens, it is not immediately disastrous. If you see the EGT go down, just open the high-speed needle a little, or in the case of a fixed jet, head for the pits and put a little bigger jet in it.
Be aware that the response time of the EGT sensor is very quick. Coming out of the corner, if you see the EGT reading lower than previous observations at the same point on the track, open the low-speed needle. Once you get used to the intricacies of tuning with the EGT, I think you’ll agree with me that tuning with the CHT is just about useless.
“Tuning is tough” (Al Nunley)
“If your data does not support the theory, get a new theory” (Al Nunley)
In general EGT response time is at least an order of magnitude slower with respect to the engine conditions. The thermal energy has to makes it way through the EGT sheath into the thermocouple inside. In the time that takes, you have gone far beyond the engine conditions which created said thermal energy.
Not in my experience. I’ve been told, many times, by drivers who I have tutored, that they see much lower temperatures as they accelerate out of corners. At the end of the long straights, where they might see temperatures of, for instance, 1100°, after breaking at the end of the straight, turning, then accelerating, they see temperatures as low as 850°. The time lapse between breaking and getting back on the throttle is only fractions of a sec.
Given that most EGTs are 1/16-1/8in sheaths, you can expect a 1-3 second delay for the sensor to register 63.2% of the temperature change. at 15000rpms, that’s 250-750 revolutions of the engine.
I also believe you are referencing single-speed karts. The Rev patterns of a shifter - about which the original post was made - would be very different from that of a single-speed kart on a long straight.