Re: Yamaha rd350 road racer
In my opinion CHT is a pretty awful way of tuning a two stroke, as is water temp. Neither of which react quick enough to generate any meaningful feedback. They do however provide a baseline for understanding engine condition. As JMobius says, we always used ambient temperature as a factor of CHT, it's been a while but I believe we aimed for 350F plus ambient, if we got much over 500 we were too hot. Unfortunately mixture had little effect generally, other factors were more important. This wasn't for an RD, but this was for other Yamaha racing engines. On the street I doubt you'll ever see anywhere near 500F as this required sustained full throttle operation. EGT and especially Lamda are much more useful. Lambda brings some fowling issues that really aren't great for street use. So that leaves EGT. I use dual EGT's on my street RD and have had good success. That's not to say they are without issue though. I record them at 20hz and when I use them as a tuning aid I only review the data from a consistent route (my favorite twisty section of road on the way to my office) post ride. And that's the real kicker here, if you are tasked with manually reading that gauge while riding on the road you are asking for more than engine trouble, especially considering that you won't be getting any valuable readings until you really wind the thing out. Moreover, you have to establish a consistent environment to read EGT. The track is great for this, the street is much harder. I've seen a tail wind reduce the EGT reading, imagine how grade, straight length, etc. can complicate things. The good news is that used data loggers are becoming cheaper by the day, the technology from the early 2000's can often record at 200hz on several channels. The loggers I use in my RD has 8 external inputs which I use for EGT and some shock pots as well as several other channels such as ambient temp and battery voltage that are integrated. I found mine used and got a good deal.