I raced at OVRP this weekend. My driving wasn’t the best and I know the problems I had in the Hairpin were really line/driving related, but I think it starts a good conversation about engine bogging / clutch setup.
I was running at about 395 lbs, 2 black/2 white springs, and 17/70 for 3.68 gearing. I would be too
In the hairpin, I was probably over slowing and the engine rpm would be below 3,400 RPM and the clutch would unlock. Getting back to 3,400 rpm, it would lock up and bog for almost 200’ and 5 seconds! I would get passed a ton here.
So, what is the correct thing to do? Go for a lockup so it comes in at say 3,600 and less likely to bog? Weights? Lower lockup so it starts pulling earlier?
Peak torque is sub-3k, so bogging sounds bad but actually isn’t when your rpm are this ‘high’. Your trace actually looks like the clutch is slipping already and struggling to re-engage, so I’d start by cleaning the drum and scraping the shoe grooves. Fully locked gives you 120 rpm/mph but you peak at 50% more than that, so that’s a lot of slip. Some of that also comes from chassis setup since the outside tire wants higher rpm than the inside tire, and chassis setup determines where the ‘average’ speed falls between those two. You can really hear it when you unload the inside tire and kart speed follows the outside tire instead of the average.
I have a theory that there’s a hysteresis to these clutches because the shoes have some friction to the spider hub, so usually they don’t disengage until well below the engagement point on decel. That makes me think your engagement point has risen a lot more than planned because of slippage.
