| So here in the Rockies the Super we buy is 91 AKI. Technically speaking, it is the same as buying 93 AKI at sea level. FOR MOST VEHICLES. A NA vehicle is sucking in less air at 3,300 feet than at sea level, to the order of 12% less air by volume. Which means your car does not need the same AKI fuel at altitude as it does at sea level. It also means it produces a lot less power. The same rule kind-of applies to a FI vehicle- more so for superchargers than turbo chargers though. The wastegate on a turbo is set to open at a certain pressure (let's say for a stage 3 TT it is 13 psi), which is absolute. So the turbo is pushing Atmosphere + 13 psi into the manifold at sea level, which is 14.7 + 13 psi = 27.7 absolute. Here in Montana it would be 12.9 + 13 = 25.9 psi, which is 6.4% less air than at sea level (but better than the 12% loss suffered by an NA vehicle). So it could be argued that a turbo vehicle would possibly need almost the same AKI at altitude as at sea level, or close to it. Now allegedly 91 AKI is good enough for up to 14 psi in our cars, which is what I can buy here. However, for almost a year I have been trying to chase down and solve the problem of why I get detonation (while boosting) that puts the car into safety boost. Mechanically the engine of my car is in almost new condition, I have the colder plugs, Z1 SM Intercoolers, and I still get it. It is worse on hot days (85+). After doing a lot of reading and chasing down possible causes of detonation (to no avail), I think I have the answer. My turbos may push the same 13 psi here as a TT at sea level, but they have to do a lot more work to get it there. The air is thinner so it takes more spinning (probably at higher RPM) to push that 13 psi into the engine. Besides the turbo spinning faster (heat) it needs to compress the air more than at lower elevation, and compressing air generates more heat. Lag is worse too, but that obviously isn't the issue I am worried about. So I have to wonder how much hotter the charge air is going into the engine than it would be at sea level. Even with the better heat soak and flow of the Z1 Intercoolers I am thinking this is too much for the 91 AKI gas. (Because the air flowing over the intercoolers is less dense, they are not going to do as good a job of cooling the charge air as at lower elevations.) I am not a thermodynamics expert, I am barely a science novice. But I am so far out of any better ideas I have to wonder if my car is just possessed. Because that is the only other answer. Any physics whizzes want to run the numbers and figure out if my hypothesis is on-track? Anyone in Denver or SLC have some input? In the meantime I purchased a case of Torco Unleaded Accelerator, and will try bumping my fuel up to 93 AKI, then 95 AKI if need be. Then we'll see if that takes care of the problems. Thoughts? Math corrections? Help?
|
