The season is over and my slick are worn. The wheelhouse limit my overall width to 11".
Currently i'm running a 10x26 Hoosier on a 8x15 rim. Best ET was a 11.88@119mph, 60ft 1.77. The engine peak power is at 6k. I have a 3.90 in the back and a four speed, at the finish line i run 5900 rpm. Should i change to a 9x28, is it a improve or do i ruin my setup?
To get the most out of that setup, I would stick with 10x26. You are quite a ways off on your et potential, the most cost effective place to look for that 0.75 will be dialing in the hit of the clutch. That will also allow you to raise launch rpm (pack more energy into your launch), while at the same time reducing your risk of broken parts.
Lets say you have an overkill clutch that can hold 1000ft/lbs behind an engine that only makes 600. If you launch the car and allow that clutch to hit with it's full 1000ftlb capacity, it's going to instantly pull an additional 400ftlbs of inertia out of the rotating assy, which causes the engine to lose rpm. Extra clutch capacity, beyond what it takes to hold the engine's torque, that's what controls how fast the clutch pulls the engine down. Too much extra clutch torque capacity, the clutch either pulls the engine down too fast (bog), knocks the tires loose, or breaks drivetrain parts. But if you dialed the initial hit of that 1000ftlb clutch all the way back to around 700ftlbs, it still holds all of the engine's 600ftlbs of torque, except now it only pulls engine rpm down at a much slower 100ftlb rate. Because the car is gaining speed while the clutch is pulling the engine down, the engine doesn't get pulled down as far.
Here's a graph based on the average acceleration rate for a 1.40 60'...
Let's say for this example that line "A" represents the 1000ftlb clutch in the example above, hitting with it's full 1000ftlbs of holding power. 1000ftlbs of holding power is going to pull that 600ftlb engine down at a 400ftlb rate. The result is the engine gets pulled down very quickly (0.325sec) to about 1800rpm. Even if the engine were still making 600ftlbs, that's only 205hp at 1800rpm. That's going to produce a huge bog, and et/60' is going to suffer a lot because of it. But if you were to use something like the ClutchTamer to cut the initial hit of that 1000ftlb clutch back to 900ftlbs, it's not going to pull the engine down as fast, which gives the car more time to accelerate before engine rpm sync's up with vehicle speed (that sync point is where the clutch actually stops slipping). The result would look more like line "B", where the car is able to accelerate to about 20mph. That raises bog rpm to about 2800 where the engine is obviously going to make a lot more power than it did at 1800. Backing the hit of that 1000ftlb clutch off to 800 would result in something like line "C", where the engine stays above 3700. Now the bog point is up to around 420hp. Back the hit off to around 700ftlbs and it would look more like line "D", as the clutch is now only pulling 100ftlbs of inertia out of the rotating assy. That extra slip time allows the engine to stay closer to it's sweet spot for HP production, now it's up to about 550hp thru the low point of the bog.
Grant
