Sorry. It made sense in my mind, but that's how legends are made.
I called Jamie Passon, and gave him my numbers for tire diameter and gear ratio. He confirmed that I should use a 35 tooth. The same number I come up with on all the charts. Well, some charts don't show the numbers for 3.73 gears.
I ordered a 35 tooth gear from him, and when I was installing it, I found that I had a 35 tooth gear in there already. It looked a tad worn, so I put the new one in. My current speedometer error remained.
Using GPS on my Android phone to check actual speed, I found that my speedo read 29 mph at 25 actual mph, at 70 mph indicated I was at 57 actual mph, at 80 mph indicated I was at 65 mph, at 120 indicated I was at 95 actual. The ratio of error increases as the speed increases.
If I plotted both sets of these numbers on a graph with MPH on both sides of the chart, the actual MPH would split the chart evenly in half right down the middle. Now, when I plot my indicated numbers on the same chart, my indicated speed line would start at the same place on the chart at "0" MPH at the lower left corner and be just above the actual line getting farther and farther away from the line as speed increased. The lines have different slopes and diverge from each other at a certain ratio that I forgot how to calculate from my algebra classes. A picture would work better to explain it, but I don't know how to make one on this PC.
I haven't put the new gear in yet to see what happened, as I had other priorities this weekend including taking a buddy and his son for a ride to show them what a sub 500 hp car versus a nearly 700hp car feels like. I'm helping them build a 1000 to 1200 hp boosted car.
The main point I tried to make to them is that either car is deadly in the wrong hands. I think they got this point as I took off from the house all smooth and slow. I lulled them into a conversation with each other long enough to distract them as I approached the entrance of a long freeway on-ramp at about 10 mph. Just when they least expected it, I suddenly blasted 500 cubic inches of Mopar muscle through 3 gears to redline. They never saw it coming, and its safe to say I put them right in shock, especially when I told them there were two more gears available after that. What are friends for after all.
