Daytona gearing

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PostPosted: Tue Sep 29, 2015 4:53 pm
Based on the trap speeds recorded at Daytona, I assume most people were using the old, taller 3.62 gear ratio and still kissing the rev limiter.

So, do we still want to mandate the shorter 3.85 in 2018?
Bruce Funderburg
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PostPosted: Tue Sep 29, 2015 6:41 pm
The calculator I ran shows 151 mph with the 3.85 ratio and the .77 5th gear, assuming a tire circumference of 70 inches, at 6,750. The 3.62 would max out at just over 160 mph.

https://wahiduddin.net/calc/calc_speed_rpm.htm
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PostPosted: Tue Sep 29, 2015 6:49 pm
Yep, I'm 99% certain that everyone is running the 3.85.
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PostPosted: Wed Sep 30, 2015 8:30 am
I ran against one car (#177) that I believe may have been running a 3.62. I base that on the fact that he and I were running comparable speeds and he appeared to be up shifting just after the apex at turn 6. The only thing that makes sense to me is that he was upshifting from 2 to 3 with a 3.62.

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PostPosted: Wed Sep 30, 2015 9:53 am
breton wrote:The calculator I ran shows 151 mph with the 3.85 ratio and the .77 5th gear, assuming a tire circumference of 70 inches, at 6,750. The 3.62 would max out at just over 160 mph.

https://wahiduddin.net/calc/calc_speed_rpm.htm


So the limiter is at 6750, not 6500?

Hmm - looks like the current tires are a bit taller than I had in my calculator too.
Last edited by BFun on Wed Sep 30, 2015 11:38 am, edited 1 time in total.
Bruce Funderburg
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PostPosted: Wed Sep 30, 2015 10:05 am
6,750 is the published rev limit (I set my shift light at 6,600.) This equates to about 120 mph in 4th gear, though hitting the limiter will cause a drop in speed to about 117. For tracks where it's not worth shifting to 5th I'm watching the MPH to keep the car at around 118 mph to avoid hitting the limiter. When we ran the car on the dyno it was still gaining horsepower up to the rev limiter (unlike the Gen2 that maxes out around 5,100 RPM.)

Surprised looking at some of the Gen 3 Daytona videos how early some were shifting and were running down in low 4,000 RPM range out of some of the corners, as shifting near the rev limit should keep the engine above 5,000 RPM. That could be the nature of the track or desire to avoid an extra shift, but it seems like it affected speed off the corner judging by the growing gap to the cars being followed.
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PostPosted: Wed Sep 30, 2015 10:55 am
I too have my shift lights programmed for 6500, so I shift prior to hitting the limiter, but I can tell you it's spot on at 6750. I had gearbox problems at Hastings where I couldn't get out of 3rd gear, and could run it to 6700 without the limiter kicking in. Just a slight bit more and the limiter banged on. Post-race data review proved out those numbers...
Last edited by srf99 on Wed Sep 30, 2015 11:13 am, edited 1 time in total.
Dan

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PostPosted: Wed Sep 30, 2015 10:59 am
The data from the 151 mph lap showed that the engine was 15 rpm from the rev limiter. So Bob's calculations are spot on.

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PostPosted: Mon Oct 05, 2015 3:07 pm
I was at 6635 rpm when I hit 150.4 mph.

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PostPosted: Mon Oct 05, 2015 3:33 pm
Was that when you were pushing me during the race. ;)
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