Gear change question

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Gear change question

Post  blu69MachI on December 15th 2016, 6:57 pm

I finally got my car to the local track. I am happy with how it performed but looking to go faster. It is all steel, 69 fastback. My fastest pass was 1.34 60 ft leaving at 4k on tb. 6.25 105.68 mph 1/8th mile track. When I go through the traps I am still in 2nd 7100rpm. 4.10 gears 31" tall hoosiers. C6 transmission. Timing is at 32 degrees. I am planning to put 4.56 in it this winter, in hopes to make it faster. Do you think 4.56 would be a good change? I want to post a video so I can get some opinions on rear suspension set up.  It has a 4 link and I think Leaves great but was debating on adding more hit to the tires.
updated the video to a clear one:

http://illiweb.com/fa/pbucket.gif4


Last edited by blu69MachI on December 16th 2016, 11:23 am; edited 2 times in total
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Re: Gear change question

Post  blu69MachI on December 15th 2016, 7:20 pm

delete


Last edited by blu69MachI on December 16th 2016, 11:27 am; edited 1 time in total
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Re: Gear change question

Post  DILLIGASDAVE on December 16th 2016, 4:50 am

Looks like it has a bit of body roll at the launch, does the 4-link have an anti-roll? Looks like it also has a decent amount of wheel-speed at the launch (vs a dead-hook), a rear gear change will probably have some effect on the amount of wheel-speed as well.
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Re: Gear change question

Post  blu69MachI on December 16th 2016, 8:11 am

No there is no anti roll bar. After you mentioned that, I paid more close attention to the video and notice it's spinning and the driver side lift. I didn't think it would of needed any thing like that since it is tubbed and caged but dang I see it clearly now. I s

I just read an article about wheel speed, good info http://www.dragracingonline.com/technical/2014/xvi_5-worsham-1.html

So, am I thinking correctly about wanting to get my 3rd gear involved in the 1/8th mile runs, instead of just 2?
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Re: Gear change question

Post  rmcomprandy on December 16th 2016, 1:51 pm

The best thing about a 4 link is that both sides do not need to share the same instant center location.

Body roll at the starting line along with the loading of both rear wheels equally can be controlled when each side has its own set-up.

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Re: Gear change question

Post  DILLIGASDAVE on December 17th 2016, 4:39 am

blu69MachI wrote:So, am I thinking correctly about wanting to get my 3rd gear involved in the 1/8th mile runs, instead of just 2?

If you only run 1/8 mile you could run more rear gear if you wanted too, especially with a big tire. It might help, it might not. But at some point more & more rear gear can end up throwing away too much usable low end torque/grunt/pull, especially on the bottle. And a big jump (either up or down) in rear gear ratio (mechanical leverage) can also have some effect making the engine think the car is now lighter/heavier than before causing an effect on how the car/engine works with the converter's stall/lockup points.
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Re: Gear change question

Post  richter69 on December 18th 2016, 12:41 pm

1.80 glide and a 4.86 imo
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