FrontEngineDragsters.Org Forum
Technical => Dan Dishon's Transmission Den => Topic started by: Dunc the Funk on December 30, 2021, 09:56:32 AM
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We have run 7.5s in the quarter at around 180mph this season & we are wanting to go a bit quicker next season.
We have a powerglide, 3.7:1 gears & Hoosier 33x15x15 tyres. We are now crossing the finish at near 8000rpm, which is our current rev limit.
I'm thinking of going to 3.5:1 or even 3.4:1 rather than winding the motor higher.
What gears/rpm do you folks use and what diameter tyres?
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What you are stating does not compute:
http://www.wallaceracing.com/calcrgr.php
This calculator is pretty reliable. I would probably run a 4.11 gear if I were you. Again, do the math. I would be looking at your converter!
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I would also look at the converter . A 3.70 gear with that tire should be fine for your combo !
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First season we ran a 4.29:1 & it was WAY too low, very violent launches. If the track was not good we had to leave in top. 3.7:1 does work well, our 60' is now down in the 1.05 sec range. I think either the converter is slipping a lot or the rev counter is telling lies.
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A1.05 is a decnt 60 ft but it seems like your finish line rpm dosent jive with your mph ! Might be worth talking to your converter guy about this !
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I run 3.89 gears and same Hoosier as OP.
We run through the lights at about 7800rpm at 192mph 7.2-- ET. 1.01 - 1.05 60 ft.. 3800 to 4200 launch rpm.
Check the converter as others had mentioned
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Thanks for responses. We don't have a data logger so I'm getting the rpm figure from onboard camera. I have reviewed the footage & it's actually only about 7500 rpm on a 178 mph run.
Using a slip calculator eg TCIs gives a figure of 11.8% (assuming no tire growth). Supercat's numbers indicate only 2.57%. At launch our motor always goes straight to 5000rpm so I guess our converter is looser? What is a normal range of slip?
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Many years ago ATI would tell us that 5% slip was a good convertor.
This was years before data recorders became common.
He used to figure it out with the Moroso slide rule.
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At the finish line my car, just ahead of the rear tire, is about 6 inches off the ground. So tire growth would be 4 to 6 inches anyway. How does that change your numbers?