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Discussion Starter #1
having a debate with a fellow. He thinks a 10.5 car does not need a rear gear change to run 1/8 then to turn around and run 1/4. If its geared perfectly to run 1/8 mile and goes through at its peak RPM in the 1/8 wouldn't it way over rev in the 1/4. Or if it was gear for 1/4 mile and hit peak rpm at the 1/4 mile stripe would it run through the 1/8 below peak rpm and therfor be slower (lazy) and be down on peak rpm and ET? Bottom line can you be totally efficient and run top ET running the same rear gear for 1/8 to 1/4??
 

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Chris, if you (your truck) wanted to be at peak engine rpm at the 1/8th mile, you would have to have around a 5.50 rear gear.....assuming 172mph @ 9500rpm....could you make that work?.....probably not.

We don't change the rear gear from 1/8th to 1/4.
 

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I have no idea the real answer.. but it seems like you are already chasing the tires for the 1st half so I cant think you would benifiet other than small changes and not expect much gain. and yes in my opinion it would not work if you had a 1/8 mile gear in for a 1/4 mile but will the other way just fine at your level.
 

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This discussion comes up a lot,Doug and I have talked about it many times,I would say 90% of the racers don't change gear and I would think that maybe the N/A guys could benefit a little,but not much.
 

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In theory yes 1/8th mile would require different gear from 1/4 to be totally 100% efficient. However we are not that sharp and if you have a gear that gets you to the 1/8 okay it and won't over-rev or hit chip going 1/4 then we leave it along/same. This applies to our power adder (twin turbo) and other power adders may think otherwise...
 

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Using only 1st and 2nd gear of a 3 spd transmission accomplishes exactly what you suggest but...does it make any difference?????
 

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Discussion Starter #7 (Edited)
Chris, if you (your truck) wanted to be at peak engine rpm at the 1/8th mile, you would have to have around a 5.50 rear gear.....assuming 172mph @ 9500rpm....could you make that work?.....probably not.

We don't change the rear gear from 1/8th to 1/4.
With my deal I run a 4.10 rear gear with a 1.57 first gear with a 2 speed trans for a final first gear ratio of 6.43 and its on the edge of blowing the tires off every time, it puts me through the 1/8 mile at 8000 my motor makes peak at 9000, I did manage to run a 4.29 like this during a 6.59 1/4 mile run at 212 right at 9050 rpm. For 1/8 mile racing only I truly believe a 1.35 first gear with a 4.56 rear gear will lower my first gear ratio to a manageable 6.15 and put me through the 1/8 at around 8700-8800. I've made all of my runs with only 43 lbs of boost through the 1/8 every time I increased boost it made the tuning launch window even smaller. With the softer 6.15 I will be able to spin the blower faster for 48 lbs which my blower is easily capable of making. This gear selection will never go 1/4 as it will put my way over my high side. On paper it should go teens. I am also dropping 60 lbs losing my Dana 60 for a Fab Housing.
 

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With my deal I run a 4.10 rear gear with a 1.57 first gear with a 2 speed trans for a final first gear ratio of 6.43 and its on the edge of blowing the tires off every time, it puts me through the 1/8 mile at 8000 my motor makes peak at 9000, I did manage to run a 4.29 like this during a 6.59 1/4 mile run at 212 right at 9050 rpm. For 1/8 mile racing only I truly believe a 1.35 first gear with a 4.56 rear gear will lower my first gear ratio to a manageable 6.15 and put me through the 1/8 at around 8700-8800. I've made all of my runs with only 43 lbs of boost through the 1/8 every time I increased boost it made the tuning launch window even smaller. With the softer 6.15 I will be able to spin the blower faster for 48 lbs which my blower is easily capable of making. This gear selection will never go 1/4 as it will put my way over my high side. On paper it should go teens. I am also dropping 60 lbs losing my Dana 60 for a Fab Housing.

I believe you agree with Doug.
 
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