what gear ratio for 1/8 mile

Old 12-31-2007, 10:33 AM
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olds48
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Default what gear ratio for 1/8 mile

Suggestoins please 9" rear
car weighs 3200lbs 496 bbc cam operating range is to 7500rpm TH400
Was running 4.88s on 28" tire trapping 98 mph at about 6-6300 rpm
recently tubbed car and running a 33"tire now would like to keep revs under 7000 since I'm just bracket racing Would 5.83s be too much?
My math brought me to a 5.5-6.0 gear.Just sounds like alot to me
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Old 12-31-2007, 10:45 AM
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SST4530
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Do you only want to run 1/8 or would you like to do 1/4 also?
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Old 12-31-2007, 11:05 AM
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mytmouz
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I was running a 29.5 tire with 5:14's in the 1/8. On motor only, it needed more.
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Old 12-31-2007, 11:12 AM
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olds48
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1/8 BLITTLE I MIGHT SETUP ANOTHER CENTER FOR 1/4 LATER AND SWAP AROUND
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Old 12-31-2007, 02:44 PM
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Tod74
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http://www.et-studios.com/motorsports/gears/gears.html
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Old 12-31-2007, 04:38 PM
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olds48
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VERY COOL .THANKS A HEAP TOD74.YOU DA MAN!
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Old 12-31-2007, 09:24 PM
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Tod74
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actually that wasn't the one I intended to post. I will see if I can find it. You can google " gear ratio calculater" and find various ones.
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Old 01-01-2008, 10:13 AM
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mcracecars
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Olds 48, some of the problems I see with trying to gear that high a gear number is that you may have problems with traction at the start, depending on the converter you use.
Also these high number gears are a little weaker than their lower number counterparts, due to the smaller diameter pinion gear, less teeth on the gear to spread the load.

In my opinion it is always better to find the best gear, convertter, tire and suspension settings to get your best 60' and not be so concerned about what rpm the car crosses the 1/8 at.
Crossing the line at the 1/4 mile is more of a concern as, by that time air resistance is slowing down the acceleration plus you dont want the motor to run out of breath before the finish line.

With a healthy torky motor like it seems you have , and running a th400, you may have traction issues running 5.83s, even with the 33 tires.
These types of gear ratios were used back in the days of modified production type racing, heavy 3600 lb camaros with motors less than 283 cids, and 4-speed trannys, just to help get the car moving.
These cars were something to see, and hearing those small blocks singing at 10000+ rpm at the line was something ....
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Old 01-01-2008, 02:05 PM
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olds48
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You know,I always figured a real low gear would cause traction problems,but it seems the opposite to me.Whan I was street driving my Olds everyday I was running 3.73s and couldn't hook up at all,or get into third in the 1/8.When I went to 4.88s I started hooking immediately,with no other changes to the car.Kinda like how granny gear helps a dump truck quit from spinning,I guess?Whereas my Impala has 2.73s and once it starts spinning,it'll go forever.
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Old 01-04-2008, 05:51 AM
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If you play around with Pages 2 and 3 of:

http://home.earthlink.net/~whshope

and use a realistic value for rear wheel horsepower, I think you'll have your answer.
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