circle track rear gear ratio info needed

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Rapid Robert

Rapid Robert

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1/3 mile high banked dirt track. 63 dart 360/904 2bbl 8&3/4. what gear ratio should I go with? and a 6200 rev limiter is required (if that info is helpful). thank you for your time. RR
 
Mcodecuda’s suggestion is a good and the simplest place to start. A more complicated but more accurate solution for your car would be to find out what the top speed is for the class and track you plan on racing on. Then use an online gear calculator to determine what ratio will have your engine hit that speed just below your 6,200 RPM redline.

If you are using an automatic trans then be sure to allow some extra RPM for some slippage of the converter. You are limited to the available gear ratios so select the closest one to your calculated needed ratio while still leaving some RPM available to go faster if you can find more power in your engine. Keep in mind you can use slightly different size tires to adjust your gear ratio, as needed. Good luck and I’ll say it is always nice to see someone running a mopar in the sea of chevys at the races!
 
I do as mentioned.
Find what trans gear ratio, diff gear, and rpm.
I use 2nd gear 2.022:1, with 3:30 diff on one track.
3rd gear 1.384:1, with 4:30 at another.
7500 chip
 
The first thing you need to know is the lowest RPM the engine will see.

Once you know that you can figure out how many RPM you need to gain going into the corner. Then it’s just simple math.
 
excellent info. I will get some specs & also see if I can locate a chebby racer (I'm the only Mopar out there!) & get some ratios. Thanks guys. RR
 
Back in the day, (which doesn't do you much good now) there were many, many 8 3/4 gear ratios produced for Mopar circle track racers. Dave Marcis used to live right down the road from me and his race shop wasn't far away. Sometime in the 80's or 90's he had an auction and sold off all of his old Mopar parts from the 70's. He had dozens of 8 3/4 chunks with every ratio needed for any track. I was shocked at how many different ones there were! He had duplicates for some of the ones he had used the most, in case he busted one. All I had ever known was 2.76, 2.94, 3.23, 3.55, 3.91, 4.10 and then typical aftermarket drag car ratios. It was an eye opener to see how many ratios there were and how small of increments they were in. If you end up needing some oddball ratio beyond a 4.30, 4.56 or 4.88...you might contact Tim Wellborn at the muscle car museum in Alabama and he could steer you to someone who would still have some of those old circle burner ratios around. Good luck to you....and go to the front!

:steering:
 
Thank you JD! well I remembered I had an A body 8&3/4 (with pumpkin) buried in my stash & yesterday I checked & it is ~ 5&1/2 turns of the pinion for one turn of both drums (not sure if it is a sure grip or if I had welded the spiders) so ~ 5:50 to 1. I could try it but that sure seems a low ratio (tires are 15"). when the time comes I will note my top speed & the lowest RPM the engine will see & how much RPM I need to gain going into the corners and all other numbers you guys mentioned that I need & I will hit up the chebby boys to see what they are running. thanks a bunch guys. I wanna kick some chebby ***! I'm pumped. RR
 
You probably aren’t going to find anything lower than 5.14 for an 8 3/4. I would start with a 4.10, run it in second gear and work from there. We ran 1/2 mile with 5.14, ran out of ignition at flag stand turned 6000.
 
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