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trying to figure out what gears I need

3K views 32 replies 7 participants last post by  ericnova72 
#1 ·
I have a 75 cj5 I use in mudd bogg competitions. I have a 427 bored 60 over. I am using dana 44 front and rear ends out of a 78 J10 truck. I have a turbo 350 with a reverse manual valve body and I am using the dana 300 transfer case. I also have 35 in boggers on it. my question is what gears should I put in it to get the maximum rpm range out of my motor. The cam is good up to 7200. I would like for it to be quicker off the line but I also need enough gear to keep the tires turning bout 6800 rpms because the track is 200 ft long.


Right now I have 410 gears in the front and the rear. in drive I am turning about 6000 rpm's in second gear I am running about 7000. I would like to keep it in drive if at all possible for less wear and tear on the tranny. Any help would be greatly appreciate.
 
#32 ·
ok so I have called everyone that I can think of and all the ones people have recommended and no one can tell me what gears I need to run they all say they need mile per hr to figure it out. Well as most people would know in the mud we don't need to know how fast we are going. So if anyone out there knows how to figure it out with out having to know the mile per hr would you PLEASE let me know thanks
 
#33 ·
You my friend are in "Trial by Error" land.

You'll need to pick a gear ratio and try it out, if it isn't enough or is too much you simply buy more gears and do it again. I know this isn't what you want to hear, but is realistically the only way. There is a lot of that going on in 4x4 circles, my cousin uses a Quickchange rear axle in his mudracer just for that reason. If the track is tacky and he can't get wheel speed he just changes to a higher ratio in the rear. He runs different diameter tires on both ends(like 6" smaller on the front) and different gear ratios on both ends, and then just slightly adjusts the rear with the Quickchange to fine tune it. The smaller front tires are geared to be always spinning a lot faster, to keep them cleaned out and pulling the front straight ahead, and the rears are then geared to closely match the pit "suction" that day with the QC gears.

Reason you can't just easily figure this out mathematically is in your case you have to have the tires spinning, not hooked like they would be on pavement, and since you are in a gooey sticky mud pit that weighs things down and are spinning big heavy tires(by racing standards) it is often HP vs RPM vs Gearing vs Tire Speed to get the wheel speed at a point you can maintain it and not get bogged down.

In this case I would say it is better to have too much gear than not enough, I would think a 4.88 front/5.13 rear might be a good place to start.
 
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