Hi Guys,

I'm a newbie, so sorry if this has been covered before.

My current project is a CJ-7 mud bogger, with a Buick V6 Stage 2 race motor (approx 525 HP, and weighs only 300 pounds). So far, I have also collected a pair of Dana 44 Scout axles.

I hope to use the stock Dana 20 transfer case, along with a 4x4 truck TH350 automatic trans. Plans also include front and rear spools, and 38 x 9.5" Bogger tires.

My question concerns choice of front and rear axle ratios. I note that dedicated mud trucks often use a lower (numerically) ratio up front for greater front wheel speed. What would be appropriate for this combination?

Any comments would be appreciated. I chose the Dana 44's for lighter weight, and lower drag. 525 HP is not really that much - will the 44's survive?

Thanks,
Terry from Starbuck, MB

well.... i have no mud racin experiance but i do know a lil about D44's (key word here is little)... with a D44 like any other diff, axle shafts and u-joint's are the first weak link followed by the locking hub's then stress move's inward to the crown and pinion and up the driveline from there... good quality axle shafts are a must and they are a waste of money if you dont have good u-joint's...

my dream combo for a front D44 is superior axle shafts with drive flanges and super-joints (sold thru randys ring and pinion or directly off pirate 4x4) locked by a ARB or detroit electrac all spun care of 4.56 or higher (numericaly lower) gear's.... good gears tho... like original dana spicers not them cheap "quality gears"... with a standard D44 gear set the lower the gear ratio the smaller the pinion size... if your wanting to build something strong then stay in the 4.10 neighbourhood... avoid the 5.13 crowd... heres a link i like to show people... not trying to sell you a ford 9" but if you look at how everything compaires... well... its a good bit of info http://performanceunlimited.com/illustrations/gears.html

the rear D44 i know theres alot of aftermarket parts.... i have heard good things about the aftermarket axles... so my guess is they can be built "fairly" stout.

nothing good can come of fully locked stock parts with alot of HP and a heavy ass tire IMHO... theres exceptions made for the guys who run 44"s on a stock D44 diff with a 454 and a huge nawzzzz bottle and say they never break nuttin... i belive em... i just dont drive like them

spool's are cheap and i see no reason why a mud bogger cant use em in both diff's... maybe rusty has sumthin to say bout this?

D20's are sorta like a mini NP205... all gear driven cast iron case... i have a early bronco D20 on my bench in the shop... cute lil bugger... look's like it would have came out of a tracker er sumthin tiny... other then the small 1310 yokes that are on mine i think its gunna be a fairly abuse resistant t-case in my 6000lb SUV.... there are aftermarket 300M tail shaft's and assorted yoke sizes for them too... good piece of driveline IMHO

light weight does help to a certain degree... i dont think you will have many issues if you blow some $$$ on beefing up the driveline a bit.... even just some good spicer life u-joints in the front axles and make sure everything look's in good shape.... fix it, race it, break it, repeat :p

Thanks for your comments. I hadn't thought about the pinion strength when in the 5.13 range - I'll take that to heart.

Any experience with Yukon Gear products?

Regards,
Terry

aint never used yukon but the people online who do seem to love there axles and gear's... and randys ring and pinion sell's all there product's and i know randy's has an awsome reputation for quality and service...

strange/U.S gear (or the canadian version of the exact same product www.bearsperformance.com ) is good stuff... i have heard nothing but good thing's about there axles and the U.S gear line.... i have seen strange/bears axles and held em in my hand... nice stuff.

i aint gunna say much about mix and matching gear ratios for front and rear tho... my brain cant decipher any logic in that.... unless your running 2 tire sizes like a 44" bogger on the back and a 35" bogger on the front one end turning faster then the other will just cause binding in the driveline...

Well the d44 choice is good. your always runnin straight (well kinda) so they hold up great. I only break then when I go airborn and don't lift on the skinny. Miss match yuor gear's only if your mis matching tire size. If your thinking of over running the frt tires for lift you can but I have not had any improvment with that. Some will argue this but I tried it and went back to matched ratio. Who came up with the numbers for your engine? Not to insult you but they do sound a bit far fetched. You may want to consider a wider tire to displace your wieght a bit better. As for your ratio in your d44 What is in it now? I personally would put it all togather run it see how it reacts and make my choice then (unless it's like 3.08 or some other tall gear) My personal choice is 4.10 due to the pinion doesn't look like a throwing star (5.13 pinions are getting weak) and if I am racing a long way from home I have a better chance of finding gear parts if needed! Oh and if you find it underpowered with 4.10 gears drop oh a bunch of giggle juice on it and watch it make 38" tires into 44s in no time!!!!!

Thanks for the good advice. It's good to hear from someone who has "been there, done that".

The D44's I have are 3.23 and badly worn. Maybe I'll start with the matched 4.10's as you suggest.

I'm not sure about the weight of the motor - 2 guys can carry it easily, and it has aluminum heads, etc. This is a 274" Busch Grand National race motor from the 1987/88 era.

About the tires - I note that the faster runners locally use narrow tires. This is in well prepped pits in Southern Manitoba. Are mud conditions a factor in tire selection? Also, I'm thinking I will have a narrow track, combined with narrow tires, that won't give the next guy a "groove" (that fits) to take advantage of. This is my own, possibly stupid, idea. Can this be a factor in competition?

Regards,
Terry

3.23 wow ya I would start with the 4.10 ! I have never been sold on skinny tires for racing I had the 9.50 36 swampers and they would dig to china. I went to 12.50 same thread had lots of e.t improvement then it was the 14.50/35 on a 15 by 15 rim and it really started to float. I settled with 35/14.5 boggers and it was a hold the #$%% on improvment. After that I cut them, that was a huge difference. Now you thoughts on "leaving a trail", well if your running the power you figure your running it won't matter as long as you pick a good line. If your digging ruts and the guy behind you get to run them, well to be honest with you your going too slow and won't be winning. The whole idea of it is to get up on plane like a boat use your front tires to steer and aim your way to other end. Ever notice the fast guys usually don't have tonnes of mud off the frt tires (in a well built pit). It's ussually a spray. Front tires are for the launch and for the guiding of the rocket. Took me a long time to get mine to do this, once I got it working right I had alot of fun! Then I wrecked now I have a bunch of work to do. Tell me about your engine!

Again, thanks for your interest, and all the tips.

I've been drag racing for many years, but a trophy second time out in my daily driver ('96 Cherokee, with 32" TSL's and lockers) got me hooked on mud. My "spare" Stage 2 motor has been gathering dust, so I thought I would put it to use.

The Buick V6 Stage 2 can be an expensive motor to build, but I lucked out and got a complete one from Muscle Motorsports in North Carolina for a very low price. They seem to specialize in used NASCAR motors. You can check them out at www.musclemotorsports.com

The motor I will be using for mud is a Buick Motorsports Stage 2 on-centre block with 4" bore. The crank is a forged Buick Motorsports piece with 3.625" stroke, for a displacement of 274". Rods are 6.5" Carrillo's. Pistons are JE, but I haven't measured the compression ratio (I believe oval track racers run a fairly high CR). Heads are Buick Motorsports Stage 2 aluminum with killer porting, port plates, etc. It has a roller cam that I haven't measured yet, Jesel individually shaft mounted roller rockers, triple valve springs, titanium retainers, etc. It also has a complete Peterson dry sump system (minus the oil reservoir), racing alternator, mini-starter, crank trigger, etc. All it needs is a good carb, headers, and a flex plate.

When I pulled the pan on this motor, everything looked so fresh I just put it back together again. The various machine shop stamps on it suggest it has been freshened at least twice, but the bearings are still std/std. I'm really looking forward to testing this thing out. These motors have a distinct sound you usually don't hear at a mud race.

BTW, I agree with your philosphy on nitrous. I've run it for many years on various cars, and always had good luck with it.

Sounds like a sweet engine!

Mud.... can be fun, but FAWK I hate the clean up after.

Oh good you have been drag racing before so you are not a cherry on being taken to the cleaners on high performance parts Nitrous should be apart of the four food groups lots of my stuff has it or has had it (ride on lawn mower) Even my tracker has plans of it. I am going to double the hp to 8hp oh ya your motor sound like a bunch of fun. What carb are you thinking?

Terry...I'm busy as hell right now and can add a lot more but I'll shoot ya what I can.
Yes...run a faster ratio in the front. I did for years with great success. 10% faster is the target for a slower machine.
I like where you're going with this.
Light weight is pricey but good. I won a lot of races with light weight and less power than a lot of other guys.
I'm not a huge fan of D44's in the rear but it will work for you if you keep the weight down. A Scout 44 in the front is a bit of overkill for you but will last forever.
If you can...get rid of the front brakes from that 44. IH calipers are really fawkin heavy. Rob some parts off a Chevy 4X and put the (front) brakes on the rear diff only. You will have plenty of stopping power. I ran this setup for years on a blown alky buggy.
Front weight will hurt you with that short wheelbase. It will "porpoise" on you. Nose will dig then bounce up and so on. If rules allow...add rack and pinion steering and kick the front diff ahead 18" or so. Move motor and tranny etc. back as far as you can.
My mud Jeep....took so much weight off the front that it would go through the mud with the nose up about a foot. Almost zero traction up front...just enough for steering.
Nice motor but a little shy on torque. Run at least a 3500 stall converter. Run a tranny brake if you can....very important if you are running leaf springs. As you may know....the leafs will wrap up on a foot brake start and bugger up your IC and anti squat values.
For you...in a 200 ft pit...figure out all your gear ratios, engine R's etc to give you about 75 MPH wheel speed. Should be 1st to 2nd shift only in low range with 4.10 in the rear.
I build rpm activated air shifters for the autos. One of the best things I ever did for consistant times.
The D-20...almost as light as a chain drive....it'll work fine. I know guys running over 1000 hp through them.
Tires...My favourite combo...35X16X15 in the rear and 33's in front....gear ratios to match that will give you the 10% or so faster in front. This helps you launch straighter and helps pull straight through out the run. They prolly won't let you run cuts in the lower class.
Use alu wheels...as light as you can buy....try to keep the rotational mass down as low as possible. Cutting the tires will take over 40 pounds off each 35" Bogger.
Heavy tires and wheels are what kill most people. I will beat all their collective asses with light tires and wheels and plenty of wheel speed. You add the big weight and you need to add to everything else....pretty soon you have a 7000 pound monster that can't get out of it's own way.
Keep it light brother...if you decide to put something on your Jeep....put it on the bench first...if it doesn't slowly float up into the air....it's too damm heavy to add to your Jeep I'll help ya some more if you need it....later...I'm swamped right now.

Thanks, guys. Lot's to think about here.

For carb choice, since the intake is set up for a square bore, I was thinking a Holley or Demon in the 650 CFM range. I know EFI would be better, but from my drag cars, I know how expensive it is. Is there a square bore carb that works better than others in the mud?

Hi Guys,

Thought you might like to see the progress on my project. I have a couple pics on Photobucket...

http://s275.photobucket.com/albums/jj293/terrypenner/

I have been pretty much following the Hairy Kanary recipe so far.

Thanks for all the help!

Regards,
Terry

Hey there! Hope the build is going good. As for carb choices I'd go with a Holley but install a "
trick kit". It is easy to do. I've done a few of them and the Jeep will run nearly anywhere!! Hairy Kanary will agree as He's my dad and has seen it himself. I had a Jeep Tuff truck racing with a Holley 750 with the kit and it never misseda beat. Much airtime too!!Lol I'll be running the same on my new Jeep build too.

Thanks, the build is going great! Just doing the roll cage now. Should be ready for Spring. A buddy donated a Holley 780 double pumper, so I think I'll try that first. It came with a trick kit box (haven't looked inside yet), so I'll add those parts if they aren't already in. What kind of Jeep are you building? Regards, Terry