Nice, stock class at KOH is something i have been eyeing to race as well.
A couple of ideas/recommendations/suggestions...
I think you are on the spot with the axle selection (HP D44 and D60) and increasing track width a bit, Although you might lose a little ground clearance with the Dan60, it will be easier to truss and having FF axles stronger for sure. I would suspect you are going to run a 3.5" lift or less to try and keep the COG as low as possible. There might be some clearance issues with the high-steer but obviously you will have to check - assume your going long arm/links with the three link and will stretch the front a few inches so that will help.
I am considering trying to get a Dana 60U (E-series rear end) from the junk yard to run instead of my older Dana 60HD since it would only cost me ~$125 and get me disc brakes, slightly bigger axle tubes, 32 spline axles, large bore spindles, and more ground clearance since the Dana 60U has the smooth bottom casting. It should have about the same WMS width, the only problem is I haven't seen one on my last few junkyard trips or I would have snagged one already.
I want to try to keep it in the 3-4" lift range to keep it lowish, but I also want to run 14" travel shocks, so it is going to certainly come down to packaging and be a compromise between wheel travel and ride height. The wheelbase must remain within 3" of stock (95" max for an EB), so I am notionally planning on 1" forward in the front and 2" back in the rear. I'll have to see what everything looks like when I start mocking it up.
I would look at lower gearing - i know its expensive but will solve a few things and save money in the long run, at least for the first race. 4.56 would be minimum i would look at. You will still be able to push it up to speed in the desert, but it will also help your crawl ratio without necessarily having the use the lower Dana20 gearset and would make the transmission happier. I would save the $ on the D20 low gear kit and put that toward axle gearing/lockers personally until you could go atlas...
I think the C4 should work great with the upgraded mods that can be done to it, I would look into the HD input shaft as well. We have had great success in our races even at lower speeds using a shrouded Fluidyne cooler with a fan, it was expensive but its built like a tank, moves a massive amount of air and works VERY well. I looked at allot of coolers before pulling the trigger on the Fluidyne, but know packaging and location will be key for your build and there are allot of quality options.
We are running 1800-1900 stall with our custom HD Torque Convertors, works for us but we run high speed mainly, don't know the Hughes stuff as I get ours made locally.
Also for the C4 and Dana20, tap and add 3/8 barbed vent lines to both vents - then run the intermediate vent (which is the transmission vent) to a catch can somewhere above the transmission, maybe behind the driver or passenger. No matter what you do that c4 will barf fluid and needs a place to go. We learned through several races there was no stopping the puking regardless of temps. We are venting the transmission into a 1 quart aluminum catch can that attaches to the bottom of the can - then running a line off the top of the can to the rear and put a breather filter on the hose to allow the trans to breathe. This allows the transmission to barf into the can and then reclaim it when it cools.
Don't bother to use the Lokar transmission dipstick, either use the stock dipstick tube and find a locking dipstick top, or buy one of the aftermarket C4 dipstick tubes and extend it. The Lokar doesn't allow you to fill up the transmission fast enough - its a really big pain and especially a painful issue during a race and even just in the shop.
I will admit, I am an automatic newbie; literally everything else I have ever owned had a manual transmission. I really appreciate you sharing your build and things you've learned; I am sure it'll save me a lot of headache discovering those issues on my own!
Based on my experience in the rocks driving other people's rigs with autos, I think I want close to a 50:1 crawl ratio at a minimum. Now, how I am going to get that gearing is something I have been going back and forth on a lot in my head.
The crawl ratio with a stock C4 and Dana 20 with 4.10s comes out to 24.8: 1. No bueno for sure. Now, even if I geared down to 5.38s (the lowest available for a HP D44), that only puts me at 32.6:1, and the motor will be screaming across the lake beds where most of the stock class guys are hitting over 70MPH (even the Toyotas ;D). Even if I put the 2.9 gear set in the C4 with the 5.38s, I will only have 38.4:1.
I don't think I can get adequate gearing for the rocks without addressing the transfer case; either a lower gear set, or an integrated doubler setup like Northwest Fab sells. If I put in the 3.06:1 Dana 20 gears that Jack O'brien sells, the 2.9 gear set for the C4, AND 5.38s, that will put me at a 47.7:1 crawl ratio which should be decent, and I think his 3.6:1 option would be too much of a gap between high and low range.
On the flip side, I could run the integrated Dana 20 doubler from Northwest Fab and the shorty 27 spline C4 adapter from Advanced Adapters (only 1" change in drivetrain length) along with the stock C4 gear set and 4.10 axles. That would give me a crawl ratio of 67.2:1 in double low. I could run over 40MPH in single low range on easier rock sections and just pop it in double low for the obstacles that warrant it. Additionally, the doubler route would end up being significantly cheaper than re-gearing the transmission, transfer case and axles. My main concern with the doubler option though is that the relatively high axle gear ratios would put added stress on the driveshafts and transfer case, and transmit more torque to the chassis. Additionally, it may make the rig a bit of a dog in high range.
I also considered an Atlas vs. building up a Dana 20, but the biggest thing turning me off aside from the high buy-in is how low you have to clock them in an EB chassis. I think I can clock the Dana 20 up enough to get pretty close to a flat belly and just have a nice, big flat skid.
Like I said, I am still torn on the gearing. I already have the install kits for the Dana 44 and Dana 60, so it would just be a matter of buying the gears at this point.
We are using the Heavy Duty Advanced Adapter housing for the Dana 20 with a 1350 flange (and double cardon 1350 driveshaft), suggest the same if your sticking with the Dana 20 - obviously your upgrading your rear driveshafts to whatever you are going to run so just sharing.
How much suspension travel do you guys have? I think 1350s would be strong enough, but I have been thinking about 1410 driveshafts purely to avoid driveshaft bind at droop.
Your engine should be perfect for the stock class, I would consider looking at a HD oil cooler and if you are going to run the stock front clip (which i think you do in this class?) then you will need to relocate it to the rear somewhere which opens up size options. I also would not run anything less than -10an lines to that engine cooler. I just got done upgrading our oil cooling setup on the racer this last week.
Steering box - although the 4x4x2 box is heavier duty than others - i would run a sector shaft double shear - Solo motorsports sells one. (I just installed one on our racer)
Also I would double shear the pitman arm to drag link end.
Good advice and things I am already considering.
Anyway, i know allot of this stuff your probably aware of and/or have planned. I am just sharing as I am jealous of the effort and plan. I really want to do the same thing but already have one racer
