Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Topic: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270 (Read 5317 times) previous topic - next topic

Re: 8.3 325hp mechanical torque and hp curve

Reply #75 – October 20, 2014, 03:39:41 am

Bob, How about a picture of this wheel, I have the 5.9BT CAC using the Bosch inline injection pump in the FL60 Freightliner rated at 190 hp, does fine, but moe fine is OK too.

Re: 8.3 325hp mechanical torque and hp curve

Reply #76 – October 20, 2014, 08:33:46 am

Cutaway of P-7100, showing items being discussed. Ignore all the Bubba comments after the first couple posts...

12 Valve AFC Mod's - New England Turbo Diesel Power

Re: 8.3 325hp mechanical torque and hp curve

Reply #77 – October 20, 2014, 09:33:34 am

Thank you Chuck, that is a great break down.

Re: 8.3 325hp mechanical torque and hp curve

Reply #78 – October 20, 2014, 11:11:23 am

Thanks Bob for the star wheel explanation and Chuck for the great link to the cut-away pump.

I once saw a tech remove the plug and adjust the star wheel, which I think I now see what happened.

It seemed the star wheel was mounted facing the rear of the coach with the turning toward the side of the engine.

But in a separate action the tech used a T-handle long male hex tool to reach in and turn one or two screws.
Don't know if a cover plate was removed before reaching to the screws. The tool was positioned toward the side of the engine. Do you know what was being adjusted with the T-handle hex wrench?

Also in Chuck's cut-out link, I am not sure how the cut out is oriented to our motorhomes.

What is top and what faces the rear of the coach (front of engine)?

Re: 8.3 325hp mechanical torque and hp curve

Reply #79 – October 20, 2014, 11:19:59 am

Ya'll are getting into stuff few people really have business messing with. These guys that crank up all the stuff on their pickup trucks are playing a completely different game than us. A) few of they actually pull any weight--their trucks are 5,000lb B) They are ignorant to the long term reliability problems they are causing.

Turning the "star wheel" doesn't increase power. It adjusts how much fuel is allowed to the engine before full boost is built up. The purpose of this is to reduce black smoke on acceleration.

Changing/removing/adjusting the fuel plate changes the max amount of fuel that is injected. At the 325hp mark, mine is pretty far up there.

More fuel can be added to make more power. Changing the fuel plate gets to a point, then displacements and what not inside the injection pump need to be modified.

I have a friend that overhauls injections pumps and injectors. These devices are very complex and take a lot to set up. "Just turning" a screw or nut here and there doesn't even begin to explain how much you can mess the fine balance of a perfectly running engine up.

BUT, if you understand what is going on, how all the components work, and totally realize the risks, then you can crank up the fuel and get more power!

Re: 8.3 325hp mechanical torque and hp curve

Reply #80 – October 20, 2014, 11:25:40 am

Looks great. Someone must have a downloadable fuelplate template(s) to allow easy copying. Nice to have a template with a HP/torque graph included for each profile. Looks pretty easy to go overboard.

If the pump were mounted in a PU, what you are looking at would be facing the back of the PU. In a diesel pusher, it would face the front of the coach. The opposite end away from the engine crankshaft pulley. The pump plugs into the timer driven off the timing gears/chain. The top is up in the photo.

Has Dodge every put a strong trans in anything?

Pierce

Re: 8.3 325hp mechanical torque and hp curve

Reply #81 – October 20, 2014, 11:56:26 am

Cummins engineer at a show long ago mentioned Chrysler had asked about turning down the torque on the early 5.9's.

Re: 8.3 325hp mechanical torque and hp curve

Reply #82 – May 14, 2015, 10:08:50 pm

To give an update to this project. I just did a 20 mile test drive down the interstate with my 4.33 rear end that I installed. I now have a 80-85mph coach with no sweat! But, my goal was to get around 75mph at 1800rpm in 6th gear. Well, 1800rpm gives 74 mph; exactly what my calculations predicted in the spreadsheet I put up earlier in this thread.

With stock 5.13 gear I had 62mph at 1800rpm in 6th gear, now it's 74mph 6th gear 1800rpm. And it pulls the minor hills we have around here no problem. I was speeding up to see how everything felt and I looked down and was doing 82mph!!! I couldn't even tell. The engine was only at 1950rpm!

My vibrations also seem to be gone, and I believe this is due to the slower spinner driveshaft.

There is a tiny bit more noise and gear whine. This is because I got a used differential out of a truck and it doesn't have "coach quality gears" that are very polished. I touched up the gears a bit, but the whine is hardly noticeable; with the radio on, it is insignificant.

I'll run it around for a while and see how it handles the rockies. I might should've gone with 4.11! Anyway, so far I am highly pleased. I can now run 70mph and the coach loves it.

Re: 8.3 325hp mechanical torque and hp curve

Reply #83 – May 14, 2015, 10:34:12 pm

I used to add heavier rear end oil to curtail the sounds on 300 cat oreds.

Re: 8.3 325hp mechanical torque and hp curve

Reply #84 – May 14, 2015, 10:47:48 pm

I swapped the rear end out on my own. I had to pull the yoke off the used rear that I bought and install a closed yoke. I just bought a new yoke ($100) because I didn't want to mess with the existing rear end in case I had to reinstall it. The diff weighs 250-300lbs. I used a harbor freight motorycle lift to install it--plus some nice redneck rigging. It's not that tough of a job, but it takes some thinking and some muscles.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #85 – May 15, 2015, 12:23:56 am

I was told that after enough miles the tooth finish polished itself smoother.

To reduce the noise a reset of the backlash was necessary if memory serves me.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #86 – May 15, 2015, 08:05:10 am

Would be great to have a factual comparison of climbing ability (same hill, same entry speed, speed at top and gear/RPM at the top) and MPG.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #87 – May 15, 2015, 09:01:11 am

Quote from: wolfe10 – May 15, 2015, 08:05:10 am

Would be great to have a factual comparison of climbing ability (same hill, same entry speed, speed at top and gear/RPM at the top) and MPG.

And would I get all that data without spending a week driving around various hills and gathering information both before and after? I have a mechanical engine, real time MPG isn't practical. I did post facts of what new RPM vs MPH are. And I posted a spread sheet with the calculations showing what changes in RPM will be for given MPH in respective gears. The calcs match up to what I observed on my test ride regarding RPM vs MPH readings.

Subjective observations show that there is plenty of power on the highway....which makes sense, because gearing was analyzed against dyno data given by cummins.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #88 – May 16, 2015, 10:11:56 am

Pictures of the process, sort of, LOL.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #89 – May 16, 2015, 10:49:56 am

Krush,

Are those magnets inside the housing not far from the drain plug?

This still leaves you with a closer set of ratios than our 4 speed with a better first gear and a taller sixth gear than our fourth gear so better fuel mileage. I expect you will be very happy with it on hills.

Pierce

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #90 – May 16, 2015, 10:57:48 am

Admire your work. Krush. And great photos!
jor

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #91 – May 16, 2015, 11:05:34 am

Quote from: Pierce & Gaylie Stewart – May 16, 2015, 10:49:56 am

Are those magnets inside the housing not far from the drain plug?

The rectangle are indeed magnets. The pictures shows "as found" before I cleaned them off. I'll get some miles on it and see if maybe I should've done 4.11! Regardless, the 4.33 is a HUGE improvement.

I got all the tricks figured out for swapping it out now. I had to do this evolution twice...the first diff they sold me was the wrong one! And I'll freely admit I should've have double checked to see if the axles fit on the floor before installing it--I know better. Anyway, the second install of the correct unit went much smoother.

The only other step was swapping yokes. It took a bit of figuring and trial and error to get the tooling right, but I used the wheel lug multiplier I got a while back and had to buy a 1inch drive 35mm socket. The nut for the yoke is 1000ft-lb. Then I just used a two jaw puller to get the old yoke off. Installed removed and installed a new seal.

Now, the 2 jaw puller didn't work for the closed yoke (the leadscrew wasn't long enough). So I made a special tool, like the OEM one. A piece of pipe with two holes in it that fits in the closed yoke part, and just put a steering wheel puller inside the pipe. Pulled it right off. Now with all the tooling made and available, the task isn't that complex---but still bull work shoving 300lbs around!

Also, first install I used what Meritor calls for in manual, 5699 RTV (and what they originally used). But second time I used Loctite 518 anerobic. RTV is a pain to clean and doesn't give me time to assemble. 518 also doesn't cure when exposed to air, so excess inside doesn't make a mess.

The one picture is of the removed 5.13 unit with polished gears. There are definitely polished and very smooth. But for less than $500 all in (minus labor), can't beat a good used unit.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #92 – May 16, 2015, 12:36:19 pm

Awesome project, and great photos. Certainly not recommended for the "average" shade tree mechanic (like me)...

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #93 – May 16, 2015, 01:27:13 pm

The 4.11 would lower highway revs a bit but raise EGTs some at the same speed and decrease coolant flow. You might end up spending more time in a lower gear. Think you made a good choice and good documentation too.

I would love to bring our 60 mph revs down about 100 rpm but with our four speed, it would make first a little taller than I would like. Right now, it's too tall to climb our driveway so have to back up it.

Pierce

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #94 – May 17, 2015, 04:08:25 pm

When we were drag racing in the sixty's we used white lead to set up a rear gear.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #95 – May 17, 2015, 04:17:59 pm

The old school newspaper method is the best--- set up the gears so the paper is crimped as you rotate it through the gears. If it cuts the paper it's to tight, and if it doesn't crimp the paper it's too loose. Works every time.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #96 – May 17, 2015, 04:55:36 pm

Yes and you can position the contact area where you like on the ring & pinion for a long lasting quiet setup.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #97 – December 28, 2015, 06:50:45 pm

End of year update. I have about 15,000 miles on the 4.33 gears and am totally happy. For rolling hills I manually select 5th gear and it handles them great. For real hill climbs, down to 4th and just climb the hill at 2200RPM and 59mph. No noticeable gear noise.

On the level in 6th gear the engine just purs along at 70-75mph with plenty of power (1800rpm). 60 to 65 is even lower rpm with plenty of power.

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #98 – December 28, 2015, 08:26:37 pm

Figured the 4.33 would be perfect. Glad you like it. How about mileage? Would think it would be good for one more MPG. Always satisfying to do it on paper and then have it work out perfectly.

Pierce

Re: Rear end gear change from 5.13 to 4.33 on 8.3 Cummins u270

Reply #99 – December 29, 2015, 09:52:25 am

I think mileage may have improved slightly. But, it's not a fair comparison because before I was driving 62-64mph and now I drive 70-75. So any increase in mpg was lost due to increase in average speed.

I seem to be getting 8.5 to 9mpg. But again, I cruise 70-75 when able. Top speed was about 95mph, for those that are curious.

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