1973 dodge Indian, motor 413, 4.56 gear/pinion change?

[browng]

question
the rpm at 55 mph is near 3000.   loud, can't talk to passengers,  the M-series trucks I drove were quieter.   I used the speed-gear-rpm calculator and compared to what was on the tach.  real world - rpm was 5% higher.   non-lockup converter; math and testing made sense.   so using max torque 2800 rpm i ran these gear ratios      32 inch tires,  Dana 70
{on low hills from a stop, it can accelerate at under 2000 rpm}   
gear     2800 rpm         mph              2000 rpm           mph
4.56         "                 58                     "                    41                 
4.11         "                 65                     "                    46         
3.73         "                 71                     "                    51             
extra notes;      going faster than 55 when going down hill (or falling off a mountain)  otherwise going 55 w/ horse trailer, w/o trailer...... 
1st idea was to go with 4.11,   55 mph is 2400 rpm,  then a car builder friend  suggested 3.73   
2nd idea, go with 3.73,    55 mph is just over 2000 rpm,   

the 413 industrial is a torque monster   the 3.73 will keep it below max torque and there is room to add gas/rpm 

what say you.

funny story;  asked Dana for their advice.  the 4 wheel drive tech said he would stay with the 4.56 and with those fast starts.   i asked him if he ever sat on top of his jeep motor at highway speeds.  He never noticed how loud his rock crawler was.    and i asked if there was RV drag racing.   He couldn't adapt.

[Mlw]

As for the R.P.M's, yep those are the specs, there's a reason we secretly all want overdrive or dreaming of changing the gearbox for a 4 speed with overdrive. Why, i'm even dreaming of changing mine to a manual.

It's an RV of 49 years old, and that's just how it was. Especially the slipping converter can be a real pain in the backside.


There is just one other question that comes to mind. How is the sound insulation of you Dog House. If there are holes in it, it's not working anymore. (Sound) isolating the floor will help a lot too.

[browng]

sure, but you didn't answer the question. 
change to a 4.11 or to a 3.73

[Eyez Open]

Do you have the power curves for this 413, along with the weight of your RV? I would expect your current gearing is setup to operate this engine at maximum torque at hwy speeds.

Gearing can make a big difference in economy but high tourqe at low rpm is needed.Compression ratio is also a big factor.

[browng]

book - max torque is at 2800 rpm    but this is not a normal gas engine.   The industrials' reach max torque at 2800, at 2900 SIGHTLY less, at 3000 drops a little more.  and so forth.  NEVER really drops off like a 440 would. 
there is not a real loss of torque above max torque rpm.  Becomes a waste of fuel.  *******      also max rpm is 4000 rpm.    it's not a red line value of 4000 rpm.  (edlebroke carb, rebuilt motor and trans)  peddle to floor and 4000 rpm is all.   
burns rubber at take off. 
weight 8000# - 9000#  (memory)
I remember this- in 1973 highway speed was 70 mph,  though Dad drove 80 on I-75. 
the engine builder (Oregon Slant-6 drag race champion)   was shocked when he learned the rear was 4.56.   "That's what you would put in dump trucks and UPS trucks that never drive out of town."   And, when driving around town 35 to 45,  engine feels like its idling.   if not going too fast.

one more bit of trivia;  I read that Winnebago got a sweet deal from Chrysler to use up those 1973 chassis.   

CHANGE TO A 4.11 or 3.73

******  think of a black powder rifle,  I can measure the powder load for a 'perfect' burn INSIDE the barrel.  OR add more powder that burns OUTSIDE the barrel.  lots of smoke, public loves it, doesn't push the ball faster.  it's done gone.

[Eyez Open]

1962 - 1965 with 4 Barrel Carb
Max Brake Horsepower: 340 @ 4600 rpm
Max Torque: 470 @ 2800 rpm
Stroke: 3.75
Bore: 4.1875
Compression: 10.1
Firing Order: 18436572

https://www.enginefacts.com/chrysler413/



Would the above be your engine? Do you have a preferred cruise speed?

That would be a lot of engine and gear ratio (4/56) to move 9000lbs. Would you know by chance if dodge used the same power train combination to carry larger heavier trucks or RV"s?...Your transmission will build up pressure under high loads low rpm.

Made simple if your powertrain runs a rig setup for 12-14000 lbs with a 3.73 that  might be a ok experiment..if not the 4.10s... The 3.73 are going to generate more heat, premium gas and who knows what mileage gains.    But sometimes one just has to go there..tread carefully

73

[browng]

preferred cruise speed   55 mph,   w/ or w/o horse trailer,   [personnel experience; i catch up to all those speed hounds by the next light or next traffic congestion, or a gas stop along the way, and often re-passed by same hounds an hour later, AND i seldom move out of right lane. ]   

It continued to see use in Chrysler mid-size and large trucks until the end of 1972.    this is a dump truck chassis disguised as a 1973 Winnebago. 

727 trans was used in everything   heavy equipment shop that will change the gear said the 727 trans was never going to be an issue. 

rear axle is 12000 lb rated 

shop was not against the 3.73      there was a big box van in the shop,  2020 model,  smaller engine and 3.73.  larger payload. 
shop wanted me to enjoy driving the Winny,  they are more confident with 4.11,  but since my motor can run the pumps at Grand Coulee Dam,  3.73 would work.   

[Mlw]

I didn't understood at first that you really wanted an answer for me about the ratio, sorry.  I do think you should consider better sound isolation.

For me, I like my engine to have torque, but I really do understand your wish to lower R.P.M's at cruisin' speeds.

1. I read that you don't have a lock converter, I've read about it a lot and seems to be able to lower the R.P.M's at your current setting 250 - 500 R.P.M. What I don't read about it is how it holds in our beloved heavy bricks, certainly with a horse trailer behind it, but would for me be another consideration if I just could find the right information.

2. When you go for a heavier differential, I think the slip of the converter will become more of an issue, certainly with a horse trailer, and therefore higher transmission fluid temperatures up till it burns.

It all comes down in what settings you use your RV the most. When it's mostly flat roads and cruisin' and you don't mind your RV becomming more sluggish then you could consider it but i guess you won't be to happy when you are driving in a mountain area with only 3 gears and no overdrive.

If you are going to put in the work, maybe this is another option to consider
https://www.classicwinnebagos.com/forum/index.php?topic=744.msg27239#msg27239

[browng]

thank you mlw
our passes around here are steep,  shifting to 2nd is fine and normal.   our 1st RV, 1982 Jayco would be in 1st and 15 mph,    but on flats it hummed at 65  but usually did 55.

I added a trans cooler.    {impression, engine runs cool even at 55.  it has correct stat.  it's just not taxed.}   {i would put a semi 12 speed manual in}

locking torque was not do-able.  i looked, shop looked

sluggish is ok,  it's a huge shoe box.   i watch our log trucks take off. they don't jack rabbit.  to me that is normal for a its size.   but my RV will squeak tires  W% at take off and beat everyone to the next light.

my view;  fast jets kill slow jets, but fast cars kill the driver plus others and that doesn't help me complete the mission.  Unless you are Russian, then drive faster. 

[browng]

more data for this motor

413 industrial  -  60000 GVW       30 tons! wow

working torque band   2000 rpm to 2400 rpm         

[Mlw]

Yeah well, the 413 is a big block so no wonder it squeeks tyres.

I think you've made your mind up yourself go for the 3.73 It can't get more worse then your first RV.

[browng]

we are going with 4.11.   DANA does not make a 3.73 that fits a 70HD.   DANA also said that 4.11 would be the best fit.  DANA rep said that we did not hear this from him, but the 4.56 should have never been put in it. 

now we a rear u-joint
cup 1.23"
outside cap  4.1"
inside snap ring 3"

[Eyez Open]

I tend to agree, it takes time and it's expensive to change up gears on a assembly line. What was on the shelf works quite well.

[73WinnieB]

I'm doing 3.73:1 in my 73 winnie but I'm also doing a diesel swap. Local shops were quoting $2800 for my gear swap... so I bought a 3:73 dana 70 hd and will adapt it to work for me. As long as you have the torque to pull it, those gears will keep the rpm down and as long as you're not gassing it alot to keep it moving, I would expect a mileage increase.

[browng]

got new 4.11 gear in and drove,  WOW WOW  WOW ...........

Math said   gear 4.11   will be   2800 rpm= 65 mph  and    2000 rpm =  46 mph           
Math said   gear 4.56   should be   2800 rpm= 58 mph  and    2000 rpm =  41 mph    (WHICH SUCKED) 
                                           real world was  3000 rpm = 55 mph   
(math and real world was not going to be perfect match)

Drove winne at highway speed AND     2500 rpm = 55 mph   (real world)   could accelerate if needed,  got to 55 the way I expect a big BIG shoe box would. (or log truck)
AND low low noise level.   My 7.3 may be louder at 55 now.      [Old gear system noise level was about the same as the cargo bay of a C-130.]

Funny reaction from me:  kept looking at gauges and tach;  "is motor still running?"  "what was that noise in the cabin?"      "is motor running?"   

[Eyez Open]

 

[Mlw]

And... How does it handle in the mountains 

glad it worked out for you and that you are happy 

[browng]

3rd gear most of climb,  2nd when we hit the switch-backs (lots of and lots of),   2nd when behind a log truck but we can pass when we reach a passing lane (what few there are)   loggers go about 40 mph MAX. 
except taking off faster out of the switch-back with the 4.56, not much changed in the passes with the 4.11.
     
HGWY 20, 34, 58 are two lanes w/turnouts and passing lanes.  lots of semis on 58.  lots of loggers on 20 and 34.  lots of sporty cars in ditches.  going fast is difficult for RV and campers.  Pass one semi and come to next switch-back and there's the next semi.  OR get to next switch-back, and a sports car is on top of guard rail.
I'm off duty and those guys are working.  Just need to be faster than them so's not blocking them.
  next summer planing on an aluminum horse trailer.  that's 2000# less,  (until Mrs fills it up )

[eXodus]

Interesting experiment.  I had thought about all those 4.56  4.11 etc.

But I went with 4L80E transmission 4 speed on a 454 - so the 4.56 work very nice while towing 5000lbs horse trailer (fully geared up with the horses inside)
It was just above 2000 RPM at 55mph - which is not ideal - you have torque - but not enough HP at that point for towing. So at any slight incline it would get slower and downshift (loud)

Let us know some towing experience with this setup.