Thank you BigErks. I live in Arizona. My next question is going to be what gauges should I install as there are only minimal gauges (automotive style) in the truck. I guess I'll post it now, although talking to you guys is going to cost me $!

 

boost, egt, and water temp is what I use. EGT is by far the most important. I remeber when I got my truck I pulled maybe 5500 lbs about 300 miles, and stock they do it, but just real real slow. Modified is a different animal. In oem trim with maybe 12500 gcvw I was going up baker grade at about 35mph.....now,I pull 28-30 lbs gcvw and go about 66mph up baker grade.

If you change the gears without making substantially more power, it will die on hills.

 

I have Autometer z series boost and egt gauges. Get a 60 psi boost, both gauges will run you about $200. Alot of other mods that will get some reliable oomph out of your truck are relatively free (Fuel plate: grind your own, boost elbow: $20, 4k gsk:$17 spring since you have a 3k already, timing bump: just need the right tools). You need the gauges to see what your engine is doing and it makes solving little, and sometimes unnoticeable issues alot easier, like a leaking boot or stuck wastegate, both of which can potentially trash an engine.

I wouldnt change your gears as of yet until you get the engine tuned, you might prefer to run a higher rpm. My setup likes the 2000 - 2300 range for towing uphill which in OD puts me between 75 and 90, a little fast for towing so I am usually on the bottom end of my engine's comfort range for holding a steady amount of boost. I am also trying to keep a 76mm bottom charger lit as well but these engines don't mind sitting near the 3k factory tach redline as much as you may think, completely different animal than a gasser.

 

Ya'll are making me re-think the gear change. I was always a big fan of the lower the rpm's the better the mpg and longevity of the engine. This tach just plain stops at 3K and has no actual red line indicated. It is visually (and intelectually) disturbing to see the needle (or what's left of it as it has broken off) pointing to the end of the range.

BTW what is a, "76mm bottom charger" and why do you want it lit?

 

Your statement about rpm and longevity hold true and if you had a 5000lb truck it would be no problem but when you only have a 2000 rpm spread from idle to full tilt some times you need to compromise.
Without overdrive to have cruise at 2000rpm you only leave about700 rpm for gear changes. It is easy to have the engine fall out of the torque range on shift changes. You will find that a lot of us have different ideas on how to accomplish something so you need to just chill, do the important fixes and make your own educated decisions.
Its just an rv so you don't need monster power just enough to do the job comfortably. I would be surprised if your trany could take much over 300hp so it wont take much to get it where you can use it comfortably. You may even decide it is all right like it is.
Pulling 15k lbs around its not going to be a power house anyway . I think we are dumping too much on you all at once. Just suffice to say you have a lot of options. I would suggest looking over the forum and search features for a couple months and then see where you want to go from there. The biggest one thing to do is the kdp unless you are a hard core gambler.
If you can do 70 at 2500 rpm you will seldom need more rpm except for hill climbing in lower gears and getting on expressways .

 

OK first things first.

A set of gauges, from the gauges search I did I figure egt, Boost and fuel pressure between the filter and pump.

Then hitch this thing up and see what it can and cannot do. From there I'll have some info and decide what needs to be done.

It seems the HP mods are fairly straight foward, just turning wrenches. Do folks around here dyno their rigs or are all the hp #'s I'm see simply calculated?

Thanks again for the help!

and I still don't know what a bottom charger is...

 

The gages you will want in order of importance are exhaust gas temp. , boost (get a 60lb gauge) , fuel pressure gage ( see post by Infidel for easiest setup), trans oil temp gage, coolant temp. if you don't already have one. With these gages you will be able to diagnose most common problems within minutes yourself.
One other preventative fix is heavy duty starter contact installation, its a $10 fix that will keep you from having trouble later. Have fun with your rig and if I can help just PM me. Your not alone I don't know what a bottom charger is either. Go to www.fostertruck.com for good deals on common parts.

 

bottom chrger referrs to some that has twin or more corectly compound turboed their engine. Using two turbos to get more air and more bost to keep egts low for more power. I run a 80 mm bottom charger, and with the upper I make around 65 psi of boost. When pulling my 50 ft trailer I run up hills at 35-40 psi ussually, in 5th gear (an over drive gear with 3.54's) But it takes power to pull the weight with that gear.

I d put gauges on it, a nice big exhuast, and a 4000 gsk, 60 lbs valve springs, exhuast brake, and plate, small injectors, and see how it pulls. With out more gears.....the 4000 gsk will help. You d be able to start a hill at 3000-3200 then it would slow down but....it would be something.

 

i dont think you need to rev further for what your gonna be doing with those gears

gauges boost, pyro, trans temp
boost elbow
fuel plate
upgrade intake and exhaust

that will give you a boat load more power and make driving alot more fun

 

Thank you for your response Orange. When you say "those gears" are you referring to the present 4's or the 3's I was thinking of going to?

 

with a gear like a 3.55 your going to change your power curver to a lower rpm, that may be fine if your tranny can handle it, your engine will make close to max power below 1500 rpm if your addin fuel and turnin up your boost, thats alot of torque on parts down low.

like with taller tires on my 3.55 truck i have to be careful not to give it too much fuel down low because it will make torque and the truck isnt moving fast enough so the clutch takes all the abuse. in your case the tranny.

with your 4 gears, you can add fuell and boost and still be in the upper operating range and speeds where you can put your foot into it and not overload the tranny with torque.

if that made any sense....

 

What I'm hearing you (and a few others) say is to trade inputting a bunch of low end torque for some rpm's. The engine will easily handle it and it will be easier on the tranny.

I guess I just have to get over the "gasser" mentality.

 

To some degree,yes. If you think you are going to want to cruise at 80-85 mph then I think you will need to do something but for most rv's 70 mph is hoofing it. If you had a 6 speed trany you could probably raise your gearing to 3.75 with good results but to keep your engine in the torque curve with 4 gears it would have poor results. If you power up your engine to 300 hp or so you could probably still go to 4.11 or 3.9 but It would be a gamble going higher than that. Just so you know most people including myself gained mpg after moderate engine power mods. My truck stock would get 19mpg on the highway now with my mods. I regularly get 20.5-21 on the highway without a load at 70mph but my milage loaded went from 12-13mpg to 11-12 mpg with a combined load of 18,000lbs.
What is the gvw rating for your truck? I would guess its around 26000lbs. with a trailer you expect to be at 22k, that is not far from the gvw and there is a reason why they put that gearing in the truck for that load. Most of the 1 ton dually diesels running around are running 4.11 gears but most of the newer ones are running an OD. and their 70mph cruising rpm is around 2250rpm in OD. I have a ford 1 ton diesel dump truck with 3.54 gears, it has an OD trans. I can only use the OD when it is empty when loaded it can not pull the load . The 7.3 N.A.engine has 180 hp. What rpm do you think a gas 360 would be cruising at with a 22000lb. load at 70 mph?Actually I don't think a 360 gas motor could even pull 22k lbs. at 70mph. Also with a gaser you wouldn't think of putting an OD on it to pull that weight. I wil shut up now, I have probably overstayed my welcome already.

 

Definately not Lifer! I welcome your input and discourse!

The GVW (on an ID tag) of the Freightliner is 33K. I plan on registering it non-commercial with a gvw of 25,999.

I have a '74 Chevy 1T Crew Cab, Longbed with a 454, RV cam and a TH400 tranny (Nicknamed "Big Blue"). It weighs 6,200 empty with my behind in the drivers seat. I have loaded it to the max with a rack on the front holding a go-kart, a bed full of tools, camping gear, a quad etc... and pulled a fully loaded toy box (my friends) that was a minimum of 10k and had no trouble gong up the grades at 75mph. The truck was dynoed at around 360 hp. (This is what I remember, don't quote me on this as I need to find the old dyno chart to verify it) I estimate the gvw was around 18K or so.

I would like similar (preferably better) performance from this rig (not as of yet named) and would very much like the capability of 75mph up-hill, fully loaded. It seems like hp mods are in my near future.

Will this silly sparkless oil burner keep making hp as long as it gets fuel? or does it have a torque / hp curve similar to a gasser? (drops off after a specific rpm is reached) I have found differing opinions on this site after a search.

Thanks for putting up with my long, multiple posts

 

You will definitely need engine mods. Your comparing a gas motor with much more displacement than your cummins. The cummins stock probably only puts out the same or 50lbs more torque than your 454 did at most with half the hp. You will want to go up to the 300-350 hp range that should put you in the 600-700 ft lb torque area. Most large trucks like yours probably can not do more than 60mph loaded and up hill probably 45 or 50 mph with the stock engine.. Since your gvw is that high you probably can go to the 3.9 diff range without too much problem as long as you do some power improvements. That or put an OD behind the trans. The OD would be preferable performance wise. 75 mph with those changes should not be a problem. Your 3k gsk should be able to do that with no problem. Its a crap shoot to go to 3.75 or higher gears as far as adequate performance goes. I hope someone else gets in here with some recommendations for you. Preferably someone with first hand experience with this situation. I do not want to steer you wrong. If you do go with an OD your goal of 2000rpm at 70 mph is in the ball park. You might want to put up a new thread in the towing forum with your specs and expectations an see who answers. The info will be seen by more people with this kind of experience. The torque of the cummins will drop off at higher rpm but I don't remember where . I think around 2000rpm but Im not sure. but just like a gaser you can't always stay at max torque range.