what RPM to shift?

[RabidRam]

Guys and Gals,



Is there such a thing as a proper RPM window to shift at in these trucks? I usually aim for somewhere around the 2K mark (everyday driving... unless I'm trying to make my own diesel symphony). With a totally stock transmission and a tick over 100K on the truck, I'm hesitant to wrap it up any tighter. HOWEVER, the reason I ask this question is because I just a read a thread on here (somewhere) that said the trucks really start pullin' at about 1800 RPM's. Am I missing out on a poo-load of power by not using more of the RPM range?



TIA,



Dave

 

[ndurbin]

the sweat spots about 2100 rpm for the cummins engine. usually reach peak torque at 1800. pump starts to defuel at 2200.



anytime i drive a hand shaker it's between 1800 and 2100. sometimes higher if i am pullin with it.



and if ya want really good MPG shift even lower and use the low end power it has. like 1500 rpms or lower.

 

[carson6]

2800 rpm

after bill k. and piers got their hand's on my rig . 2800 rpm feel's realy good:--)

 

[MGordon]

I shift at about 2500 rpm.



I did read somewhere that for best millage you should shift at 1400 rpm. What a PITA that would be. Leaving a stop light, I'd have to shift 4 times in about 15 seconds.

 

[dremelts]

I probably shift at about 2000 during normal daily driving. But when I'm pulling the trailer I wind it out to about 2600 or until it starts to defuel. Especially when going from 3rd to 4th because there is such a large RPM drop.

 

[HeavyHauler]

1400 - 1500

I've talked with Cummins about this and they told me that if I started shifting at 1400 RPM which is close to peak torque for the ISB I would get more out of my truck not to mention better mileage. They also recommend accelerating fairly quickly, don't run the hell out of it but don't lug it at the same time.



You guys that shift at 2000 and over, especially over 2500 are nuts. You're just running your truck to death. You don't shift a gas pusher at 5000 RPM do you? You've gotta remember that the red line for these things is at about 3200 RPM. It makes no since to shift that high anyway, the motor doesn't even sound good that high. Not good to wind em out that high.



Also, if you've ever driven a big rig, you can get used to popping the accelerator a little bit to prevent lugging the motor if you don't accelerate quick enough.

 

[KLockliear]

Despite what Cummins says, peak torque is made on a 24v at around 2600rpm. Peak HP is at 2700rpm. Normal driving, shift around 2500, so that puts you back around 1900 or so after the just... just shy of at plateau in the torque. These motors have a basically flat torque curve above 2100 or so, all the way to 2700.



Complete powerband is 1900-2900. More power on tap in that area than any other.

 

[MCummings]

Certified Nut

Originally posted by HeavyHauler

You guys that shift at 2000 and over, especially over 2500 are nuts.

I guess when I hit the ratchet shifter at 3,900RPM to go into 3rd gear was a little "high" in the RPM ?





I usually shift above 2K and below 2,800 when I'm n the street,, but that's a side effect of big turbo's and big injectors. Using power below 1,500RPM just turns on the mosquito executioner.



Merrick Cummings Jr

 

[RabidRam]

Thanks for the response! Obviously since this thread is in the "First Timers" category of the site, you all know that I am no expert when it comes to any aspect of these awesome trucks.



BUT 1400?!:--)



What does that put the engine rebuild at... about 2 million miles? I can see Cummins wanting to cover their rears by picking such a low number... but my stacks don't even start to sing until about 1800.



It seems as though my current shifting habits fall about mid-range in the replies I have received.



KLockliear... thanks for the chart!

 

[tbrudder]

From the dodgeram.org FAQ section:

http://dodgeram.org/tech/dsl/FAQ/engine_op.htm



Correspondence from Cummins states not to operate the engine under the peak torque RPM (1600) at full-throttle conditions for over 60 seconds, so at times, shifting so low is bad. Also noted that they put these engines in test cells and run them at the redline for hundreds of hours at a time with no observed ill effects.



And the 24V will even survive a quick trip to 4000 RPM. Don't plan on trying this one, myself.



All that said, I've had pretty good results shifting from 2200 to 2900, depending on conditions--peak power's 2700, but 3 to 4 seems to be a big RPM drop, especially with a trailer an no HP mods. But I'm pretty new here, too, so take that with a grain of salt.



--Ty

 

[TomGolden]

I am not claiming to be an expert at either engine internals or clutches, but I remember a year or two back, several other knowledgable people (I want to say Peter from South Bend Clutch among them) said shifting anywhere near 1500 RPM can severly damage your clutch, and if you shift that low and then hammer the go pedal, you can literally twist the center right out of even a South Bend clutch



I usually shift at 2K on the street, and between 2300 - 2500 RPM when getting on the freeway.



Of course for those who have a slush-o-matic transmission, you have no control over when it shifts anyway, so you're just along for the ride :-laf :-{}

 

[carson6]

slush -o-matic?

I have full control with my rightfoot. . I can upshift @ a bog(light foot) or do 2800 rpm shift's with the smokepedel all the way down(Floorboard) and I have a free hand to do more important thing's like hold a boob or a beer or tune a radio... but you won't catch me with a silly STICK in my hand!. S. dosen't your leftleg get tired?

 

[carson6]

Mr cumming's,3900...WOW

3500rpm @115 mph was my limit because my mirror's folded in and scared me!

 

[shoveljunk]

rpm

TDR issue # 40- page 132. It is worth reading (The Way We Were). Horse power calculation, Okay to down shift, Run it like you stole it, are some of the paragraphs. I almost always drive to save fuel! I also drive according to traffic condition. slow traffic, low rpm. Jump on the hi-way at full throttle and almost never floor it all at once. Big hills, lots of throttle and RPMs and an eye on the water temp. And oh ya- It's a His and hers SIX SPEED all the way.



Learned it from RJ trucking. I drove his '73 Pete conventional with a Cummins Big cam 400 and a 13 speed Road Ranger

 

[dremelts]

Re: 1400 - 1500

Originally posted by HeavyHauler

You guys that shift at 2000 and over, especially over 2500 are nuts. You're just running your truck to death. You don't shift a gas pusher at 5000 RPM do you?

That gasser engine is not rated for continuous duty at max RPM either like our Cummins engines are.

 

[rbattelle]

Heavyhauler,



Your comment about shifting at 2000 RPM seems a bit odd. You seem to be suggesting we should shift at some constant percentage of redline RPM. So let's say you have a gasser with a redline of 6000 RPM, and you shift at 2000. That's 33% of redline. Then, if we apply that to the Cummins with a redline of 3200 RPM, you'd have to shift at 1056 RPM. No way.



In my opinion (emphasize opinion), shifts should be made in the 2000 RPM range for optimum fuel economy, power, and to prevent lugging as you enter the next gear. Despite what Cummins told you, I think 1400-1500 RPM is way too low. After a cold weather warmup, I do tend to shift a little earlier - 1800 or so.

 

[HeavyHauler]

Well guys I was just restating what I was told my Cummins. They told me that peak torque began about 1450 on the ISB 5. 9 in the Dodge. Furthermore, they told me that shifting anywhere above 1500 was "spinning" the engine. Which makes sense, because anytime I run mine over 2000, I get loads of smoke and my engine sounds like it's going to fall apart or send a rod flying through the side of my engine. And no, nothing is wrong with my truck, they all sound like that and I don't see how you guys could shift at nearly 2500 RPM. It sounds pretty bad to me, and I don't see how it couldn't to you. They also said the obvious, which is to shifit lower on lighter loads that you would on heavier loads.



Granted, I had the same reaction as you all did when I heard this, but then I thought, "I'm not the one that designed the engine, they did. " Also, I'm not saying that I always shift at 1400, I rarely do because I like to hear the turbo sing too much. However, I do usually shift between 1500 - 1750 or so. I was just stating to the thread starter what Cummins told me. But I don't think it's a good idea to run these engines as high as some of you do under normal, daily driving.



Also, to the guy that said peak torque is at 2900 on these engines. You need to recheck your figures. Our engines are advertised at 460 lb. ft. of torque at 1600 RPM (SIXTEEN-HUNDRED). Don't you think that if these trucks produced anymore Dodge would advertise it? If your statement was true, our engines would be rated at some 830 lb. ft. of torque at your figure (proportionally).



Don't you think this would be a big selling point? I think Ford and Chevy would be a little frightened at the thought of competing with a Cummins that produced that much torque. Remember, use common sense, we're not driving Peterbilts here.



Another point, check out some fuel mileage threads here. It is widely accpeted that running your motor anywhere over 2000 RPM is killer to your fuel mileage.



So I really don't feel like being attacked anymore, stick to answering the original question. I've made my piece and told you my OPINION. I'm not making this a constitutional law.

 

[carson6]

look @ your egt's not your tach...

lower rpm's mean higher egt's under load or at least mine think's so ! also mine sound's like a humming bird above 2000 rpm

 

[rbattelle]

Heavyhauler,



I didn't meant to sound like I was attacking you. I apologize if I came across that way.

 

[Texas Diesel]

Here is my opinion, just dont throw rocks at me.



Under revving is wayyyyy worse than over revving, in OD (6th in my case) it feels bad if I try to run it under 2000 RPM.



Interestng info:



The Marine version (same bottom end) runs 2600 all day.



Cummins says the bottom end of ALL ISB's is rated at 4400 RPM, it's the valves hitting the pistons that limit RPM.