Best RPM to pull at? Lets discuss

Cummins Driver

Cummins Driver

THE Cummins Driver
Joined
May 16, 2007
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So I was doing a little thinking.

These arent exactly real world numbers, but more of an example, and for people to think about and comment on.

Say if i were to pull work stock. And keep in mind im not sure what the ideal wheel speed would be with a running sled.

3400rpm in 2nd gear is 23.XXmph wheel speed
2400rpm in 3rd gear is 23.XXmph wheel speed

Now, for my question. With the charger i will be running, my truck should be pulling hard at 2400rpm, and it should pull to 3400rpm, but it will probably be about out of steam RPM wise with my current setup.

Looking at my latest dyno. It should be stronger now, and will definately turn some more RPM before fueling cuts back(2800rpm was about it before the pusher pump), but i have attatched the sheet to look at anyways.

My guess is at 3400rpm, my torque will be around 500ft/lbs with the fueling i have now. At 2400rpm, my graph shows torque was still over 700ft lbs. Horsepower also starts to drop off slightly up around 3k RPM by the graph, but remember it was out of fuel at 2800rpm. Horsepower was still right at its peak at 2400rpm.

So what i am looking at is this:

2nd gear/3400rpm/ 500? torque/280? horsepower
3rd gear/2400rpm/ 720tq/335 horsepower

So, I think on a running sled i could get into 3rd and be somewhere around 2200-2400rpm. Im an automatic, so I could unlock the converter right when the sled hits and stay on the charger. I know i cant run 3rd on a "drag" type sled, but on a running sled, it seems as if I am in a lot better range for putting down power with a small charger.

I have noticed a lot of trucks(12 valves) that turn 4k rpm or so with a fairly small charger seem to lose a lot of speed at the end before they get to that RPM where they will no longer drop, but sustain the RPM.

So if I went on and shifted to 3rd, would my truck hold its wheel speed better towards the end of the track until i had to unlock the converter? As opposed to maybe running 2nd the whole track, and having it pull back down to around 2400-2600rpm before it would quit falling?

Sorry for the long post, but I may be trying my luck at a running sled soon, and this got me to thinking about what gear would be best.

Eric

IMG_1584.JPG
 
WOT!!!!!!!!:rockwoot::st:


you would just have to experiment and see how your truck responded to each. If it kept gaining rpms in 3rd, then id say shift it, if it lost in 3rd, id say stay in 2nd.
 
I am no expert but in my mind it makes little sense that if you can turn more rpms and be out of you power curve then the only thing that could happen is that you eventually get pulled back into the highest part of the curve. On the other hand if the sled hits to hard and just drops rpm down below the peak and no peel out at end of hook.
 
Yeah, ultimately it would be best to be able to just try both and see what was best. 3:55's and 3rd is a pretty tall gear.

Just looking at the numbers though, it should hold speed in 3rd better because of the hp/tq that is getting to the ground. I have seen a lot of trucks keep grabbing gears and then fall off the turbo at the end or unlock the converter to keep on top of it that won.

I would probably be best running 2nd with some taller tires. Those calculations were with the 265's i have on the truck now, but I plan to go with 305's when i buy tires so that should bring the RPM down some in 2nd gear.

I was just thinking out loud and wondered what everyone else thought.

Eric
 
With 700tq you won't run 3rd. Takes 1200tq to run in 3rd but it all depends on tire size and gear ratio. I am speaking of 3.73's. You may hold 2800 rpm mid track. All tracks are different.
 
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With a fairly loose sled, Im pretty certain it would run 3rd for at least part of the track. Not sure that it would gain any speed, or hold it to the end though.

Why would it run 2nd when its out of the peak hp/tq, and not run 3rd in its peak hp/tq curve?
 
not so sure about the numbers and rpms

I have yet to be on a dyno so dont crucify me

I am assumin you have a stock motor and maybe bigger injectors and turbo???

I know last year with stock motor and just injectors and a prostreet 66 I could carry second gear which totals 14.3 to 1 and 3200 rpm - meaning the motor never came under that rpm pullin - so the torque band couldnt be that far off

with this years motor - polished/ported/cam/bigger valves/bigger turbo/same injectors and 14.3:1 gear, I carry 3600 rpm in second gear with no issues. I cannot carry drive gear at any rpm - it either blows the tires or comes under the turbo

so to be fair in your question - what are you runnin for equipment on your motor that it is all done at say 2800 rpm and on the downhill slide after that even tho it will run to say 3200 rpm?.

yes theoretically you should run better at your tq peak, but that doesnt necessarily equate to good ground speed and distance, especially if you lose ground speed because your 700 ft lbs torque blew the tires away whereas 500 ft lbs doesnt blow the tires away which results in more traction and thereby more distance
 
I personally think 2nd gear will be your best bet. Even with my 265s 3rd gear was just a little tall. I also think youll see less breakage pulling at the higher rpm in 2nd.
 
I will be running a stock 3rd gen turbo, pulling against stock turbo trucks. I mainly drive my truck, but ill be pulling it a couple times this year after i get my turbo on i hope.

When i dyno'd i didnt have my carter pusher pump on the truck. It was pretty much done at 2800rpm. Now with my carter and a clean fuel filter, it will pull to 3500rpm without much problem.

Right now, I am just running stock 215 injectors, a #0, 4k, and 191 DV's. I have some New Era 370's, but i doubt i will have them in when i pull. Id say im around 350-360hp or so right now. Maybe over 800ft lbs?

Seeing as the turbo is a stock 3rd gen unit, it shouldnt fall off until it gets WAY down in the RPM. But, I still would like to keep it above 2k RPM.

I may be better off in 2nd gear just letting it crank and then pull down some at the end, I was just curious what other guys thought about it. I wish i could try pulling it both ways. 3:55's and 3rd is a pretty big gear, so im not sure that it would work that great, but just looking at the #'s it seems like it would do pretty well, so i was looking for opinions.

Here is a video of me running 2nd gear with a "drag" type sled. I had the same setup i do now, except i have traction bars, better blocks, my pusher pump, and a bigger stock charger now. My truck is at the 1:26 mark. Oh, and the reason it was squatting bad was that i was in a hurry making the blocks and one of the passenger side block slid off the stop, so only the drivers side was blocked:bang:hehe:

YouTube - Harrodsburg Pure Stock Diesel Class

Eric
 
teddybear said:
I personally think 2nd gear will be your best bet. Even with my 265s 3rd gear was just a little tall. I also think youll see less breakage pulling at the higher rpm in 2nd.
Click to expand...

I think 305's and 2nd probably will be a good gear for me. Just need some more timing though:hehe:

And im sure that breakage would be less in 2nd....

Eric
 
I'd say 2nd gear with 305's and 3.55's... I tried 3rd once and it fell flat and shifted down to 2nd at the end... If I had locked it in 2nd I would have prolly gained another 20ft... That was with my stock charger on my 24v... That was with just the drag comp and pretty comparible numbers to yours... I don't remember where my peak hp was though...
 
I'm in your same boat with pulling. I do better in 2nd spinning 32-3400rpm down the track than jumping into direct.
 
You are running a 2.6 charger. Its obviously going to run good up there with that much air. Im not playing with much air here.

Eric
 
Rodram2002 said:
I'm in your same boat with pulling. I do better in 2nd spinning 32-3400rpm down the track than jumping into direct.
Click to expand...

Im guessing mine will probably do the best like that too, but thought id get some opinions on the matter.

Are you running a stock charger, or bigger?

Eric
 
Cummins Driver said:
Im guessing mine will probably do the best like that too, but thought id get some opinions on the matter.

Are you running a stock charger, or bigger?

Eric
Click to expand...

Stock charger sir! I tried 3rd the first day and 2nd the second day at the same track and picked up close to 10ft staying in 2nd locked vs. 3rd locked. Like stated above, we just don't have the power on a stock charger to pull in 3rd and keep the momentum going.

Since we don't have much power or wheel speed to work with I'd say stick with second and concentrate on putting the power to the ground and good launches.

I had a good launch both days and that helped me a lot. I never broke traction until the end of the track.
 
Yeah, its looking like 2nd is going to be my best bet. Id really like to bump my timing up to around 19* because i think that would really make it run better up top, but im going to have to wait a while before i do that.

I think 4:10's and 3rd gear might be an alright setup, but I dont like them for the road, and i definately am not going to spend the $$ to swap to them.

Eric
 
I'll be tryin 4.10's and 3rd here if I ever get time to get mine done! But I have a larger charger than you....
 
Six_leaker said:
With 700tq you won't run 3rd. Takes 1200tq to run in 3rd but it all depends on tire size and gear ratio. I am speaking of 3.73's. You may hold 2800 rpm mid track. All tracks are different.
Click to expand...

Just curious why you say that? I have no where near 1200tq and pull third all the time with 3.73s and 33s. Or does this only apply to a 12v?
 
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