HO comes alive at 2k, why the wait?

[MCummings]

Re: 2K powerband Hit

Originally posted by Diesel Freak

I have always had this.

With injectors it is even more pronounced, so that leads me to believe that it has to do with the ECM fueling curves. The HP/TQ graphs in the brochures are suspect after seeing the actual TQ/HP curves for my truck with just 275's. The only thing I agree with on the brochures is the RPM where peak HP comes in at. With 275's I had 233 HP at 2750 rpm with peak torque at 2450 rpm. When I added the puck, the attitude of the engine changed completely. The smooth transition to the 2K "hit" was gone. Now it rips and snorts from 1600 rpm... that is why my clutch died... wet pavement is also a real PITA!

I don't agree with the dyno charts either. My truck felt like a dog below 1,500RPM (as in, didn't get out of the way of Honda's and other imports)

When my truck was stock it felt like it picked up about 50HP instantly at ~2K RPM



Now, I'm killing my clutch. Pulls hard from 1,500RPM to about 2,800RPM. Just waiting for the Bank account to recover from daily life, a PE COMP, and DD1's so I can get a clutch.



MerrickNJr

 

[Wheaties]

MCummings:



Yes, I have seen the torque/hp curves. I think I slept with them under my pillow while I waited for my truck to be built and shipped.



What I am talking about, does not seem to be reflected in the published stock engine curves, HO or otherwise. It feels a lot like a switch got flipped on somewhere, say to the afterburners, and it occurs pretty much around 2000 rpm.



When we look at the torque curve, it is flat at this point, so there should be no surprises. Likewise, the HP curve shows power is steadily increasing, not increasing sharply.



I think that what I'm talking is specific to the stock HO for some reason. Surprisingly, I have to agree with other posters; when a box is added the spike isn't nearly as noticeable. When Fred and I drove a truck nearly identical to mine, but with an EZ , the spike wasn't there.



Thanks to the other posters for affirming that my truck isn't the only one with this behavior. Now if someone can say with certainty exactly why...



Matt

 

[Diesel Freak]

I think it has to do with two things... . emissions, and extending driveline life.



The ECM is programed to meet emissions standards, so it waits to add fuel untill there is enough boost to burn it all. Dyno time can really let you understand why on a stock engine, fuel follows boost... . to eliminate smoke.



on a bombed engine it is just the reverse. My truck is overfueled off the bottom to give faster spool up..... it smokes!



Acceleration dyno runs always give lower than actual HP/TQ readings... . this is because the turbo is having to play catch the engine... . (lag)



The curves that DC published are probably taken from a loaded dyno run where the turbo is completely spooled up and max fuel is available. A loaded dyno run pulls the engine down from a pre-determined RPM. This is just like hitting a VERY steep hill loaded to MAX GVW and lugging the engine down to 1500 RPM from 2700 RPM... this way the turbo does hot have to play catch the engine.



For clarification of what turbo lag does to performance. When I dyno'd my truck the acceleration run gave me a peak HP of 267 HP at 2450 RPM with 31 psi of boost..... the loaded dyno run was completely different... 294 HP at 1950 RPM and 38 psi of boost.



This was on the 1000 HP Mustang dyno at Excessive Motorsports here in Hillsboro



I hope I have not confused anyone here

 

[MCummings]

#ad




I tinkered with this picture. . Is this how it feels ?



This is how my stock ETC at 75K felt like. (Just less HP/TQ)



MerrickNJr

 

[Diesel Freak]

the Dodge graphs are not accurate!



TQ=dHP/dt (I probably just broke another physical law, so someone please correct me if I made a mistake... . the books are at home )



or



(TQxRPM)/5252=HP

 

[Vaughn MacKenzie]

Matt, I think part of your problem is John let you take his truck for a spin at the BBQ LOL . I did notice John's truck seemed more responsive off idle and have less spike around 2000rpm than my ETH does. It was a lot of fun to drive a hot Auto with DTT installed, the only Auto backed Cummins I had driven before 2 weeks ago were stock, very boring. I must say I liked John's (Mopar Muscle) truck very much, it is an interesting perspective after driving BOMBed manuals.



How is your Espar doing by the way, getting some chilly mornings to test it out with yet??



Vaughn

 

[PHaller]

Boy, am I ever glad I have the venerable 12 valved engine! Power from 1600 all the way to about 3450, with Piers govenor spring kit. No flat torque spots, great power, million mile pump and better mileage too. No worries about boxes and electron flows, com links and engine data ports. Just diesel nervana!

-Paul R. Haller-

 

[Kingram]

Another "lugger"

I'm very new to the cummins also, but my observations have been like Dave D said. Pulls real good from about 1100 to 1800. Then, it just revs. Tows the lightweight 7000k travel trailer the very best at about 18-19k.



If you look at the torque chart, you can see where it levels off. My truck feels just like that chart looks. I'm used to the gassers that pull harder the higher they rev. After 2k, I find myself sometimes actually leaning forward



I don't know why my experience is different from what others have said unless it is because mine is basically stock still.



FWIW, I have the 235HP/5spd.



Chris

 

[Big P]

Matt, I know exactly what you are talking about. This is my first diesel truck, it has 1700mi on it, and the power curve is alot different than my old v-10. My truck moves pretty good when it hits about 2000rpm all the way to about 2700rpm and I can easily see 21lbs of on the guage. I think that maybe it takes the larger turbo on the H. O. 's a bit longer to build boost.

 

[Spaceace]

I must be the only lucky one

My ETH pulls strong and evenly WOT from 1000-3200 RPMs. My face wrinkles like a jet pilot on a carrer takeoff.



mwheaton,

I do believe the incresed mileage claims of the higher RPMs. (Disclaimer: TO A POINT) Most of it depends on the grade. The trip computer will usually verify when you are doing it right.



Is a 1600 RPM idle out of the question?... . different DEE gear ratios?... . or 12 speeds using max of 600 engine RPMs... . RPM limiter 1600-2200 RPMs..... hhhhmmmmm

100% power band

 

[johnrv4]

I have to agree with DieselFreak. On both my '98 12V and my '01. 5 Truck, maximum boost cannnot be reached until the engine is at approximately 1900rpm. I think (like DieselFreak) that more fueling is allowed as the boost reaches it peak. On my '98 if you were pulling a load up a mountain, as soon as the rpm dropped below 1900, the boost would start to drop off. As the boost dropped off so did the power. It seems that the 24V responds in a similar fashion. If you are at 1900rpm or above and punch it, it accelerates much faster because the boost builds up to maximum immediately instead of building slowly like it does at a lower rpm where it can not obtain peak boost.

 

[Floor It]

My truck did the same thing when new, no real pulling power at low rpms when not pulling- I was mad. After all my research it is from emissions. At low rpms the ECM will not put fuel to the engine until it see's enough boost so the engine will meet the NOX gas and particulet matter emission laws. When towing at lower rpms the engine does have power because towing causes engine to be running along with more boost at low rpms which equals more fuel that can be put to the engine which equals POWER. At 2000 rpm- no towing- is when there is enough boost to cause this surge of power come on. The auto guys will feel it sooner because the torque converter will let engine get to boost sooner. As for towing, if it is a light load lower rpms is better for mpg, but not if your in too high of a gear lugging engine just to get to low rpms. What MCummings said is right when towing really heavy loads, your better to tow in a lower gear and raise the rpm and then is when you will get better mpg's while towing at higher rpm's. Sorry this was sooooo long, SEE-YA guys John

 

[Wheaties]

Vaughn, Fred, George, and John

Yes, this issue came to light after driving everyone's bombed truck. Well, to be accurate, Fred let me try his, and I took a ride with John in his truck and another ride with Fred in Batman's -- they were all very impressive!



But in a later conversation with Toolman Tim, we were talking about turbo lag and his pursuit of its elimination. I commented that I thought the HO seemed to have a lot of it; you press the pedal and wait. So Tim and Steve and I took a drive around the block in my truck. Their observation was that it seemed to occur at around 2000 rpm, and that the turbo might not have anything to do with it. So I posted to see what you all thought.



Judging by the responses and more recent observations, it doesn't seem to be the turbo, so much as the ECM limiting fuel until the rpms and air are available. I agree this is probably an emissions thing, keeping soot and NO2 down.



I'm also encouraged by the few that observe that this is most pronounced when the truck isn't pulling and empty. As this is my daily driver, I do a lot of this kind of driving. Also, as a result of this discussion, I have discovered that I can get better accelleration by shifting later than I have been, closer to 2700-2800 rpm, which leaves me very near 2000 for the next gear.

This works very well for hard accelleration.



Hey, I'm really happy with the Cummins, I've just been wondering why I get an extra boost at 2k.



BTW, Vaughn, that Espar is awesome. I've had a few start failures due to bubbles in the fuel line (the Espar has a separate line back to the tank), but this is expected as we get the bugs out. I may get my first cold morning tomorrow--feels pretty strange looking forward to cold weather. It sounds like a little turbine firing up. I'm waiting for one of the neighbors to knock on my door one morning to tell me my truck is making some strange noises



Matt

 

[Bad340fish]

SMOG

Ok I didn;t read all of the replies so it might be mentioned already.



I am willing to bet its an emisions thing. Emisions are going to be worse at the lower rpms due to the lower boost levels. If you watch even a stock 12V truck they will puff a little when they take off from a stop. I couldn't make my 24V smoke if I wanted to when it was stock.



Solution=Add EX box, or the VA although I have never used a VA I am sure they have similiar results from what I have read on here.

 

[RustyJC]

I Now Know How to Cure It!!

Installed the Edge EZ and Jardine 4" exhaust this weekend. The 2000 RPM "spike" disappeared - this thing pulls like Jack the Bear now. The only problem is trying to wipe this s***-eating grin off of my face!



Rusty