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Peak Torque RPM

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FellowTraveler

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A advertised stock specs go the 6.5 td peak tq is 440 ft lbs @ 1.8k rpm's is there any other way to determine actual peak tq after mods w/o dyno? I ask this because dyno's and automatic transmissions don't give an accurate figure mostly because of transmission slippage.
 
Perhaps get an Edge gauge and data log? The Edge can read RPM's (as reported by the ECM) and compute torque (also can calculate HP). Ok, sure, the Edge might not get the actual torque figure correct (actually, it displays the HP and torque figures in terms of what is occurring right at that moment, so a value of 0 is common), but it does know when the number is rising and falling. From there just dump the data and graph it out.
 
JayTheCPA said:
Perhaps get an Edge gauge and data log? The Edge can read RPM's (as reported by the ECM) and compute torque (also can calculate HP). Ok, sure, the Edge might not get the actual torque figure correct (actually, it displays the HP and torque figures in terms of what is occurring right at that moment, so a value of 0 is common), but it does know when the number is rising and falling. From there just dump the data and graph it out.
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Now that's and interesting idea! The zero is common while cruising on flat ground isn't it?
 
JayTheCPA said:
Correct. And this makes sense given that the net power produced (from an accelerometer standpoint) is nil.

Only potential limitation of data logging through the Edge is the refresh rate / speed of the OBD-II communication.
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On a dyno even with - of estimated parasitic loss there is much more slippage with converter being unlocked so dyno figures are pretty much useless IMHO.
 
Just by seat of pants sort of things, my peak torque is around 2100-2300rpm. With my water/methanol active, it seems to bring peak torque to around 1800-2500rpm.
 
pacificdrumma said:
FWIW, my truck dynoed 320rwtq and 380rwtq at about 2100-2300rpms both times.. peak power was around 3100-3300 IIRC
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Decent tq #'s, it's what mods one has that determines the rpm points tq/hp. I haven't done the dyno because I feel it is not accurate when an auto trans is in the mix and trying to pick peoples brains on what alternatives there are to determine at least peak tq rpm's........Even stock & tuned 6.5td dyno #'s are all over the place between the "S" & "F" version as Wester's dyno results show for a few 1998 GMT400 6.5td's......
 
FellowTraveler said:
I haven't done the dyno because I feel it is not accurate when an auto trans is in the mix and trying to pick peoples brains on what alternatives there are to determine at least peak tq rpm's........
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From a RPM perspective, absolutely correct. The Burb made an interesting loop (yes a complete circle) when we looked at power versus RPM's.

We decided on speed (mph) versus power was the better measure as 3'rd did lock the TCC and put raw power to the wheels.

From what I have seen of turbo diesel engines in general (including the 6.5), even though the peak torque occurs very quickly, it slowly falls off over the RPM band (hence why diesels are stated as having a 'flat' power curve).

HP curve on the other hand looks more like a gasser with a sinusoidal appearance.


Question is: what is the goal in determining the peak torque RPM?
 
The stock spec for max torque on my 6.5td is 430 ft lbs @ 1.8k rpm I suspect that number is under full boost w/GM8 turbo as torque multiplayer however all the mods I have done has raised that rpm point and just trying to determine most efficient rpm's for cruising with and w/o loaded M101a3.

I'm going to check out the EDGE like you suggested to get a better idea of what is going on w/my setup, how is the refresh rate or is it real time on data logging?
 
Considering, the 6.5td off boost cruising is like the 6.5 N/A so your looking at 340 ft lbs tq max @ 1.7k rpm........with stock setup.
 
Have not used the data logging feature so cannot comment on refresh rates.

The Edge does display ECM values in real time.

One feature I have used is the 0 - 60 time capture and that one seems rather accurate.
 
For anyone reading with a 98 or 97 and older, IIRC peak torque is supposed to be 385, IDK if that is at the crank or the wheels though, GM never specifies.

I need to get on a chassis dyno to compare it to the butt dyno, but I feel peak torque is at around 1800, and is pretty flat from 2000 on down, and falls off pretty bad after 1700.

Horsepower really comes on over 2 grand, so it seems to run real happy at 2250.
 
Agreed. My sweet spot when I'm cruising is about 2200-2300rpm. She gets the best mileage there and has great power when I get into it.
 
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