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Increasing towing torque to overcome gear ratio change

Practical Diesel Tuning

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Discussion and questions related to the course Practical Diesel Tuning

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I would first like to say that I am very pleased with the Diesel Tuning Fundamentals and the Practical Diesel Tuning course. I have a 2010 6.7 cummins with compound turbos, Hamilton Camshaft, 45% injectors and a few other modifications that I installed into a 92 F350. The current tune is not a stock tune and it is locked so I am unable to see the complete tables of the tune. I have been logging data while driving the truck and then I start comparing my data to a stock tune to look for differences. I have attached a file with some data I logged for one of the instructors to review to see if there is room for tuning improvements or if I am fighting a mechanical gear ratio problem when towing a fairly heavy load. A second question that I have is in regards to the camshaft I installed. It is a Hamilton Cams 178/208 cam. Their documentation states that this cam helps to kill in cylinder EGR by having the least overlap of when the intake and exhaust valves are open. I have read that the factory 6.7 cam actually increases in cylinder EGR. On the Intake Cam Lift specs it shows 2 different timing numbers: one is -10.0 and the other is 8.0. On the exhaust Cam lift specs those numbers are 45.0 and -17.0. Are the camshaft specs beneficial when making timing and injector pulse width changes to a tune? I suppose I would need the factory camshaft specs to compare these numbers and also have a better knowledge of what those numbers actually refer to. Thanks in advance for any help you can provide.

Attached Files

Scott,

I've read through your scenario and looked at your data log information in the doc. I'll get the easy one out of the way early. My experience tuning diesels with non-stock cams has not forced me to change my approach based on cam selection. Basically you'd need to be on a steady state dyno woking out 'mean best timing' tables to actually document the performance differences. Not worth consideration in this case (your mileage may vary).

With regard to your tune and quest for more torque. The first thing I'd like to call out is your request for a higher indicated torque in the log file. Remember that the engine can only calculate torque correctly if the fueling rates have not been altered. Its my guess that the fueling rates have been altered so it's unreasonable to assume that the fueling rate indicated in the log file is still correlated to the actual torque output. In fact the engine may indicate 600 ft-lbs and actually be producing 1000ft-lbs. The indicated torque is just where the engine starts it's fueling lookup. From there it's going to call out an mm3 value and then from there the mm3 will call up an 'injector on-time (uS) and fuel pressure. Without seeing the tune we cannot trust the torque value or the mm3 value to be real. With regard to actual useful fuel rate data in these logs, we can only know the pulsewidth, pressure, and nozzle size.

To get to the bottom of you question "is there room for tuning improvements or am I fighting a mechanical gear ratio problem?" I would start by looking at your gauge data. In the doc you say that lambda shows 2.0 or higher and EGTs do not exceed 1000*F while pulling sustained. From that data alone I would say that you can push the truck much harder. I would continue to allow the truck to add fuel up to 1200* sustained (very safe). Its a shame we cannot see the tune and make some small adjustments from here but I'm afraid that's the extent of information I can offer given that limitation.

Nick

Thanks for clearing up the camshaft question. I've always wondered about that.

Now I am in the process of building my own CSP5 tune now. I will be using a 2010 base file. Here is what I have done so far:

I increased one "pedal to torque " column. It is the column at 50% tps. The column prior to 50% is 1% and the column after 50% is 100%. I rarely get above 50% percentage while driving normal or towing. I increased torque requested amounts in increments of 75, 125,175 ft lbs per tune and then made it 100% for Tune 5. I assumed that the ECM is incrementally calculating torque requested between the 1% column and the 50% column for TPS% between those ranges. I know you said this is a preference or feel so I'll see how this works. Then I adjusted the following tables:

Torque to Fuel table in the 900-2800 rpm range I increased 10%,20%,30%,40% (tunes 2-5)

Fuel Pressure Base Mpa in the 900-2800 rpm range I increased 10%,20%,30%,40% (tunes 2-5)

I then took these numbers and calculated out what the pulse widths would be at 1500 and 1800 rpms at 150nm torque just to get an idea of what timing should be for 50% fuel delivery BTDC. I was coming up with a pretty close range of 3-4 degrees BTDC. If I look at the stock timing tables the timing is -0.9 to 1.0 degree. Since you said I can't really trust my data numbers since we don't have all of the current tune information I figured I'd get my timing tables figured out and load my tune up and start logging data. If I look at various timing data from the current tune 3-4 degrees BTDC is what I am finding this tune to be in similar RPM ranges. I figured if my new tune is close to what is in the ECM now I'll have a good idea of where to make changes since I'll be able log data and compare that data with the tune file which I can't do now. Does that sound like a plan?

Scott,

Sounds like a good plan. I would encourage you to be a little gentler on your fuel pressure additions. You'll likely have a loud truck with that much extra pressure. Maybe avoid touching the FRP tables until phase 2. Your call. Keep us posted.

Nick,

I'll follow your advice and only increase the torque to fuel tables for starters. The data logs were showing higher FP numbers than stock. That's was my reasoning for increasing FP too.

Scott