" “…. But Its The Torque That Gets You Up The Hill”"
When I talk to owner operators and techs about the subject of horsepower and torque many tell me the above statement. The above statement is true and if you don’t put enough torque to the drive axles you won’t climb that hill. It’s how fast you climb that hill is what horsepower is all about. So, unless you’re torqueing down bolts or doing specs on driveline components a torque number without an RPM number is useless and we can’t talk about one without talking about the other. I understand why people think this way and Detroit may be partially to blame.
When you compare and test drive many factory DDEC programs it’s easy to see how torque is often seen as a better way to size up how powerful a program is. Let’s compare four different 1993-1997 12.7 Series 60 6067GK60 programs:
1. (430hp@1810rpm 1250ftlbs@1200rpm),
2. (430hp@1810rpm 1350 ftlbs@1200rpm)
3. (430hp@1810rpm 1450 ftlbs@1200rpm) and
4. (430hp@1810rpm 1550ftlbs@1200 rpm).
Detroit says they’re all “four-thirties” but they’re only making 430 horsepower when they’re turning just below 1810 rpm. Drivers tend to say the 1350ftlbs 430 only makes power at high rpm while the 1550ftlbs 430 “falls on its face” when rpm climbs. Unless your running at 1800 rpm all four of these programs make different amounts of horsepower and when you do the math you’ll see just why these programs perform so differently. There are many, many ways to calculate horsepower but I like to use this simple equation. Wheel torque multiplied by wheel rpm then divided by 5252. This gets you your wheel horsepower. The same equation can be applied to calculate flywheel horsepower when you substitute in flywheel torque and engine rpm. Lucky for us, flywheel, horsepower and torque are what Detroit uses when they rate their programs. To keep things simple let’s, calculate how much horsepower the 1350ftlbs 430hp program makes vs. the 1550ftlbs 430hp program at 1200 rpm.
Step 1: 1350ftlbs x 1200 rpm = 1,620,000
Step 2: 1,620,000 / 5252 = 308.45 flywheel hp@1200 rpm.
Now let’s calculate the 1550ftlbs 430hp.
Step 1: 1550ftlbs x 1200 rpm = 1,860,000
Step 2: 1,860,000 / 5252 = 354.15 flywheel hp@1200rpm.
If horsepower is calculated throughout the RPM range a more detailed picture of what a program will feel like and how it will perform is created. Next time you compare programs I suggest you use this equation. I do this analysis with most programs I build and if you know what you want to build in terms of horsepower as rpm climbs I can get it done.
I apologize for not always being available to answer the phone. Business growth has been overwhelming and I am grateful for that. I enjoy conversations with likeminded owner operators and technicians in the industry but sometimes I have to choose between having those conversations or doing DDEC repairs and programming. When I have your DDEC on my bench I dedicate blocks of time so I can focus on your problem. While I focus on your problem frequent phone calls can break my focus so sometimes I have to let it ring. I am looking into solutions to this problem so I appreciate your patience.
Written by Fernando DeMoura, Diesel Control Service LLC. www.dieselcontrolservice.com Phone 412-327-9400