Why advance timing?

[SLang]

I am a new member to the TDR but have enjoyed monitoring your site for the last couple months.



I am new to the "little" Cummins, but have been working on BCII and BCIII Cummins for a while. It's great when you have a tried and true engine to copy like the NTC.



I have been involved with several HPC (high performance cummins) some reaching as high as 700-800 HP. And on the big engines when it comes to power and durability, the timing is always retarded. This is evident in factory Cummins. The difference between a 350HP and 400HP is retarded timing on the 400HP.



So what gives? Why does everyone on this forum seem to want to advance the timing (15-16 deg BTC I believe in the norm) instead of leaving it at factory of retarding it?



Sorry the long first post, but I figure I would start my adventure on the TDR out right.

 

[Animal]

I’m not completely sure this is correct, just my opinion so here it goes.



The Cummins in our Rams have to adhere to EPA regulations and are tuned accordingly, but the larger over the road engines are set/tuned for performance and when you increase the power you have to retard the timing to control the cylinder pressure. Our Rams aren’t running at best performance settings and we increase time for performance and fuel economy. Also the over OTR trucks have time advances on the pump but our engines have fixed timing. A lot of talk goes into this subject as to best timing settings, the people with high RPM pumps have theirs set high but the consensus for best performance and MPG use 15 to 15. 5.



This is how I understand it but I’m sure there are other opinions.

 

[John_P]

SLang:



In Issue #29 of "The Register" (page#33) Joe Donnelly

wrote a very good article on fuel pump timing.



In part, Joe wrote the following:



"For Cummins B and C series engines, the timing is part

of the CPL (Control Parts List), which is basically the

emissions "recipe" that we use to certify the engine

with the EPA. There is a tolerance band around that

timing. Timing is one of the many things that the

performance engineers consider when they're

developing a rating. Putting it simply, they have to

balance cylinder pressure limits with emissions and

power requirements. "



Adavancing the timing will... (Good Characteristics)



- Increase cylinder temperatures/pressures (power)

- Increase fuel economy (yes, economy is better)

- Decrease exhaust temperature

- Decrease your output of hydrocarbons-a pollutant



However, advancing the timing will. . (Bad Characteristics)



- Increase the amount of black smoke particulates-

a pollutant at peak torque

- Increase your output of NOx-a pollutant



(quoted material by Joe Donnelly through Josh Berman,

Cummins)



I have found all of this to be true on my 96' CTD. My

"timing" is set at 17. 5



-----------

John_P

 

[Skydiver]

Low end power

I usually run my cummins around 1500 rpm. What does advancing the timing do to low end power and economy?