I recently swapped in a set of reman injectors since I knew I had at least 1 badly leaking injector. I know you're supposed to do pump and injectors at the same time but only 55k on the IP so I figured I'd go for it. I've been playing with different timing settings and it's interesting what works better so far. A lot of online info has people reporting better performance on a turbo IDI with retarded timing anywhere from 6-7.5, yet others report advanced timing to offer better performance on a turbo IDI. When I bought my 1990 the IP was timed at about 10.2 or so and ran okay with little to no smoke and got about 15-16mpg on the highway. I backed the timing down and nothing ever improved. Now with the reman injectors I started with timing at 7.1 and it didn't seem to run all that well--poor idle, more smoke, and no extra power that i could notice. I advanced the timing to 8.8 and it ran much better. Since then I advanced the timing just a hair, haven't checked it on the meter yet, and it runs even better--pretty clean idle, less smoke, good power. I found some older info suggesting that ULSD burns differently than the old high-sulfur fuel and that advancing the timing compensates for this difference--9.7 degrees was the calculated number to compensate for ULSD. So far my own experience seems to parallel this idea of advancing the timing to maintain power and performance.

So I guess I am mostly trying to understand why would some people's report better performance with slightly retarded timing yet others find slightly advanced timing to be better? Are there variables during the pump rebuild process that can affect the best timing setting? Wear in the injection pump itself? Injector pop pressures?

 

Probably the biggest thing is the fuel quality/cetane value for the area. It sucks that gas is federally mandated to be listed with it's power rating, but not diesel. My trucks love 7BTDC.
Retarded timing, is safer timing, compared with too advanced timing. Reduces cylinder pressures and turbo lag. The more black smoke you get; the less efficient you'll be.

Don't forget, the mind can be fooled with more noise = equaling more power. If your brain hears more diesel rattle, it may try and convince you, you have more engine power, when in reality, the truck isn't anymore powerful. Ideally, you'll set the timing somewhere, drive for 3 back to back tanks of fuel and check fuel mileage. As long as you don't drive harder or softer and drive the same route, use the same fuel station, drive during the same season of year, you should find the most efficient setting; this will be the most powerful too. When driving for optimum performance, you want to feel what feels "free" rolling down the road, at your average speed, using as little fuel as possible. Not trying to romp on it, see what sounds cool and rolls the most coal.
I once got 17 MPG @ 55mph in my F250 dually 4x4 stake body, box truck at 7 BTDC. I say once, because that was her best all time, driving down the interstate, picking up a swing set I think it was, for my sisters kids.

 

I know that tuners for later model diesels advance timing to generate more power. Make sure you don't turn up your fuel delivery screw without first installing a pyrometer.

 

This seems to match my finding that I have to use cetane to get good performance. That is also advancing the timing, chemically.

 

many many many many moons ago, when diesel fuel was only 35 cents for a gallon if 65 cetane fuel, my 88 got 22 mpg with a C6 trans(no overdrive)
these days with the crap they call diesel i am lucky to see 40 cetane......and only get 12 or so mpg.

 

Wow 65 cetane must've been nice. I found that with the advanced timing I seemed to lose some top end when pulling a hill and higher EGTs. Today I backed things down to about 7.6 and adjusted the TPS for new idle settings and aside from a bit more smoke on a coldish start I have way better power pulling a steep hill and EGTs stayed a bit lower around 850-900. No obviously noticeable smoke while driving even at WOT.

Just as an aside I can't imagine not owning timing equipment unless you really have a well trained ear. I know trial, error, and test drives will get you there but seeing how such tiny physical adjustments make a big difference in how the engine performs it sure is nice to have a numerical value to at least use as a reference point for adjustments.