So last week I finally jumped a tooth and went 1/8 above the timing mark. Drove around in town some then hit the highway for 140 miles. Here's what I have noticed so far.

1. Little loss on bottom end and more bottom end smoke.
2. Feels like the turbo is a little slower on initial acceleration. This could be the cause of more low end smoke.
3. The motor sounds smoother on the top end. Before when i would run out 4th the motor sounded wrapped tight around 70 and that's when i would shift. Now seems like it isn't straining as hard and pushed to 75 before getting the same sound from before at 70. Speed was done using gps.
4. Definitely more responsive on top end.

Ultimately I think I may roll it back to the stock timing mark and see what i have there. I really don't like that extra bottom end smoke.

Onemoparnut, I know you have been having issues with your fan but have you noticed any of the same i listed?

 

I would back it off a little and run a timing spacer.

 

Second stock timing and the spacer.

 

The spacer alone won't give me enough timing.

 

Just curious, at that advance (1 tooth plus 1/8) how does your ksb behave - does it still rattle up the idle when cold?

 

Hasn't been cold enough yet here in Texas and i haven't manually activated it.

 

The spacer doesn't necessarily give you more timing. It gives you a wider dynamic range of timing advance.

You still have to set your static timing, so as to establish where the dynamic range plays.



"1. Little loss on bottom end and more bottom end smoke.
2. Feels like the turbo is a little slower on initial acceleration. This could be the cause of more low end smoke."

- Understand that when you advance the injection event timing, you basically are allowing more time for the heat of combustion, to be converted to actual work at the crankshaft. With more heat being converted to to at the crankshaft, there's less heat being wasted via the exhaust gases.
- Remember, our turbocharger is powered by the heat in the exhaust gasses. Less heat to drive the turbine means less power to the compressor, hence, lower boost. Changing nothing else, less boost means less power / more smoke.



3. The motor sounds smoother on the top end. Before when i would run out 4th the motor sounded wrapped tight around 70 and that's when i would shift. Now seems like it isn't straining as hard and pushed to 75 before getting the same sound from before at 70. Speed was done using gps.
4. Definitely more responsive on top end.

- Keep in mind we're dealing with a timing thing. The initiation and termination of the injection event, relative to the crankshaft position. Holding that thought, we've also got the window of time regarding the initiation and termination of the injection event itself. With a given injection (pop) pressure, it takes a given amount of time to inject the given volume of fuel, meaning, it'll take longer to inject a larger volume of fuel (wider window). Ideally, we'd inject the majority of the fuel just before TDC. But we're stuck with the given window of injection (said windows width is ultimately determined by the throttle). With that, we try to advance the timing so as to keep the injection window in an optimum place relative to the crankshaft hence, the smoother high RPM operation.

Speeding up the crankshaft gives us less time to inject the fuel in an optimal fashion. Again, we're stuck with a relatively wide injection window.

At best, our dynamic advance is a compromise as with more and more timing advance, negative torque increases (the engine is trying to run backward) and reduces the net power out the crankshaft.


- So say the voices.


Getting back to the spacer, it allows one to, at low engine RPM, operate with less timing advance (stockish) , thus a little more heat out the exhaust to better spool/power the turbo, while still allowing notably more timing advance to better burn a larger quantity of fuel in the higher engine RPM.


Make sense?

 

Not entirely; but it's not your fault I'm not the quickest quail in the covey!

My truck is bone stock and my incentive to advance the timing (slightly) would be strictly to better my fuel mileage.

You mention the "dynamic" timing spacer allows for use of more fuel at higher RPMs (which is clearly an advantage for a power machine with the IP turned up). Would the spacer help my bone stock truck attain better fuel mileage?

Again, I'm a .

Thanks.

 

It should increase mpg a little. (I wouldn't know . . . . . . stomping my throttle all the time. ).

 

BC847, Thanks for your lengthy response. I have an understanding of how it all works and just thought i would post my results for others contemplating the modification.

My comment about the spacer was in regards to the comment about going back to stock timing and adding the spacer. Like you stated, larger injectors and increased pop pressures require more timing to operate efficiently. I have larger injectors with increased pop pressures. I was already to the head and wasn't getting the performance I thought i should be getting.


Prior to jumping a tooth:
Dyno results had shown a 30hp gain when activating the ksb for the 3rd pull. Probably could have been more if done on the first run before heat soaking the motor.

 

Mine seems to rattle more at an idle but be smoother going down the road. There seems to be less low end smoke and it spools a little better.

 

I skipped a tooth, and the pump is at the stock mark. Hard to say the difference, but it definitely is louder in low rpms, and very smooth at higher rpms. Reason it is hard to say is because I hadn't driven it for a year! David, do you think it would be beneficial to do a timing spacer, even with the timing skipped a tooth?

 

Yeah, think i may have gone a hair to far. I'm going to back it down to the timing mark and see how it does.

 

I had the timing to the head when I jumped a tooth. It pulled hard once it spooled but fell way off in the upper rpms. I backed it off some and it runs much better now.