Thread: Inj pump timing ''worth the hassle''

Hey folks.

I am hoping some of you have played with the pump timing since it was last discussed on here.

So do the benefits outweigh the hassles of doing it.

Are we getting a noticable increase in power or is it only a ''bees dicks'' worth only visible on a dyno.


thanks in advance

Justin

there is an automatic advance that takes care of the timing advancement as engine speeds increase. But as you inject more fuel it burns for longer from about the same effective starting point..

for the sake of this discussion I'll state injection as being statically set to TDC its not IRL but it makes it easy for the purpose of explination

if you dont need a lot of power and your idling then your injection is at TDC and you get a little bit of fuel burning and it pushes the piston down for lets say 1/4 of its stroke as its burning and then the remaining distance is done by the thermal expansion of the gas, when it hits BDC then the exhaust valve opens and whats left (which isnt much) expands out into the exhaust system to help spin the turbo as the pistion starts coming up.

so now when your screaming along and your coasting on a slight down hill and using just enough power to maintain speed (again magically this will require exactly the same quantity of fuel as idling) your still injecting the same amount of fuel but you need it earlier so by the time the fire gets going the piston is at TDC and then exactly the same as before you get 1/4 of a stroke of burning power and 3/4 of expansion before the exhaust opens and the gasses go on their merry way to annoy some greeny in an electric car.

so thats what the auto advance does moves the start time of injection in the same way that the timing advances in a petrol engine with speed but without the hassle of having to retard it if you have low manifold pressure, Why? because the manifold pressure of a diesel is alway at about 1 atmosphere and never below it. (well not by enough to have to worry about vac advance)

So when you want more power you need more fuel and the 2 ways of doing this are by raising the injection pressure which means more fuel in a set period which is what the new electronic and hydraulicly controlled injectors do but you dont have them so you have to lenghten the injection time.

IF you did that by moving the start of the injection cycle then the engine can try to run backwards (piston being pushed down against the inertail motion of the engine) every time it fires. This can actually be achieved in some diesel engines but generally not very well and its quite impressive to see the look of shock when a truckie cant work out why he now has 18 reverse gears 2 forwards and his aircleaner is belching the white smoke of a diesel running on low compression. The real side effect of moving the injection too far forwards (before top dead center) is that it will knock and excessive diesel knock is generally a recipie for pistions trying to turn themselves inside out, bent rods, smashed bearings, bent cranks, dropped cranks and bits that should be internal becoming exernal. Most fequently its a bit of all of the above. So the simple solution is to leave the start time alone and just increase the duration of the injection cycle. Thats not to say it cant be done some engines move the start time and some others move both.

But Ive meandered off the track. (and some would say onto an entirely different section of the map book)

So were stuck with increasing the duration of the injection

so with the engine idling along and your foot flat to the boards (ignoring the other influences on injection like the govenor and the boost compensator) your injection is starting at TDC and then instead of burning the fuel for 1/4 of the stroke its buring it for near on 15/16ths of the stroke leaving just a little bit at the bottom for the flame to go out so your not putting fire down the pipes and into the turbo (which is cool if you want glowing exhaust manifolds, burning the valves killing the turbo and while providing some Huge power to spin the turbo and make boost levels that most people would read as tyre pressures) when the exhaust valves open again at BDC.

The best part of this is that due to the circular motion of the crank when the piston is at about halfway the relative position of the crank means that as it passes 1/2 way the crank is providing the biggest lever it can to the piston and with the fire still on and the combustion process really cranking you get the most power you can get and anything left over is going to be useful at providing drive but more useful for driving the turbo..

And surprisingly given that the time it takes for the burn to start at higher RPMS with a larger injection quantity is the same as we're not injecting the fuel any faster (faster injection requires higher injection pressures) at higher RPMS we just inject the fuel at the same relative time as a high speed low power setting and let it burn longer. simple hey.

Turboing engines as opposed to NA engine do have different timing requirement but since we're only talking about a turbo engine and not modifying one from being turbo to na or vice versa its not a big problem for this topic.

is that helpful?