9mm vs 11mm pumps

[darrenjlobb]

Also, the highest powered XUD I've seen proven on paper is running a 9mm and hasn't blown yet.

Who ran over 213 on 9mm? Although pretty besides the point lol,

Reliability doesn't really come into it, you really just have to get your head around the way the pump works....

In short there are two ways to increase the ammount of fuel the engine gets, A is the change the injection length, and b is to inject more at any one time.

By putting an 11mm head on, more fuel is injected per *mm pf plunger stroke than with say a 9mm head, so in effect, you can put more fuel in, in the same duration....this will always be the case, as you cant change it other than fiddling with dv's / nozzles.

So the only way to make 9mm pumps make more fuel / power, is to increase the length of the injection more than normally possible. All the throttle lever does in a VE, is increase the injection length, and the lda allows it to increase even more. By changing out levers / lda parts etc, you can increase "travel" on the control collar, which in turn allows you to run a longer duration than is possible on a normal "stock" pump, without running silly high idles. This will only work for so long though, as longer injections eventually just start making silly heat / egts, and not much more power, which is where big nozzles / heads come in, to dump the fuel in faster (particually with DI)

IMO the bigger head makes for a much more fun drive / responsive engine (other people will agree with me here?) and also makes getting plenty of fuel much easier, BUT the biggest problem doing this at home, is is throws every aspect of the pump calibration out the window...including the timing curve, and smoke control, as your suddenly linging in double the fuel across the throttle travel, so for a well setup 11mm pump, you need to spend alot of time fiddling with timing parts / gov parts to make it controllable again.

Obviously retaining a 9mm head, allows you to control the smoke much more easily, and other than the normal timing loss's from extra traval, it remains fairly much stock, which is a good thing if you want plug and play.

Theres lots of plus and negs about both sides of it. But me personally....bigger plunger everytime!