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#15
by
fspGTD
on 09 Feb, 2006 12:00
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Yes, it is very surprising! Reduced fueling causes reduced torque in a diesel. If fueling were maintained higher, it may very well produce significantly more power and torque! :shock:
There are a number of factors possibly contributing to a difference in pump dyno versus real world performance, but I'm not sure if they're the main culprit behind the 4000RPM fuel dropoff or not:
* fuel temperature precisely regulated (to a little over 40 deg C in my case) on the pump dyno, versus varying in the real world (I have not measured mine, but would like to!)
* fuel supply line pressurized slightly on the pump dyno to the given specifications (about 2psi in my case), versus being under suction, pulling fuel from the tank and through a filter when on the car.
* fuel injectors are different, "test orifice injectors" with different characteristics and set to their own breaking pressures versus the real stock injectors (or in my case, non-stock injectors.)
* There is potential for the RPM of a chassis dyno machine or G-tech to be miscalibrated, however with the pump dyno giving an RPM readout resolution to the nearest single RPM, it would seem to be very trustworthy.
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#16
by
Mark(The Miser)UK
on 09 Feb, 2006 17:03
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Yes, it is very surprising! Reduced fueling causes reduced torque in a diesel. If fueling were maintained higher, it may very well produce significantly more power and torque! :shock:
There are a number of factors possibly contributing to a difference in pump dyno versus real world performance, but I'm not sure if they're the main culprit behind the 4000RPM fuel dropoff or not:
* fuel temperature precisely regulated (to a little over 40 deg C in my case) on the pump dyno, versus varying in the real world (I have not measured mine, but would like to!)
* fuel supply line pressurized slightly on the pump dyno to the given specifications (about 2psi in my case), versus being under suction, pulling fuel from the tank and through a filter when on the car.
* fuel injectors are different, "test orifice injectors" with different characteristics and set to their own breaking pressures versus the real stock injectors (or in my case, non-stock injectors.)
* There is potential for the RPM of a chassis dyno machine or G-tech to be miscalibrated, however with the pump dyno giving an RPM readout resolution to the nearest single RPM, it would seem to be very trustworthy.
Jake
What account is this test giving of real life loading and the positive feedback that would come through the spaceship [oops aneroid]? Could this graph effectively be only showing a series of 'no-load' cruising speeds 'pencilled' together to form an artificial graph...
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#17
by
DVST8R
on 09 Feb, 2006 18:17
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So... the mystery is: what is pulling back fueling on my pump as early as 4000RPM? Could it really be the main governor spring? Could there be some other unexplained phenomena at work here?
The "ski jump" like characteristic of the fueling curve approaching 4500RPM is also very intriguing. I'm not quite sure as of yet about what to make of this.
The only way I know of to solve that mystery, is to pull the pump apart and put somthing other then a spring in where the main spring is. I have used a piece of fuel line in the past, it has a little give like a 1/32nd - 1/6th of an inch. This would take the spring out of play and let you know if it is being pulled. My suspetion is that it is using the main spring, They had to have designed it that long for a reason. In my NON expert look at the graph, I would say that your shimming it of a 1/4" as i recall only gained you about 500rpm's. If you compare the slope of the stock graph where it begins to fall off, and the slope of the modified, they are approximatley the same from 3500-4000, at which time I would guess that the govnor completely overcomes the preload and pulls it down like stock. But like I said I'm no expert.
As far as the ski jump it might just be a dyno annomoly that happened that round? or it seems to be really close to where your timing adavace runs out, though I'm quite certian that fuel delivery and delivery timing are independent in the pump.
Finally what did the fuel injection shop have to say for the dyno? did they give any indication as to why the ski jump and why the fuel curve, or how to change the fuel curve?
You also need to try your modified timming cover on a dyno pull and see how much extra it gives you as of right now even if you had "full" fuel to burn to 5500 or 6000 rpm you would be running out of time to burn it.
...One more thought to this already long post... Mabey it drops at 4000rpm because the pump has hit the delivery wall?
Anyway lots to think about and discuss. :wink:
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#18
by
Mark(The Miser)UK
on 09 Feb, 2006 19:17
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...One more thought to this already long post... Mabey it drops at 4000rpm because the pump has hit the delivery wall?
Anyway lots to think about and discuss. :wink:
If it was a max fuel available limit; wouldn't the slope drop off slower say 8cc @4000rpm and 4 cc @8000 rpm? Just a brain storm (all 10 cells working for that one!) :shock:
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#19
by
lord_verminaard
on 09 Feb, 2006 19:27
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Hmm, maybe the plunger is skipping on the camplate at around 4500 rpm? I thought (dangerous thing) that I read once that was a problem with the TDI's when they approached 4500 rpms or so. I guess the only real way to know is to completely take the govenor springs out of the equation and see if fueling starts dropping the same way. I'd be willing to bet that it would.
Wonder if "pumpmaster Giles" could shed some light on this situation?
Brendan
84 Scirocco 8v
00 Camaro L36 M49
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#20
by
fspGTD
on 09 Feb, 2006 21:39
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All the data points shown for my "Fueling" plot as well as the "Fueling, Stock Spec" plot are at full throttle position and with 10.8 psi boost pressure applied to the LDA.
I talked about the question of why the fueling is dropping off earlier than the governor was expected to kick in with the guys at the diesel injection shop that helped with the test. The latest theory cooking down there is that there is a maximum flow limit being reached in the inlet port of the high pressure head.
Certainly "disabling" the main governor spring and retesting would help confirm or deny my belief that it's something other than the governor spring acting at 4000RPM, however it may not be practical for me to run the complete injection pump dyno testing process through again.
At first, I dismissed the possibility of camplate float, because the stock pump didn't seem to have any dropoff at 4000RPM nor did it seem logical for the camplate to float prior to the rated speed (which is above 5000RPM.) However, I am now re-thinking this possiblity. Pehaps at higher flow rates, a greater pressure drop is caused through the inlet port. This "increased suction" on the fill cycle would increase the tendency for the camplate to float now, wouldn't it!
The test and possible fix would be to shim the plunger return springs to a higher pressure and see if it makes any difference.
Now that I think more about it, I do recall noticing a pronounced noise coming from the pump happening at about 2000RPM (4000 crank rpm)... right where the dropoff in fueling starts!
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#21
by
fspGTD
on 09 Feb, 2006 23:59
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Here is a corny video of me running the pump test bench for my first time while Jay is running my digital camera for his first time. I take it up to a little over 2000 pump RPM, then drop it down too far and it runs backwards a little. :oops:
http://media.putfile.com/VE_Pump_Test
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#22
by
Giles@PerformanceDiesel
on 10 Feb, 2006 18:54
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hi guys
during my R & D with my pumps i have found that there is def camplate
float at higher rpms.
i've tried diferent spring rates and it helps allot.
Giles
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#23
by
VWRacer
on 11 Feb, 2006 05:59
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Jake, I too was wondering about the fuel dropping after 4000 RPMs. Assuming that it is NOT the main gov'nor spring (which it shouldn't be, right?), then could it be that the pump is actually pumping at full capacity, and that volume per stroke is dropping? The line looks too steep for that, but it's a thought.
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#24
by
Giles@PerformanceDiesel
on 12 Feb, 2006 07:08
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I injection pump dyno tested my GTD Autocrosser's VE injection pump successfully yesterday! Although it was more time/effort than I had previously expected, it was a lot of fun, and I feel that I came home with some really great data on my pump
looking at your graph you show that u have aprox 78cc at 1200rpm
i gather that is with full boost ?
the more important fueling is the no boost fuel off idle.
did u record that?
let me know
and yes the 86cc of andy's pump was not maxed out by any means
but he still had stock no boost fueling.
Giles
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#25
by
fspGTD
on 13 Feb, 2006 21:27
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Stan: regarding fueling rates... We're probably over-analyzing this, but I added some calculations of the fuel curve plots, now showing the following:
Fueling (quantity per stroke, which would correlate with crank torque)
Fueling x RPM (or the fuel rate, which would correlate with horsepower)
Fueling x RPM x RPM (may not represent anything real, but nonetheless kind of interesting to look at)
It is interesting to note that the fuel rate indeed peaks at 4000 crank RPM then starts a decline. Fueling*RPM^2 however is fairly constant from 4000-4800RPM, and then abruptly makes a downward turn.
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#26
by
andy2
on 14 Feb, 2006 18:16
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It is interesting to note that the fuel rate indeed peaks at 4000 crank RPM then starts a decline. Fueling*RPM^2 however is fairly constant from 4000-4800RPM, and then abruptly makes a downward turn.
Thats interesting as my Giles powered AAZ pulls hard to exactly 4500 rpm and Still works ok to about 4700 rpm.I guess these 1.9er's arn't all that bad of revers afterall
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#27
by
Hey
on 17 Feb, 2006 12:05
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So... the mystery is: what is pulling back fueling on my pump as early as 4000RPM? Could it really be the main governor spring? Could there be some other unexplained phenomena at work here?
You will need to find some stiffer spring for your injection pump head. Maybe there is no cam floating with stock pump at 4000RPM... but I don't think your spring can still be call "stock" spring....they have worked a lot.
Maybe some shim would also help.