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#15
by
R.O.R-2.0
on 13 Oct, 2011 07:38
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basically, when the pump is off boost, its capable of about the same fueling as the n/a pump.
but when the boost picks up, it moves the LDA stop, and kicks up the fuel. i imagine that the LDA adds the equivalent of 3-4 turns on the fuel screw.. it moves quite a bit, i tested mine with some pressure, and it makes the stop lever move a considerable amount.
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#16
by
fatmobile
on 13 Oct, 2011 21:29
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The pin does limit fuel on boost. Off boost, the LDA arm sits at the same location as the pin and there's no difference. On boost, the arm moves, allowing additional fueling and effectively extending the available fuel map.
It's been so long since I've been into one of those pumps, but as I recall, through a monkey-motion series of levers,the LDA allows the control collar to slide lower on the plunger and to cover the control port for a greater duration. Fuel screw only changes the position of the fuel map and the LDA extends the fuel map, to the best of my memory.
Chris
The LDA arm can't sit at the same position as the pin off boost,..
The pin is what the lever hits when it's floored.
That would be like saying the LDA arm holds the lever in the same position off boost as an NA pump does when it's floored.
When you went to put the lid on; the lever would be floored to the pin, instead it sits at rest and the LDA slides in next to it
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#17
by
Luckypabst
on 13 Oct, 2011 22:56
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That's exactly what I'm saying. Remove the boost hose to LDA, run around at WOT and it acts just like a NA pump, because the LDA arm is at the same location as the pin would be in a NA pump (limiting travel of the control collar lever). Now, while at WOT and full boost, reinstall that boost hose and you have a wider fuel map as the LDA arm responds to the boost signal (as the LDA arm moves and allows the control collar lever additional movement).
I don't follow the last statement. The lever won't be against the stop pin when you install the pump cover unless you're also holding the throttle arm against the max-speed stop. If you don't remove the fixed pin and install the LDA, the pin and LDA arm will sit side-by-side and not interfere with one another but the fixed stop pin will not allow the control collar lever the additional movement under boost.
Anyone have comparison photos?
Chris
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#18
by
fatmobile
on 19 Oct, 2011 07:39
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The pump is capable of pushing out just as much fuel NA or TD.
The LDA arm doesn't limit the control collar lever to the same place.
With the LDA in place the lever won't move as far without boost
The LDA limits fuel off boost, so off boost you won't get much smoke with the boost line disconnected,.. but you will with an NA pump.
Yet you say it acts just like an NA pump.
Pretty obvious the LDA arm is keeping the lever from moving off boost, but you say it's sitting in the same place as the pin in the NA pump,..
the one that allows smoke off boost.
If the lever was able to move all the way to the pin off boost,.. there would be smoke just like an NA pump.
There is no extra movement provided by the LDA arm, there is no extra fuel provided by it or extra travel of the lever. It simply limits fuel off boost.
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#19
by
R.O.R-2.0
on 19 Oct, 2011 07:54
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The pump is capable of pushing out just as much fuel NA or TD.
The LDA arm doesn't limit the control collar lever to the same place.
With the LDA in place the lever won't move as far without boost
The LDA limits fuel off boost, so off boost you won't get much smoke with the boost line disconnected,.. but you will with an NA pump.
Yet you say it acts just like an NA pump.
Pretty obvious the LDA arm is keeping the lever from moving off boost, but you say it's sitting in the same place as the pin in the NA pump,..
the one that allows smoke off boost.
If the lever was able to move all the way to the pin off boost,.. there would be smoke just like an NA pump.
There is no extra movement provided by the LDA arm, there is no extra fuel provided by it or extra travel of the lever. It simply limits fuel off boost.
my experiences are quite contradicting to your statements..
an n/a pump, and a TD pump not connected to boost, supply the EXACT SAME fueling.. take an LDA head off, mark the lever movement. then mark where the stop pin is.. the stop pin is farther back than the LDA lever.
i have LESS fueling than with the n/a pump top.. yet more boost. how does that work out if the n/a and LDA fueling are the same? less fuel but more boost? and no smoke on the bottom end?
the LDA allows n/a fueling while off boost. then when you hit the boost, thats when the LDA really helps out. particularly over 10 psi boost..
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#20
by
Luckypabst
on 19 Oct, 2011 08:31
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I kinda agree with R.O.R. there...
Like I said, it's been a long time since I did this mod and I'm going off memory but as I observed from comparing things side-by-side, operating the LDA & watching the arm move relative to the stop pin position, it was clear to me that the LDA allows a wider fuel map, extending available fueling beyond what's allowed by the fixed pin, only on boost.
It really would help to have photos of an LDA pump top next to an NA body to see where the LDA arm limits fuel off boost compared to the fixed pin, then to see the upper limit with the LDA pin pushed down in it's travel as if at max boost.
Chris
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#21
by
R.O.R-2.0
on 19 Oct, 2011 08:51
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I kinda agree with R.O.R. there...
Like I said, it's been a long time since I did this mod and I'm going off memory but as I observed from comparing things side-by-side, operating the LDA & watching the arm move relative to the stop pin position, it was clear to me that the LDA allows a wider fuel map, extending available fueling beyond what's allowed by the fixed pin, only on boost.
It really would help to have photos of an LDA pump top next to an NA body to see where the LDA arm limits fuel off boost compared to the fixed pin, then to see the upper limit with the LDA pin pushed down in it's travel as if at max boost.
Chris
damn it, knew i should have taken pics.. too bad the car is all bolted together. i would almost consider taking the TD pump top off just to prove a point or 12..
anyways, i played with the LDA and n/a pump tops. eye-balled the hell out of both. but even with the naked eye, the LDA allows more travel than the n/a pump limiter pin allows..
anyways, the LDA adds what i would say is like 3-4 turns more fuel screw when the LDA is actuated to 100%
idk how many PSI it takes to fully actuate the LDA, but it DOES allow more fueling, i know that for sure.. my car sounds different on boost now. it seems to growl more out the pipe when boost sets in..
i used to think the same thing.. LDA and N/A pumps had identical fueling, just the TD limits the off boost fueling.. but thats wrong..
they have the same fuel curve when the LDA is not hooked to boost.. but when you hook up the LDA, it supplys MUCH MORE fuel..
this is a good test, someone take and install a LDA on a n/a pump, with the limiter pin still in the pump.. then knock the limiter pin out of the way.. after that is done, you will be able to use the full travel of the LDA arm, and will prolly say "HOLY S#!T" when you floor it for the first time..
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#22
by
fatmobile
on 19 Oct, 2011 22:04
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So if you floor a pump with an LDA (not connected to boost) there will be just as much smoke as an NA pump?
When you eyeballed the LDA arm,.. did you put it under boost and see where it sat?
That's the only way I can think of that would give any idea of real LDA arm travel.
The max fuel a pump can put out is to the point where the RPMs hang.
An NA pump can do that.
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#23
by
Luckypabst
on 20 Oct, 2011 09:20
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If it's set-up right, there shouldn't be much smoke at all, floored & off-boost. I can usually only see my NA Rabbit smoking in the headlights of a car behind me, but almost nothing during daylight. With a turbo and no enrichment (either LDA with no boost reference or NA pump), you should see even less smoke since there will be boost present at full throttle, same as Ecodiesel.
I never really understood the hanging throttle thing (but I've never turned my pumps up that high either). Seems like the only way the throttle could hang is if the mods performed are creating a mechanical issue where the pump can't return the control collar to idle on its own. As long as the control collar returns, there's no way the pump head can get excess fuel beyond what the throttle input dictates. Governor mods effect the balance between collar return spring and governor... fuel screw effects the pivot point of the control lever... LDA arm effects the stroke of the control lever. The first two options effect ratios and mechanical advantages designed into the pump, the LDA swap preserves design features and only increases control collar travel.
Increasing fuel on an NA pump still gives a linear fuel curve, regardless of conditions. An LDA pump gives a linear fuel curve as well, to handle off-boost conditions but adds fuel as needed as boost and load increase (boost increase extends the available fuel 'window', load increase via additional throttle input makes use of this additional 'window').
Chris
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#24
by
R.O.R-2.0
on 20 Oct, 2011 11:54
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So if you floor a pump with an LDA (not connected to boost) there will be just as much smoke as an NA pump?
When you eyeballed the LDA arm,.. did you put it under boost and see where it sat?
That's the only way I can think of that would give any idea of real LDA arm travel.
The max fuel a pump can put out is to the point where the RPMs hang.
An NA pump can do that.
yes, i used my air compressor, and made the LDA work the full range of its travel..
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#25
by
Luckypabst
on 20 Oct, 2011 12:40
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I removed the LDA cover and cycled the diaphragm with my finger... same result.
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#26
by
R.O.R-2.0
on 20 Oct, 2011 12:45
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I removed the LDA cover and cycled the diaphragm with my finger... same result.
yup..
either way, the lda off boost is about the same as the limiter pin, positioning wise..