Yea thats all I had ever heard of too.

Hey panZZER,

take my Holly elements (MW 6.5mm) for 75 EUR/each and have them installed and adjusted by 616.
I am in the US (Madison, Wi , Fayetteville, Ar and Columbus, Oh) next week, so you can save on shipping if you let me know within the next 12 hours (and tell me how we can manage the shipment within the US).

Tom

Hey Tom, I would still like to work a deal for the Floyd 7.5mm...

Columbus, OH is my home town!

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

I've got just a second here, and will comment further on the above posts, but I thought I would X2 the idea of Tomnik's 6.5MWs for anyone who is looking for the easiest, "plug and play" element upgrade, Tomnik's are your best bet. And if he is going to be in the USA, now is the time to get them.

Alternatively, There are 8mm MW elements which I was quoted a price on, (have to check my notes to refresh), but when I went to place an order, they were out of stock and not sure when they were going to make more, as such, I decided to develop a method to use more common, and available, 10mm elements.

I have not seen the end of delivery angle on the 8mm element plunger to be sure how user friendly they would be as a "plug and play" element upgrade, but after hearing that 617a with 10mm elements run, (I have one of the same elements), I would feel somewhat comfortable trying the 8s as is, if they are in stock.

Again, Tom's should not require any major governor tuning as they are not a big step in size and the end of injection angle was determined for our MW IPs specifically.

Got to go, more later,

Tom-- Bring Them-and plan on sending from Arkansas

Well folks--I got my order in within 12 hr's like the man said.
now i gotta come up with some rent money--Hey-anybody need some 309D Euro truck parts?

Have you landed in the US?? let me know whats your scedule.

Tom -You have to talk to me if we are to take care of it.

This is a post I wrote in the diesel discussion section relating to the lift pump pressures effect on engine performance and longevity. As it stalled the thread, I am transferring it over here. I edited it some. It starts with the answer to a question about fuel pressure and performance.

The lift pump pressure does have an influence on the engine out put, as, if I open a bypass valve I have, (to make priming easer with the high relief pressure), the idle speed will drop about 100-150 RPM, and that is at idle.

I have a theory why higher pressure is beneficial, but haven't thought of a good way of tying everything together. That being said, I will attempt to lay the ground work as to the basis of the theory.

The element is like a syringe with a check valve, (the delivery valve), on the end, and a hold in the side 3/4 of the way down from the top.

Now to start, the plunger is at the bottom, (bellow the fill hole in the side), and the syringe is full of fuel. When the plunger is pushed up, fuel will be expelled from the fill hole until the piston passes and seals the hole from the upper volume of fuel. At this point pressure is generated in the syringe, and fuel is forced out the check valve. The plunger continues to push out fuel until only 25% of the start volume remains in the syringe.

Here is where things get interesting, (well to me anyway), at this point there is a sealed chamber full of fuel, the only possible opening is the check valve which only lets fuel flow out, not in.

The plunger needs to go back down bellow the fill port to allow the syringe to be refilled for the next cycle, but, with a check valve blocking the only possible source that could be used to vent the syringe, allowing air to replace the area, (volume), created as the piston moves down in the sealed syringe, how will the piston be able to overcome the vacuum and move down?

I think what happens is that the pressure inside the syringe, (element), as the result of the vacuum that is created as the piston tries to move down, drops to a point where the remaining fuel in the element actually boils, (the result of a high vacuum), expanding in volume, which allows the piston to move down. Now once the fill port is opened, the pressure in the element needs to be restored to at, or above, atmospheric pressure to condense the boiled fuel and refill the element.

I can see how the base fuel pressure can have a big effect on quickly the pressure is restored in the element let alone the filling of the element at high speeds.

There is more to this, but lets see what everyone thinks of this nugget of thought.

wouldn't we call that 'cavitation'?

wouldn't that decrease the lifespan of the pump?

There must be some control for this, such as the collars on the delivery valves. Their dimensions and spacing from the fluting must be based, at least partially, on maintaining balance between the pressure in the injector lines and preventing cavitation in the elements.

Once the fuel stops flowing through the injector, the delivery valve shuts to maintain a certain level of line pressure. After the end of delivery, the volume of fuel that was delivered is not replaced by the delivery valve.

Take a syringe that is full of water and compress the plunger half way down. Then place your finger over the tip to seal it, and try to pull the plunger back to where it started. The only way the plunger will be able to move back would be to have air leak past the piston, or, if the water starts to boil because the internal pressure has dropped to the point where water boils at the current temperature.

The Element plunger and barrel are no different. The element generates thousands of pounds of pressure, so the seal between the plunger and the barrel is very good. Once the delivery valve is closed, there is no path for fuel to enter the area bellow the delivery valve and above the piston, during the duration of the plungers downward stroke in which fuel was delivered on the upward stroke. At idle this distance is very little, but as more fuel is delivered the distance the plunger needs to travel either under High pressure or Low pressure increases.

Cavitation in the element would certainly destroy it after time, agreed?

This cannot be happening to any notable amount.

Acknowledge that I am just brainstorming with you here, you obviously have much more experience with these pumps.

Why do you think the the DV closes before the plunger begins descent?

Couldn't the pressure differential created as the plunger recedes be the reason the DV closes in a timely fashion? ie.. the rush of fluid past the DV collar slams the DV closed.

More importantly, the plunger has a relief (control helix) cut that meets a relief port after the effective stroke has completed.

In this case not necessarily. I am very familiar with cavitation burning of hi-performance boat props which actually can burn or erode an aluminum prop in short order, but the stainless steel ones hold up fine.

In the case of a prop, there is an edge of a blade separating the high and low pressures where the cavitation starts. This edge will be compromised much like a razor blades sharp edge when heated with a lighter.

In the case of the element, there is a sealed chamber with only a low pressure area because the high pressure area is isolated by the delivery valve, and until the fill port is uncovered, the plunger separates the low pressure from the fuel supply chamber. Because the pressure will the same everywhere in the chamber, the fuel will boil thought the chamber as apposed to at an edge between high and low pressures.

There is a point where the top edge of the plunger, and the top edge of the fill port are exposed, ( at the point where the plunger drops below the top of the fill port), however, once the fill port is opened, the pressure inside the barrel starts to rise, and the fuel will condense back to a liquid which has less volume than in a gaseous form. The condensation of the fuel aids in the drawing of fuel into the element.

To recap, I am comparing the known destructive caviation created by a prop where there is an edge at the point between a high pressure liquid and a low pressure area, and the elements sealed chamber, where the pressure is equal everywhere during the caviattion, with an edge at the point where the already low pressure is exposed to a higher pressure. ( this case is opposite of the prop).

I have a delivery valve with an eroded seat that I am confident was eroded by the high pressure above the delivery valve trying to get to the low pressure of the element via a defect in the seat. The rapid and extreme drop in pressure caused the fuel to boil as it passed through the defect in the valve seat, and over time eroded the seat in one spot.

When the fill port is opened the pressure in the element will go up as apposed to going down, condensing the fuel as apposed to boiling it, so I am leaning to the side of thinking that the condensing of the cavitated fuel is not as destructive to edges as the actual cavitation of the fuel is.

This is where my thinking that the higher supply fuel pressure may be beneficial because the higher pressure will help raise the element pressure faster, thus reducing the exposure of the top edge of the plunger to any cavitation created when the supply fuel is exposed to the low pressure of the element when the fill port is opened.

The Delivery Valves have strong springs that keep the DV piston seated against the seat. As fuel is pushed out of the element the DV piston will move or chatter depending on the rate of fuel being expelled from the element. Once the flow stops, the spring will seat the piston and seal off the line pressure from the element.

Now the delivery valve does have a feature, (the collar), that does allow the displacement of a very specific amount of fuel as it closes. This displaced volume controls the residual line pressure after the end of injection. Modification of the collar will alter the displaced volume, which will raise or lower the residual line pressure depending on whether the displacement was increased or decreased.

In order for the delivery valve to allow the same amount of fuel that was injected to flow back into the element, there would need to be a blatted of some sort to store the fuel, instead of it being injecting it into the prechameber.



That is exactly how it works. The higher pressure in the line pushes on the collar. Only the volume from the bottom of the collar to the tapered seat is displaced when the DV closes. Any additional volume of fuel that might make it past the collar would go out of the element through the helix and would do nothing to aid in the refilling of the displaced volume of fuel.

Yes. the control helix controls the end of delivery and thus the amount of fuel delivered. The helix will allow fuel to flow out of the element during the remaining upward stroke, after the end of delivery, and will allow fuel to flow back in during the initial portion of the downward stroke until the plunger reaches the point of lift where the end of delivery took place. At such time, the chamber of fuel in the element is isolated from the supply fuel chamber, and the remaining volume of fuel that was delivered can not be refilled until the plunger travels down to the point of lift where the fill port is uncovered by the top of the plunger.

It is the distance that the plunger needs to travel, from the point where the helix is closed off, to where the fill port is opened by the top of the plunger, that determines the volume of fuel that can not be filled until the fill port is opened by the top of the plunger. It is this volume, (the delivered volume), that the cavitation compensates for until the fill port is uncovered.

I can't see any other way the thing will work. If the fuel behaved like air I could see how it could work, but with the hydraulic properties of the fuel, it has to be boiling to temporarily make up for the delivered volume. If that was not happening, the plunger would stop dead due to a hydraulic lock.

Thanks for getting me up to speed, I see exactly the moment you are referring to.

I agree, a vacuum must be created there and is desirable, to some degree.

However, I still believe that vaporization would be avoided if at all possible. And I think it may be.

Lets do some math.

We need to find the volume of this space.
On a 5.5mm element, what is the diameter of the plunger?
...and a rough guess for the maximum stroke during this moment in question.

let me jump in here.
I asked a guru a while ago what happens in that moment.
He told me that I am basically right but it was never an issue when developing the pumps. The time is very short and the velocity of the plunger downwards is high enough to overcome the vacuum. I wonder if the spring pulling down the plunger is strong enough to boil the fuel.
The consequence of a weak spring is hammering between the roller and the cam, noisy.
Cavitation takes place in the barrel just at the upper edge of the port and the inner wall of the barrel when the fuel flows with high speed out of the element when the plunger moves up and the port is almost closed. Very common on petrol pumps.
I have no other explanation than boiling but hard for me to believe for diesel and veggie oil.
At end of injection the element fuel pressure drops to ambient (in the gallery) but the plunger still moves up just pumping fuel through the return groove and the port. When the plunger moves down it draws fuel into the element quite fast until the port is closing. Can the flow and sudden port closing create a relative over pressure (in theory only as the plunger keeps moving down) and therefore reducing the vacuum effect for that time when the volume above the plunger is isolated?

Tom