I finally had a few minutes to sit down and take a couple pictures of some old HPFP's and share with the community. The goal of this is primarily to take some of the magic out of how this particular HPFP works, show how the unit itself *could* be upgraded if you had the time, money, and desire, and also show why we (VTT) decided to just spin the damn thing faster.
First, lets look at the beautiful, albeit dirty HPFP connected to a vacuum pump:
Oh, whoops, was that a VTT hat in there by accident? Almost looks like an advertisement!
Removing the HPFP from the vacuum pump is simple. Resultantly you're left with this marvel of modern engineering:
Here is the control valve:
When you first pop open the HPFP, you'll be met with a loss of fluid. How much? Top secret, which is code for "proprietary industry info", which in this case also means I forgot since it's been years since I pulled it apart. I'd recommend weighing the assy before and after disassembly and calculating fluid weight/volume the old fashioned way. I digress. This is, sort of, what you'll see:
I say "sort of" because it's in a state of disassembly here; you'll see three pistons with "shoes" that ride on the swash plate (angled thing on the left side). You see the triple chambers of the pump here; each get their own piston/shoe/spring/etc. which we'll go into more in a bit. First, though, how to disassemble them all easy like I show? Make a tool if you don't want to do it like a savage:
It's easy as pie to take them out now:
I've heard people prattle on about how the HPFP has to be assembled in a clean room and no one can ever even peek inside or the wizards will fly out. Little did you know, cat fur is an important ingredient. Supporting fuzz provided by Walter the Metric Cat:
Let's get into how it actually works.
Disregard the heat marks on that swash plate; that is a long story that involved some stubborn disassembly and a torch that was near by. Decisions were made. Yours shouldn't look like that.
So looking at the above picture, you see the swash plate turns when driven by the engine. This causes the pistons to move in and out, flexing the bellows with each pump stroke. The bellows fit nice and tight within the actual pump cavity and it simply takes up more or less space. You'll also see that the cavities have, in general, one fuel inlet/outlet. One hole does it all, so to speak.
Do to my less-than-stellar photography skills it's hard to see. Lets see if we can see better with terrible brightness and MSPaint:
Here are the "magic" parts assembled:
Quick rundown of how it works:
-piston/shoe is at thinnest part of swash plate
-fuel rushes in between cavity and bellows
-some minor compression of bellows occurs -not significant
-swash plate rotates
-piston/shoe ride swash plate and get driven in towards pump
-bellows is forced to expand
-during expansion of bellows, the volume in the chamber decreases; this causes a drastic pressure increase (fuel isn't compressible)
-check valve that let fuel into camber closes
-fuel is forced to pump outlet under significant (we hope) pressure
Simple as that.
Remember though, there are 3 of them. I haven't pressure tested the cavity to see where in the internal plumbing the check valves are relative to each chamber; doesn't matter for our purposes.
Let's have a look at a few basic measurements. Note: Despite using calipers/depth mic, these are not precision measurements, they were done with one hand while taking a picture with the other; the goal is to give you a general idea of size, don't go engineering something based off these numbers and get pissed at me when it's off 20 thousandths.
Depth mic to inside lip of bottom of hole:
Thickest part of swash plate:
Thinnest part of swash plate:
Thickness of piston guides:
Whoah whoah whoah!!!! That isn't stock. Add 0.040" to that measurement for stock thickness. It's almost like mine are custom machined for some strange purpose. Hmmm. Anyone want to guess what that was?
On a pump like this, that flows due to compressing/expanding the bellows, you could increase flow capacity a few ways:
1: Increase diameter of bellows. As you can see... not much (any) room for this.
2: Increase compression of bellows. Doable.
3: Increase pump stroke via upgraded swash plate. Doable.
I almost immediately wrote off the idea of getting a custom bellows made; it's expensive. If the quantity were sufficient it'd be worth looking at it but that still doesn't increase pump capacity by itself.
What I did was machine 40 thousandths off the top of the piston guide, and install 40 thousandths of washers between the piston guide and the bellows; this'll let it compress a little more before being smashed back into the HPFP on the compression stroke. It's not a lot but should help. It'll also make the HPPF respond a little better to higher LPFP pressures. Hmmm.
You could machine the pump down a small amount, change swash plate to one that throws more, but then you need a custom bellows, or just hope the bellows are ok with the extra compression/expansion... how much would that help? 20%?
Or you could spin it faster like the diesel guys do and the modern cam driven HPFP's are -put a 4 lobe cam on a HPFP designed to be driven by a 2 lobe cam and you effectively oversped it by 100%.
So you all have enough info to conjecture and play design engineer. Ask questions -I'll answer. I have several methods that will absolutely 100% work to make this pump output more volume and pressure, but... none of them are really practical/cost effective compared to the shotgun from us or even port injection. It's doable as a one-off pet project but not really as a production piece without significant investment. Unless of course one of you come up with a better method/idea, in which case more power to you and I'll be the first to congratulate you.
Our take? Enter the VTT shotgun.
Chris
First, lets look at the beautiful, albeit dirty HPFP connected to a vacuum pump:
Oh, whoops, was that a VTT hat in there by accident? Almost looks like an advertisement!
Removing the HPFP from the vacuum pump is simple. Resultantly you're left with this marvel of modern engineering:
Here is the control valve:
When you first pop open the HPFP, you'll be met with a loss of fluid. How much? Top secret, which is code for "proprietary industry info", which in this case also means I forgot since it's been years since I pulled it apart. I'd recommend weighing the assy before and after disassembly and calculating fluid weight/volume the old fashioned way. I digress. This is, sort of, what you'll see:
I say "sort of" because it's in a state of disassembly here; you'll see three pistons with "shoes" that ride on the swash plate (angled thing on the left side). You see the triple chambers of the pump here; each get their own piston/shoe/spring/etc. which we'll go into more in a bit. First, though, how to disassemble them all easy like I show? Make a tool if you don't want to do it like a savage:
It's easy as pie to take them out now:
I've heard people prattle on about how the HPFP has to be assembled in a clean room and no one can ever even peek inside or the wizards will fly out. Little did you know, cat fur is an important ingredient. Supporting fuzz provided by Walter the Metric Cat:
Let's get into how it actually works.
Disregard the heat marks on that swash plate; that is a long story that involved some stubborn disassembly and a torch that was near by. Decisions were made. Yours shouldn't look like that.
So looking at the above picture, you see the swash plate turns when driven by the engine. This causes the pistons to move in and out, flexing the bellows with each pump stroke. The bellows fit nice and tight within the actual pump cavity and it simply takes up more or less space. You'll also see that the cavities have, in general, one fuel inlet/outlet. One hole does it all, so to speak.
Do to my less-than-stellar photography skills it's hard to see. Lets see if we can see better with terrible brightness and MSPaint:
Here are the "magic" parts assembled:
Quick rundown of how it works:
-piston/shoe is at thinnest part of swash plate
-fuel rushes in between cavity and bellows
-some minor compression of bellows occurs -not significant
-swash plate rotates
-piston/shoe ride swash plate and get driven in towards pump
-bellows is forced to expand
-during expansion of bellows, the volume in the chamber decreases; this causes a drastic pressure increase (fuel isn't compressible)
-check valve that let fuel into camber closes
-fuel is forced to pump outlet under significant (we hope) pressure
Simple as that.
Remember though, there are 3 of them. I haven't pressure tested the cavity to see where in the internal plumbing the check valves are relative to each chamber; doesn't matter for our purposes.
Let's have a look at a few basic measurements. Note: Despite using calipers/depth mic, these are not precision measurements, they were done with one hand while taking a picture with the other; the goal is to give you a general idea of size, don't go engineering something based off these numbers and get pissed at me when it's off 20 thousandths.
Depth mic to inside lip of bottom of hole:
Thickest part of swash plate:
Thinnest part of swash plate:
Thickness of piston guides:
Whoah whoah whoah!!!! That isn't stock. Add 0.040" to that measurement for stock thickness. It's almost like mine are custom machined for some strange purpose. Hmmm. Anyone want to guess what that was?
On a pump like this, that flows due to compressing/expanding the bellows, you could increase flow capacity a few ways:
1: Increase diameter of bellows. As you can see... not much (any) room for this.
2: Increase compression of bellows. Doable.
3: Increase pump stroke via upgraded swash plate. Doable.
I almost immediately wrote off the idea of getting a custom bellows made; it's expensive. If the quantity were sufficient it'd be worth looking at it but that still doesn't increase pump capacity by itself.
What I did was machine 40 thousandths off the top of the piston guide, and install 40 thousandths of washers between the piston guide and the bellows; this'll let it compress a little more before being smashed back into the HPFP on the compression stroke. It's not a lot but should help. It'll also make the HPPF respond a little better to higher LPFP pressures. Hmmm.
You could machine the pump down a small amount, change swash plate to one that throws more, but then you need a custom bellows, or just hope the bellows are ok with the extra compression/expansion... how much would that help? 20%?
Or you could spin it faster like the diesel guys do and the modern cam driven HPFP's are -put a 4 lobe cam on a HPFP designed to be driven by a 2 lobe cam and you effectively oversped it by 100%.
So you all have enough info to conjecture and play design engineer. Ask questions -I'll answer. I have several methods that will absolutely 100% work to make this pump output more volume and pressure, but... none of them are really practical/cost effective compared to the shotgun from us or even port injection. It's doable as a one-off pet project but not really as a production piece without significant investment. Unless of course one of you come up with a better method/idea, in which case more power to you and I'll be the first to congratulate you.
Our take? Enter the VTT shotgun.
Chris